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POCGLayer and Anti-aliased CGPaths
 

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    <p>I am drawing several <code>CGPaths</code> in a Cocoa view in the drawRect method on an iPad. I started out drawing them straight to the <code>UIGraphicsGetCurrentContext()</code> context, but performance went south when my paths got really long. Based on <a href="https://stackoverflow.com/questions/2701783/iphone-jagged-edges-when-applying-perspective-to-calayer">several</a> other questions, I started looking into using <code>CGLayer</code>s.</p> <p>So what I do now is to render a path inside of the <code>CGContextRef</code> I get from calling <code>CGLayerGetContext</code>. Here's the basic outline of what I'm doing:</p> <pre class="lang-c prettyprint-override"><code>// rect comes from the drawRect: method layer = CGLayerCreateWithContext(context, rect.size, NULL); layerContext = CGLayerGetContext(layer); CGContextSetLineCap(layerContext, kCGLineCapRound); // Set the line styles CGContextSetLineJoin(layerContext, kCGLineJoinRound); CGContextSetLineWidth(layerContext, 1.0); CGContextSetStrokeColorWithColor(layerContext, [UIColor blackColor].CGColor); // Create a mutable path path = CGPathCreateMutable(); // Move to start point //... for (int i = 0; i &lt; points.count; i++) { // compute controlPoint and anchorPoint //... CGPathAddQuadCurveToPoint(path, nil, controlPoint.x, controlPoint.y, anchorPoint.x, anchorPoint.y); } // Stroke the path CGContextAddPath(layerContext, path); CGContextStrokePath(layerContext); // Add the layer to the main context CGContextDrawLayerAtPoint(context, CGPointZero, layer); </code></pre> <p>Now, I get good performance drawing, but my lines are extremely jagged and do not seem to be anti-aliased. I've tried adding</p> <pre class="lang-c prettyprint-override"><code>CGContextSetShouldAntialias(layerContext, YES); CGContextSetAllowsAntialiasing(layerContext, YES); CGContextSetInterpolationQuality(layerContext, kCGInterpolationHigh); </code></pre> <p>to the code above to no avail. I've even set the anti-aliasing properties on the main <code>context</code>, with no change. I took screen shots of the same code results, but with the second image being the image created from drawing in the <code>CGLayer</code>. As you can see, it is really jagged, despite being the same code, just drawing into a <code>layerContext</code>. How can I get the lines in the <code>CGLayer</code> to be smooth?</p> <p><img src="https://i.stack.imgur.com/bAPc3.png" alt="smooth lines"> <img src="https://i.stack.imgur.com/g1EWk.png" alt="jagged lines"></p>
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