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POPython & Pygame: Ball collision with interior of circle
 

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  1. POPython & Pygame: Ball collision with interior of circle
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    <p>I'm making a game in which balls bounce around the <em>inside</em> of a much larger circle. The larger circle doesn't move.</p> <p>Here's the code that I'm currently using for these collisions:</p> <pre><code>def collideCircle(circle, ball): """Check for collision between a ball and a circle""" dx = circle.x - ball.x dy = circle.y - ball.y distance = math.hypot(dx, dy) if distance &gt;= circle.size + ball.size: # We don't need to change anything about the circle, just the ball tangent = math.atan2(dy, dx) ball.angle = 2 * tangent - ball.angle ball.speed *= elasticity + 0.251 angle = 0.5 * math.pi + tangent ball.x -= math.sin(angle) ball.y += math.cos(angle) </code></pre> <p>It is based on the wonderful tutorial by Peter Collingridge <a href="http://www.petercollingridge.co.uk/pygame-physics-simulation/collisions" rel="noreferrer">over here</a>.</p> <p>The circle and ball objects are both classes, with (x,y), radius, angle and speed.</p> <p>I am having two problems with this method, however:</p> <ol> <li>The ball bounces from (what I suspect) is its "anchor point", which seems to be in the top right corner of the circle.</li> <li>When colliding with the bottom 5% of the circle, is fails to bounce high enough and therefore "sinks" out of the screen. I am guessing that this is because the bounce is not high enough to move the ball above its (incorrectly placed) "anchor point"?</li> </ol> <p>Having looked at possible solutions already on here, notably "Fast circle collision detection" [Link deleted due to spam link limit], which, although in Java is using the same method, these all deal with external collisions, whereas I am looking at bouncing a ball around the interior of a circle.</p> <p>Here is also the class definitions of the Ball() and the Circle():</p> <pre><code>class Ball(): def __init__(self, (x,y), size): """Setting up the new instance""" self.x = x self.y = y self.size = size self.colour = (0,128,255) self.thickness = 0 self.speed = 0.01 self.angle = math.pi/2 def display(self): """Draw the ball""" pygame.draw.circle(screen, self.colour, (int(self.x), int(self.y)), self.size, self.thickness) def move(self): """Move the ball according to angle and speed""" self.x += math.sin(self.angle) * self.speed self.y -= math.cos(self.angle) * self.speed (self.angle, self.speed) = addVectors((self.angle, self.speed), gravity) self.speed *= drag class Circle(): def __init__(self, (x,y), size): """Set up the new instance of the Circle class""" self.x = x self.y = y self.size = size self.colour = (236, 236, 236) self.thickness = 0 self.angle = 0 # Needed for collision... self.speed = 0 # detection against balls def display(self): """Draw the circle""" pygame.draw.circle(screen, self.colour, (int(self.x), int(self.y)), self.size, self.thickness </code></pre> <p>Thanks in advance, Nathan</p>
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