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Fezziwig
04-06-2013, 04:39 PM
I need to draw lots of cubes and so I'm using VBOs.

I need them to have vertexes(obviously), normals and textures, so I've defined all the data like this:


GLfloat cubeVertexData[] =
{
1.0f, 1.0f, 1.0f, // 0
0.0f, 1.0f, 1.0f, // 1
0.0f, 0.0f, 1.0f, // 2
1.0f, 0.0f, 1.0f, // 3
1.0f, 0.0f, 0.0f, // 4
1.0f, 1.0f, 0.0f, // 5
0.0f, 1.0f, 0.0f, // 6
0.0f, 0.0f, 0.0f // 7
};


GLfloat cubeNormalData[] =
{
0.0f, 0.0f, 1.0f, // Front
1.0f, 0.0f, 0.0f, // Right
0.0f, 1.0f, 0.0f, // Top
-1.0f, 0.0f, 0.0f, // Left
0.0f, -1.0f, 0.0f, // Bottom
0.0f, 0.0f, -1.0f // Back
};


GLfloat cubeTextureData[] =
{
0.0f, 0.0f, // 0
1.0f, 0.0f, // 1
1.0f, 1.0f, // 2
0.0f, 1.0f // 3
};

Now the problem is I'm not sure how to go about indexing. At the moment I have just stuck everything in one index like this which I imagine is wrong.


GLubyte cubeIndex[] =
{
// Vertex
0,1,2, 2,3,0, // Front
0,3,4, 4,5,0, // Right
0,5,6, 6,1,0, // Top
1,6,7, 7,2,1, // Left
7,4,3, 3,2,7, // Bottom
4,7,6, 6,5,4, // Back


0,0,0, 0,0,0, // Front
1,1,1, 1,1,1, // Right
2,2,2, 2,2,2, // Top
3,3,3, 3,3,3, // Left
4,4,4, 4,4,4, // Bottom
5,5,5, 5,5,5, // Back


0,1,2, 2,3,0, // Front
0,1,2, 2,3,0, // Right
0,1,2, 2,3,0, // Top
0,1,2, 2,3,0, // Left
0,1,2, 2,3,0, // Bottom
0,1,2, 2,3,0 // Back
};

What do I need to do and then which arguments do I put in glDrawElements?
Any help is much appreciated.
Thanks,
Rowan.

Dark Photon
04-08-2013, 06:07 AM
I need to draw lots of cubes ... What do I need to do and then which arguments do I put in glDrawElements?
For best efficiency, look at using instanced rendering.

With that, you don't respecify how to draw a cube over, and over and over... You specify it once, and then just provide instance variation data which says how the instances vary (e.g. different modeling transform, different color, etc.).

Two main ways to do that. the ARB_instanced_arrays (http://www.opengl.org/registry/specs/ARB/draw_instanced.txt) method (glVertexAttribDivisor (http://www.opengl.org/sdk/docs/man3/xhtml/glVertexAttribDivisor.xml)) and the ARB_draw_instanced (http://www.opengl.org/registry/specs/ARB/instanced_arrays.txt) method (see glDrawElementsInstanced() (http://www.opengl.org/sdk/docs/man3/xhtml/glDrawElementsInstanced.xml)).