OpenGL ES液体着色器

Question

I currently have a particle system in place in android opengl. The physics are all taken care of and the particles draw to the screen great. Only problem is that they render as GL_Points. So they are just colored squares. I was wondering if anyone knows how to combine the points into blobs that looks like liquid when the particles are close enough. It would be nice being able to avoid textures but any shader suggestions would be much appreciated.

Answer 1

There are techniques like marching cubes to create a mesh out of a cloud of points. but this would never run on a smart phone in real time. unless you simulate a super tiny blob of liquid.

You could raytrace the rendering using grid marching and particules in vicinity could have a distance threshold that would get the pixel to exit the marching loop and render some color according to the distance of the nearby particles at this point. which would be very very heavy for a smartphone (but perfecly doable for, say, a GTX480).

you could give up high technology and use billboard rendering, each point becomes 4 points (either thanks to a geometry shader or thanks to some CPU side particle field expansion copy pass into a buffer of quads) then use spherical billboard rendering with the correct blending setup (additive would be nice) to avoid billboards from walking over each other and need sorting, which would kill your perf on a small device.

here some resource about spherical billboards: http://www.gamerendering.com/category/particle-systems/

You could invent your own billboard rendering shader based on a field-evaluation for each pixel. the billboard geometry would only be a "support" that would work like a space partitionning optimization. Instead of marching a grid you would know that if you are evaluating a fragment right now, it is BECAUSE you ARE in the vicinity of a particle field. Thus you could accelerate the research of narby particles and calculating the blob field out of those, and decide of the rendering of your pixel from that. note that the result could be a discard if the influence function returns something under the threshold. this would help create surfaces with clear interface, like water. (and not gases like smoke or vapor). but it would require to prepare a nice lookup structure into a texture at each frame. like say a cube texture with particles information in it, for fast lookup in the shaders. i doubt this can be done on smartphone excepts for super small simulations.

Answer 2

You are looking for a technology called meta balls . Here is a reference: http://nullcandy.com/2d-metaballs-in-xna/