I'm making a Minecraft style game and currently storing 36 vertices and texture coordinates per cube. Could I make an EBO for only the position and leave the texture coordinates as they are?
OK i think thsi is how i will do it.
I would have an array of 24 vertices(3*GLfloat) and 24 texture coordinates(2*GLfloat) for the corners
then i would have an EBO pointing to the corners with 36 indices
So memory total = 24*3*4 + 24*2*4 + 36*4 = 624 bytes
instead of
36*3*4 + 36*2*4 = 720 bytes
No, you can't, however you can make it only use 24 vertices.
You can define each face with 4 vertices:
0, 0, 0
1, 0 0
1, 1, 0
0, 1, 0
Then the ibo would contain the data
0, 1, 3,
3, 1, 2
If you define each face separately, so that there's no overlap between separate faces, you need 6 * 4 = 24 vertices
If you calculate the byte count (let's say 1 value is 4 bytes) then your current solution is 36 * (3 * 4 + 3 * 4 + 2 * 4) = 1152 bytes. With only 24 vertices and the ibo (you need 36 value in the ibo for 1 cube) that becomes 24 * (3 * 4 + 3 * 4 + 2 * 4) + 36 * 4 = 912 bytes. (I counted the vertices, normals and texture coordinates, but if you have any more data, then the gap becomes bigger)
This is normally solved by adding an extra layer of indirection.
So, your GL_ELEMENT_ARRAY_BUFFER will point to a vertex buffer containing two ints: one of which is a lookup for the position, the other of which is a lookup for the texcoord. In your vertex shader you read these, then use them to lookup other buffers (or textures) to get the actual data.
Of course, that means that your vertex fetching is a little more complex, which may negate any theoretical performance improvement from using less data. GPUs are counter-intuitive like that: sometimes the fast path involves using more memory.
