Texturing VBOs (Vertex Buffer Objects)

Question

I'm currently working on a procedural planet generation tool that works by taking a cube, mapping it to a sphere and then applying a heightmap to each face to generate terrain.

I'm using a VBO for each face which is created using the following method:

void Planet::setVertexBufferObject()
{
 Vertex* vertices;
 int currentVertex;
 Vertex* vertex;

 for(int i = 0; i < 6; i++)
 {
  // bottom face
  if(i == 0)
  {
   glBindBuffer(GL_ARRAY_BUFFER, bottomVBO);    
  }
  // top face
  else if(i == 1)
  {
   glBindBuffer(GL_ARRAY_BUFFER, topVBO);    
  }
  // front face
  else if(i == 2)
  {
   glBindBuffer(GL_ARRAY_BUFFER, frontVBO);    
  }
  // back face
  else if(i == 3)
  {
   glBindBuffer(GL_ARRAY_BUFFER, backVBO);    
  }
  // left face
  else if(i == 4)
  {
   glBindBuffer(GL_ARRAY_BUFFER, leftVBO);    
  }
  // right face
  else
  {
   glBindBuffer(GL_ARRAY_BUFFER, rightVBO);    
  } 

  vertices = (Vertex*)glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY);

  currentVertex = 0;

  for(int x = 0; x < size; x++)
  {
   for(int z = 0; z < size; z++)
   {
    currentVertex = z * size + x;

    vertex = &vertices[currentVertex];

    vertex->xTextureCoord = (x * 1.0f) / 512.0f;
    vertex->zTextureCoord = (z * 1.0f) / 512.0f;

    Vector3 normal;

    vertex->xNormal = normal.x;
    vertex->yNormal = normal.y;
    vertex->zNormal = normal.z;

    vertex->x = heightMapCubeFace[i][x][z][0];
    vertex->y = heightMapCubeFace[i][x][z][1];
    vertex->z = heightMapCubeFace[i][x][z][2];

    vertex->x *= (1.0f +((heightMaps[i][z][x]/256.0f) * 0.1));
    vertex->y *= (1.0f +((heightMaps[i][z][x]/256.0f) * 0.1));
    vertex->z *= (1.0f +((heightMaps[i][z][x]/256.0f) * 0.1));
   }
  }
  glUnmapBuffer(GL_ARRAY_BUFFER);
  glBindBuffer(GL_ARRAY_BUFFER, 0);
 }
}

I have left out the setIndexBufferObject() method as that is working OK.

I am then rendering the sphere using this method:

void Planet::render()
{
    // bottom face

    glBindBuffer(GL_ARRAY_BUFFER, bottomVBO);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, bottomIBO);

    glEnableClientState(GL_TEXTURE_COORD_ARRAY);
    glTexCoordPointer(2, GL_FLOAT, sizeof(Vertex), BUFFER_OFFSET(6 * sizeof(float)));

    glEnableClientState(GL_NORMAL_ARRAY);
    glNormalPointer(GL_FLOAT, sizeof(Vertex), BUFFER_OFFSET(3 * sizeof(float)));

    glEnableClientState(GL_VERTEX_ARRAY);
    glVertexPointer(3, GL_FLOAT, sizeof(Vertex), BUFFER_OFFSET(0));

 TextureManager::Inst()->BindTexture(textueIDs[0]);
 glClientActiveTexture(GL_TEXTURE0+textueIDs[0]);
 glDrawElements(GL_TRIANGLE_STRIP, numberOfIndices, GL_UNSIGNED_INT, BUFFER_OFFSET(0)); 

    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_NORMAL_ARRAY);
    glDisableClientState(GL_TEXTURE_COORD_ARRAY);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

 // next face and so on...

The textures are being loaded in using free image, as you can see from the above code I am just using the example texture manager that came with freeimage.

Why is binding the texture not working?

score 1 · Accepted Answer · answered Nov 07 '10 at 21:22

Why is binding the texture not working?

Describing very specifically the behavior you're seeing, or better attaching a URL to a screenshot, goes a long way when trying to get through graphics questions.

Next, you need to include the gl error state or at least demonstrate that within the code that you're checking and failing if glGetError() doesn't return GL_NO_ERROR.

Your VBO / draw element state looks reasonable though you've deliberately omitted the definition of the index buffer object so we'll take it on faith that you're sending real indices into your glDrawElements() call. For a sanity check, do the glDrawElements() call with the raw indices pointer rather than binding a VBO for the elements.

You've also omitted the type definition of Vertex which is required to know if the offsets you're supplying to glTexCoordPointer() are consistent with the struct definition.

Lastly, I'm guessing most people on the forum don't know "free image" which I believe is what you've stated you're using to load textures with. If there's a texturing problem it's impossible to see because of the opaque nature of using this 3rd party library to set up texturing on your behalf.

If they've confused texture IDs, set up a wrap mode that isn't supported, not set the minification filter consistent with the expected mipmapping (on/off), not enabled texturing, or set the texture environment mode such that the modulation with the base geometry color is not as you expect - all of these would make texturing not work / appear to be working.

To troubleshoot just use the library for texture load and use the texture ID they provide. Then set up the filter modes and texture environment yourself. Turn off mipmapping while troubleshooting. Incomplete mipmap chains is a very common error when texturing.

You can also turn off per-fragment operations to simplify your troubleshooting. Disable blending, depth testing, and scissoring.

Assuming your texture is power of two dimensions or your implementation supports NPOT, try these settings immediately before drawing:

glDisable(GL_DEPTH_TEST);
glDisable(GL_BLEND);
glDisable(GL_SCISSOR_TEST);
glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
glBindTexture(GL_TEXTURE_2D, texID);
glTexEnvi(GL_TEXTURE_ENV_MODE, GL_REPLACE); // turn off modulation
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); // turn off mipmapping
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP); // turn off repeats
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

score 1 · Answer 2 · answered Nov 07 '10 at 21:53

1

glClientActiveTexture(GL_TEXTURE0+textueIDs[0]);

What are you trying to do here?

The active texture unit has nothing to do with a random texture object.

answered Nov 07 '10 at 21:53

genpfault

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Texturing VBOs (Vertex Buffer Objects)

2 Answers2