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Asked: 2026-05-30T13:56:33+00:00

This is what I am getting when reading a FBX File Normals Count =

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This is what I am getting when reading a FBX File

Normals Count        = 6792
TextureCoords Count =  6792
Faces =                2264
Vertices =             3366

What I dont get is why I have less Vertices than Normals / TextCoords

I need your help to understand when I should use Index Buffer and when not

Index buffers help to reduce bandwidth to the Graphics Card, got it.
Index buffers help to not repeat the vertex with the SAME data, got it.

Let’s say I have a model with 1000 Vertices and 3000 Faces formed from those Vertices,
thus an Index Buffer of 9000 elements (3 indices per face)

I have 1000 unique Positions array but 9000 unique TextCoords plus Normals array

If the Vertices were only the Position, that is the best scenario for the Index Buffer, no redundant Vertices

But it happens that I also have TextureCoords and Normals, and per face they can have different values per Position, in other words, the Position shared between faces but with different attributes for each face

So the uniqueness of the Vertex will be -Position AND TextureCoord AND Normal-

It will be unlikely I have repeated vertices with that full combination then the Indices are useless, right?

I will need to repeat the Position for each TextureCoord AND Normal

In the end seems I can’t take advantage of having only 1000 Indexed-Positions

Then my point is , I don’t need Indices right? or am I missunderstanding the concepts?

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1 Answer

  1. Editorial Team

    It will be unlikely I have repeated vertices with that full combination then the Indices are useless, right?

    In the event that you have a model where every face has its own entirely unique texture coordinates, yes, indices won’t help you very much. Also, you don’t have repeated vertices; you have repeated positions. Positions aren’t vertices; they’re part of a vertex’s data, just like the normal, texcoord, etc.

    However, I defy you to actually show me such a model for any reasonable object (ie: something not explicitly faceted for effect, or something not otherwise jigsawed together as far as its texture coordinates are concerned). And for a model with 3000 individual faces, so no cubes.

    In the real world, most models will have plenty of vertex reuse. If yours don’t, then either your modeller is terrible at his job, or it is a very special case.

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