Performance drop when changing vertex colors

Unity Engine
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1

I am making a game with procedurally generated levels and geometry (long trails from some game objects).
Unfortunately, Unity works in a wrong way with modification of mesh attributes (position, colors, etc).

Another posts about the same problem:
http://forum.unity3d.com/threads/118723-Huge-performance-loss-in-Mesh.CreateVBO-for-dynamic-meshes-IOS
http://forum.unity3d.com/threads/111870-Procedural-mesh-update-slow-on-iphone-4

I’m creating a regular grid mesh (440 verts and 798 tris) that is something like a half-pipe with regular grid. I want to colorize a subset of vertices dynamically.

Here some stats from my iPhone 4. Rendering a mesh takes 0.5 ms, but when changing vertex colors each frame (for each vertex) i get 9ms. Using double buffering from posts above improves it to 6ms.
Using colors32 instead of colors not making any difference.

Actually, when I modify any attributes on mesh - vertices, normals, tangents, colors, I get spikes and renderer utilization about 6-9ms.

Maybe it is possible to achieve the same effect using vertex shaders?

2

Setting vertex colors is relatively slow because Unity has to convert the Color array into something usable. Fortunately Unity 4 has Mesh.colors32, so you can use a Color32 array instead.

–Eric

3

I get same slowdown even when not touching the colors array. I also tried storing colors in tangents.
When I comment just one line in my update: mesh.vertices = localVertices; the mesh render takes 0.5ms. Just assigning new values (but with the same tris count and layout) to any of mesh arrays cause huge performance drop. That’s strange…