January 26, 2012 Lecture 4: Updating Pixels CS 354 Computer Graphics http://www.cs.utexas.edu/~mjk/teaching/cs354_s12/ University of Texas

1. CS 354 Pixel Updating Mark Kilgard University of Texas January 26, 2012

9. A Simplified Graphics Pipeline Application Vertex batching & assembly Triangle assembly Triangle clipping Triangle rasterization Fragment shading Depth testing Color update Application- OpenGL API boundary Framebuffer NDC to window space Got to here in last lecture Depth buffer

25. Examples of Complex Shaders

26. Fragment Shaders in the Pipeline Geometry Program 3D Application or Game OpenGL API GPU Front End Vertex Assembly Vertex Shader Clipping, Setup, and Rasterization Fragment Shader Texture Fetch Raster Operations Framebuffer Access Memory Interface CPU – GPU Boundary OpenGL 3.3 Attribute Fetch Primitive Assembly Parameter Buffer Read programmable fixed-function Legend

30. A Simplified Graphics Pipeline Application Vertex batching & assembly Triangle assembly Triangle clipping Triangle rasterization Fragment shading Depth testing Color update Application- OpenGL API boundary Framebuffer NDC to window space Depth buffer Ensure closer objects obscure (hide) more distant objects

31. Depth Buffer Visualized Window-space Z white = 1.0 (far), black = 0.0 (near) Window-space 1-Z white = 0.0 (near), black = 1.0 (far) Depth-tested 3D scene How depth values are really stored in the depth buffer

32. Not Just for View Occlusion Depth Buffers also Useful for Shadow Generation Without Shadows With Shadows Projected Shadow Map Light’s View Light’s View Depth

35. Depth Test Operation 0.8 0.65 time pixel depth fragment depth 0.65<0.8 is true 0.65 0.72 0.65<0.8 is false 0.65 depth test passes depth test fails

37. A Simplified Graphics Pipeline Application Vertex batching & assembly Triangle assembly Triangle clipping Triangle rasterization Fragment shading Depth testing Color update Application- OpenGL API boundary Framebuffer NDC to window space Depth buffer Write shaded color to color buffer