OpenGL VBO - load a normals index

Question

Okay I have the following code that works correctly. It loads a vertex array, a normal array and a vertex index array then draws them with some simple light shading.

To load the buffers:

//Load Buffers
//vertices
glGenBuffers(1, &vertexbuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glBufferData(GL_ARRAY_BUFFER, verts.size() * sizeof(verts), &verts[0], GL_STATIC_DRAW); //verts is std::vector<float>
//normals
glGenBuffers(1, &normalbuffer);
glBindBuffer(GL_ARRAY_BUFFER, normalbuffer);
glBufferData(GL_ARRAY_BUFFER, normals.size() * sizeof(normals), &normals[0], GL_STATIC_DRAW); //normals is std::vector<float>
//indices
glGenBuffers(1, &elementbuffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, elementbuffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices.size() * sizeof(GLushort), &indices[0] , GL_STATIC_DRAW);
//indices is std::vector<unsigned short> and in this working example only
//contains indices into the vertex array (I will add interleaved normal indices)

To draw the buffers:

//Draw Object
glEnableClientState( GL_VERTEX_ARRAY );
glEnableClientState( GL_NORMAL_ARRAY );

//vertices
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE, 0, (void*)0);
glEnableVertexAttribArray(0);

//Indices
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, elementbuffer);

//Normals
glBindBuffer(GL_ARRAY_BUFFER, normalbuffer);
glNormalPointer(GL_FLOAT, 0, (void*)0 );

//Draw the mesh
glDrawElements( GL_TRIANGLES, indices.size(), GL_UNSIGNED_SHORT, (void*)0);

//Clean up
glDisableVertexAttribArray(0);
glDisableVertexAttribArray(1);

In this code, normals are not indexed. I would like to change it so that the normals are based on the the index in indices[] (same as vertices are now). indices[] is interleaved (not in the above code) as such: {vertex index,normal index,vertex index,normal index...}.

I've been trying to get this to work for some time without success and every example I've found online seems to use a different approach to VBOs making it very difficult to combine multiple examples into one that does what I need.

Help would be greatly appreciated. And if I'm doing anything in a less than ideal way, I'm open to suggestions.

Answer 1

In this code, normals are not indexed.

They most certainly are. They merely share the same index as the position.

What you want is not generally possible. All vertex attributes must use the same index. You must convert your multi-indexed data to single-indices per vertex.

There are techniques you could use to avoid this, but they generally require semi-advanced hardware and will lower your overall vertex throughput performance.