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POiOS CoreGraphics: Draw arc, determine arc angles from intersecting chord theorem
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  1. POiOS CoreGraphics: Draw arc, determine arc angles from intersecting chord theorem
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    copied!<p>I'm trying to figure out how to draw an arc in CoreGraphics. I understand which method calls to make and how to compute the angles in the following scenario.</p> <pre><code>---------- | | *--------* </code></pre> <p>When the points are both in the bottom of the rect. However when two points are in other locations, I don't know how to calculate the correct angle.</p> <pre><code>---------* | | *--------- </code></pre> <p>See bottom portion of my image.</p> <p><img src="https://i.stack.imgur.com/sUoKh.png" alt="enter image description here"></p> <p>Ray Wenderlich has a <a href="http://www.raywenderlich.com/2106/core-graphics-101-arcs-and-paths" rel="nofollow noreferrer">great tutorial</a> about creating arcs for only in the first mentioned point positions.</p> <pre><code>// sample code for creating arc for path from bottom of rect CGMutablePathRef createArcPathFromBottomOfRect(CGRect rect, CGFloat arcHeight) { CGRect arcRect = CGRectMake(rect.origin.x, rect.origin.y + rect.size.height - arcHeight, rect.size.width, arcHeight); CGFloat arcRadius = (arcRect.size.height/2) + (pow(arcRect.size.width, 2) / (8 * arcRect.size.height)); CGPoint arcCenter = CGPointMake(arcRect.origin.x + arc.size.width/2, arcRect.origin.y + arcRadius); CGFloat angle = acos(arcRect.size.width/ (2*arcRadius)); CGFloat startAngle = radians(180) + angle; CGFloat endAngle = radians(360) - angle; CGMutablePathRef path = CGPathCreateMutable(); CGPathAddArc(path, NULL, arcCenter.x, arcCenter.y, arcRadius, startAngle, endAngle, 0); return path; } </code></pre> <p>How do I calculate the angle when in other situations as depicted at the bottom of my image?</p>
 

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