Re: [PyOpenGL-Users] glVertexAttribPointer(); loading platform-specific functions

[Joshua D. <joshuardavis@q.com>]

>> This is a bug in the shaders module.  Turns out that  
>> glGetProgramivARB
> and glGetProgramiv have different roles?!  Basically it looks like  
> it's
> glGetObjectParameteriv that's supposed to be used for the  
> glGetProgramiv
> validity check call (at least, if I use that and disable core GL I get
> the correct operation).  Going to have to look into the function
> definitions more to be sure that the alternate declaration works.

Your changes to shaders.py have gotten me past that problem. Thanks  
very much.

I now have two versions of my program. The first uses the legacy  
glVertexPointer() stuff and works perfectly. The second is altered,  
as little as possible, so that it uses the modern  
glVertexAttribPointer() stuff instead. It raises no errors but  
generates no fragments. Here is the glVertexPointer() version of the  
two crucial functions...

def initializeShaders():
     global shaderProgram
     vertexCode = """
     void main()
     {
         gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
         gl_FrontColor = gl_Color;
     }"""
     fragmentCode = """
     void main()
     {
         gl_FragColor = gl_Color;
     }"""
     vertexShader = compileShader(vertexCode, GL_VERTEX_SHADER)
     fragmentShader = compileShader(fragmentCode, GL_FRAGMENT_SHADER)
     shaderProgram = compileProgram(vertexShader, fragmentShader)

def handleDisplayEvent():
     global vertexBufferObject, shaderProgram
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
     glUseProgram(shaderProgram)
     vertexBufferObject.bind()
     glEnableClientState(GL_VERTEX_ARRAY)
     glEnableClientState(GL_COLOR_ARRAY)
     glVertexPointer(3, GL_FLOAT, 24, vertexBufferObject)
     glColorPointer(3, GL_FLOAT, 24, vertexBufferObject + 12)
     glDrawArrays(GL_TRIANGLES, 0, 9)
     vertexBufferObject.unbind()
     glDisableClientState(GL_VERTEX_ARRAY)
     glDisableClientState(GL_COLOR_ARRAY)
     glUseProgram(0)
     glFlush()
     glutSwapBuffers()

...and here are those same functions, rewritten to use  
glVertexAttribPointer().

def initializeShaders():
     global shaderProgram, positionLocation, colorLocation
     vertexCode = """
     attribute vec3 position;
     attribute vec3 color;
     void main()
     {
         gl_Position = gl_ModelViewProjectionMatrix * vec4(position,  
1.0);
         gl_FrontColor = vec4(color, 1.0);
     }"""
     fragmentCode = """
     void main()
     {
         //gl_FragColor = gl_Color;
         gl_FragColor = vec4(1.0, 0.0, 1.0, 1.0);
     }"""
     vertexShader = compileShader(vertexCode, GL_VERTEX_SHADER)
     fragmentShader = compileShader(fragmentCode, GL_FRAGMENT_SHADER)
     shaderProgram = compileProgram(vertexShader, fragmentShader)
     positionLocation = glGetAttribLocation(shaderProgram, 'position')
     colorLocation = glGetAttribLocation(shaderProgram, 'color')

def handleDisplayEvent():
     global vertexBufferObject, shaderProgram, positionLocation,  
colorLocation
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
     glUseProgram(shaderProgram)
     vertexBufferObject.bind()
     glEnableVertexAttribArray(positionLocation)
     glEnableVertexAttribArray(colorLocation)
     glVertexAttribPointer(positionLocation, 3, GL_FLOAT, False, 24,  
vertexBufferObject)
     glVertexAttribPointer(colorLocation, 3, GL_FLOAT, False, 24,  
vertexBufferObject + 12)
     glDrawArrays(GL_TRIANGLES, 0, 9)
     vertexBufferObject.unbind()
     glDisableVertexAttribArray(positionLocation)
     glDisableVertexAttribArray(colorLocation)
     glUseProgram(0)
     glFlush()
     glutSwapBuffers()

Am I missing something obvious? Any suggestions on how to debug further?

Josh