Using multitexture with vertex arrays

OpenGL OpenGL: Advanced Coding
1

I’m setting up two texture coord arrays in opengl for texture units one and two. I do this with glClientActiveTextureARB.

With one unit everything works fine. My initial texture displays with the proper texture coords. However, when I enable unit two rather than displaying the new texture with the first, the first is displayed again with the coords in the second texture coordinate array. I can’t seem to get the second texture to display at all.

I’m sure my units are set up right because the texturing works fine in immediate mode. Below is the code I use to set up the texture arrays :

glActiveTextureARB(GL_TEXTURE1_ARB);
glClientActiveTextureARB(GL_TEXTURE1_ARB);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glTexCoordPointer(2, GL_FLOAT, sizeof(terrainVertex), &vertexList[0].s1);


glActiveTextureARB(GL_TEXTURE0_ARB);
glClientActiveTextureARB(GL_TEXTURE0_ARB);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glTexCoordPointer(2, GL_FLOAT, sizeof(terrainVertex), &vertexList[0].s);

Any suggestions are greatly appreciated.

[This message has been edited by Macinkross (edited 06-25-2003).]

2

The third parameter in glTexCoordPointer is the stride. That is, the byte offset between consecutive array elements. You probably should pass 0 as the stride. That means the array is tightly packed.

-SirKnight

[This message has been edited by SirKnight (edited 06-25-2003).]

3

No, the stride is right, SirKnight.

The array is called vertexList which is an array of a struct I have called terrainVertex. In terrainVertex I store a vertex position (three floats) and two texture coords (two floats each).

Out of desperation, I tried 0 and (as I expected) it yielded completely bogus results.

That said, thanks for the suggestion. This glitch is halting development on my project and I have a deadline coming up. I really need to figure out whats wrong. If anyone can help please feel free to suggest something.

4

Since you only pasted a code snippet, I figured I’d ask just in case:

Did you remember to

  1. glEnable(GL_TEXTURE_2D); on each texture unit?
  2. Bind the textures for each texture unit?
5

Did you try glGetError()?

– Tom

6

Tom: No errors are thrown. Good idea though.

JotDot: As far as I know I set everything up right. I’m going to post the rest of my code in case someone can spot something.

This is called every time the render loop runs.

  /* Texture Unit 0
______________________________________________________*/

    glActiveTextureARB(GL_TEXTURE0_ARB);
    glEnable(GL_TEXTURE_2D);
    finalTex.bindTexture();
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);

    glClientActiveTextureARB(GL_TEXTURE0_ARB);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);

    
    /*Texture Unit 1
________________________________________________________*/
    glActiveTextureARB(GL_TEXTURE1_ARB);
    glEnable(GL_TEXTURE_2D);
    detailMap.bindTexture();
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_BLEND);

    glClientActiveTextureARB(GL_TEXTURE1_ARB);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);

The only thing I really added from immediate mode are the two lines below where I set up each unit ( I enable texture arrays for each client state).

I think there must be something little I’m doing wrong but I can’t seem to find it.

7

I’m not really an expert in all this so I made a simple test app using your code that you posted. I loaded up two textures, set up the client vertex array, used your code shown, and then used glDrawElements() to display my image.

It works fine.

Without knowing more, I am assuming the problem lays somewhere else. ie: Currently the only way I could get this particular code to have the “first” texture to appear using the second set of texture coordinates - was to use a texture id of zero for the first unit, then the “first” texture number for the 2nd stage. Not saying that this is your problem though.

8

Thanks JotDot.

The more I work with this, the more I’m starting to think its a driver problem. --Of course I’ve blamed things on the driver or compiler in the past and ALWAYS find that it is infact my fault. So, I dunno.

I’m going to keep working though. Thanks for the help.