Efficiency when rearranging arrays in OpenGL

Question

Imagine I have a vertex array and an index array. Suppose it is possible to rearrange the elements in the index array so that a single call glDrawElements with GL_TRIANGLE_STRIP draws the desired figure. Another possibility would be to call glDrawElements with GL_TRIANGLES but this would make the index array longer.

Does it really matter in terms of efficiency (I mean real efficiency, not some microoptimizations) which way I choose or is the underlying routine the same anyway?

A side note: The reason I am reluctant to rearrange my elements to use GL_TRIANGLE_STRIP is that because I think that the triangles in the strip will have alternating winding. Am I wrong?

Answer 1

There's no really performance differences between a call with GL_TRIANGLE_STRIP and GL_TRIANGLES.

Now if you can rearrange your indices for maximizing post-transform vertex cache, you can have huge performance gains. I did so years ago for rendering large terrain patches and observed 10 to 15 times FPS speedups (using some kind of Hilbert curve scheme).

Answer 2

I think that GL_TRIANGLE_STRIP and GL_TRIANGLES are quite as efficient, if your indices are ordered in a way to maximize vertex transform cache. Of course it will take more memory to store.