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• Building a clip area in a UIView from path objects in its subviews

  - by hkatz

  I'm trying to produce a clipping area in a UIView that's generated from path objects in its subviews. For example, I might have one subview containing a square and another containing a circle. I want to be able to produce a clip in the parent superview that's the union of both these shapes. Can someone explain how to do this? About all I've been able to figure out so far is that: 1 - the superview's drawRect: method is called before its subviews' drawRects are, and 2 - the ContextRef that's accessible in all three instances is the same. Other than that I'm stumped. Thanks, Howard

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• Anomalous results getting color components of some UIColors

  - by hkatz

  I'm trying to extract the rgb components of a UIColor in order to hand-build the pixels in a CGBitmapContext. The following sample code works fine for most of the UIColor constants but, confusingly, not all. To wit: CGColorRef color = [[UIColor yellowColor] CGColor]; const float* rgba = CGColorGetComponents(color); float r = rgba[0]; float g = rgba[1]; float b = rgba[2]; float a = rgba[3]; NSLog( @"r=%f g=%f b=%f a=%f", r, g, b, a); The results for [UIColor yellowColor] above are r=1.000000 g=1.000000 b=0.000000 a=1.000000, as expected. [UIColor redColor] gives r=1.000000 g=0.000000 b=0.000000 a=1.000000, again as expected. Similarly for blueColor and greenColor. However, the results for [UIColor blackColor] and [UIColor whiteColor] seem completely anomalous, and I don't know what I'm doing wrong (if indeed I am). To wit, [UIColor blackColor] gives r=0.000000 g=1.000000 b=0.000000 a=0.000000, which is a tranparent green, and [UIColor whiteColor] gives r=1.000000 g=1.000000 b=0.000000 a=0.000000, which is a transparent yellow. I'd appreciate it if somebody could either: (1) explain what I'm doing wrong (2) replicate my anomalous results and tell me it's not me, or (3) hit me over the head with a big hammer so it stops hurting so much. Howard

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