Object Space Ambient Occlusion

Idea #

Computed per vertex:

1. Compute of the adjacent triangle areas

2. construct a normal oriented disc, with that area at that vertex

3. for each pair of discs, compute how much they occlude each other

4. per vertex

   

Complexity #

Naively:

Improved with hiearchical disc structure:

Shadowed Occluders Problem #

An area can be occluded by two discs, that are also occluding themselves, so too much occlusion is calculated.

Solution #

• Have multiple AO passes
• Use occlusion values from previous pass to weight occlusion of this pass

Large Triangles Problem #

Since the object space ambient occlusion values are calculated per vertex only, the values will be interpolated along the faces, with might not be accurate and even be visibly wrong.