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POiOS - Drawing efficiency (update on slider change)
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copied!<p>I am colouring an image on iOS. I am using a slider to select the colour.</p> <p>When I have "Update Events" on the slider set to continuous, the function that gets called is getting called a lot (the slider goes from 0 to 1535) and so the user interface isn't very responsive.</p> <p>Is there a way I can make the following code more efficient? I realise I'm starting a new drawing context every time I call the function - can I "save" this context and re-use it?</p> <p>Thanks in advance.</p> <pre><code>- (IBAction)bodyColourChanged:(UISlider *)sender { // get the UIColor from self.colourArray UIColor *color = [self.colourArray objectAtIndex:sender.value]; UIImage *myImage = [UIImage imageNamed:@"body.png"]; // Begin a new image context to draw the coloured image onto UIGraphicsBeginImageContext(self.bodyView.image.size); // Get a reference to the context we created CGContextRef context = UIGraphicsGetCurrentContext(); // Set the fill colour //[[UIColor colorWithRed:color.CGColor green:green blue:blue alpha:1.0] setFill]; [color setFill]; // translate/flip the graphics context (for transforming from CG* coords to UI* coords CGContextTranslateCTM(context, 0, self.bodyView.image.size.height); CGContextScaleCTM(context, 1.0, -1.0); // set the blend mode and the original image CGContextSetBlendMode(context, kCGBlendModeOverlay); CGRect rect = CGRectMake(0, 0, self.bodyView.image.size.width, self.bodyView.image.size.height); CGContextDrawImage(context, rect, myImage.CGImage); // Set a mask that matches the shape of the image, then draw (colour burn) a coloured rectangle CGContextClipToMask(context, rect, self.bodyView.image.CGImage); CGContextAddRect(context, rect); CGContextDrawPath(context, kCGPathFill); // Generate a new UIImage from the graphics context we drew onto UIImage *colouredImage = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); self.bodyView.image = colouredImage; } </code></pre> <p>EDIT: The image I'm colouring is quite large. It's 1541 x 2000 pixels because I want to be able to zoom in without loss of quality. Maybe this is the issue. I'll keep tinkering to see what I can find out.</p>

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