opengl spec 4.4 core

1. The OpenGL R Graphics System: A Specication (Version 4.4 (Core Prole) - March 19, 2014) Mark Segal Kurt Akeley Editor (version 1.1): Chris Frazier Editor (versions 1.2-4.4 ): Jon Leech Editor (version 2.0): Pat Brown

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Contents 1 Introduction 1 1.1 Formatting of the OpenGL Specication . . . . . . . . . . . . . . 1 1.1.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 What is the OpenGL Graphics System? . . . . . . . . . . . . . . 2 1.2.1 Programmers View of OpenGL . . . . . . . . . . . . . . 2 1.2.2 Implementors View of OpenGL . . . . . . . . . . . . . . 2 1.2.3 Our View . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2.4 Fixed-function Hardware and the Compatibility Prole . . 3 1.2.5 The Deprecation Model . . . . . . . . . . . . . . . . . . 3 1.3 Related APIs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3.1 OpenGL Shading Language . . . . . . . . . . . . . . . . 4 1.3.2 OpenGL ES . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3.3 OpenGL ES Shading Language . . . . . . . . . . . . . . 5 1.3.4 WebGL . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3.5 Window System Bindings . . . . . . . . . . . . . . . . . 6 1.3.6 OpenCL . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.4 Filing Bug Reports . . . . . . . . . . . . . . . . . . . . . . . . . 7 2 OpenGL Fundamentals 8 2.1 Execution Model . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2 Command Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2.1 Data Conversion For State-Setting Commands . . . . . . 12 2.2.2 Data Conversions For State Query Commands . . . . . . 14 2.3 Command Execution . . . . . . . . . . . . . . . . . . . . . . . . 15 2.3.1 Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.3.2 Flush and Finish . . . . . . . . . . . . . . . . . . . . . . 18 2.3.3 Numeric Representation and Computation . . . . . . . . . 18 2.3.4 Fixed-Point Data Conversions . . . . . . . . . . . . . . . 22 i 4. CONTENTS ii 2.4 Rendering Commands . . . . . . . . . . . . . . . . . . . . . . . 24 2.5 Context State . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.5.1 Generic Context State Queries . . . . . . . . . . . . . . . 24 2.6 Objects and the Object Model . . . . . . . . . . . . . . . . . . . 25 2.6.1 Object Management . . . . . . . . . . . . . . . . . . . . 25 2.6.2 Buffer Objects . . . . . . . . . . . . . . . . . . . . . . . 26 2.6.3 Shader Objects . . . . . . . . . . . . . . . . . . . . . . . 27 2.6.4 Program Objects . . . . . . . . . . . . . . . . . . . . . . 27 2.6.5 Program Pipeline Objects . . . . . . . . . . . . . . . . . 27 2.6.6 Texture Objects . . . . . . . . . . . . . . . . . . . . . . . 27 2.6.7 Sampler Objects . . . . . . . . . . . . . . . . . . . . . . 28 2.6.8 Renderbuffer Objects . . . . . . . . . . . . . . . . . . . . 28 2.6.9 Framebuffer Objects . . . . . . . . . . . . . . . . . . . . 28 2.6.10 Vertex Array Objects . . . . . . . . . . . . . . . . . . . . 28 2.6.11 Transform Feedback Objects . . . . . . . . . . . . . . . . 29 2.6.12 Query Objects . . . . . . . . . . . . . . . . . . . . . . . 29 2.6.13 Sync Objects . . . . . . . . . . . . . . . . . . . . . . . . 29 2.6.14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 3 Dataow Model 30 4 Event Model 33 4.1 Sync Objects and Fences . . . . . . . . . . . . . . . . . . . . . . 33 4.1.1 Waiting for Sync Objects . . . . . . . . . . . . . . . . . . 35 4.1.2 Signaling . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.1.3 Sync Object Queries . . . . . . . . . . . . . . . . . . . . 37 4.2 Query Objects and Asynchronous Queries . . . . . . . . . . . . . 38 4.2.1 Query Object Queries . . . . . . . . . . . . . . . . . . . 42 4.3 Time Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 5 Shared Objects and Multiple Contexts 47 5.1 Object Deletion Behavior . . . . . . . . . . . . . . . . . . . . . . 48 5.1.1 Side Effects of Shared Context Destruction . . . . . . . . 48 5.1.2 Automatic Unbinding of Deleted Objects . . . . . . . . . 48 5.1.3 Deleted Object and Object Name Lifetimes . . . . . . . . 48 5.2 Sync Objects and Multiple Contexts . . . . . . . . . . . . . . . . 49 5.3 Propagating Changes to Objects . . . . . . . . . . . . . . . . . . 49 5.3.1 Determining Completion of Changes to an object . . . . . 50 5.3.2 Denitions . . . . . . . . . . . . . . . . . . . . . . . . . 51 5.3.3 Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 OpenGL 4.4 (Core Prole) - March 19, 2014 5. CONTENTS iii 6 Buffer Objects 53 6.1 Creating and Binding Buffer Objects . . . . . . . . . . . . . . . . 54 6.1.1 Binding Buffer Objects to Indexed Targets . . . . . . . . . 56 6.2 Creating and Modifying Buffer Object Data Stores . . . . . . . . 59 6.2.1 Clearing Buffer Object Data Stores . . . . . . . . . . . . 64 6.3 Mapping and Unmapping Buffer Data . . . . . . . . . . . . . . . 65 6.3.1 Unmapping Buffers . . . . . . . . . . . . . . . . . . . . . 70 6.3.2 Effects of Mapping Buffers on Other GL Commands . . . 70 6.4 Effects of Accessing Outside Buffer Bounds . . . . . . . . . . . . 71 6.5 Invalidating Buffer Data . . . . . . . . . . . . . . . . . . . . . . 71 6.6 Copying Between Buffers . . . . . . . . . . . . . . . . . . . . . . 72 6.7 Buffer Object Queries . . . . . . . . . . . . . . . . . . . . . . . . 73 6.7.1 Indexed Buffer Object Limits and Binding Queries . . . . 74 6.8 Buffer Object State . . . . . . . . . . . . . . . . . . . . . . . . . 76 7 Programs and Shaders 77 7.1 Shader Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 7.2 Shader Binaries . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 7.3 Program Objects . . . . . . . . . . . . . . . . . . . . . . . . . . 82 7.3.1 Program Interfaces . . . . . . . . . . . . . . . . . . . . . 89 7.4 Program Pipeline Objects . . . . . . . . . . . . . . . . . . . . . . 108 7.4.1 Shader Interface Matching . . . . . . . . . . . . . . . . . 111 7.4.2 Program Pipeline Object State . . . . . . . . . . . . . . . 114 7.5 Program Binaries . . . . . . . . . . . . . . . . . . . . . . . . . . 114 7.6 Uniform Variables . . . . . . . . . . . . . . . . . . . . . . . . . . 117 7.6.1 Loading Uniform Variables In The Default Uniform Block 124 7.6.2 Uniform Blocks . . . . . . . . . . . . . . . . . . . . . . . 128 7.6.3 Uniform Buffer Object Bindings . . . . . . . . . . . . . . 132 7.7 Atomic Counter Buffers . . . . . . . . . . . . . . . . . . . . . . . 133 7.7.1 Atomic Counter Buffer Object Storage . . . . . . . . . . 133 7.7.2 Atomic Counter Buffer Bindings . . . . . . . . . . . . . . 134 7.8 Shader Buffer Variables and Shader Storage Blocks . . . . . . . . 134 7.9 Subroutine Uniform Variables . . . . . . . . . . . . . . . . . . . 136 7.10 Samplers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 7.11 Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 7.12 Shader Memory Access . . . . . . . . . . . . . . . . . . . . . . . 142 7.12.1 Shader Memory Access Ordering . . . . . . . . . . . . . 142 7.12.2 Shader Memory Access Synchronization . . . . . . . . . 144 7.13 Shader, Program, and Program Pipeline Queries . . . . . . . . . . 148 7.14 Required State . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 OpenGL 4.4 (Core Prole) - March 19, 2014 6. CONTENTS iv 8 Textures and Samplers 159 8.1 Texture Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 8.2 Sampler Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 8.3 Sampler Object Queries . . . . . . . . . . . . . . . . . . . . . . . 168 8.4 Pixel Rectangles . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 8.4.1 Pixel Storage Modes and Pixel Buffer Objects . . . . . . . 169 8.4.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 8.4.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 8.4.4 Transfer of Pixel Rectangles . . . . . . . . . . . . . . . . 170 8.4.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 8.5 Texture Image Specication . . . . . . . . . . . . . . . . . . . . 183 8.5.1 Required Texture Formats . . . . . . . . . . . . . . . . . 186 8.5.2 Encoding of Special Internal Formats . . . . . . . . . . . 187 8.5.3 Texture Image Structure . . . . . . . . . . . . . . . . . . 191 8.6 Alternate Texture Image Specication Commands . . . . . . . . . 196 8.6.1 Texture Copying Feedback Loops . . . . . . . . . . . . . 204 8.7 Compressed Texture Images . . . . . . . . . . . . . . . . . . . . 204 8.8 Multisample Textures . . . . . . . . . . . . . . . . . . . . . . . . 211 8.9 Buffer Textures . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 8.10 Texture Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 216 8.11 Texture Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 8.11.1 Active Texture . . . . . . . . . . . . . . . . . . . . . . . 219 8.11.2 Texture Parameter Queries . . . . . . . . . . . . . . . . . 219 8.11.3 Texture Level Parameter Queries . . . . . . . . . . . . . . 220 8.11.4 Texture Image Queries . . . . . . . . . . . . . . . . . . . 222 8.12 Depth Component Textures . . . . . . . . . . . . . . . . . . . . . 225 8.13 Cube Map Texture Selection . . . . . . . . . . . . . . . . . . . . 225 8.13.1 Seamless Cube Map Filtering . . . . . . . . . . . . . . . 226 8.14 Texture Minication . . . . . . . . . . . . . . . . . . . . . . . . 227 8.14.1 Scale Factor and Level of Detail . . . . . . . . . . . . . . 227 8.14.2 Coordinate Wrapping and Texel Selection . . . . . . . . . 229 8.14.3 Mipmapping . . . . . . . . . . . . . . . . . . . . . . . . 234 8.14.4 Manual Mipmap Generation . . . . . . . . . . . . . . . . 236 8.14.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 8.15 Texture Magnication . . . . . . . . . . . . . . . . . . . . . . . . 237 8.16 Combined Depth/Stencil Textures . . . . . . . . . . . . . . . . . 238 8.17 Texture Completeness . . . . . . . . . . . . . . . . . . . . . . . . 238 8.17.1 Effects of Sampler Objects on Texture Completeness . . . 239 8.17.2 Effects of Completeness on Texture Application . . . . . . 239 8.17.3 Effects of Completeness on Texture Image Specication . 240 OpenGL 4.4 (Core Prole) - March 19, 2014 7. CONTENTS v 8.18 Texture Views . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 8.19 Immutable-Format Texture Images . . . . . . . . . . . . . . . . . 244 8.20 Invalidating Texture Image Data . . . . . . . . . . . . . . . . . . 249 8.21 Clearing Texture Image Data . . . . . . . . . . . . . . . . . . . . 250 8.22 Texture State and Proxy State . . . . . . . . . . . . . . . . . . . . 252 8.23 Texture Comparison Modes . . . . . . . . . . . . . . . . . . . . . 255 8.23.1 Depth Texture Comparison Mode . . . . . . . . . . . . . 255 8.24 sRGB Texture Color Conversion . . . . . . . . . . . . . . . . . . 255 8.25 Shared Exponent Texture Color Conversion . . . . . . . . . . . . 256 8.26 Texture Image Loads and Stores . . . . . . . . . . . . . . . . . . 