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Point sprite question

Started by coderchris Dec 29, 2006 at 5:02 PM 1 replies 550+ views

Original Post

coderchris

116

coderchris

Dec 29, 2006 at 5:02 PM

Ill get straight to the question: Is it possible to rotate a point sprite? When I say rotate, I mean I want an independent rotation for each of my point sprites. Im vertex bound at the moment and I need some way to render lots of rotated sprites. Im currently using hardware instancing but Im using quads for the sprites, so for every sprite there is 4 verticies. I figure that with point sprites I could have 4 times as many objects. If its not possible to directly rotate them, are there any shader tricks I can use to do so?

sirob

105

sirob

Dec 29, 2006 at 5:42 PM

Point Sprites themselves don't support rotation. What you can do is rotate the texture being sampled, either using Texture Transformation Matrices, or by directly changing the texcoords in a shader. Both methods will suffer some performance loss.

Are you sure you're vertex limited? Most particle systems are fillrate limited, how have you determined that isn't the case?

Hope this helps.

coderchris

Author

116

coderchris

Dec 29, 2006 at 5:52 PM

thanks for the reply

about the vertex limitation, I was at first using actual sphere geometry, and as I lowered the vertex count on the spheres, it got loads faster. I then switched to using simple rotated textured quads, which sped it up even more. The total number of pixels being rendered each time is roughly the same, so im fairly sure its vertex limited, unless I am missing something

So, i guess I can try shifting the texture coordinates in the pixel shader, though Im not exactly sure how this is done.

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