iphoneobjective-cioscocoaquartz-graphics

Detect if CGPoint within polygon

I have a set of CGPoints which make up a polygon shape, how can I detect if a single CGPoint is inside or outside of the polygon?

Say, the shape was a triangle and the CGPoint was moving hoizontally, how could I detect when it crossed the triangle line?

I can use CGRectContainsPoint when the shape is a regular 4-sided shape but I can't see how I would do it with an odd shape.

Solution

  • You can create a CG(Mutable)PathRef (or a UIBezierPath that wraps a CGPathRef) from your points and use the CGPathContainsPoint function to check if a point is inside that path. If you use UIBezierPath, you could also use the containsPoint: method.