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0 pointsboblemarin14y ago0 comments

The particle positions are indeed computed in Javascript, and even if the version you tried only had 30000 of them, the "real 80000" version [ http://minimal.be/lab/fluGL/index80000.html ] does not raise my CPU usage that much.

A more clever way to code that animation would be to pass the mouse position to the GL shaders that would compute themselves the particle positions, and I think modern GPUs are very optimized for that kind of stuff.

Please don't be too rude, cause it was my first WebGL experiment.

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3 comments · 1 top-level

ajross14y ago· 2 in thread

Apologies if I seemed rude, it's really very nice. But yes: a shader absolutely could compute a particle position based on a previous value (and other state, and inputs like mouse position, etc...) as a mapping between, say, a 1D texture and a 1D output framebuffer that gets used as the next frame's source texture. Honestly, given the apparent performance this is what I had assumed was happening.

corysama14y ago

Having the GPU compute position updates into a texture would indeed be orders of magnitude faster, but it would require the vertex shader to read from a texture to get the results. Unfortunately, vertex texturing is an extension that is not required in the WebGL standard and not supported on a significant percentage of machines. It's almost a shame that vertex texturing makes really fun demos really easy to make. Every time I see a VT demo, there are dozen of comments crying "Doesn't work for me. WebGL is broken!"

ajross14y ago

No need to read the texture in the vertex shader. Render to a buffer object and use that as your vertex array. But broadly yes: that's the problem with OpenGL support, and WebGL in particular is still very bleeding edge.

I'd be pretty surprised if vertex texture fetch wasn't supported though. It works on basically all hardware from the PVR SGX on up. Unified shaders are pervasive on both phones and desktops. I did find this, though, which implies that for a while that the browsers weren't properly exposing support:

http://stackoverflow.com/questions/4349389/webgl-texture-acc...

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