Hi all, sorry for the confusing title, its really hard for me to explain what i want. So i created this image :)

Ok so the two RED dots are points on an image. The distance between them isnt important.

What I want to do is, Using the coordinates for the two dots, work out the angle of the space between them (as shown by the black line between the red dots)

Then once the angle is found, on the last red dot, create two points which cross the angle of the first line. Then from that, scan a Half semicircle and get the coordinates of every pixel of the image that the orange line passes.

I dnot know if this makes any sense to you lot so i drew another picture:

As you can see in the second picture, my idea is applied to a line drawn on a black canavs. The two red dots are the starting coordinates then at the end of the two dots, a less then half semicircle is created. The part that is orange shows the pixels of the image that should be recorded.

I have no clue how to start this, so if anyone has any ideas on how i can or on what i need to do, any help is much appreciated :)