257 8.26.1 Image Unit Queries . . . . . . . . . . . . . . . . . . . . . 266 9 Framebuffers and Framebuffer Objects 267 9.1 Framebuffer Overview . . . . . . . . . . . . . . . . . . . . . . . 267 9.2 Binding and Managing Framebuffer Objects . . . . . . . . . . . . 269 9.2.1 Framebuffer Object Parameters . . . . . . . . . . . . . . 272 9.2.2 Attaching Images to Framebuffer Objects . . . . . . . . . 274 9.2.3 Framebuffer Object Queries . . . . . . . . . . . . . . . . 275 9.2.4 Renderbuffer Objects . . . . . . . . . . . . . . . . . . . . 278 9.2.5 Required Renderbuffer Formats . . . . . . . . . . . . . . 281 9.2.6 Renderbuffer Object Queries . . . . . . . . . . . . . . . . 281 9.2.7 Attaching Renderbuffer Images to a Framebuffer . . . . . 282 9.2.8 Attaching Texture Images to a Framebuffer . . . . . . . . 284 9.3 Feedback Loops Between Textures and the Framebuffer . . . . . . 288 9.3.1 Rendering Feedback Loops . . . . . . . . . . . . . . . . . 288 9.3.2 Texture Copying Feedback Loops . . . . . . . . . . . . . 290 9.4 Framebuffer Completeness . . . . . . . . . . . . . . . . . . . . . 290 9.4.1 Framebuffer Attachment Completeness . . . . . . . . . . 291 9.4.2 Whole Framebuffer Completeness . . . . . . . . . . . . . 292 9.4.3 Required Framebuffer Formats . . . . . . . . . . . . . . . 295 9.4.4 Effects of Framebuffer Completeness on Framebuffer Op- erations . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 9.4.5 Effects of Framebuffer State on Framebuffer Dependent Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 9.5 Mapping between Pixel and Element in Attached Image . . . . . . 296 9.6 Conversion to Framebuffer-Attachable Image Components . . . . 297 9.7 Conversion to RGBA Values . . . . . . . . . . . . . . . . . . . . 297 9.8 Layered Framebuffers . . . . . . . . . . . . . . . . . . . . . . . . 297 OpenGL 4.4 (Core Prole) - March 19, 2014 8. CONTENTS vi 10 Vertex Specication and Drawing Commands 300 10.1 Primitive Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 10.1.1 Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 10.1.2 Line Strips . . . . . . . . . . . . . . . . . . . . . . . . . 302 10.1.3 Line Loops . . . . . . . . . . . . . . . . . . . . . . . . . 302 10.1.4 Separate Lines . . . . . . . . . . . . . . . . . . . . . . . 302 10.1.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 10.1.6 Triangle Strips . . . . . . . . . . . . . . . . . . . . . . . 303 10.1.7 Triangle Fans . . . . . . . . . . . . . . . . . . . . . . . . 304 10.1.8 Separate Triangles . . . . . . . . . . . . . . . . . . . . . 304 10.1.9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 10.1.10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 10.1.11 Lines with Adjacency . . . . . . . . . . . . . . . . . . . 304 10.1.12 Line Strips with Adjacency . . . . . . . . . . . . . . . . . 306 10.1.13 Triangles with Adjacency . . . . . . . . . . . . . . . . . 306 10.1.14 Triangle Strips with Adjacency . . . . . . . . . . . . . . . 307 10.1.15 Separate Patches . . . . . . . . . . . . . . . . . . . . . . 308 10.1.16 General Considerations For Polygon Primitives . . . . . . 309 10.1.17 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 10.2 Current Vertex Attribute Values . . . . . . . . . . . . . . . . . . . 309 10.2.1 Current Generic Attributes . . . . . . . . . . . . . . . . . 309 10.2.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 10.2.3 Vertex Attribute Queries . . . . . . . . . . . . . . . . . . 312 10.2.4 Required State . . . . . . . . . . . . . . . . . . . . . . . 312 10.3 Vertex Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 10.3.1 Specifying Arrays for Generic Vertex Attributes . . . . . . 312 10.3.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318 10.3.3 Vertex Attribute Divisors . . . . . . . . . . . . . . . . . . 318 10.3.4 Transferring Array Elements . . . . . . . . . . . . . . . . 319 10.3.5 Primitive Restart . . . . . . . . . . . . . . . . . . . . . . 319 10.3.6 Robust Buffer Access . . . . . . . . . . . . . . . . . . . . 320 10.3.7 Packed Vertex Data Formats . . . . . . . . . . . . . . . . 321 10.3.8 Vertex Arrays in Buffer Objects . . . . . . . . . . . . . . 321 10.3.9 Array Indices in Buffer Objects . . . . . . . . . . . . . . 322 10.3.10 Indirect Commands in Buffer Objects . . . . . . . . . . . 323 10.4 Vertex Array Objects . . . . . . . . . . . . . . . . . . . . . . . . 323 10.5 Drawing Commands Using Vertex Arrays . . . . . . . . . . . . . 325 10.5.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 10.6 Vertex Array and Vertex Array Object Queries . . . . . . . . . . . 335 10.7 Required State . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337 OpenGL 4.4 (Core Prole) - March 19, 2014 9. CONTENTS vii 10.8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338 10.9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338 10.10Conditional Rendering . . . . . . . . . . . . . . . . . . . . . . . 338 11 Programmable Vertex Processing 340 11.1 Vertex Shaders . . . . . . . . . . . . . . . . . . . . . . . . . . . 340 11.1.1 Vertex Attributes . . . . . . . . . . . . . . . . . . . . . . 340 11.1.2 Vertex Shader Variables . . . . . . . . . . . . . . . . . . 346 11.1.3 Shader Execution . . . . . . . . . . . . . . . . . . . . . . 351 11.2 Tessellation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362 11.2.1 Tessellation Control Shaders . . . . . . . . . . . . . . . . 363 11.2.2 Tessellation Primitive Generation . . . . . . . . . . . . . 368 11.2.3 Tessellation Evaluation Shaders . . . . . . . . . . . . . . 377 11.3 Geometry Shaders . . . . . . . . . . . . . . . . . . . . . . . . . . 382 11.3.1 Geometry Shader Input Primitives . . . . . . . . . . . . . 383 11.3.2 Geometry Shader Output Primitives . . . . . . . . . . . . 384 11.3.3 Geometry Shader Variables . . . . . . . . . . . . . . . . . 385 11.3.4 Geometry Shader Execution Environment . . . . . . . . . 385 12 392 13 Fixed-Function Vertex Post-Processing 393 13.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393 13.2 Transform Feedback . . . . . . . . . . . . . . . . . . . . . . . . 394 13.2.1 Transform Feedback Objects . . . . . . . . . . . . . . . . 394 13.2.2 Transform Feedback Primitive Capture . . . . . . . . . . 396 13.2.3 Transform Feedback Draw Operations . . . . . . . . . . . 400 13.3 Primitive Queries . . . . . . . . . . . . . . . . . . . . . . . . . . 402 13.4 Flatshading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402 13.5 Primitive Clipping . . . . . . . . . . . . . . . . . . . . . . . . . . 404 13.5.1 Clipping Shader Outputs . . . . . . . . . . . . . . . . . . 405 13.5.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406 13.6 Coordinate Transformations . . . . . . . . . . . . . . . . . . . . 406 13.6.1 Controlling the Viewport . . . . . . . . . . . . . . . . . . 406 13.7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410 14 Fixed-Function Primitive Assembly and Rasterization 411 14.1 Discarding Primitives Before Rasterization . . . . . . . . . . . . 412 14.2 Invariance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413 14.3 Antialiasing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413 OpenGL 4.4 (Core Prole) - March 19, 2014 10. CONTENTS viii 14.3.1 Multisampling . . . . . . . . . . . . . . . . . . . . . . . 414 14.4 Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 14.4.1 Basic Point Rasterization . . . . . . . . . . . . . . . . . . 418 14.4.2 Point Rasterization State . . . . . . . . . . . . . . . . . . 419 14.4.3 Point Multisample Rasterization . . . . . . . . . . . . . . 419 14.5 Line Segments . . . . . . . . . . . . . . . . . . . . . . . . . . . 419 14.5.1 Basic Line Segment Rasterization . . . . . . . . . . . . . 420 14.5.2 Other Line Segment Features . . . . . . . . . . . . . . . . 422 14.5.3 Line Rasterization State . . . . . . . . . . . . . . . . . . 425 14.5.4 Line Multisample Rasterization . . . . . . . . . . . . . . 425 14.6 Polygons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425 14.6.1 Basic Polygon Rasterization . . . . . . . . . . . . . . . . 425 14.6.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428 14.6.3 Antialiasing . . . . . . . . . . . . . . . . . . . . . . . . . 428 14.6.4 Options Controlling Polygon Rasterization . . . . . . . . 429 14.6.5 Depth Offset . . . . . . . . . . . . . . . . . . . . . . . . 429 14.6.6 Polygon Multisample Rasterization . . . . . . . . . . . . 430 14.6.7 Polygon Rasterization State . . . . . . . . . . . . . . . . 431 14.7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431 14.8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431 14.9 Early Per-Fragment Tests . . . . . . . . . . . . . . . . . . . . . . 432 15 Programmable Fragment Processing 433 15.1 Fragment Shader Variables . . . . . . . . . . . . . . . . . . . . . 433 15.2 Shader Execution . . . . . . . . . . . . . . . . . . . . . . . . . . 434 15.2.1 Texture Access . . . . . . . . . . . . . . . . . . . . . . . 435 15.2.2 Shader Inputs . . . . . . . . . . . . . . . . . . . . . . . . 436 15.2.3 Shader Outputs . . . . . . . . . . . . . . . . . . . . . . . 438 15.2.4 Early Fragment Tests . . . . . . . . . . . . . . . . . . . . 442 16 443 17 Writing Fragments and Samples to the Framebuffer 444 17.1 Antialiasing Application . . . . . . . . . . . . . . . . . . . . . . 444 17.2 Multisample Point Fade . . . . . . . . . . . . . . . . . . . . . . . 444 17.3 Per-Fragment Operations . . . . . . . . . . . . . . . . . . . . . . 445 17.3.1 Pixel Ownership Test . . . . . . . . . . . . . . . . . . . . 445 17.3.2 Scissor Test . . . . . . . . . . . . . . . . . . . . . . . . . 446 17.3.3 Multisample Fragment Operations . . . . . . . . . . . . . 448 17.3.4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 OpenGL 4.4 (Core Prole) - March 19, 2014 11. CONTENTS ix 17.3.5 Stencil Test . . . . . . . . . . . . . . . . . . . . . . . . . 450 17.3.6 Depth Buffer Test . . . . . . . . . . . . . . . . . . . . . . 451 17.3.7 Occlusion Queries . . . . . . . . . . . . . . . . . . . . . 452 17.3.8 Blending . . . . . . . . . . . . . . . . . . . . . . . . . . 453 17.3.9 sRGB Conversion . . . . . . . . . . . . . . . . . . . . . 460 17.3.10 Dithering . . . . . . . . . . . . . . . . . . . . . . . . . . 460 17.3.11 Logical Operation . . . . . . . . . . . . . . . . . . . . . 461 17.3.12 Additional Multisample Fragment Operations . . . . . . . 463 17.4 Whole Framebuffer Operations . . . . . . . . . . . . . . . . . . . 464 17.4.1 Selecting Buffers for Writing . . . . . . . . . . . . . . . . 464 17.4.2 Fine Control of Buffer Updates . . . . . . . . . . . . . . 468 17.4.3 Clearing the Buffers . . . . . . . . . . . . . . . . . . . . 470 17.4.4 Invalidating Framebuffer Contents . . . . . . . . . . . . . 473 17.4.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474 18 Reading and Copying Pixels 475 18.