Why won't CG shaders work with GL 3.2? - opengl

Question

I've tried everything to get OpenGL 3.2 to render with CG shaders in my game engine but I have had no luck. So I decided to make a bare minimal project but still shaders won't work. In theory my test project should just render a red triangle but it is white because the shader is not doing anything.
I'll post the code here:
#include <stdio.h>
#include <stdlib.h>
#include <vector>
#include <string>
#include <GL/glew.h>
#include <Cg/cg.h>
#include <Cg/cgGL.h>
#include <SDL2/SDL.h>
int main()
{
SDL_Window *mainwindow;
SDL_GLContext maincontext;
SDL_Init(SDL_INIT_VIDEO);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
mainwindow = SDL_CreateWindow("Test", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 512, 512, SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN);
maincontext = SDL_GL_CreateContext(mainwindow);
glewExperimental = GL_TRUE;
glewInit();
_CGcontext* cgcontext;
cgcontext = cgCreateContext();
cgGLRegisterStates(cgcontext);
CGerror error;
CGeffect effect;
const char* string;
std::string shader;
shader =
"struct VS_INPUT"
"{"
" float3 pos : ATTR0;"
"};"
"struct FS_INPUT"
"{"
" float4 pos : POSITION;"
" float2 tex : TEXCOORD0;"
"};"
"struct FS_OUTPUT"
"{"
" float4 color : COLOR;"
"};"
"FS_INPUT VS( VS_INPUT In )"
"{"
" FS_INPUT Out;"
" Out.pos = float4( In.pos, 1.0f );"
" Out.tex = float2( 0.0f, 0.0f );"
" return Out;"
"}"
"FS_OUTPUT FS( FS_INPUT In )"
"{"
" FS_OUTPUT Out;"
" Out.color = float4(1.0f, 0.0f, 0.0f, 1.0f);"
" return Out;"
"}"
"technique t0"
"{"
" pass p0"
" {"
" VertexProgram = compile gp4vp VS();"
" FragmentProgram = compile gp4fp FS();"
" }"
"}";
effect = cgCreateEffect(cgcontext, shader.c_str(), NULL);
error = cgGetError();
if(error)
{
string = cgGetLastListing(cgcontext);
fprintf(stderr, "Shader compiler: %s\n", string);
}
glClearColor ( 0.0, 0.0, 1.0, 1.0 );
glClear ( GL_COLOR_BUFFER_BIT );
float* vert = new float[9];
vert[0] = 0.0; vert[1] = 0.5; vert[2] =-1.0;
vert[3] =-1.0; vert[4] =-0.5; vert[5] =-1.0;
vert[6] = 1.0; vert[7] =-0.5; vert[8]= -1.0;
unsigned int m_vaoID;
unsigned int m_vboID;
glGenVertexArrays(1, &m_vaoID);
glBindVertexArray(m_vaoID);
glGenBuffers(1, &m_vboID);
glBindBuffer(GL_ARRAY_BUFFER, m_vboID);
glBufferData(GL_ARRAY_BUFFER, 9 * sizeof(GLfloat), vert, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(0);
CGtechnique tech = cgGetFirstTechnique( effect );
CGpass pass = cgGetFirstPass(tech);
while (pass)
{
cgSetPassState(pass);
glDrawArrays(GL_TRIANGLES, 0, 3);
cgResetPassState(pass);
pass = cgGetNextPass(pass);
}
glDisableVertexAttribArray( 0 );
glBindVertexArray(0);
delete[] vert;
glBindBuffer(GL_ARRAY_BUFFER, 0);
glDeleteBuffers(1, &m_vboID);
glDeleteVertexArrays(1, &m_vaoID);
SDL_GL_SwapWindow(mainwindow);
SDL_Delay(2000);
SDL_GL_DeleteContext(maincontext);
SDL_DestroyWindow(mainwindow);
SDL_Quit();
return 0;
}
What am I doing wrong?

Answer 1

I compiled the code and got the same result. So I added a CG error handler to get a bit more of information:
void errorHandler(CGcontext context, CGerror error, void * appdata) {
fprintf(stderr, "%s\n", cgGetErrorString(error));
}
...
cgSetErrorHandler(&errorHandler, NULL);
When cgSetPassState and cgResetPassState were called I got the following error message:
Technique did not pass validation.
Not really very informative, of course. So I used GLIntercept to trace all OpenGL calls to a log file.
This time, when glewInit was called I got the following error message in the log file:
glGetString(GL_EXTENSIONS)=NULL glGetError() = GL_INVALID_ENUM
According OpenGL documentation, glGetString must not be called with GL_EXTENSIONS, was deprecated in 3.0, and glGetStringi must be used instead.
Finally, I found the issue in the GLEW library: http://sourceforge.net/p/glew/bugs/120/
I removed GLEW dependency and tested with gl3.h (and more recent glcorearb.h). I got the same error, but this time when cgGLRegisterStates was called.
I also tried CG trace.dll, just to get the same error (7939 = 0x1F03 = GL_EXTENSIONS):
glGetString
{
input:
name = 7939
output:
return = NULL
}
Then, I tested OpenGL 3.1 (SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 1);), and found that it was working fine:
glGetString(GL_EXTENSIONS)="GL_AMD_multi_draw_indirec..."
That is, the 3.1 context was compatible with previous OpenGL versions, but 3.2 not.
After a bit of Internet digging I found that you can create this type of compatible OpenGL context with SDL, just adding this line to the code:
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_COMPATIBILITY);
IMHO, CG Toolkit needs this type of compatibility profile.

Answer 2

"Cg 3.1 context does not yet support forward-compatible OpenGL contexts!"
Source:
http://3dgep.com/introduction-to-shader-programming-with-cg-3-1/
As the Cg project seems to be abandoned, it's also not likely to happen.