CS 148: Summer 2016Introduction of Graphics and ImagingZahid Hossain

OpenGL

http://www.pling.org.uk/cs/cgv.html

SoFar:TheoryofRasterization

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 2

Observation

• Applytransformation• Barycentric Interpolation• Rasterize• ComputeLightandShading(Moreonitlater)• LookupTextures(Moreonitlater)• Andlotmore….

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 3

Observation

• Applytransformation• Barycentric Interpolation• Rasterize• ComputeLightandShading(Moreonitlater)• LookupTextures(Moreonitlater)• Andlotmore….

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 4

To Millions of Triangles

and Billions of Fragments

Observation

• Applytransformation• Barycentric Interpolation• Rasterize• ComputeLightandShading(Moreonitlater)• LookupTextures(Moreonitlater)• Andlotmore….

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 5

To Millions of Triangles

and Billions of Fragments

SIMD(Single Instruction Multiple Data)

GraphicsHardware

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2560 cores! (upto 1733 MHz, 8GB Mem)http://www.geforce.com/hardware/10series/geforce-gtx-1080

GTX1080

Advice

Leaveimplementationoflow-levelfeaturestotheexperts.

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 7

Advice

Leaveimplementationoflow-levelfeaturestotheexperts.

Why?

• Abstractawayhardwaredifferences

• Rasterizationshouldbefast

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 8

Introducing…

Industry Standard API for Computer Graphics(Cross Platform, since 1992)

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NottheOnlyOne

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RelatedAPIsintheOpenGLFamily

GoogleMaps

AngryBirdsbyRovio

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RelatedAPIsintheOpenGLFamily

GoogleMaps

AngryBirdsbyRovio

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OpenGL1.x

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OpenGL1.x:Why?

•Easytolearn!•Littlecode•Instructional

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SimpleFirstProgram

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WhatOpenGLIsNot

OpenGLisnotawindowingsystem

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IntroducingGLUT(GLUtilityToolkit)

• Simplecross-platformwindowingAPI• glutInitDisplay(), glutInitWindowSize(..)

• Bindings:C,C++,Fortran,Ada,…• Features:• Multiplewindows,menus• Keyboard/mouse/otherinput• Assortedcallbacks:idle,timers• Basicfontsupport‘• glutSolidTeapot, glutSolidSphere, glutSolidCube, …

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IntroducingGLUT(GLUtilityToolkit)

• Simplecross-platformwindowingAPI• glutInitDisplay(), glutInitWindowSize(..)

• Bindings:C,C++,Fortran,Ada,…• Features:• Multiplewindows,menus• Keyboard/mouse/otherinput• Assortedcallbacks:idle,timers• Basicfontsupport‘• glutSolidTeapot, glutSolidSphere, glutSolidCube, …

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Other options: glfw, SDL

IntroducingGLU(GLUtility)• High-levelgraphicscommands• Not includedinOpenGLES• Someinterestingfeatures:• Mappingbetweenworldandscreencoordinates• Texturingsupport• Tessellationandothergeometricutilities• OpenGLerrorcodelookup• Moreprimitives:spheres,cylinders,disks,…• Camerasupport:gluLookAt, gluOrtho2D, …

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SimpleFirstProgram

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Projection Matrix !(GL_PROJECTION)

SimpleFirstProgram

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Camera and Model Matrices Combined !

(GL_MODELVIEW)

gluLookAt(eye,at,up)

defines thecamera/viewingmatrix!

whereistheviewpoint?

whereisitpointed?

whichwayisup?

eyeat

up

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gluPerspective(fovy,aspect,near,far)

TheRedbook, fig.3-14(p.155)

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TransformationRecall

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TransformationRecall

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NDC à Viewport Transformation à Final Image

glViewport(x,y,width,height)

(x,y)atlowerleft

height

width

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Primitive[prim-i-tiv]:

AsmallpieceofgeometrythatcanberenderedinOpenGL;e.g.triangles,lines,pointsetc.

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OpenGLPrimitiveTypes

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http://www.opengl2go.net/wp-content/uploads/2015/10/gl-primitives-with-background.png

OpenGLPrimitives(Triangles)

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1 2

3

4 5

6

OpenGLPrimitives(TriangleStrip)

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1

2

3

4

5

OpenGLPrimitives(TriangleStrip)

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1

2

3

4

5

Immediate Mode(Deprecated)

Color:glColor3f(red,green,blue)

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v1

v2

v3

GL,GLU,andGLUTnotationsgl...

e.g.,glColor3f(...)coreOpenGLfunction

glu...e.g.,gluLookAt(...)

OpenGLutilityfunction,makescommontaskseasier(defined intermsofgl...functions)

glut...e.g.,glutSolidTeapot(...)

