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ic0de

Particles on the GPU

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So I just figured out how to make a rocket launcher work in terms of physics and now I need to make a kick ass trail of smoke and flames to complete it.

I know making particle effects are pretty straightforward but I was wondering If there was a way to not only render but also simulate particles on the GPU. Seeing as the particles don't affect gameplay whatsoever I assumed this was possible. I expected that I could make an emitter object on the CPU side and the GPU would take over the rest after being fed the position of the emitter. Could anyone possibly point me in the right direction for how to have the GPU actually create polygons without having them fed from the cpu?

Thanks. Edited by ic0de

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A Geometry shader can create polygons on the GPU. The most important question, however, is do you need the particles to collide with the level geometry? (if so you'd need to have the entire physics level on the gpu etc and I don't think it would be worth it. If your particles just follow some mathmatic trajectory (say they just have position, velocity, and acceleration) then you could just pass those to the GPU once and let the GPU integrate the new position each frame quite easily. If you're working in 2D or can use point sprites you don't even need a geometry shader.

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[quote name='zacaj' timestamp='1347928935' post='4981076']
A Geometry shader can create polygons on the GPU. The most important question, however, is do you need the particles to collide with the level geometry? (if so you'd need to have the entire physics level on the gpu etc and I don't think it would be worth it.
[/quote]

my particles simply float downward and fade

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[quote name='zacaj' timestamp='1347929411' post='4981080']
Should be doable then [img]http://public.gamedev.net//public/style_emoticons/default/smile.png[/img] Is the game 3D or 2D?
[/quote]

100% 3d. I just don't wan't to consume bandwidth sending a bunch of little polygons to the gpu if they could be done on the gpu itself

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As long as your particles are just quads it will be much easier (and more efficient) to use point sprites. I'd suggest you look into them before you go diving into geometry shaders

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[quote name='ic0de' timestamp='1347929902' post='4981086']
[quote name='zacaj' timestamp='1347929593' post='4981083']
What GL version you targeting?
[/quote]

I'm targeting GL 2.1 as far as I know there should be an extension for geometry shaders
[/quote]

Nvidia will have support for it under 2.1 and IIRC AMD with DX10 class hardware, but you can forget about Intel.... unless it supports GL3+ explicitly.

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This is also do-able with instancing. You store the base verts for a single quad as per-vertex data and the info that is unique to each particle as per-instance data (one instance per-particle), then draw. It doesn't have the advantage of a GS of only needing to do the calculations once per-particle (it's once per-vertex instead) but also doesn't have the overhead of having the GS stage active, so it may run faster on some hardware (I can easily enough simulate 1,000,000 particles at semi-playable framerates on the GPU using a similar setup). Instancing is also available on a wider range of hardware, but - again - YMMV where Intel drivers are concerned.

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