After coming across this thread, I had an idea - if this technique can be applied to a 2D game, why haven't I seen it in a 3D one? So, I set out to create a demo of it in 3D this morning. Click me to download. The technique is described in that thread, however, I apply it to 3D: -Create a plethora of billboards with a texture that represents the metaball's charge. -Render all the billboards using additive blending to a render target. -Combine said render target to the scene using a shader. The shader checks if the metaballs charge is > than the threshold - if so, it is rendered. (I actually cheat and use saturate(Charge - Threshold) / (1.0f - Threshold) to smooth it out instead.) -Color the metaballs. In the demo I provided, it's slowed down significantly by physics, but the technique is very fast, and is basically dependent on your fill rate. However, your metaballs may appear different depending on camera angle. If someone has the performance to spare, I'd imagine that a really good looking water simulation could be made out of this and a low threshold. Also, someone far more intelligent than me can probably figure out how to extract world-space normals from the billboards, allowing for cubemap reflections and a million other fancy effects. Tell me what you think!

It's not too hard to add normals. Basically when you're rendering your billboards, you need to calculate xy values such that x and y are of the range[-1, 1] (where (-1, -1) is the bottom left corner of your quad, and so on). Then you output these x and y values along with your weight value (height), and you scale x and y by the weight.

float dist = length(xyPos);float weight = CalcGaussianWeight(dist);xyPos *= weight;return float4(xyPos, 0, weight);

Then in your final pass where you sample the summed weights, you can calculate a normal like this:

float3 normal = normalize(float3(sample.x/sample.w,                                 sample.y/sample.w,                                  max(sample.w - 0.08f, 0)));

Of course you may need to negate your Z depending on your coordinate system.

This is a screen from a little demo I made with this technique a while back:

Awesome - helpful as always, MJP.

I decided to use cubemap reflections, a non-spherical (paint splat) heightmap/brush, with normals:



[Edited by - Akitsune on March 10, 2010 3:59:09 AM]

Thanks! No, not like you'd expect from a billboard method - that's what makes it pretty neat.

Updated the demo, WASD to see for yourself:

http://astraios.net/test/Meta.zip

I'd share the source, but I'm using 3D middleware and it's horribly organized. If someone REALLY wants it, just ask.

PS: Try changing the Drop.png texture to any other grayscale picture.

edit: fixed to new link, source included

Right. I render the billboards using back-front sorting, so the z position is proper.

Correct - metaballs contribute from any distance. This is a limitation, but it isn't a huge one and is barely noticeable - this is what the threshold and billboard size should be adjusted to minimize artifacts. I'm working on adding depth so I can retrieve the world position from the metaballs and eventually use triplanar texturing which like likely have artifacts due to this.

I tried your demo on Windows 7 x64 and it gives me an error saying that is is not a valid Win32 application.

Quote:Original post by maspeir
I tried your demo on Windows 7 x64 and it gives me an error saying that is is not a valid Win32 application.

Looks like I forgot to build in x86 mode, sorry! Uploading a fixed version.