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POiOS DrawRect code optimisation
 

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  1. POiOS DrawRect code optimisation
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    <p><img src="https://i.stack.imgur.com/7Y2uK.png" alt="enter image description here"> <img src="https://i.stack.imgur.com/musYh.png" alt="enter image description here">Most of the time the code below works correctly and draws paths based upon the user's gestures. However, when the app initially launches the drawRect method isn't able to keep pace with the pan gesture, meaning that the pan gesture is sometimes called multiple times before drawrect is able to draw. This results in a space where the path should be drawn. How could I improve this please?</p> <pre><code>- (void)pan:(UIPanGestureRecognizer *)pan { if (pan.state == UIGestureRecognizerStateChanged) { inputPathCounter++; CGPoint velocity = [pan velocityInView:self]; previousPoint2 = previousPoint1; previousPoint1 = currentPoint; currentPoint = [pan locationInView:self]; float velocityMagnitude = sqrtf(velocity.x * velocity.x + velocity.y * velocity.y); float clampedVelocityMagnitude = clamp(VELOCITY_CLAMP_MIN, VELOCITY_CLAMP_MAX, velocityMagnitude); float normalizedVelocity = (clampedVelocityMagnitude - VELOCITY_CLAMP_MIN) / (VELOCITY_CLAMP_MAX - VELOCITY_CLAMP_MIN); float lowPassFilterAlpha = STROKE_WIDTH_SMOOTHING; float newThickness = (STROKE_WIDTH_MAX - STROKE_WIDTH_MIN) * normalizedVelocity + STROKE_WIDTH_MIN; self.lineWidth = self.lineWidth * lowPassFilterAlpha + newThickness * (1 - lowPassFilterAlpha); CGPoint mid1 = midPoint(previousPoint1, previousPoint2); CGPoint mid2 = midPoint(currentPoint, previousPoint1); CGMutablePathRef subpath = CGPathCreateMutable(); CGPathMoveToPoint(subpath, NULL, mid1.x, mid1.y); CGPathAddQuadCurveToPoint(subpath, NULL, previousPoint1.x, previousPoint1.y, mid2.x, mid2.y); CGRect drawBounds = CGPathGetBoundingBox(subpath); path = [[Path alloc] init]; path.width = self.lineWidth; [self selectedColor]; path.bezierPath = [UIBezierPath bezierPathWithCGPath:subpath]; path.num = inputPathCounter; CGPathRelease(subpath); CGRect drawBox = drawBounds; drawBox.origin.x -= self.lineWidth * 2.0; drawBox.origin.y -= self.lineWidth * 2.0; drawBox.size.width += self.lineWidth * 4.0; drawBox.size.height += self.lineWidth * 4.0; [self setNeedsDisplayInRect:drawBox]; } else if (pan.state == UIGestureRecognizerStateEnded | pan.state == UIGestureRecognizerStateCancelled) { [self saveImage]; self.lineWidth = STROKE_WIDTH_MIN; } } - (void)drawRect:(CGRect)rect { CGContextRef context = UIGraphicsGetCurrentContext(); if(layer == nil) { //NSLog(@"reload layer"); layer = CGLayerCreateWithContext(context, bounds.size, NULL); layerContext = CGLayerGetContext(layer); CGContextScaleCTM(layerContext, scale, scale); viewRect = CGRectMake(0, 0, self.bounds.size.width, self.bounds.size.height); //NSLog(@"viewrect %f %f",viewRect.size.width, viewRect.size.height); CGContextSaveGState(layerContext); UIGraphicsBeginImageContext (viewRect.size); CGContextTranslateCTM(layerContext, 0, self.image.size.height/scale); CGContextScaleCTM(layerContext, 1.0, -1.0); CGContextDrawImage(layerContext, viewRect, self.image.CGImage); UIGraphicsEndImageContext(); CGContextRestoreGState(layerContext); } UIBezierPath *bezierPath = path.bezierPath; CGContextAddPath(layerContext, bezierPath.CGPath); CGContextSetLineWidth(layerContext, path.width); CGContextSetStrokeColorWithColor(layerContext, path.color.CGColor); CGContextSetLineCap(layerContext, kCGLineCapRound); CGContextStrokePath(layerContext); CGContextDrawLayerInRect(context, viewRect, layer); } </code></pre>
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    1. PTQuestion
    1. USSimon
    1. USSimon
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    1. COHow big is the image and why not create the layer before `drawRect` is ever called?
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      1. POiOS DrawRect code optimisation
      1. USWain
    2. COThe image is 2048 x 1024. Too big? But the problem also occurs (less frequently) even if I take out the image.
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      1. POiOS DrawRect code optimisation
      1. USSimon
    3. COWell, move the initialisation code for the layer and then do some time profiling to localise your issue.
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      1. POiOS DrawRect code optimisation
      1. USWain
 

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