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475 18.2 Reading Pixels . . . . . . . . . . . . . . . . . . . . . . . . . . . 475 18.2.1 Selecting Buffers for Reading . . . . . . . . . . . . . . . 475 18.2.2 ReadPixels . . . . . . . . . . . . . . . . . . . . . . . . . 477 18.2.3 Obtaining Pixels from the Framebuffer . . . . . . . . . . 477 18.2.4 Conversion of RGBA values . . . . . . . . . . . . . . . . 480 18.2.5 Conversion of Depth values . . . . . . . . . . . . . . . . 480 18.2.6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480 18.2.7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480 18.2.8 Final Conversion . . . . . . . . . . . . . . . . . . . . . . 480 18.2.9 Placement in Pixel Pack Buffer or Client Memory . . . . . 481 18.3 Copying Pixels . . . . . . . . . . . . . . . . . . . . . . . . . . . 483 18.3.1 Blitting Pixel Rectangles . . . . . . . . . . . . . . . . . . 483 18.3.2 Copying Between Images . . . . . . . . . . . . . . . . . 487 18.4 Pixel Draw and Read State . . . . . . . . . . . . . . . . . . . . . 489 19 Compute Shaders 491 19.1 Compute Shader Variables . . . . . . . . . . . . . . . . . . . . . 493 20 Debug Output 494 20.1 Debug Messages . . . . . . . . . . . . . . . . . . . . . . . . . . 495 20.2 Debug Message Callback . . . . . . . . . . . . . . . . . . . . . . 497 20.3 Debug Message Log . . . . . . . . . . . . . . . . . . . . . . . . 498 20.4 Controlling Debug Messages . . . . . . . . . . . . . . . . . . . . 498 OpenGL 4.4 (Core Prole) - March 19, 2014 12. CONTENTS x 20.5 Externally Generated Messages . . . . . . . . . . . . . . . . . . . 500 20.6 Debug Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 20.7 Debug Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502 20.8 Asynchronous and Synchronous Debug Output . . . . . . . . . . 503 20.9 Debug Output Queries . . . . . . . . . . . . . . . . . . . . . . . 504 21 Special Functions 507 21.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507 21.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507 21.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507 21.4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507 21.5 Hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507 21.6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508 22 Context State Queries 509 22.1 Simple Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . 509 22.2 String Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511 22.3 Internal Format Queries . . . . . . . . . . . . . . . . . . . . . . . 513 22.3.1 Supported Operation Queries . . . . . . . . . . . . . . . . 514 22.3.2 Other Internal Format Queries . . . . . . . . . . . . . . . 517 23 State Tables 525 A Invariance 600 A.1 Repeatability . . . . . . . . . . . . . . . . . . . . . . . . . . . . 600 A.2 Multi-pass Algorithms . . . . . . . . . . . . . . . . . . . . . . . 601 A.3 Invariance Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . 601 A.4 Tessellation Invariance . . . . . . . . . . . . . . . . . . . . . . . 603 A.5 Atomic Counter Invariance . . . . . . . . . . . . . . . . . . . . . 605 A.6 What All This Means . . . . . . . . . . . . . . . . . . . . . . . . 606 B Corollaries 607 C Compressed Texture Image Formats 609 C.1 RGTC Compressed Texture Image Formats . . . . . . . . . . . . 609 C.1.1 Format COMPRESSED_RED_RGTC1 . . . . . . . . . . . . 610 C.1.2 Format COMPRESSED_SIGNED_RED_RGTC1 . . . . . . . 611 C.1.3 Format COMPRESSED_RG_RGTC2 . . . . . . . . . . . . . 611 C.1.4 Format COMPRESSED_SIGNED_RG_RGTC2 . . . . . . . . 612 C.2 BPTC Compressed Texture Image Formats . . . . . . . . . . . . 612 OpenGL 4.4 (Core Prole) - March 19, 2014 13. CONTENTS xi C.2.1 Formats COMPRESSED_RGBA_BPTC_UNORM and COMPRESSED_SRGB_ALPHA_BPTC_UNORM . . . . . . . . 613 C.2.2 Formats COMPRESSED_RGB_BPTC_SIGNED_FLOAT and COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT . . . . . . 619 C.3 ETC Compressed Texture Image Formats . . . . . . . . . . . . . 621 C.3.1 Format COMPRESSED_RGB8_ETC2 . . . . . . . . . . . . 625 C.3.2 Format COMPRESSED_SRGB8_ETC2 . . . . . . . . . . . . 632 C.3.3 Format COMPRESSED_RGBA8_ETC2_EAC . . . . . . . . . 632 C.3.4 Format COMPRESSED_SRGB8_ALPHA8_ETC2_EAC . . . . 635 C.3.5 Format COMPRESSED_R11_EAC . . . . . . . . . . . . . . 635 C.3.6 Format COMPRESSED_RG11_EAC . . . . . . . . . . . . . 638 C.3.7 Format COMPRESSED_SIGNED_R11_EAC . . . . . . . . . 639 C.3.8 Format COMPRESSED_SIGNED_RG11_EAC . . . . . . . . 642 C.3.9 Format COMPRESSED_RGB8_PUNCHTHROUGH_ALPHA1_ETC2 . . 642 C.3.10 Format COMPRESSED_SRGB8_PUNCHTHROUGH_ALPHA1_ETC2 . 649 D Proles and the Deprecation Model 650 D.1 Core and Compatibility Proles . . . . . . . . . . . . . . . . . . 651 D.2 Deprecated and Removed Features . . . . . . . . . . . . . . . . . 651 D.2.1 Deprecated But Still Supported Features . . . . . . . . . . 651 D.2.2 Removed Features . . . . . . . . . . . . . . . . . . . . . 652 E Version 4.2 657 E.1 New Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . 657 E.2 Deprecation Model . . . . . . . . . . . . . . . . . . . . . . . . . 658 E.3 Changed Tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . 658 E.4 Change Log for Released Specications . . . . . . . . . . . . . . 659 E.5 Credits and Acknowledgements . . . . . . . . . . . . . . . . . . 661 F Version 4.3 664 F.1 Restructuring . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664 F.2 New Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . 665 F.3 Deprecation Model . . . . . . . . . . . . . . . . . . . . . . . . . 666 F.4 Changed Tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . 666 F.5 Change Log for Released Specications . . . . . . . . . . . . . . 667 F.6 Credits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674 F.7 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . 676 OpenGL 4.4 (Core Prole) - March 19, 2014 14. CONTENTS xii G Version 4.4 677 G.1 New Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . 677 G.2 Deprecation Model . . . . . . . . . . . . . . . . . . . . . . . . . 678 G.3 Change Log for Released Specications . . . . . . . . . . . . . . 678 G.4 Credits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689 G.5 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . 690 H OpenGL Registry, Header Files, and ARB Extensions 691 H.1 OpenGL Registry . . . . . . . . . . . . . . . . . . . . . . . . . . 691 H.2 Header Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 691 H.3 ARB and Khronos Extensions . . . . . . . . . . . . . . . . . . . 692 H.3.1 Naming Conventions . . . . . . . . . . . . . . . . . . . . 693 H.3.2 Promoting Extensions to Core Features . . . . . . . . . . 693 H.3.3 Extension Summaries . . . . . . . . . . . . . . . . . . . 693 H.3.4 Bindless Textures . . . . . . . . . . . . . . . . . . . . . . 717 H.3.5 Compute Variable Group Size . . . . . . . . . . . . . . . 717 H.3.6 Indirect Parameters . . . . . . . . . . . . . . . . . . . . . 717 H.3.7 Seamless Cubemap per Texture . . . . . . . . . . . . . . 717 H.3.8 Shader Draw Parameters . . . . . . . . . . . . . . . . . . 717 H.3.9 Shader Group Vote . . . . . . . . . . . . . . . . . . . . . 717 H.3.10 Sparse Textures . . . . . . . . . . . . . . . . . . . . . . . 718 OpenGL 4.4 (Core Prole) - March 19, 2014 15. List of Figures 3.1 Block diagram of the GL pipeline. . . . . . . . . . . . . . . . . . 31 8.1 Transfer of pixel rectangles. . . . . . . . . . . . . . . . . . . . . 170 8.2 Selecting a subimage from an image . . . . . . . . . . . . . . . . 175 8.3 A texture image and the coordinates used to access it. . . . . . . . 196 8.4 Example of the components returned for textureGather. . . . . 232 10.1 Vertex processing and primitive assembly. . . . . . . . . . . . . . 300 10.2 Triangle strips, fans, and independent triangles. . . . . . . . . . . 303 10.3 Lines with adjacency. . . . . . . . . . . . . . . . . . . . . . . . . 304 10.4 Triangles with adjacency. . . . . . . . . . . . . . . . . . . . . . . 306 10.5 Triangle strips with adjacency. . . . . . . . . . . . . . . . . . . . 307 11.1 Domain parameterization for tessellation. . . . . . . . . . . . . . 368 11.2 Inner triangle tessellation. . . . . . . . . . . . . . . . . . . . . . . 372 11.3 Inner quad tessellation. . . . . . . . . . . . . . . . . . . . . . . . 375 11.4 Isoline tessellation. . . . . . . . . . . . . . . . . . . . . . . . . . 377 14.1 Rasterization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411 14.2 Visualization of Bresenhams algorithm. . . . . . . . . . . . . . . 421 14.3 Rasterization of non-antialiased wide lines. . . . . . . . . . . . . 423 14.4 The region used in rasterizing an antialiased line segment. . . . . 424 17.1 Per-fragment operations. . . . . . . . . . . . . . . . . . . . . . . 445 18.1 Operation of ReadPixels. . . . . . . . . . . . . . . . . . . . . . . 475 xiii 16. List of Tables 2.1 GL command sufxes . . . . . . . . . . . . . . . . . . . . . . . . 12 2.2 GL data types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.3 Summary of GL errors . . . . . . . . . . . . . . . . . . . . . . . 17 4.1 Initial properties of a sync object created with FenceSync. . . . . 34 6.1 Buffer object binding targets. . . . . . . . . . . . . . . . . . . . . 55 6.2 Buffer object parameters and their values. . . . . . . . . . . . . . 55 6.3 Buffer object state. . . . . . . . . . . . . . . . . . . . . . . . . . 61 6.4 Buffer object state set by MapBufferRange. . . . . . . . . . . . 68 6.5 Indexed buffer object limits and binding queries . . . . . . . . . . 75 7.1 CreateShader type values and the corresponding shader stages. . 79 7.2 GetProgramResourceiv properties and supported interfaces . . . 99 7.3 OpenGL Shading Language type tokens . . . . . . . . . . . . . . 106 7.4 Query targets for default uniform block storage, in components. . 118 7.5 Query targets for combined uniform block storage, in components. 118 7.6 GetProgramResourceiv properties used by GetActiveUniformsiv. 122 7.7 GetProgramResourceiv properties used by GetActiveUniform- Blockiv. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 7.8 GetProgramResourceiv properties used by GetActiveAtomic- CounterBufferiv. . . . . . . . . . . . . . . . . . . . . . . . . . . 125 7.9 Interfaces for active subroutines . . . . . . . . . . . . . . . . . . 138 7.10 Interfaces for active subroutine uniforms . . . . . . . . . . . . . . 138 8.1 PixelStore* parameters. . . . . . . . . . . . . . . . . . . . . . . 169 8.2 Pixel data types. . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 8.3 Pixel data formats. . . . . . . . . . . . . . . . . . . . . . . . . . 174 8.4 Swap Bytes bit ordering. . . . . . . . . . . . . . . . . . . . . . . 174 8.5 Packed pixel formats. . . . . . . . . . . . . . . . . . . . . . . . . 