Improved Area Lighting in WebGL & ThreeJS

Question

I have been working on an area lighting implementation in WebGL similar to this demo:

http://threejs.org/examples/webgldeferred_arealights.html

The above imp

Answer 1

Let's agree that casting point is always on the edge.

Let's say that "lit part" is the part of space that is represented by extruded light's quad along its normal.

If surface point sits in the lit part, then you need to calculate the plane that holds that point, it's normal vector and light's normal. Intersection between that plane and light's would give you two points as options (only two, because casting point is always on the edge). So test those two to see which one contributes more.

If the point is not in the lit part, then you could calculate four planes, each has surface point, its normal and one of the vertices of the light's quad. For each light-quad vertex you would have two points (vertex + one more intersection point) to test which contributes the most.

This should do the trick. Please give me feedback if you encounter any counterexample.