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quesutions about index drawing

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Is index drawing popular in games? If yes, how do they arrange the normal and texcoord? There are a lot of situations that a vertex can have more than one normal and texcoord, so the vertices will be split into copies with their own normal and texcoord in some model files, but is this good? because there will be a few vertex that are repeated, isn't it the aim of index drawing to reduce vertex repetition rate?

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Index drawing is the main form of drawing.

A vertex is not just the position; it is the combination of all the attributes which makes it up, so as soon as one thing is different it is two vertices.

In practise however this isn't a problem; very few vertices on the average model have this problem (identical position, different uv/normal).

The main reason for index drawing is in fact to reduce GPU overhead; if you reference the same index twice then the GPU can use a cached result as the calculation must be the same for both instances - which is the reason that if any input varies it is a new vertex; the output isn't the same after all.

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Indices also enable you to concatenate primitives which is really useful for reducing your draw call count.

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