177 xiv 17. LIST OF TABLES xv 8.6 UNSIGNED_BYTE formats. Bit numbers are indicated for each component. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 8.7 UNSIGNED_SHORT formats . . . . . . . . . . . . . . . . . . . . . 179 8.8 UNSIGNED_INT formats . . . . . . . . . . . . . . . . . . . . . . 180 8.9 FLOAT_UNSIGNED_INT formats . . . . . . . . . . . . . . . . . . 181 8.10 Packed pixel eld assignments. . . . . . . . . . . . . . . . . . . . 182 8.11 Conversion from RGBA, depth, and stencil pixel components to internal texture components. . . . . . . . . . . . . . . . . . . . . 185 8.12 Sized internal color formats. . . . . . . . . . . . . . . . . . . . . 190 8.13 Sized internal depth and stencil formats. . . . . . . . . . . . . . . 191 8.14 Generic and specic compressed internal formats. . . . . . . . . . 192 8.15 Internal formats for buffer textures . . . . . . . . . . . . . . . . . 215 8.16 Texture parameters and their values. . . . . . . . . . . . . . . . . 218 8.17 Texture, table, and lter return values. . . . . . . . . . . . . . . . 224 8.18 Selection of cube map images. . . . . . . . . . . . . . . . . . . . 226 8.19 Texel location wrap mode application. . . . . . . . . . . . . . . . 230 8.20 Legal texture targets for TextureView. . . . . . . . . . . . . . . . 241 8.21 Compatible internal formats for TextureView . . . . . . . . . . . 242 8.22 Depth texture comparison functions. . . . . . . . . . . . . . . . . 256 8.23 sRGB texture internal formats. . . . . . . . . . . . . . . . . . . . 257 8.24 Mapping of image load, store, and atomic texel coordinate components to texel numbers. . . . . . . . . . . . . . . . . . . . . . . . 261 8.25 Supported image unit formats, with equivalent format layout qual- iers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264 8.26 Texel sizes, compatibility classes, and pixel format/type combina- tions for each image format. . . . . . . . . . . . . . . . . . . . . 266 9.1 Framebuffer attachment points. . . . . . . . . . . . . . . . . . . . 283 9.2 Layer numbers for cube map texture faces. . . . . . . . . . . . . . 298 10.1 Triangles generated by triangle strips with adjacency. . . . . . . . 308 10.2 Vertex array sizes (values per vertex) and data types for generic vertex attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 10.3 Packed component layout for non-BGRA formats. . . . . . . . . . 321 10.4 Packed component layout for BGRA format. . . . . . . . . . . . . 321 10.5 Packed component layout for UNSIGNED_INT_10F_11F_11F_- REV format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322 10.6 Indirect commands and corresponding indirect buffer targets. . . . 323 11.1 Generic attribute components accessed by attribute variables. . . . 341 OpenGL 4.4 (Core Prole) - March 19, 2014 18. LIST OF TABLES xvi 11.2 Generic attributes and vector types used by column vectors of ma- trix variables bound to generic attribute index i. . . . . . . . . . . 342 11.3 Scalar and vector vertex attribute types . . . . . . . . . . . . . . . 342 13.1 Transform feedback modes . . . . . . . . . . . . . . . . . . . . . 398 13.2 Provoking vertex selection. . . . . . . . . . . . . . . . . . . . . . 403 15.1 Correspondence of ltered texture components to texture base components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436 17.1 RGB and alpha blend equations. . . . . . . . . . . . . . . . . . . 456 17.2 Blending functions. . . . . . . . . . . . . . . . . . . . . . . . . . 458 17.3 Logical operations . . . . . . . . . . . . . . . . . . . . . . . . . 462 17.4 Buffer selection for the default framebuffer . . . . . . . . . . . . 465 17.5 Buffer selection for a framebuffer object . . . . . . . . . . . . . . 465 17.6 DrawBuffers buffer selection for the default framebuffer . . . . . 466 18.1 PixelStore parameters. . . . . . . . . . . . . . . . . . . . . . . . 478 18.2 ReadPixels GL data types and reversed component conversion for- mulas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482 18.3 ReadPixels index masks. . . . . . . . . . . . . . . . . . . . . . . 483 18.4 Compatible internal formats for copying . . . . . . . . . . . . . . 489 20.1 Sources of debug output messages . . . . . . . . . . . . . . . . . 495 20.2 Types of debug output messages . . . . . . . . . . . . . . . . . . 496 20.3 Severity levels of messages . . . . . . . . . . . . . . . . . . . . . 496 20.4 Object namespace identiers . . . . . . . . . . . . . . . . . . . . 502 21.1 Hint targets and descriptions . . . . . . . . . . . . . . . . . . . . 508 22.1 Context prole bits . . . . . . . . . . . . . . . . . . . . . . . . . 512 22.2 Internal format targets . . . . . . . . . . . . . . . . . . . . . . . . 514 23.1 State Variable Types . . . . . . . . . . . . . . . . . . . . . . . . . 526 23.2 Current Values and Associated Data . . . . . . . . . . . . . . . . 527 23.3 Vertex Array Object State (cont.) . . . . . . . . . . . . . . . . . . 528 23.4 Vertex Array Object State (cont.) The ith attribute defaults to a value of i. . . . . . . . . . . . 529 23.5 Vertex Array Data (not in Vertex Array objects) . . . . . . . . . . 530 23.6 Buffer Object State . . . . . . . . . . . . . . . . . . . . . . . . . 531 23.7 Transformation state . . . . . . . . . . . . . . . . . . . . . . . . 532 23.8 Coloring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533 OpenGL 4.4 (Core Prole) - March 19, 2014 19. LIST OF TABLES xvii 23.9 Rasterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534 23.10Rasterization (cont.) . . . . . . . . . . . . . . . . . . . . . . . . . 535 23.11Multisampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536 23.12Textures (state per texture unit) . . . . . . . . . . . . . . . . . . . 537 23.13Textures (state per texture unit (cont.) . . . . . . . . . . . . . . . 538 23.14Textures (state per texture object) . . . . . . . . . . . . . . . . . . 539 23.15Textures (state per texture object) (cont.) . . . . . . . . . . . . . . 540 23.16Textures (state per texture image) . . . . . . . . . . . . . . . . . . 541 23.17Textures (state per texture image) (cont.) . . . . . . . . . . . . . . 542 23.18Textures (state per sampler object) . . . . . . . . . . . . . . . . . 543 23.19Texture Environment and Generation . . . . . . . . . . . . . . . . 544 23.20Pixel Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . 545 23.21Pixel Operations (cont.) . . . . . . . . . . . . . . . . . . . . . . . 546 23.22Framebuffer Control . . . . . . . . . . . . . . . . . . . . . . . . 547 23.23Framebuffer (state per target binding point) . . . . . . . . . . . . 548 23.24Framebuffer (state per framebuffer object) This state is queried from the currently bound read framebuffer.549 23.25Framebuffer (state per attachment point) . . . . . . . . . . . . . . 550 23.26Renderbuffer (state per target and binding point) . . . . . . . . . . 551 23.27Renderbuffer (state per renderbuffer object) . . . . . . . . . . . . 552 23.28Pixels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553 23.29Pixels (cont.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554 23.30Shader Object State . . . . . . . . . . . . . . . . . . . . . . . . . 555 23.31Program Pipeline Object State . . . . . . . . . . . . . . . . . . . 556 23.32Program Object State . . . . . . . . . . . . . . . . . . . . . . . . 557 23.33Program Object State (cont.) . . . . . . . . . . . . . . . . . . . . 558 23.34Program Object State (cont.) . . . . . . . . . . . . . . . . . . . . 559 23.35Program Object State (cont.) . . . . . . . . . . . . . . . . . . . . 560 23.36Program Object State (cont.) . . . . . . . . . . . . . . . . . . . . 561 23.37Program Object State (cont.) . . . . . . . . . . . . . . . . . . . . 562 23.38Program Object State (cont.) . . . . . . . . . . . . . . . . . . . . 563 23.39Program Object State (cont.) . . . . . . . . . . . . . . . . . . . . 564 23.40Program Interface State . . . . . . . . . . . . . . . . . . . . . . . 565 23.41Program Object Resource State . . . . . . . . . . . . . . . . . . . 566 23.42Program Object Resource State (cont.) . . . . . . . . . . . . . . . 567 23.43Vertex and Geometry Shader State (not part of program objects) . 568 23.44Query Object State . . . . . . . . . . . . . . . . . . . . . . . . . 569 23.45Image State (state per image unit) . . . . . . . . . . . . . . . . . 570 23.46Atomic Counter Buffer Binding State . . . . . . . . . . . . . . . 571 23.47Shader Storage Buffer Binding State . . . . . . . . . . . . . . . . 572 OpenGL 4.4 (Core Prole) - March 19, 2014 20. LIST OF TABLES xviii 23.48Transform Feedback State . . . . . . . . . . . . . . . . . . . . . 573 23.49Uniform Buffer Binding State . . . . . . . . . . . . . . . . . . . 574 23.50Sync (state per sync object) . . . . . . . . . . . . . . . . . . . . . 575 23.51Hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 576 23.52Compute Dispatch State . . . . . . . . . . . . . . . . . . . . . . 577 23.53Implementation Dependent Values . . . . . . . . . . . . . . . . . 578 23.54Implementation Dependent Values (cont.) . . . . . . . . . . . . . 579 23.55Implementation Dependent Values (cont.) . . . . . . . . . . . . . 580 23.56Implementation Dependent Version and Extension Support . . . . 581 23.57Implementation Dependent Vertex Shader Limits . . . . . . . . . 582 23.58Implementation Dependent Tessellation Shader Limits . . . . . . 583 23.59Implementation Dependent Tessellation Shader Limits (cont.) . . 584 23.60Implementation Dependent Geometry Shader Limits . . . . . . . 585 23.61Implementation Dependent Fragment Shader Limits . . . . . . . . 586 23.62Implementation Dependent Compute Shader Limits . . . . . . . . 587 23.63Implementation Dependent Aggregate Shader Limits . . . . . . . 588 23.64Implementation Dependent Aggregate Shader Limits (cont.) . . . 589 23.65Implementation Dependent Aggregate Shader Limits (cont.) . . . 590 23.66Implementation Dependent Aggregate Shader Limits (cont.) The minimum value for each stage is MAX_stage_UNIFORM_BLOCKS MAX_UNIFORM_BLOCK_SIZE / 4 + MAX_stage_UNIFORM_COMPONENTS . . . . . . . . . . . 591 23.67Debug Output State The initial value of DEBUG_OUTPUT is TRUE in a debug context and FALSE in a non-debug context. . . . . . . . . . . . . . . 592 23.68Implementation Dependent Debug Output State . . . . . . . . . . 593 23.69Implementation Dependent Values (cont.) . . . . . . . . . . . . . 594 23.70Implementation Dependent Values (cont.) . . . . . . . . . . . . . 595 23.71Internal Format Dependent Values . . . . . . . . . . . . . . . . . 596 23.72Implementation Dependent Transform Feedback Limits . . . . . . 597 23.73Framebuffer Dependent Values . . . . . . . . . . . . . . . . . . . 598 23.74Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . 599 C.1 Mode-dependent BPTC parameters . . . . . . . . . . . . . . . . . 615 C.2 Partition table for 2 subset . . . . . . . . . . . . . . . . . . . . . 