I need to find the exact XY coordinate where a circle collides with another circle calculated between frames. This means that I take the coordinate of the moving circle on the previous frame and take its coordinate on the current frame. Then I need to find the position where the circle collides some time along this line segment.

*In the diagram below, the blue circle moves from the previous frame (upper) to the current frame (intersecting, lower). During this time it would have hit where the dashed circle is. I need to find the coordinate of the green point.*
![](https://i.sstatic.net/C93cI.png)
*Also note that it may be possible for the blue circle to entirely pass through the red circle. There would then be two points, so the first must be used.*