The GPU - UW Extension Certificate Program in Game Development ...

UW EXTENSION


CERTIFICATE PROGRAM IN

GAME DEVELOPMENT


2
ND

QUARTER:

ADVANCED GRAPHICS

The GPU

Goals

1.
Understand how the GPU works (high
-
level)

2.
Review the basic rendering pipeline

GPU as a state machine


GPU records state and renders based on that state


Examples of state:


Resources: textures and geometry


Transformations


Alpha blending function


Render targets


State management can be complex


Multiple components must cooperate with each other


Redundant/inappropriate state changes can hurt
perf

GPU as a sequential command processor


GPU reads commands from a FIFO and runs them


CPU fills the FIFO, GPU consumes it


There is a lag between CPU and GPU


Depends on the FIFO length and run
-
time timings


If the FIFO is typically empty, the CPU is bottleneck


But there’s no lag


If the FIFO is typically full, the GPU is bottleneck


This allows CPU to do “other stuff” while GPU works


High
-
performance games require paying attention

GPU render algorithm


Convert all vertices into an internal representation


Run the vertex pipeline or vertex shader


Group internal vertices into triangles


Clip (cut) triangles to the view frustum


Rasterize the triangles into pixels


Convert the pixels into colors


Run the pixel pipeline or pixel shader


Apply colors to the output render target

What does the state specify?


It specifies how to perform all rendering operations:


Input data (geometry, textures…)


Output data (render target)


Vertex pipeline transform


Grouping, clipping and rasterization parameters


Pixel pipeline transformation


Z
-
buffer and stencil operation values


Blending formula: applying colors to render target


Sometimes, multiple states affect a single operation


Sometimes, a single state affects multiple operations

Vertex and pixel pipelines


Why move calculations between them?


It’s good for balancing the computation load


Typically there are many more pixels than vertices


Pixel stage allows us to add some detail in a balanced way,
without multiplying the calculations


Mind the extreme cases:


Far
-
away object


Many vertices with fewer pixels


Close
-
up object


Many pixels with fewer vertices


State
-
based or fully programmable (
shaders
)