616 C.3 Partition table for 3 subset . . . . . . . . . . . . . . . . . . . . . 617 C.4 Anchor index values for the second subset of two-subset partitioning618 C.5 Anchor index values for the second subset of three-subset partitioning618 C.6 Anchor index values for the third subset of three-subset partitioning 618 C.7 Endpoint and partition parameters for block modes . . . . . . . . 621 OpenGL 4.4 (Core Prole) - March 19, 2014 21. LIST OF TABLES xix C.8 Block formats for block modes . . . . . . . . . . . . . . . . . . . 622 C.9 Pixel layout for a 8 8 texture using four COMPRESSED_RGB8_- ETC2 compressed blocks. . . . . . . . . . . . . . . . . . . . . . . 624 C.10 Pixel layout for an COMPRESSED_RGB8_ETC2 compressed block. 626 C.11 Texel Data format for RGB8_ETC2 compressed textures formats . 627 C.12 Two 2 4-pixel subblocks side-by-side. . . . . . . . . . . . . . . 628 C.13 Two 4 2-pixel subblocks on top of each other. . . . . . . . . . . 628 C.14 Intensity modier sets for individual and differential modes: . . 629 C.15 Mapping from pixel index values to modier values for COMPRESSED_RGB8_ETC2 compressed textures . . . . . . . . . . 630 C.16 Distance table for T and H modes. . . . . . . . . . . . . . . . 631 C.17 Texel Data format for alpha part of COMPRESSED_RGBA8_ETC2_- EAC compressed textures. . . . . . . . . . . . . . . . . . . . . . . 633 C.18 Intensity modier sets for alpha component. . . . . . . . . . . . . 634 C.19 Texel Data format for RGB8_PUNCHTHROUGH_ALPHA1_ETC2 compressed textures formats . . . . . . . . . . . . . . . . . . . . 643 C.20 Intensity modier sets if opaque is set and if opaque is unset. . 645 C.21 Mapping from pixel index values to modier values for COMPRESSED_RGB8_PUNCHTHROUGH_ALPHA1_ETC2 compressed textures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 646 E.1 New token names . . . . . . . . . . . . . . . . . . . . . . . . . . 659 F.1 New token names . . . . . . . . . . . . . . . . . . . . . . . . . . 667 OpenGL 4.4 (Core Prole) - March 19, 2014 22. Chapter 1 Introduction This document, referred to as the OpenGL Specication or just Specication hereafter, describes the OpenGL graphics system: what it is, how it acts, and what is required to implement it. We assume that the reader has at least a rudimentary understanding of computer graphics. This means familiarity with the essentials of computer graphics algorithms and terminology as well as with modern GPUs (Graphic Processing Units). The canonical version of the Specication is available in the ofcial OpenGL Registry, located at URL http://www.opengl.org/registry/ 1.1 Formatting of the OpenGL Specication Starting with version 4.3, the OpenGL Specication has undergone major restructuring to focus on programmable shading, and to describe important concepts and objects in the context of the entire API before describing details of their use in the graphics pipeline. 1.1.1 This subsection is only dened in the compatibility prole. 1.1.2 This subsection is only dened in the compatibility prole. 1 23. 1.2. WHAT IS THE OPENGL GRAPHICS SYSTEM? 2 1.2 What is the OpenGL Graphics System? OpenGL (for Open Graphics Library) is an API (Application Programming Inter- face) to graphics hardware. The API consists of a set of several hundred procedures and functions that allow a programmer to specify the shader programs, objects, and operations involved in producing high-quality graphical images, specically color images of three-dimensional objects. Most of OpenGL requires that the graphics hardware contain a framebuffer. Many OpenGL calls control drawing geometric objects such as points, lines, and polygons, but the way that some of this drawing occurs (such as when antialiasing or multisampling is in use) relies on the existence of a framebuffer and its properties. Some commands explicitly manage the framebuffer. 1.2.1 Programmers View of OpenGL To the programmer, OpenGL is a set of commands that allow the specication of shader programs or shaders, data used by shaders, and state controlling aspects of OpenGL outside the scope of shaders. Typically the data represent geometry in two or three dimensions and texture images, while the shaders control the geometric processing, rasterization of geometry and the lighting and shading of fragments generated by rasterization, resulting in rendering geometry into the framebuffer. A typical program that uses OpenGL begins with calls to open a window into the framebuffer into which the program will draw. Then, calls are made to allocate an OpenGL context and associate it with the window. Once a context is allocated, OpenGL commands to dene shaders, geometry, and textures are made, followed by commands which draw geometry by transferring specied portions of the geometry to the shaders. Drawing commands specify simple geometric objects such as points, line segments, and polygons, which can be further manipulated by shaders. There are also commands which directly control the framebuffer by reading and writing pixels. 1.2.2 Implementors View of OpenGL To the implementor, OpenGL is a set of commands that control the operation of the GPU. Modern GPUs accelerate almost all OpenGL operations, storing data and framebuffer images in GPU memory and executing shaders in dedicated GPU processors. However, OpenGL may be implemented on less capable GPUs, or even without a GPU, by moving some or all operations into the host CPU. The implementors task is to provide a software library on the CPU which implements the OpenGL API, while dividing the work for each OpenGL command OpenGL 4.4 (Core Prole) - March 19, 2014 24. 1.2. WHAT IS THE OPENGL GRAPHICS SYSTEM? 3 between the CPU and the graphics hardware as appropriate for the capabilities of the GPU. OpenGL contains a considerable amount of information including many types of objects representing programmable shaders and the data they consume and generate, as well as other context state controlling non-programmable aspects of OpenGL. Most of these objects and state are available to the programmer, who can set, manipulate, and query their values through OpenGL commands. Some of it, however, is derived state visible only by the effect it has on how OpenGL oper- ates. One of the main goals of this Specication is to describe OpenGL objects and context state explicitly, to elucidate how they change in response to OpenGL commands, and to indicate what their effects are. 1.2.3 Our View We view OpenGL as a pipeline having some programmable stages and some state- driven xed-function stages that are invoked by a set of specic drawing operations. This model should engender a specication that satises the needs of both programmers and implementors. It does not, however, necessarily provide a model for implementation. An implementation must produce results conforming to those produced by the specied methods, but there may be ways to carry out a particular computation that are more efcient than the one specied. 1.2.4 Fixed-function Hardware and the Compatibility Prole Older generations of graphics hardware were not programmable using shaders, although they were congurable by setting state controlling specic details of their operation. The compatibility prole of OpenGL continues to support the legacy OpenGL commands developed for such xed-function hardware, although they are typically implemented by writing shaders which reproduce the operation of such hardware. Fixed-function OpenGL commands and operations are described as alternative interfaces following descriptions of the corresponding shader stages. 1.2.5 The Deprecation Model Features marked as deprecated in one version of the Specication are expected to be removed in a future version, allowing applications time to transition away from use of deprecated features. The deprecation model is described in more detail, together with a summary of the commands and state deprecated from this version of the API, in appendix D. OpenGL 4.4 (Core Prole) - March 19, 2014 25. 1.3. RELATED APIS 4 1.3 Related APIs Other APIs related to OpenGL are described below. Most of the specications for these APIs are available on the Khronos Group websites, although some vendor- specic APIs are documented on that vendors developer website. 1.3.1 OpenGL Shading Language The OpenGL Specication should be read together with a companion document titled The OpenGL Shading Language. The latter document (referred to as the OpenGL Shading Language Specication hereafter) denes the syntax and semantics of the programming language used to write shaders (see chapter 7). Descrip- tions of shaders later in this document may include references to concepts and terms (such as shading language variable types) dened in the OpenGL Shading Language Specication. OpenGL 4.4 implementations are guaranteed to support version 4.40 of the OpenGL Shading Language. All references to sections of that specication refer to that version. The latest supported version of the shading language may be queried as described in section 22.2. The core prole of OpenGL 4.4 is also guaranteed to support all previous versions of the OpenGL Shading Language back to version 1.40. In some implementations the core prole may also support earlier versions of the Shading Language, and may support compatibility prole versions of the Shading Language for versions 1.40 and earlier. In this case, errors will be generated when using language features such as compatibility prole built-ins not supported by the core prole API. The #version strings for all supported versions of the OpenGL Shading Language may be queried as described in section 22.2. The OpenGL Shading Language Specication is available in the OpenGL Reg- istry. 1.3.2 OpenGL ES OpenGL ES is a royalty-free, cross-platform API for full-function 2D and 3D graphics on embedded systems such as mobile phones, game consoles, and ve- hicles. It consists of well-dened subsets of OpenGL. OpenGL ES version 1.1 implements a subset of the OpenGL 1.5 xed-function API, OpenGL ES 2.0 implements a subset of the OpenGL 2.0 shader-based API, and OpenGL ES 3.0 implements a subset of OpenGL 3.3. OpenGL ES versions also include some additional functionality taken from later OpenGL versions or specic to OpenGL ES. It is OpenGL 4.4 (Core Prole) - March 19, 2014 26. 