OpenGL ES 1 multi-texturing with different uv coordinates

Question

I need to render an object using multi-texturing but both the textures have different uv coordinates for same object. One is normal map and other one is light map.

Please provide any useful material regarding this.

Answer 1

In OpenGL ES 2 you use shaders anyway. So you're completely free to use whatever texture coordinates you like. Just introduce an additional attribute for the second texture cooridnate pair and delegate this to the fragment shader, as usual:

...
attribute vec2 texCoord0;
attribute vec2 texCoord1;

varying vec2 vTexCoord0;
varying vec2 vTexCoord1;

void main()
{
    ...
    vTexCoord0 = texCoord0;
    vTexCoord1 = texCoord1;
}

And in the fragment shader use the respective coordinates to access the textures:

...
uniform sampler2D tex0;
uniform sampler2D tex1;
...
varying vec2 vTexCoord0;
varying vec2 vTexCoord1;

void main()
{
    ... = texture2D(tex0, vTexCoord0);
    ... = texture2D(tex1, vTexCoord1);
}

And of course you need to provide data to this new attribute (using glVertexAttribPointer). But if all this sounds very alien to you, then you should either delve a little deeper into GLSL shaders or you actually use OpenGL ES 1. In this case you should retag your question and I will update my answer.

EDIT: According to your update for OpenGL ES 1 the situation is a bit different. I assume you already know how to use a single texture and specify texture coordinates for this, otherwise you should start there before delving into multi-texturing.

With glActiveTexture(GL_TEXTUREi) you can activate the ith texture unit. All following operations related to texture state only refer to the ith texture unit (like glBindTexture, but also glTexEnv and gl(En/Dis)able(GL_TEXTURE_2D)).

For specifying the texture coordinates you still use the glTexCoordPointer function, as with single texturing, but with glCientActiveTexture(GL_TEXTUREi) you can select the texture unit to which following calls to glTexCoordPointer and glEnableClientAttrib(GL_TEXTURE_COORD_ARRAY) refer.

So it would be something like:

//bind and enable textures
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, <second texture>);
glTexEnv(<texture environment for second texture>);   //maybe, if needed
glEnable(GL_TEXTURE_2D);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, <first texture>);
glTexEnv(<texture environment for first texture>);   //maybe, if needed
glEnable(GL_TEXTURE_2D);

//set texture coordinates
glClientActiveTexture(GL_TEXTURE1);
glTexCoordPointer(<texCoords for second texture>);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glClientActiveTexture(GL_TEXTURE0);
glTexCoordPointer(<texCoords for first texture>);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);

//other arrays, like glVertexPointer, ...

glDrawArrays(...)/glDrawElements(...);

//disable arrays
glClientActiveTexture(GL_TEXTURE1);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glClientActiveTexture(GL_TEXTURE0);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);

//disable textures
glActiveTexture(GL_TEXTURE1);
glDisable(GL_TEXTURE_2D);
glActiveTexture(GL_TEXTURE0);
glDisable(GL_TEXTURE_2D);

The reason I set the parameters for the second texture before the first texture is only so that after setting them we end up with texture unit 0 active. I think I have already seen drivers making problems when drawing and another unit than unit 0 was active. And it's always a good idea to leave a more or less clean state at the end, which means the default texture unit (GL_TEXTURE0) active, as otherwise code that doesn't care about multi-texturing could get problems.

EDIT: If you use immediate mode (glBegin/glEnd) instead of vertex arrays, then you don't use glTexCoordPointer, of course. In this case you also don't need glClientAttribTexture, of course. You just need to use glMultiTexCoord(GL_TEXTUREi, ...) with the appropriate texture unit (GL_TEXTURE0, GL_TEXTURE1, ...) instead of glTexCoord(...). But if I'm informed correctly, OpenGL ES doesn't have immediate mode, anyway.