A Crash Course on Programmable Graphics Hardware

Li-Yi Wei

2005

at Tsinghua University, Beijing

Why do we need graphics hardware?

The evolution of graphics hardware

SGI Origin 3400 NVIDIA Geforce 7800

7 years of graphics

accelenation.com/?doc=123&page=1

Ray tracing

General & flexible

Intuitive

Global illumination

Hard to accelerate

Polygonal graphics pipeline

Local computation

Easy to accelerate

Not general

Unintuitive

Graphics hierarchy

Layered approachLike network layers

EncapsulationEasy programming

Driver optimization

Driver workaround

Driver simulation

ProtectionHardware error check

Overview

Graphics pipelineOnly high level overview (so you can program),

not necessarily real hardware

GPU programming

Graphics pipeline

Application

Mostly on CPU

High level workUser interface

Control

Simulation

Physics

Artificial intelligence

Host

Gatekeeper of GPU

Command processing

Error checking

State managementContext switch

Geometry

Vertex processor

Primitive assembly

Clip & cull

Viewport transform

Vertex Processor

Process one vertex at one timeNo information on other vertices

Programmable

Transformation

Lighting

Transformation

Global to eye coordinate system

Lighting

Diffuse

Specular

Transform & Light on Vertex Processor

A sequence of assembly instructions

(more on this later)

Primitive Assembly

Assemble individual vertices into triangle (or line or point)

Performance implicationA triangle is ready only when all 3 vertices are

Vertex coherence & caching

Clipping & Culling

Backface cullingRemove triangles facing away from view

Eliminate ½ of the triangles in theory

Clipping against view frustumTriangles may become quadrilaterals

Viewport transform

From floating point range [-1, 1] x [-1, 1] to integer range [0, height-1] x [0, width-1]

Rasterization

Convert primitives (triangles, lines) into pixels

Barycentric coordinate

Attribute interpolation

Triangles into pixels

Attribute interpolation

Interpolation

Barycentric

Perspective correct interpolation

incorrect correct

Fragment processor

Fragment: corresponds to a single pixel and includes color, depth, and sometimes texture-coordinate values.

Compute color and depth for each pixel

Most interesting part of GPU

Texture

Optional (though hard to avoid)

Cache dataHide latency from FB

Sampling/filteringI told you this last time

ROP (Raster Operation)

Write to framebuffer

ComparisonZ, stencil, alpha, window

Framebuffer

Storing buffers and textures

Connect to display

CharacteristicsSize

Bandwidth

Latency

Conceptual programming model

Inputs (read-only)Attributes

Constants

Textures

Registers (read-write)Used by shader

Outputs (write-only)Attributes

Simple example

HPOS: position

COL0: diffuse color

MOV o[HPOS], v[HPOS];

MOV o[COL0], v[COL0];

More complex example

o[COL0] = v[COL0] + constant*v[HPOS];

MOV o[HPOS], v[HPOS];

MOV R0, v[COL0];

MAD R0, v[HPOS], c[0], R0;

MOV o[COL0], R0;

Sample instruction set

A real example

High-level shading language

Writing assembly is Painful

Not portable

Not optimize-able

High level shading language solves theseCg, HLSL

Cg example

Applications

Too many of them for me to describe here

The only way to learn is try to programUseless for you even if I try to describe

Look at developer websiteNVIDIA, ATI, GPGPU

Homework

Try to program GPU!Even without NVIDIA GPU, you can download

the emulator

Stanford course on graphics hardwarehttp://www.graphics.stanford.edu/courses/

cs448a-01-fall/

History of graphics hardware7 years of graphicsaccelenation.com/?doc=123&page=1