Fix the valid umbra detection.
This looks better b/c every vertex will have one ray shooting at it, such that
we don't miss the corner.
This performs better too, due to the polygon intersection is removed and less ray
intersection. 2x performance for rect and circle for spot shadow in test app.
b/17288227
b/15598793
b/16712006
Change-Id: I4a5ee397b9e192e93c8e35e6260b499e3e38a6f4
Get rid of compuation of the intersection for penumbra and convex hull for umbra.
Use simple circle / normal to compute the penumbra and simple intersection for umbra.
The new way could be 2x to 4x faster from rectangle to round shape.
And this part is roughly half of the shadow computation, or 2/3 of spot shadow
computation.
This improve the spot shadow spikeness too.
b/16712006
b/14976551
Change-Id: I02911784868731369efa73f76fc915bc08248600
Now the theta = 0 should be on +x axis.
And cos(theta) should correctly represent x value.
Without this fix, the poly theta (from atan2) can be wrongly rotated 90 degrees.
Also, make sure the incoming polygon is CW for the shadow system.
This fix visual artifacts in recent regression for spot shadows.
bug:13553955
Change-Id: I9bbf54db094e7f133326da4dae4610962da849c1