1.3. RELATED APIS 5 straightforward to port code written for OpenGL ES to corresponding versions of OpenGL. OpenGL and OpenGL ES are developed in parallel within the Khronos Group, which controls both standards. OpenGL 4.3 includes functionality initially dened in OpenGL ES 3.0, for increased compatibility between OpenGL and OpenGL ES implementations. The OpenGL ES Specications are available in the Khronos API Registry at URL http://www.khronos.org/registry/ 1.3.3 OpenGL ES Shading Language The Specication should also be read together with companion documents titled The OpenGL ES Shading Language. Both versions 1.00 and 3.00 should be read. These documents dene versions of the OpenGL Shading Language designed for implementations of OpenGL ES 2.0 and 3.0 respectively, but also supported by OpenGL implementations. References to the OpenGL Shading Language Speci- cation hereafter include both OpenGL and OpenGL ES versions of the Shading Language; references to specic sections are to those sections in version 4.40 of the OpenGL Shading Language Specication. OpenGL 4.4 implementations are guaranteed to support both versions 1.00 and 3.00 of the OpenGL ES Shading Language. The #version strings for all supported versions of the OpenGL Shading Lan- guage may be queried as described in section 22.2. The OpenGL ES Shading Language Specications are available in the Khronos API Registry. 1.3.4 WebGL WebGL is a cross-platform, royalty-free web standard for a low-level 3D graphics API based on OpenGL ES 2.0. Developers familiar with OpenGL ES 2.0 will recognize WebGL as a shader-based API using a form of the OpenGL Shading Language, with constructs that are semantically similar to those of the underly- ing OpenGL ES 2.0 API. It stays very close to the OpenGL ES 2.0 specication, with some concessions made for what developers expect out of memory-managed languages such as JavaScript. The WebGL Specication and related documentation are available in the Khronos API Registry. OpenGL 4.4 (Core Prole) - March 19, 2014 27. 1.3. RELATED APIS 6 1.3.5 Window System Bindings OpenGL requires a companion API to create and manage graphics contexts, windows to render into, and other resources beyond the scope of this Specication. There are several such APIs supporting different operating and window systems. 1.3.5.1 GLX - X Window System Bindings OpenGL Graphics with the X Window System, referred to as the GLX Specication hereafter, describes the GLX API for use of OpenGL in the X Window System. It is primarily directed at Linux and Unix systems, but GLX implementations also exist for Microsoft Windows, MacOS X, and some other platforms where X is available. The GLX Specication is available in the OpenGL Registry. 1.3.5.2 WGL - Microsoft Windows Bindings The WGL API supports use of OpenGL with Microsoft Windows. WGL is documented in Microsofts MSDN system, although no full specication exists. 1.3.5.3 MacOS X Window System Bindings Several APIs exist supporting use of OpenGL with Quartz, the MacOS X window system, including CGL, AGL, and NSOpenGLView. These APIs are documented on Apples developer website. 1.3.5.4 EGL - Mobile and Embedded Device Bindings The Khronos Native Platform Graphics Interface or EGL Specication describes the EGL API for use of OpenGL ES on mobile and embedded devices. EGL implementations supporting OpenGL may be available on some desktop platforms as well. The EGL Specication is available in the Khronos API Registry. 1.3.6 OpenCL OpenCL is an open, royalty-free standard for cross-platform, general-purpose parallel programming of processors found in personal computers, servers, and mobile devices, including GPUs. OpenCL denes interop methods to share OpenCL memory and image objects with corresponding OpenGL buffer and texture objects, and to coordinate control of and transfer of data between OpenCL and OpenGL. This allows applications to split processing of data between OpenCL and OpenGL; for example, by using OpenCL to implement a physics model and then rendering and interacting with the resulting dynamic geometry using OpenGL. OpenGL 4.4 (Core Prole) - March 19, 2014 28. 1.4. FILING BUG REPORTS 7 The OpenCL Specication is available in the Khronos API Registry. 1.4 Filing Bug Reports Bug reports on the OpenGL and OpenGL Shading Language Specications can be led in the Khronos Public Bugzilla, located at URL http://www.khronos.org/bugzilla/ Please le bugs against Product: OpenGL, Component: Specication, and the appropriate version of the specication. It is best to le bugs against the most re- cently released versions, since older versions are usually not updated for bugxes. OpenGL 4.4 (Core Prole) - March 19, 2014 29. Chapter 2 OpenGL Fundamentals This chapter introduces fundamental concepts including the OpenGL execution model, API syntax, contexts and threads, numeric representation, context state and state queries, and the different types of objects and shaders. It provides a frame- work for interpreting more specic descriptions of commands and behavior in the remainder of the Specication. 2.1 Execution Model OpenGL (henceforth, the GL) is concerned only with processing data in GPU memory, including rendering into a framebuffer and reading values stored in that framebuffer. There is no support for other input or output devices. Programmers must rely on other mechanisms to obtain user input. The GL draws primitives processed by a variety of shader programs and xed- function processing units controlled by context state. Each primitive is a point, line segment, patch, or polygon. Context state may be changed independently; the setting of one piece of state does not affect the settings of others (although state and shader all interact to determine what eventually ends up in the framebuffer). State is set, primitives drawn, and other GL operations described by sending commands in the form of function or procedure calls. Primitives are dened by a group of one or more vertices. A vertex denes a point, an endpoint of a line segment, or a corner of a polygon where two edges meet. Data such as positional coordinates, colors, normals, texture coordinates, etc. are associated with a vertex and each vertex is processed independently, in order, and in the same way. The only exception to this rule is if the group of vertices must be clipped so that the indicated primitive ts within a specied region; in this case vertex data may be modied and new vertices created. The type of clipping 8 30. 2.1. EXECUTION MODEL 9 depends on which primitive the group of vertices represents. Commands are always processed in the order in which they are received, although there may be an indeterminate delay before the effects of a command are realized. This means, for example, that one primitive must be drawn completely before any subsequent one can affect the framebuffer. It also means that queries and pixel read operations return state consistent with complete execution of all previously invoked GL commands, except where explicitly specied otherwise. In general, the effects of a GL command on either GL state or the framebuffer must be complete before any subsequent command can have any such effects. Data binding occurs on call. This means that data passed to a GL command are interpreted when that command is received. Even if the command requires a pointer to data, those data are interpreted when the call is made, and any subsequent changes to the data have no effect on the GL (unless the same pointer is used in a subsequent command). The GL provides direct control over the fundamental operations of 3D and 2D graphics. This includes specication of parameters of application-dened shader programs performing transformation, lighting, texturing, and shading operations, as well as built-in functionality such as antialiasing and texture ltering. It does not provide a means for describing or modeling complex geometric objects, although shaders can be written to generate such objects. In other words, OpenGL provides mechanisms to describe how complex geometric objects are to be rendered, rather than mechanisms to describe the complex objects themselves. The model for interpretation of GL commands is client-server. That is, a program (the client) issues commands, and these commands are interpreted and processed by the GL (the server). The server may or may not operate on the same computer or in the same address space as the client. In this sense, the GL is network transparent. A server may maintain a number of GL contexts, each of which is an encapsulation of current GL state and objects. A client may choose to be made current to any one of these contexts. Issuing GL commands when a program is not current to a context results in undened behavior. There are two classes of framebuffers: a window system-provided framebuffer associated with a context when the context is made current, and application-created framebuffers. The window system-provided framebuffer is referred to as the default framebuffer. Application-created framebuffers, referred to as framebuffer objects, may be created as desired, A context may be associated with two framebuffers, one for each of reading and drawing operations. The default framebuffer and framebuffer objects are distinguished primarily by the interfaces for congur- ing and managing their state. The effects of GL commands on the default framebuffer are ultimately con- OpenGL 4.4 (Core Prole) - March 19, 2014 31. 2.2. COMMAND SYNTAX 10 trolled by the window system, which allocates framebuffer resources, determines which portions of the default framebuffer the GL may access at any given time, and communicates to the GL how those portions are structured. Therefore, there are no GL commands to initialize a GL context or congure the default framebuffer. Similarly, display of framebuffer contents on a physical display device (including the transformation of individual framebuffer values by such techniques as gamma correction) is not addressed by the GL. Allocation and conguration of the default framebuffer occurs outside of the GL in conjunction with the window system, using companion APIs described in section 1.3.5. Allocation and initialization of GL contexts is also done using these companion APIs. GL contexts can be associated with different default framebuffers, and some context state is determined at the time this association is performed. It is possible to use a GL context without a default framebuffer, in which case a framebuffer object must be used to perform all rendering. This is useful for applications needing to perform offscreen rendering. OpenGL is designed to be run on a range of platforms with varying capabilities, memory, and performance. To accommodate this variety, we specify ideal behavior instead of actual behavior for certain GL operations. In cases where deviation from the ideal is allowed, we also specify the rules that an implementation must obey if it is to approximate the ideal behavior usefully. This allowed variation in GL behavior implies that two distinct GL implementations may not agree pixel for pixel when presented with the same input, even when run on identical framebuffer congurations. Finally, command names, constants, and types are prexed in the C language binding to OpenGL (by gl, GL_, and GL, respectively), to reduce name clashes with other packages. The prexes are omitted in this document for clarity. 