Reflection of a circle from another circle

Question

Work with iPhone and Objective C.

I am working on a game and I need to properly reflect the ball from the circle object. I try to do this as the intersection of a line and a circle. I have a ball position outside the circle, and I have a new ball position that will be inside the circle the next time the draw is updated. I know the intersection point of the line (ball trajectory) and the circle. Now I want to rotate the end point of the ball path relative to the intersection point to get the correct angle of reflection from the tangent.

The following is known:

• ball current x, y
• ball end x, y
• ball radius
• circle center x, y
• circle radius
• the intersection point of the ball path and the circle x and y

I know that I need to find the angle of incidence between the tangent line and the incoming ball, which will also be equal to my angle of reflection. I think, as soon as I recognize these two angles, I can subtract them from 180 to get my rotation angle, and then rotate the end point around the intersection angle by this amount. I just don’t know how.

Answer 1

First, you should note that the center of the ball should not be inside the circle to indicate that there is a reflection or rebound. As long as the distance between the center of the ball and the circle is less than the radius of the ball, there will be a rebound.

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Answer 2

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