ios + OpenGL/OpenVG/Core Graphics/cocos2d. The most optimal algorithm of checking if a point is inside a region?

Question

I use the algorithm of checking if a point is inside a region:

• draw a point with color1

• draw a region with color2

• check if point still has color1

So the main problem for me is the last step.

I know it is possible to do this with core graphics but it is probably slow. In OpenVG and OpenGL it could be faster but:

• I can't find any examples

• it requires 2 cycles of built-in draw function - draw a point and a region on the first call and check color on the second. And the same operation for each region separately.