2.2 Command Syntax The Specication describes OpenGL commands as functions or procedures using ANSI C syntax. Languages such as C++ and Javascript which allow passing of argument type information permit language bindings with simpler declarations and fewer entry points. Various groups of GL commands perform the same operation but differ in how arguments are supplied to them. To conveniently accommodate this variation, we adopt a notation for describing commands and their arguments. GL commands are formed from a name which may be followed, depending on the particular command, by a sequence of characters describing a parameter to the OpenGL 4.4 (Core Prole) - March 19, 2014 32. 2.2. COMMAND SYNTAX 11 command. If present, a digit indicates the required length (number of values) of the indicated type. Next, a string of characters making up one of the type descriptors from table 2.1 indicates the specic size and data type of parameter values. A nal v character, if present, indicates that the command takes a pointer to an array (a vector) of values rather than a series of individual arguments. Two specic examples are: void Uniform4f( int location, float v0, float v1, float v2, float v3 ); and void GetFloatv( enum pname, float *data ); In general, a command declaration has the form rtype Name{ 1234}{ b s i i64 f d ub us ui ui64}{ v} ( [args ,] T arg1, . . ., T argN [, args] ); rtype is the return type of the function. The braces ({}) enclose a series of type descriptors (see table 2.1), of which one is selected. indicates no type descriptor. The arguments enclosed in brackets ([args ,] and [, args]) may or may not be present. The N arguments arg1 through argN have type T, which corresponds to one of the type descriptors indicated in table 2.1 (if there are no letters, then the arguments type is given explicitly). If the nal character is not v, then N is given by the digit 1, 2, 3, or 4 (if there is no digit, then the number of arguments is xed). If the nal character is v, then only arg1 is present and it is an array of N values of the indicated type. For example, void Uniform{1234}{if}( int location, T value ); indicates the eight declarations void Uniform1i( int location, int value ); void Uniform1f( int location, float value ); void Uniform2i( int location, int v0, int v1 ); void Uniform2f( int location, float v0, float v1 ); void Uniform3i( int location, int v0, int v1, int v2 ); void Uniform3f( int location, float v0, float v1, float v3 ); OpenGL 4.4 (Core Prole) - March 19, 2014 33. 2.2. COMMAND SYNTAX 12 Type Descriptor Corresponding GL Type b byte s short i int i64 int64 f float d double ub ubyte us ushort ui uint ui64 uint64 Table 2.1: Correspondence of command sufx type descriptors to GL argument types. Refer to table 2.2 for denitions of the GL types. void Uniform4i( int location, int v0, int v1, int v2, int v3 ); void Uniform4f( int location, float v0, float v1, float v2, float v3 ); Arguments whose type is xed (i.e. not indicated by a sufx on the command) are of one of the GL data types summarized in table 2.2, or pointers to one of these types. Since many GL operations represent bitelds within these types, transfer blocks of data in these types to graphics hardware which uses the same data types, or otherwise requires these sizes, it is not possible to implement the GL API on an architecture which cannot satisfy the exact bit width requirements in table 2.2. The types clampf and clampd are no longer used, replaced by float and double respectively together with specication language requiring parameter clamping1. 2.2.1 Data Conversion For State-Setting Commands Many GL commands specify a value or values to which GL state of a specic type (boolean, enum, integer, or oating-point) is to be set. When multiple versions of such a command exist, using the type descriptor syntax described above, any such version may be used to set the state value. When state values are specied using 1 These changes are backwards-compatible at the compilation and linking levels, and are being propagated to man pages and header les as well. OpenGL 4.4 (Core Prole) - March 19, 2014 34. 2.2. COMMAND SYNTAX 13 GL Type Description Bit Width boolean 1 or more Boolean byte 8 Signed twos complement binary integer ubyte 8 Unsigned binary integer char 8 Characters making up strings short 16 Signed twos complement binary integer ushort 16 Unsigned binary integer int 32 Signed twos complement binary integer uint 32 Unsigned binary integer fixed 32 Signed twos complement 16.16 scaled integer int64 64 Signed twos complement binary integer uint64 64 Unsigned binary integer sizei 32 Non-negative binary integer size enum 32 Enumerated binary integer value intptr ptrbits Signed twos complement binary integer sizeiptr ptrbits Non-negative binary integer size sync ptrbits Sync object handle (see section 4.1) bitfield 32 Bit eld half 16 Half-precision oating-point value encoded in an unsigned scalar float 32 Floating-point value clampf 32 Floating-point value clamped to [0, 1] double 64 Floating-point value clampd 64 Floating-point value clamped to [0, 1] Table 2.2: GL data types. GL types are not C types. Thus, for example, GL type int is referred to as GLint outside this document, and is not necessarily equivalent to the C type int. An implementation must use exactly the number of bits indicated in the table to represent a GL type. ptrbits is the number of bits required to represent a pointer type; in other words, types intptr, sizeiptr, and sync must be large enough to store any CPU address. sync is dened as an anonymous struct pointer in the C language bindings while intptr and sizeiptr are dened as integer types large enough to hold a pointer. OpenGL 4.4 (Core Prole) - March 19, 2014 35. 2.2. COMMAND SYNTAX 14 a different parameter type than the actual type of that state, data conversions are performed as follows: When the type of internal state is boolean, zero integer or oating-point values are converted to FALSE and non-zero values are converted to TRUE. When the type of internal state is integer or enum, boolean values of FALSE and TRUE are converted to 0 and 1, respectively. Floating-point values are rounded to the nearest integer. If the resulting value is so large in magnitude that it cannot be represented by the internal state variable, the internal state value is undened. When the type of internal state is oating-point, boolean values of FALSE and TRUE are converted to 0.0 and 1.0, respectively. Integer values are converted to oating-point, with or without normalization as described for specic commands. For commands taking arrays of the specied type, these conversions are performed for each element of the passed array. Each command following these conversion rules refers back to this section. Some commands have additional conversion rules specic to certain state values and data types, which are described following the reference. Validation of values performed by state-setting commands is performed after conversion, unless specied otherwise for a specic command. 2.2.2 Data Conversions For State Query Commands Query commands (commands whose name begins with Get) return a value or values to which GL state has been set. Some of these commands exist in multiple versions returning different data types. When a query command is issued that returns data types different from the actual type of that state, data conversions are performed as follows: If a command returning boolean data is called, such as GetBooleanv, a oating-point or integer value converts to FALSE if and only if it is zero. Otherwise it converts to TRUE. If a command returning integer data is called, such as GetIntegerv or Get- Integer64v, a boolean value of TRUE or FALSE is interpreted as one or zero, respectively. A oating-point value is rounded to the nearest integer, unless the value is an RGBA color component, a DepthRange value, or a depth OpenGL 4.4 (Core Prole) - March 19, 2014 36. 2.3. COMMAND EXECUTION 15 buffer clear value. In these cases, the query command converts the oating- point value to an integer according to the INT entry of table 18.2; a value not in [1, 1] converts to an undened value. If a command returning oating-point data is called, such as GetFloatv or GetDoublev, a boolean value of TRUE or FALSE is interpreted as 1.0 or 0.0, respectively. An integer value is coerced to oating-point. Single- and double-precision oating-point values are converted as necessary. If a value is so large in magnitude that it cannot be represented by the returned data type, then the nearest value representable using the requested type is returned. When querying bitmasks (such as SAMPLE_MASK_VALUE or STENCIL_- WRITEMASK) with GetIntegerv, the mask value is treated as a signed integer, so that mask values with the high bit set will not be clamped when returned as signed integers. Unless otherwise indicated, multi-valued state variables return their multiple values in the same order as they are given as arguments to the commands that set them. For instance, the two DepthRange parameters are returned in the order n followed by f. 2.3 Command Execution Most of the Specication discusses the behavior of a single context bound to a single CPU thread. It is also possible for multiple contexts to share GL objects and for each such context to be bound to a different thread. This section introduces concepts related to GL command execution including error reporting, command queue ushing, and synchronization between command streams. Using these tools can increase performance and utilization of the GPU by separating loosely related tasks into different contexts. Methods to create, manage, and destroy CPU threads are dened by the host CPU operating system and are not described in the Specication. Binding of GL contexts to CPU threads is controlled through a window system binding layer such as those described in section 1.3.5. 2.3.1 Errors The GL detects only a subset of those conditions that could be considered errors. This is because in many cases error checking would adversely impact the performance of an error-free program. The command OpenGL 4.4 (Core Prole) - March 19, 2014 37. 