GLUTfunctions

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GL,GLU,andGLUTnotations

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glVertex3f(...)...3f takes3floats...3d takes3doubles...3i takes3integers

...2f takes2floats

...4f takes4floats(etc)

ComposingTransformationsglLoadMatrixf(A);glMultMatrixf(B);glMultMatrixf(C);

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ConvenienceFunctions

• glTranslatef(tx, ty, tz)

• glRotatef(degrees, x, y, z)

• glScalef(sx, sy, sz)

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HierarchicalModeling

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translate(0,4)drawTorso()pushMatrix()

translate(1.5,0)rotateX(leftHipRotate)drawThigh()pushMatrix()

translate(0,-2)rotateX(leftKneeRotate)drawLeg()...

popMatrix()popMatrix()pushMatrix()

translate(-1.5,0)rotateX(rightHipRotate)// Draw the right side...

...x

y

CurrentMatrix =translate(0,4)translate(1.5,0)rotateX(leftHipRotate)translate(0,-2)rotate(leftKneeRotate)

MatrixStack

translate(0,4)translate(0,4)translate(1.5,0)rotateX(leftHipRotate)

OpenGLMatrixStack

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OpenGL1.xPipeline(Simplified)

http://upload.wikimedia.org/wikipedia/commons/b/bb/Pipeline_OpenGL_%28en%29.pngCS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 39

OpenGL1.xPipeline(Unsimplified)

http://www.opengl.org/documentation/specs/version1.1/state.pdf

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 40

OpenGL1.xPipeline(Unsimplified)

http://www.opengl.org/documentation/specs/version1.1/state.pdf

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PiecesofthePipeline

Stores“subroutines”

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GLuint boxList;boxList = glGenLists(1);glNewList(boxList, GL_COMPILE);

// draw boxglEndList(boxList);…glCallList(boxList);

PiecesofthePipeline

Stores“subroutines”

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PiecesofthePipeline

Constructgeometricobjects

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PiecesofthePipeline

Changegeometry

Storeprimitiveshapes

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 45

PiecesofthePipeline

Changegeometry

Storeprimitiveshapes

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Includes Clipping

PiecesofthePipeline

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Fragment[frag-muhnt]:

Thedatanecessarytogenerateasinglepixel’sworthofaprimitive.

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PiecesofthePipeline

Modifyandcombineper-pixel

information

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PiecesofthePipeline

Prepareimagetobedisplayed

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OpenGLStateMachine

ChangeStateDrawDraw

ChangeStateDraw

ChangeStateChangeState

Draw

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OpenGLStateMachine

glColor3f(…)

glEnable(…)

glLineStipple(…)

glGetFloatv(…)

glIsEnabled(…)

glGetLineStipple(…)

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SetState GetState

OpenGLStateMachine

glColor3f(…)

glEnable(…)

glLineStipple(…)

glGetFloatv(…)

glIsEnabled(…)

glGetLineStipple(…)

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Efficiently managing state changes is a major implementation challenge

SetState GetState

OUT OF DATE.

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OUT OF DATE.

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VertexLighting

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Normal

Avectorperpendiculartoasurface;constantoveraplane

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 57

https://en.wikipedia.org/wiki/Normal_(geometry)

SpecifyingNormals

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1

2

3

1

2

3

VertexLighting

• DiffuseTerm

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VertexLighting

• SpecularTerm

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Camera

VertexLighting

• SpecularTerm

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Camera

VertexLighting

• SpecularTerm

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Camera

AmbientLight

VertexLighting

• SpecularTerm

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Camera

AmbientLight

VertexLighting

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EnableaLight

Setupmaterial

VertexLighting

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EnableaLight

Setupmaterial

Note: w=0 is directional light

glutSolidTeapot specifies the normal in this case

VertexLighting:Types

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 66

http://www.computing.northampton.ac.uk/~gary/csy3019/images3d/lightSources.gif

Vertex&IndexBuffers

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Vertex/IndexBuffer

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 68

8 vertices only

Vertex/IndexBuffer

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Drawing with triangles: 36 vertices!

8 vertices only

Vertex/IndexBuffer

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 70

8 vertices only

Vertices={v0,v1,..V7}

Indices={0,1,2,0,2,3,1,5,6,1,6,2…...}v0

v1

v2

v3

v5

v6

v7

Vertex/IndexBuffer

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NextGenerationAPIs

• Vulkan (NextgenOpenGL)• DirectX12(Microsoft)• Metal(Apple)

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NextGenerationAPIs

• Vulkan (NextgenOpenGL)• DirectX12(Microsoft)• Metal(Apple)

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 73

CS 148: Summer 2016Introduction of Graphics and ImagingZahid Hossain

OpenGL

http://www.pling.org.uk/cs/cgv.html