Python & Pygame: Ball collision with interior of circle

Question

I\'m making a game in which balls bounce around the inside of a much larger circle. The larger circle doesn\'t move.

Here\'s the code that I\'m currently us

Answer 1

I'm glad you liked my tutorial. I like your variation, it should actually be simpler.

First, I think you need change the test for collision to:

if distance >= circle.size - ball.size:

Because the larger the ball size, the smaller the distance between its centre and the centre of the circle can be. This should make the balls bounce at the right place (inside the circle).

Then I think you just need to swap the signs for the x and y and everything should work.

ball.x += math.sin(angle)
ball.y -= math.cos(angle)

To move the ball by the correct distance you can calculate the overlap:

overlap = math.hypot(dx, dy) - (circle.size - ball.size)

if overlap >= 0:
  tangent = math.atan2(dy, dx)
  ball.angle = 2 * tangent - ball.angle
  ball.speed *= elasticity

  angle = 0.5 * math.pi + tangent
  ball.x += math.sin(angle)*overlap
  ball.y -= math.cos(angle)*overlap

Good luck