running on every pixel inside a circle

Question

Let's say I have many small bitmaps and I draw a big circle around them but not necessary all bitmaps are inside of the circle (like some can be half way in or have their edges stick out) and I want to run on every single pixel of the bitmaps in the circle (meaning pixels that are outside of the circle wont be counted, only the parts that are inside), how do I go about doing that, I know how to run on every pixel of all the bitmap, but not in a specific shape..

Answer 1

You need to create an imaginary grid, or rather a grid that is only useful in that it will help you solve the problem at hand. This is the grid that you will assign all the bitmaps to a position on, imagining that the circle's center is to be located at (0,0).

You then use a little math

to find if a pixel as it is relative to its bitmap's position on the grid, is within the radius of the circle.

Of course the distance formuala is

Or if you rather it is the sqrt( a^2 + b^2 ). where 'a' is the difference in x and 'b' is the difference in y between 2 points.