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POHow to have smooth sketch drawing on iPhone
 

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    <blockquote> <p><strong>Possible Duplicate:</strong><br> <a href="https://stackoverflow.com/questions/5076622/iphone-smooth-sketch-drawing-algorithm">iPhone smooth sketch drawing algorithm</a> </p> </blockquote> <p>I want to develop a iPhone app that support sketch drawing.</p> <p>I used some codes like this in touchesMoved:</p> <pre><code>UIGraphicsBeginImageContext(self.view.frame.size); [drawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)]; CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound); CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0); CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 0.0, 0.0, 1.0, 1.0); CGContextBeginPath(UIGraphicsGetCurrentContext()); CGContextMoveToPoint(UIGraphicsGetCurrentContext(), points.pointB.x, points.pointB.y); CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), points.pointA.x, points.pointA.y); CGContextStrokePath(UIGraphicsGetCurrentContext()); drawImage.image = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); </code></pre> <p>See:</p> <p><img src="https://i.stack.imgur.com/qV9iD.png" alt="curves not smooth"></p> <p>The curve is not smooth enough. </p> <p>I have tried Catmull-Rom Spline method using some codes form sourceforge.net/projects/curve/files/</p> <p>See:</p> <p><img src="https://i.stack.imgur.com/pPIWr.png" alt="smooth curves"></p> <p>This time the curve is much more smooth but it has 2 problems:</p> <ol> <li><p>Catmull-Rom Spline uses many cubic bezier curve segments and a quadratic bezier curve segment to form a curve. The quadratic bezier curve segment cannot be determine when the touch end. And I cannot plot quadratic segment before a user removing his finger from screen. I can only plot cubic segments when user is drawing so he will feel some delay. The curve lag behind he finger when the finger move fast. </p></li> <li><p>The algorithm corrects corners too much so user cannot draw a star with sharp corners. </p></li> </ol> <p>I have a great desire to provide a very good drawing environment for user like "Sketch Book" app by Autodesk. (see image below)</p> <p>See:</p> <p><img src="https://i.stack.imgur.com/3DqHS.png" alt="very smooth"></p> <p>The app provides smooth curves and it also allows me to draw a star with sharp corners. </p> <p>How can I do that on iPhone? Which algorithm I can use to achieve good quality like "Sketch Book"? Any codes for my reference?</p> <p>Thanks!!</p>
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