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PO2d collision between line and a point
 

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    <p>Im trying to understanding collision detection in 2d world. I recently got this tutorials <a href="http://www.gotoandplay.it/_articles/2003/12/bezierCollision.php" rel="nofollow">http://www.gotoandplay.it/_articles/2003/12/bezierCollision.php</a>. I have question which puzzled me a lot - on the flash demo ball is dropping without responding if i try to swap the starting and end point. Can someone explain me , how the simulation works. I have modified this the sample code. It works perfect until the start and end point are swapped, Here is same code in objective c</p> <p>Thanks in advance. .</p> <pre><code>-(void)render:(ccTime)dt { if(renderer) { CGPoint b = ball.position; float bvx = ball.vx; float bvy = ball.vy; bvx += .02; bvy -= .2; b.x += bvx; b.y += bvy; float br = ball.contentSize.width/2; for ( int p = 0 ; p &lt; [map count] ; p++ ) { line *l = [map objectAtIndex:p]; CGPoint p0 = l.end; CGPoint p1 = l.start; float p0x = p0.x, p0y = p0.y, p1x = p1.x, p1y = p1.y; // get Angle // float dx = p0x - p1x; float dy = p0y - p1y; float angle = atan2( dy , dx ); float _sin = sin ( angle ); float _cos = cos ( angle ); // rotate p1 ( need only 'x' ) // float p1rx = dy * _sin + dx * _cos + p0x; // rotate ball // float px = p0x - b.x; float py = p0y - b.y; float brx = py * _sin + px * _cos + p0x; float bry = py * _cos - px * _sin + p0y; float cp = ( b.x - p0x ) * ( p1y - p0y ) - ( b.y - p0y ) * ( p1x - p0x ); if ( bry &gt; p0y - br &amp;&amp; brx &gt; p0x &amp;&amp; brx &lt; p1rx &amp;&amp; cp &gt; 0 ) { // calc new Vector // float vx = bvy * _sin + bvx * _cos; float vy = bvy * _cos - bvx * _sin; vy *= -.8; vx *= .98; float __sin = sin ( -angle ); float __cos = cos ( -angle ); bvx = vy * __sin + vx * __cos; bvy = vy * __cos - vx * __sin; // calc new Position // bry = p0y - br; dx = p0x - brx; dy = p0y - bry; b.x = dy * __sin + dx * __cos + p0x; b.y = dy * __cos - dx * __sin + p0y; } } ball.position = b; ball.vx = bvx; ball.vy = bvy; if ( b.y &lt; 42) { ball.position = ccp(50, size.height - 42); ball.vx = .0f; ball.vy = .0f; } } } </code></pre>
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    1. CODid you just port it or are you familiar with Bezier math?
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