1	Cg: C for Graphics Jon Moon Based on slides by Eugene Lee
2	Overview Cg Basics Vertex Shaders Fragment Shaders Using Cg in OpenGL
3	What is Cg? Cg is a high level shader language Made by NVIDIA, but supports other GPUs Programmer writes in a language similar to C Cg compiler produces hardware-specific optimized assembly code
4	Halflife 1 vs. Halflife 2
5	http://www.daionet.gr.jp/~masa/rthdribl/index.html
6	Overview Motivation Vertex Shaders Fragment Shaders Using Cg in OpenGL Questions?
7	The Vertex Shader Program executed once per vertex Takes per-vertex input such as position, normal, color, light position, etc. Determines per-vertex data such as position, color, depth, etc. But can do more!
8	The Vertex Shader
9	A Vertex Program struct VertexInput { float4 position : POSITION; float3 normal : NORMAL; } void NormalShade( VertexInput input, out float4 outPosition : POSITION, out float3 outColor : COLOR, const uniform float4x4 modelViewProjMatrix) { outPosition = mul(modelViewProjMatrix, input.position); outColor = abs(input.normal); }
10	Binding Semantics Predefined “names” POSITION, NORMAL, etc.
11	Vertex Shader: Input Varying parameters Color, normal, texture coordinates, etc. Data specified for each element
12	Vertex Shader: Input Uniform Parameters Data that remains constant over each element Parameter shadowing
13	Vertex Shader: Output Output serves as varying input to fragments “Custom data” usually output as texcoords
14	Types in Cg Syntax similar to C Basic types int, float, half, fixed, bool Vector/Matrix types int4, float3, bool2, float4x4 Arrays int a[3], float4x4 matrices[4][4]
15	Playing with types Vector initialization and swizzling float4 vec4 = float4(1, 1, 1, 0); float3 vec3 = vec4.yzw; float3 color = vec3.rgb; float3 position = 1.xxx;
16	Overview Motivation Vertex Shaders Fragment Shaders Using Cg in OpenGL Questions?
17	The Fragment Shader Program executed once per rasterized pixel. Takes varying output from vertex program. Certain outputs, like TEXCOORD0 interpolated. Determines final color, depth for pixel.
18	The Fragment Shader
19	A Fragment Program
20	A Fragment Program
21	Performance Fragment Programs are Expensive! Try to do as much as possible in vertex programs. Try to keep fragment programs small. Note: not all hardware supports fragments Rhodes 453 has Quadro FX GPU’s, which DO support fragment programs
22	Overview Motivation Vertex Shaders Fragment Shaders Using Cg in OpenGL Questions?
23	Initializing Cg Create a context CGcontext cgContext = CgGL.cgCreateContext(); Select and enable Profile int cgVertexProfile = CgGL.CG_PROFILE_VP20; CgGL.cgGLEnableProfile(cgVertexProfile); Create & Load program CGprogram cgVertexProgram = CgGL.cgCreateProgramFromFile(cgContext, CgGL.CG_SOURCE, "Normal.cg", cgVertexProfile, "Normal", null); CgGL.cgGLLoadProgram(cgVertexProgram1);
24	Executing Cg Get handles for parameters CGparameter mvpMatrix = CgGL.cgGetNamedParameter(cgVertexProgram, “ModelViewProjMatrix”); Set parameters CgGL.cgGLSetStateMatrixParameter( mvpMatrix, CgGL.CG_GL_MODELVIEW_PROJECTION_MATRIX, CgGL.CG_GL_MATRIX_IDENTITY) Bind program CgGL.CgGLBindProgram(cgVertexProgram); Rendering glBegin()…
25	Cg in Action: Normal Shader First demo: using 1 vertex shader to shade a cube based on its normal Based on OpenGLDemo02 from last week First look at Normal.cg, then at the Java code to actually use it
26	Normal.cg struct VertexInput { float4 position : POSITION; float3 normal : NORMAL; }; struct VertexOutput { float4 position : POSITION; float3 color : COLOR0; }; VertexOutput Normal(const VertexInput input, const uniform float4x4 ModelViewProjMatrix) { VertexOutput output; output.position = mul(ModelViewProjMatrix, input.position); output.color = (input.normal+1)/2; return output; }
27	Vertex.java: declarations protected CGcontext cgContext; protected int cgVertexProfile; protected static CGprogram cgVertexProgram; protected static CGparameter cgModelViewProjMatrix;
28	Vertex.java: initializations cgContext = CgGL.cgCreateContext(); cgVertexProfile = CgGL.CG_PROFILE_VP20; CgGL.cgGLEnableProfile( cgVertexProfile); cgVertexProgram = CgGL.cgCreateProgramFromFile( cgContext, CgGL.CG_SOURCE, "Normal.cg", cgVertexProfile, "Normal", null); CgGL.cgGLLoadProgram(cgVertexProgram); cgModelViewProjMatrix = CgGL.cgGetNamedParameter( cgVertexProgram, "ModelViewProjMatrix");
29	Vertex.java: Display loop CgGL.cgGLBindProgram(cgVertexProgram); CgGL.cgGLSetStateMatrixParameter( cgModelViewProjMatrix, CgGL.CG_GL_MODELVIEW_PROJECTION_MATRIX, CgGL.CG_GL_MATRIX_IDENTITY);
30	More than 1 Vertex Program Can use different vertex (fragment) programs for different geometry! Initialize programs as you would normally 1 context, 1 vertex profile, many programs, many loads, etc. In display loop, bind appropriate VP before gl_Begin() … gl_End(). To use another VP, simply bind to it before the next gl_Begin() … gl_End().
31	TwoVertex.java Code very similar to Vertex.java We load the pastel normal shader for the front and back faces, then load the bright normal shader for the rest of the cube Note that we needed to gl_End() after the first 2 faces, then bind our next VP, then gl_Begin(GL_QUADS) again
32	SinWave.cg float3 SinWave(float3 tex : TEXCOORD0) : COLOR { return (sin(sin(23tex.xtex.y)-10*tex.y)+1)/2; } This shader is just using the texture coordinates, and some math. Like position and normal, these are made available by OpenGL automatically But if SinWave needed other parameters, we would obtain and modify them as usual.
33	Fragment.java: declaration, init Very similar to Vertex, except with all “vertex”es replaced with “fragment”s We make sure to specify the texture coordinates for the corners of each face Texture coords are interpolated across polygons, so fragment programs can use them readily
34	Lambertian, a la PA1 Vertex program finds the normal and light vectors in world space, outputting those as COLOR0, COLOR1 Fragment program gets interpolated normal, light vector for each pixel and calculates lighting
35	Lambertian.java Does standard declare, init: 1 context, 2 profiles (create, enable), 2 programs (create, load) Gets, sets all necessary variables for both programs In display loop, bind both VP and FP That’s it!
36	Some Tips Check for errors! CgErrorException.checkCgError(); Debug output in shaders Normals, incident directions, different terms in BRDFs, etc. Can compile .cg programs cgc –profile vp20 –entry (function name) Program.cg
37	PA1: Cg Shaders portion Write a couple of shading models Must set the input parameters to cg programs. Reference Lambertian shader code provided
38	Resources NVIDIA Cg: http://developer.nvidia.com/page/cg_main.html Cg User Manual: http://developer.nvidia.com/object/cg_users_manual.html Also in Cg Toolkit folder http://www.cgshaders.org