Revision as of 09:53, 17 September 2010

Ambient-Occlusion Vertex Color

Vertex color can be used to store ambient occlusion (AO) lighting information.

Pros

Vertex color AO works well for meshes that use tiled textures, like environment models, because the tiling prevents unique lighting from being added to the textures. In this case texture-based AO would require a separate non-tiled texture using a second set of UVs, which would increase the texture memory and also increase the vertex count for the model (to store the 2nd set of UVs).

Cons

The downside of vertex color is that AO resolution is dependent on the complexity of the mesh. The less vertices there are, the less precise the shading will be. More edges can be added to the model, but it usually requires a tedious manual process.

Examples

CryEngine2 uses vertex color for baked ambient occlusion, see the Sandbox Manual.

Methods

Vertex AO in 3ds Max

The simplest way to bake vertex color AO in 3ds Max is to use Radiosity. For additional methods, see the thread Baking Vertex Illumination without using radiosity on the Polycount forum.

1. Place skylight anywhere.

1. Set Sky color to white.
2. Turn on "Cast Shadows" (optional).

1. Render -> Render.

1. Advance lighting tab.
2. Select Advanced Lighting Rollout.
3. Set advance lighting to radiosity.
   1. Radiosity Processing Parameters Rollout.
   2. Initial quality = 95.
   3. Refine Iterations (All Objects) = 1.
   4. Indirect Light Filte r= 1.
4. Rendering Parameters
   1. Re-Use Direct Illumination from Radiosity Solution.
5. Under Radiosity Processing Parameters click start.

1. Select all the geometry.

1. Command Panel -> Utility Tab -> More...
   1. Assign Vertex Colors.
   2. Vertex Illum.
   3. Lighting Only.
   4. Color by Vertex.
   5. Radiosity -> Reuse Direct Illum. From Solution.
   6. Assign to Selected.

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Vertex AO in Maya

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