Hello.

I have a question about glDrawElements and vertex, normal and texcoordinate indices.

If I have geometric vertex, vertex normals and texture vertices, each with its own indices.

Which of those indices may I use?

If I have this code:

glVertexAttribPointer(vertexHandle, 3, GL_FLOAT, GL_FALSE, 0,
(const GLvoid*) &teapotVertices[0]);
glVertexAttribPointer(normalHandle, 3, GL_FLOAT, GL_FALSE, 0,
(const GLvoid*) &teapotNormals[0]);
glVertexAttribPointer(textureCoordHandle, 2, GL_FLOAT, GL_FALSE, 0,
(const GLvoid*) &teapotTexCoords[0]);

glEnableVertexAttribArray(vertexHandle);
glEnableVertexAttribArray(normalHandle);
glEnableVertexAttribArray(textureCoordHandle);

glBindTexture(GL_TEXTURE_2D, thisTexture->mTextureID);
glUniformMatrix4fv(mvpMatrixHandle, 1, GL_FALSE,
(GLfloat*)&modelViewProjection.data[0] );
glDrawElements(GL_TRIANGLES, NUM_TEAPOT_OBJECT_INDEX, GL_UNSIGNED_SHORT,
(const GLvoid*) &teapotIndices[0]);

What should hold teapotIndices?

Thanks.

Thanks for your answer but, what should I do? I must order them for each vertex, texcoord and normal...

I am stupid, but I can't find what I'm looking for.

I'm very very very new on OpenGL ES 2.0 development.

I only want to know if I have to order them.

If have this:

f v1/vt1/vn1 v2/vt2/vn2 v3/vt3/vn3

I must use the following array:

v1/v2/v3 vt1/vt2/vt3 vn1/vn2/vn3

I want to use glDrawElements, so I need indices for its third parameter.

Thanks.

The indices should be the same for all 3 parameters. Maybe you could use interleaved data.

The point is that while OBJ files relate to the glBegin/End way, they can't EVER work with newer methods.

Like I posted in the other two threads in this page (sigh...), you must "flatten" them to linear data.
You don't have to do it all the way if you don't need to, of course, since having indices helps the GPU work better with caching, but you need to fix shared data.

A 3D box is an excellent example of a model that must be flattened all the way.
With glBegin/End it could have 8 vertices, texcoords, and normals.
With anything newer it must have 24 of each.

The main difference between, say, the above cube and an actual model is that an actual model is continuous, while a box isn't. A real model usually wont have these "edges", it would be all roundish and in one piece.

This is why while the indices may be different, it is usually just to spare on file size by compacting many values into one.
An example to this would be a big 2D grid, where you might have 1000x1000 vertices and texcoords, but can get along just fine with 1 normal if you didn't edit normals.
In this case, you can just "add" the missing data and fix the indices. This way you will still have at the end a full list of indices, and a working model.

It's easier, however, to just go all the way and completely turn the model into linear data, so I suggest you to do that unless your world is very detailed and actually needs to be efficient.
You can always make it more efficient if you notice this is a bottleneck (remember, optimize when you NEED to, not when you WANT to).

Sorry, I've forgotten to metion that I'm working with OpenGL ES 2.0 for Android.