Question

I’m working on Android, but this is a java question.

I have an image and an array of points.

I would like to create a new image that has only what’s in the polygon defined by the array of points. What’s not inside I would like to have transparent.

What’s a good way to do this?

Thanks.

Answer 1

If speed is not an option, you can simply test if the polygon contains each point of the resulting image. http://en.wikipedia.org/wiki/Point_in_polygon

If speed is an option, then I would recommend using a scan line filling method to fill only the area covered by the polygon. http://www.cse.ohio-state.edu/~gurari/course/cse693s04/cse693s04su77.html

Both are simple* to implement and I will not explain both here. Just follow the links.