0

I'm trying to animate large meshes representing tiles of water using the GPU.

So far I managed to update "on the fly" the vertices of a mesh. I mean on the fly because the mesh isn't actually updated, it remains flat, it's just its vertices that get modified right before rendering, using a vertex shader.

However, I also need to re-compute the normals to make it look realistic. Doing so requires me to have access to the position of other vertices than the current one. The 4 adjacent vertices would be good enough. However this can't be done in a single pass since a vertex shader only has access to the current vertex.

Thus, I would like to modify the vertices in a first pass to simulate the waves, store these updated vertices somewhere, and reuse them in a second path in order to update the normals as well.

Am I thinking about this correctly ? I just started to learn shaders yesterday so I'm a noob.

I read something about rendering to a texture which could allow me to share data between the first and the second pass. Is it the right way ? If so, how can I do that ? I failed to find code samples about this.

I'm trying to do this on Unity 5.6.3 if it matters. Thanks !

Virus721
  • 8,061
  • 12
  • 67
  • 123

1 Answers1

0

My gut feeling is, if the position is parametric, why can't the normal be parametric as well? Why would you need adjacent vertices? You could even maybe compute the normal in the fragment shader and have more precision, like a normal map.

The RenderTexture approach doesn't seem great to me, rather convoluted and not very efficient (multiple passes, needs to store vertex data in a texture, need to figure out adjacency...).

If you still want to try such an approach, I would suggest you look at running a compute shader on a structured buffer, then have your vertex shader tap into that buffer for getting the vertex position/normal based on its index. With this in mind, you wouldn't even need a mesh at all, you could just use DrawProcedural or DrawProceduralIndirect with the desired vertex count.

This of course depends on your target API and hardware, but these days compute shaders are pretty widely supported (the whole "storing data in a texture" approach is more of an ancient hack, albeit still in use unfortunately).

benblo
  • 877
  • 8
  • 18