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)