Using the vertices, instead of ray casting for the triangulation.
This request a dynamic index buffer associated with vertex buffer,
so we update the VertexBuffer to support it.
The ambient shadow could be 3x-6x times faster for circle and rect now.
b/16712006
b/14257173
Change-Id: I2f22a8fe19bc59acee5c18e4a3a395acd5042a66
Basically we compute the shadow as a strip of triangles, whose alpha value
is the strength of the shadow.
We use the normal to extend the geometry.
And we use static function and try to avoid new/malloc in the computation.
Change-Id: I382286f1cad351bd5ff983f76f446c075819dcaf
