David's Blog

Mostly Hobby Stuff

Archive for March 2011

Fluid Integration and Smoke

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Over the last few days I have been adding support for PhysX fluids to my particle engine, in addition to a few enhancement+fixes to the particle engine itself. The big advantage of the fluid integration is not that it provides SPH(which is nice), but that it provides fast and robust collision detection and interaction with physical objects.

Anyway below I show a couple of screen shots of a small demo level I made, the first is the demo running(it runs at 60 to 30fps depending on resolution) and the second shows the editor with my node based particle editor. With respect to performance, it is mostly fill rate limited(unsurprisingly), I really should investigate using a low resolution render target for low frequency objects.

Some things I added to improve the quality of the results:

  • I rotate the billboard normals away from the centre of the particle, to create a fake volumetric effect. This vastly improves the quality of the lighting for particles. (not sure where this idea came from, I think I read about it somewhere, I just can’t remember where…:-(
  • I added particle sorting, surprisingly, most of the time this is not even needed for many smoke like effects(partly due to the implicit sorting due to emission order perhaps).
  • I used the relative screen space depth to fade the edges of the particles near intersection. This is done with a bunch of shader nodes, I really should combine these into one node since it is quite a common operation.
  • I use my own emitter, not the one built into PhysX, this allows detailed control of the emission parameters(eg distribution of particles within the emission cone etc)
  • I expose more or less all of the fluid settings, however I havent gotten around to sorting them and allowing distributions to be assigned to appropriate parameters.

Written by therealdblack

March 20, 2011 at 11:00 pm

Posted in Graphics, Hobby Game, XNA

Shallow Water Simulator, OpenCL + Rigid Body Interaction

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Just a quick update to post a video of my current progress on my shallow water simulator.

Recently I converted the simulator to OpenCL(from plain C# code) and added rigid body to water and water to rigid body interaction. The conversion to run in parallel was very straightforward, for the rigid body interaction I subdivide the collision shapes into triangles when they first touch the waters bounding box, then just process each triangle separately using atomic operations to update the height and velocity fields. I need to investigate the performance in more detail and generally optimize things, but the initial conversion seems quite fast(the ducks scene runs at 45+fps when not recording video).

I have also added FFT wave simulation for small scale details and/or providing a nice water effect when interaction is not needed(although this is not shown in the video). You can find further details about this method at http://tessendorf.org/ .

Written by therealdblack

March 6, 2011 at 5:51 pm