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PODrawing on a zoomable view
 

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    <p>I'm working on a small drawing application, which has a basic requirement of supporting zoom-in/out. I have two main issues:</p> <ol> <li><p>Drawing doesn't appear crisp and clear, when view is zoomed/transformed. Is there a better approach, or is there a way to improve the drawing when the view is zoomed?</p></li> <li><p>The drawing performance is slow, when drawing on 1200 x 1200 pts canvas (on iPhone). Any chance I can improve it for large canvas sizes?</p></li> </ol> <p><strong>Zooming Code:</strong></p> <pre><code>- (void)scale:(UIPinchGestureRecognizer *)gestureRecognizer { [self adjustAnchorPointForGestureRecognizer:gestureRecognizer]; UIView *canvas = [gestureRecognizer view]; if ([gestureRecognizer state] == UIGestureRecognizerStateBegan || [gestureRecognizer state] == UIGestureRecognizerStateChanged) { // Calculate the drawing view's size CGSize drawingViewSize = ...; // Calculate the minimum allowed tranform size // Developer's Note: I actually wanted to use the size 1/4th of the view // but self.view.frame.size doesn't return the correct (actual) width and height // It returns these values inverted i.e. width as height, and vice verse. // The reason is that the view appears to be transformed (90 degrees). // Since there's no work-around this, so for now, I'm just using fixed values. CGSize minTranformSize = CGSizeMake(100.0f, 100.0f); if ((minTranformSize.width &gt; drawingViewSize.width) &amp;&amp; (minTranformSize.height &gt; drawingViewSize.height)) { minTranformSize = drawingViewSize; } // Transform the view, provided // 1. It won't scale more than the original size of the background image // 2. It won't scale less than the minimum possible transform CGSize transformedSize = CGSizeMake(canvas.frame.size.width * [gestureRecognizer scale], canvas.frame.size.height * [gestureRecognizer scale]); if ((transformedSize.width &lt;= drawingViewSize.width) &amp;&amp; (transformedSize.height &lt;= drawingViewSize.height) &amp;&amp; (transformedSize.width &gt;= minTranformSize.width) &amp;&amp; (transformedSize.height &gt;= minTranformSize.height)) { canvas.transform = CGAffineTransformScale([canvas transform], [gestureRecognizer scale], [gestureRecognizer scale]); } [gestureRecognizer setScale:1.0]; } else if ([gestureRecognizer state] == UIGestureRecognizerStateEnded) { // Recenter the container view, if required (piece is smaller than the view and it's not aligned) CGSize viewSize = self.view.bounds.size; if ((canvas.frame.size.width &lt; viewSize.width) || (canvas.frame.size.height &lt; viewSize.height)) { canvas.center = CGPointMake(viewSize.width/2, viewSize.height/2); } // Adjust the x/y coordinates, if required (piece is larger than the view and it's moving outwards from the view) if (((canvas.frame.origin.x &gt; 0) || (canvas.frame.origin.y &gt; 0)) &amp;&amp; ((canvas.frame.size.width &gt;= viewSize.width) &amp;&amp; (canvas.frame.size.height &gt;= viewSize.height))) { canvas.frame = CGRectMake(0.0, 0.0, canvas.frame.size.width, canvas.frame.size.height); } canvas.frame = CGRectIntegral(canvas.frame); } } </code></pre> <p><strong>Drawing Code</strong></p> <pre><code>- (void)draw { CGContextRef context = UIGraphicsGetCurrentContext(); CGContextSaveGState(context); if (self.fillColor) { [self.fillColor setFill]; [self.path fill]; } if ([self.strokeColor isEqual:[UIColor clearColor]]) { [self.path strokeWithBlendMode:kCGBlendModeClear alpha:1.0]; } else if (self.strokeColor) { [self.strokeColor setStroke]; [self.path stroke]; } CGContextRestoreGState(context); } </code></pre>
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