OpenGL binding textures to vertex buffer objects (with CG Shaders)

Question

I'll get straight to the point:

I have created a structure for my vertices:

struct Vertex3D
{
    Vector3D position;
    Vector2D textureCoordinate;
    Vector3D normal;
}

I then import a particular *.dae file and bind it to a OpenGL Vertex Buffer, which is constructed out of a list of Vertex3D structured vertices. All goes well, the mesh imports and is displayed, I can manipulate it with shaders, but I have a problem.

What I also do is load up and assign a texture to it. Aftewards I'm trying to display it in this manner:

glEnableVertexAttribArray(0);
glEnableVertexAttribArray(8);
glEnableVertexAttribArray(2);

glBindBuffer(GL_ARRAY_BUFFER, this->_entries[i].VB);
glVertexAttribPointer(0,3, GL_FLOAT, GL_FALSE, sizeof(RomCommon::Vertex3D), 0); // Vertices
glVertexAttribPointer(8,2, GL_FLOAT, GL_FALSE, sizeof(RomCommon::Vertex3D), (const GLvoid*)sizeof(RomCommon::Vector3D)); // Supposed texture position
glVertexAttribPointer(2,3, GL_FLOAT, GL_FALSE, sizeof(RomCommon::Vertex3D),  (const GLvoid*)(sizeof(RomCommon::Vector2D) + sizeof(RomCommon::Vector3D))); // Supposed normal position
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, this->_entries[i].IB);
glBindTexture(GL_TEXTURE_2D, 3);
glDrawElements(GL_TRIANGLES, this->_entries[i]._indexCount, GL_UNSIGNED_INT, 0);

glDisableVertexAttribArray(0);
glDisableVertexAttribArray(8);
glDisableVertexAttribArray(2);

My problem is that the texture is not displayed. Only the color from the texture's first pixel is assigned (in my case it's blue). I've used gDEBugger to debug the whole process, and I can tell that the VertexBuffer seems to be set up correctly, the image of the texture is loaded up correctly, yet it won't be displayed.

I have tried searching and trying out different aspects of debugging, this includes:

making sure glEnable(GL_TEXTURE_2D) is set up;
adding glEnable(GL_LIGHTING) and glDisable(GL_LIGHTING);
using glDisable(GL_DEPTH_TEST); glDisable(GL_BLEND); and glDisable(GL_SCISSOR_TEST); before binding the texture
fetching for errors
searching for strange messages
double checking the vertex buffer in the memory (literaly going through the elemnts and cross comparing what's in the *.dae file)

EDIT

I am using CG Shaders with this. Here is the Vertex Program:

struct vsOutput {


 float4 position : POSITION;
  float2 texCoord : TEXCOORD0;
  float3 color    : COLOR;
};

vsOutput VS_Main(      float4 position : POSITION,
                           float2 texCoord : TEXCOORD0,
                           float3 color    : COLOR,
                           uniform float4x4 ModelViewProj
                           )
{
  vsOutput OUT;

  OUT.position = mul(ModelViewProj, position);
  OUT.texCoord = texCoord;
  OUT.color = color;

  return OUT;   
}

And the Fragment Program:

struct fsOutput {
  float4 color : COLOR;
};

fsOutput FS_Main(
    float2 texCoord : TEXCOORD0,
    uniform sampler2D decal : TEX0
)
{ 
    fsOutput OUT;
    OUT.color = tex2D(decal,texCoord);
    return OUT;
}

I could add more details about my project if necessary, though from what I've traced, the problem seems to be somewhere in the rendering of the vertex buffers.

EDIT

I've also found that because I'm using CG, the vertexAttribPointers should be different (8 is for TEXCOORD0) so I changed the general description based on that.

SOLUTION EDIT

Many thanks to the few chaps in the comments who opened my mind to look at the problem from a different perspective and actually do some more reading. Here is the solution:

    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(8);
    glEnableVertexAttribArray(2);

    glBindBuffer(GL_ARRAY_BUFFER, this->_entries[i].VB);
    glVertexAttribPointer(0,3, GL_FLOAT, GL_FALSE, sizeof(RomCommon::Vertex3D), 0); // Vertices
    glVertexAttribPointer(8,2, GL_FLOAT, GL_FALSE, sizeof(RomCommon::Vertex3D), (const GLvoid*)sizeof(RomCommon::Vector3D)); // Supposed texture position
    glVertexAttribPointer(2,3, GL_FLOAT, GL_FALSE, sizeof(RomCommon::Vertex3D),  (const GLvoid*)(sizeof(RomCommon::Vector2D) + sizeof(RomCommon::Vector3D))); // Supposed normal position
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, this->_entries[i].IB);


/* Solution start */
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);
    glTexCoordPointer(2, GL_FLOAT, sizeof(RomCommon::Vertex3D), (const GLvoid*)12);
        glBindTexture(GL_TEXTURE_2D, 3);
        glDrawElements(GL_TRIANGLES, this->_entries[i]._indexCount, GL_UNSIGNED_INT, 0);
    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
/* Solution end */


    glDisableVertexAttribArray(0);
    glDisableVertexAttribArray(8);
    glDisableVertexAttribArray(2);

My problem was that I was only passing texture coordinates to the shader, but did not push it to the OpenGL state machine (if that's a good expression). I think this has something to do with the fact that I am using CG shaders and not GLSL shaders, though I could be wrong. The code is loosely based on a few examples and explanations that I read, but they were all based on GLSL shaders and they were working, hence the dediction. Anyway, it is now resolved.

I see no shaders. That might be the problem with rendering of vertex buffers. You specified vertex attributes (0, 1 and 2) but gave no meaning to them. And oh, you don't bind textures to VBOs; you bind them to texture units and access as uniform sampler* variables in GLSL. — Bartek Banachewicz
I have shaders, but did not specify them in the description (I can add both vertex and fragment shader functions if necessary). They are enabled before glEnableVertexAttribArray(0); and disabled after glDisableVertexAttribArray(2); I am also using CG Shaders, but they work in a similar way I presume. — karmalis
Please forgive my ignorance, I am not that good at these things. How do you render UVs as color again? — karmalis
@karmalis: Just assign the texture coordinate as output color. I'm also a bit unsure about how Cg does assign vertex attribute location so to VS_Main parameters. with GLSL you either have to use glGetAttributeLocation to retrieve the location index based on its name, or assign it explicitly in the layout. — datenwolf

genpfault genpfault · Accepted Answer · 2013-01-29T15:46:30

glBindTexture(GL_TEXTURE_2D, 3);

I'd be wary of forcing texture object IDs on OpenGL. Technically it ought to work but using glGenTextures() to acquire texture IDs is a better idea.

OpenGL binding textures to vertex buffer objects (with CG Shaders)

1 Answers