2.3. COMMAND EXECUTION 16 enum GetError( void ); is used to obtain error information. Each detectable error is assigned a numeric code. When an error is detected, a ag is set and the code is recorded. Further errors, if they occur, do not affect this recorded code. When GetError is called, the code is returned and the ag is cleared, so that a further error will again record its code. If a call to GetError returns NO_ERROR, then there has been no detectable error since the last call to GetError (or since the GL was initialized). To allow for distributed implementations, there may be several ag-code pairs. In this case, after a call to GetError returns a value other than NO_ERROR each subsequent call returns the non-zero code of a distinct ag-code pair (in unspecied order), until all non-NO_ERROR codes have been returned. When there are no more non-NO_ERROR error codes, all ags are reset. This scheme requires some positive number of pairs of a ag bit and an integer. The initial state of all ags is cleared and the initial value of all codes is NO_ERROR. Table 2.3 summarizes GL errors. Currently, when an error ag is set, results of GL operation are undened only if an OUT_OF_MEMORY error has occurred. In other cases, there are no side effects unless otherwise noted; the command which generates the error is ignored so that it has no effect on GL state or framebuffer contents. Except as otherwise noted, if the generating command returns a value, it returns zero. If the generating command modies values through a pointer argument, no change is made to these values. These error semantics apply only to GL errors, not to system errors such as memory access errors. This behavior is the current behavior; the action of the GL in the presence of errors is subject to change, and extensions to OpenGL may dene behavior currently considered as an error. Several error generation conditions are implicit in the description of every GL command. If a command that requires an enumerated value is passed a symbolic constant that is not one of those specied as allowable for that command, an INVALID_ENUM error is generated. This is the case even if the argument is a pointer to a symbolic constant, if the value or values pointed to are not allowable for the given command. If a negative number is provided where an argument of type sizei or sizeiptr is specied, an INVALID_VALUE error is generated. If memory is exhausted as a side effect of the execution of a command, an OUT_OF_MEMORY error may be generated. OpenGL 4.4 (Core Prole) - March 19, 2014 38. 2.3. COMMAND EXECUTION 17 Error Description Offending command ignored? INVALID_ENUM enum argument out of range Yes INVALID_VALUE Numeric argument out of range Yes INVALID_OPERATION Operation illegal in current state Yes INVALID_FRAMEBUFFER_OPERATION Framebuffer object is not complete Yes OUT_OF_MEMORY Not enough memory left to exe- cute command Unknown STACK_OVERFLOW Command would cause a stack overow Yes STACK_UNDERFLOW Command would cause a stack underow Yes Table 2.3: Summary of GL errors The Specication attempts to explicitly describe these implicit error conditions (with the exception of OUT_OF_MEMORY2) wherever they apply. However, they apply even if not explicitly described, unless a specic command describes different behavior. For example, certain commands use a sizei parameter to indicate the length of a string, and also use negative values of the parameter to indicate a null- terminated string. These commands do not generate an INVALID_VALUE error, because they explicitly describe different behavior. Otherwise, errors are generated only for conditions that are explicitly described in the Specication. When a command could potentially generate several different errors (for example, when it is passed separate enum and numeric parameters which are both out of range), the GL implementation may choose to generate any of the applicable errors. When an error is generated, the GL may also generate a debug output message describing its cause (see chapter 20). The message has source DEBUG_SOURCE_- API, type DEBUG_TYPE_ERROR, and an implementation-dependent ID. Most commands include a complete summary of errors at the end of their description, including even the implicit errors described above. 2 OUT_OF_MEMORY is not described because it can potentially be generated by any GL command, even those which do not explicitly allocate GPU memory. OpenGL 4.4 (Core Prole) - March 19, 2014 39. 2.3. COMMAND EXECUTION 18 Such error summaries are set in a distinct style, like this sentence. In some cases, however, errors may be generated for a single command for reasons not directly related to that command. One such example is that deferred processing for shader programs may result in link errors detected only when at- tempting to draw primitives using vertex specication commands. In such cases, errors generated by a command may be described elsewhere in the specication than the command itself. 2.3.2 Flush and Finish Implementations may buffer multiple commands in a command queue before sending them to the GL server for execution. This may happen in places such as the network stack (for network transparent implementations), CPU code executing as part of the GL client or the GL server, or internally to the GPU hardware. Coarse control over command queues is available using the command void Flush( void ); which causes all previously issued GL commands to complete in nite time (although such commands may still be executing when Flush returns). The command void Finish( void ); forces all previously issued GL commands to complete. Finish does not return until all effects from such commands on GL client and server state and the framebuffer are fully realized. Finer control over command execution can be expressed using fence commands and sync objects, as discussed in section 4.1. 2.3.3 Numeric Representation and Computation The GL must perform a number of oating-point operations during the course of its operation. Implementations normally perform computations in oating-point, and must meet the range and precision requirements dened under Floating-Point Com- putation below. These requirements only apply to computations performed in GL operations outside of shader execution, such as texture image specication and sampling, and OpenGL 4.4 (Core Prole) - March 19, 2014 40. 2.3. COMMAND EXECUTION 19 per-fragment operations. Range and precision requirements during shader execution differ and are specied by the OpenGL Shading Language Specication. In some cases, the representation and/or precision of operations is implicitly limited by the specied format of vertex, texture, or renderbuffer data consumed by the GL. Specic oating-point formats are described later in this section. 2.3.3.1 Floating-Point Computation We do not specify how oating-point numbers are to be represented, or the details of how operations on them are performed. We require simply that numbers oating-point parts contain enough bits and that their exponent elds are large enough so that individual results of oating- point operations are accurate to about 1 part in 105. The maximum representable magnitude for all oating-point values must be at least 232. x 0 = 0 x = 0 for any non-innite and non-NaN x. 1 x = x 1 = x. x + 0 = 0 + x = x. 00 = 1. (Occasionally further requirements will be specied.) Most single-precision oating-point formats meet these requirements. The special values Inf and Inf encode values with magnitudes too large to be represented; the special value NaN encodes Not A Number values resulting from undened arithmetic operations such as 0 0. Implementations are permitted, but not required, to support Inf s and NaN s in their oating-point computations. Any representable oating-point value is legal as input to a GL command that requires oating-point data. The result of providing a value that is not a oating- point number to such a command is unspecied, but must not lead to GL interruption or termination. In IEEE arithmetic, for example, providing a negative zero or a denormalized number to a GL command yields predictable results, while providing a NaN or an innity yields unspecied results. 2.3.3.2 16-Bit Floating-Point Numbers A 16-bit oating-point number has a 1-bit sign (S), a 5-bit exponent (E), and a 10-bit mantissa (M). The value V of a 16-bit oating-point number is determined by the following: V = (1)S 0.0, E = 0, M = 0 (1)S 214 M 210 , E = 0, M = 0 (1)S 2E15 1 + M 210 , 0 < E < 31 (1)S Inf , E = 31, M = 0 NaN , E = 31, M = 0 OpenGL 4.4 (Core Prole) - March 19, 2014 41. 2.3. COMMAND EXECUTION 20 If the oating-point number is interpreted as an unsigned 16-bit integer N, then S = N mod 65536 32768 E = N mod 32768 1024 M = N mod 1024. Any representable 16-bit oating-point value is legal as input to a GL command that accepts 16-bit oating-point data. The result of providing a value that is not a oating-point number (such as Inf or NaN ) to such a command is unspecied, but must not lead to GL interruption or termination. Providing a denormalized number or negative zero to GL must yield predictable results. 2.3.3.3 Unsigned 11-Bit Floating-Point Numbers An unsigned 11-bit oating-point number has no sign bit, a 5-bit exponent (E), and a 6-bit mantissa (M). The value V of an unsigned 11-bit oating-point number is determined by the following: V = 0.0, E = 0, M = 0 214 M 64 , E = 0, M = 0 2E15 1 + M 64 , 0 < E < 31 Inf , E = 31, M = 0 NaN , E = 31, M = 0 If the oating-point number is interpreted as an unsigned 11-bit integer N, then E = N 64 M = N mod 64. When a oating-point value is converted to an unsigned 11-bit oating-point representation, nite values are rounded to the closest representable nite value. While less accurate, implementations are allowed to always round in the direction of zero. This means negative values are converted to zero. Likewise, nite positive values greater than 65024 (the maximum nite representable unsigned 11-bit oating-point value) are converted to 65024. Additionally: negative innity is converted to zero; positive innity is converted to positive innity; and both positive and negative NaN are converted to positive NaN . OpenGL 4.4 (Core Prole) - March 19, 2014 42. 2.3. COMMAND EXECUTION 21 Any representable unsigned 11-bit oating-point value is legal as input to a GL command that accepts 11-bit oating-point data. The result of providing a value that is not a oating-point number (such as Inf or NaN ) to such a command is unspecied, but must not lead to GL interruption or termination. Providing a denormalized number to GL must yield predictable results. 2.3.3.4 Unsigned 10-Bit Floating-Point Numbers An unsigned 10-bit oating-point number has no sign bit, a 5-bit exponent (E), and a 5-bit mantissa (M). The value V of an unsigned 10-bit oating-point number is determined by the following: V = 0.0, E = 0, M = 0 214 M 32 , E = 0, M = 0 2E15 1 + M 32 , 0 < E < 31 Inf , E = 31, M = 0 NaN , E = 31, M = 0 If t

opengl spec 4.4 core

Technology

query objects

shared objects

framebuffer objects

renderbuffer objects

shader objects

texture objects

specication version

binding buffer objects