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stickben

index buffers

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I need a little help with index buffers. Im writing a terrain engine, and so far I loaded all the vertices of my terrain into a vertex buffer, and then I load the offsets of the vertices into the index buffer. My question is, is there any specific order that the verticies need to go into the vertex buffer? As of now i get nothing when I render from the index buffer. thanks, Ben

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There is no specific order in which you have to put vertices in the vertex buffer but...

There IS a specific order in which you have to use them. How you use them is determined by the index buffer.

The clockwise rule applies to how your vertices are referenced and used by the indices.

If your vertices are declared like this:
{0, 1, 2, 3, 4, 5, 6, 7}

in this order to result in these positions:
0--1--2--3

4--5--6--7

then your index buffer should contain something like:
{0, 1, 4, 4, 1, 5, 1, 2, 5, 5, 2, 6, 2, 3, 6, 6, 3, 7}
in order to call DrawIndexedPrimitive() with the triangle list specification.

DX will try to render triangles using the clockwise order so it will go to vertex 0, 1 and 4 for the first triangle, then to vertex 4, 1 and 5 for the next one and so on.

You can generate your vertex and index values based on your map width in # of tiles or vertices or whatever. There is a mathematical progression (a pattern) that you can code to.

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