StackOverflow2013

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copied!<p>I took HABJAN's solution, which worked well, and converted it to Objective-C. The Objective-C code is as follows:</p> <pre><code>bool LineIntersectsLine(CGPoint l1p1, CGPoint l1p2, CGPoint l2p1, CGPoint l2p2) { CGFloat q = (l1p1.y - l2p1.y) * (l2p2.x - l2p1.x) - (l1p1.x - l2p1.x) * (l2p2.y - l2p1.y); CGFloat d = (l1p2.x - l1p1.x) * (l2p2.y - l2p1.y) - (l1p2.y - l1p1.y) * (l2p2.x - l2p1.x); if( d == 0 ) { return false; } float r = q / d; q = (l1p1.y - l2p1.y) * (l1p2.x - l1p1.x) - (l1p1.x - l2p1.x) * (l1p2.y - l1p1.y); float s = q / d; if( r < 0 || r > 1 || s < 0 || s > 1 ) { return false; } return true; } bool LineIntersectsRect(CGPoint p1, CGPoint p2, CGRect r) { return LineIntersectsLine(p1, p2, CGPointMake(r.origin.x, r.origin.y), CGPointMake(r.origin.x + r.size.width, r.origin.y)) || LineIntersectsLine(p1, p2, CGPointMake(r.origin.x + r.size.width, r.origin.y), CGPointMake(r.origin.x + r.size.width, r.origin.y + r.size.height)) || LineIntersectsLine(p1, p2, CGPointMake(r.origin.x + r.size.width, r.origin.y + r.size.height), CGPointMake(r.origin.x, r.origin.y + r.size.height)) || LineIntersectsLine(p1, p2, CGPointMake(r.origin.x, r.origin.y + r.size.height), CGPointMake(r.origin.x, r.origin.y)) || (CGRectContainsPoint(r, p1) && CGRectContainsPoint(r, p2)); } </code></pre> <p>Many thanks HABJAN. I will note that at first I wrote my own routine which checked each point along the gradient, and I did everything I could do to maximize performance, but this was immediately far faster.</p>

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