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查看繪製內部陰影的生成代碼。除了陰影創建部分外,所有內容都非常清晰並且易於理解。copysign。Core Graphics的內部陰影
我明白copysign確實,但爲什麼以及如何實際使用下面的代碼。
0.1的值似乎不顯着xOffset值。
CGContextRef context = UIGraphicsGetCurrentContext();
UIColor* shadow = [UIColor redColor];
CGSize shadowOffset = CGSizeMake(-2, -0);
CGFloat shadowBlurRadius = 2;
UIBezierPath* rectanglePath = [UIBezierPath bezierPathWithRect: CGRectMake(50, 50, 50, 50)];
[[UIColor grayColor] setFill];
[rectanglePath fill];
CGRect rectangleBorderRect = CGRectInset([rectanglePath bounds], -shadowBlurRadius, -shadowBlurRadius);
rectangleBorderRect = CGRectOffset(rectangleBorderRect, -shadowOffset.width, -shadowOffset.height);
rectangleBorderRect = CGRectInset(CGRectUnion(rectangleBorderRect, [rectanglePath bounds]), -1, -1);
UIBezierPath* rectangleNegativePath = [UIBezierPath bezierPathWithRect: rectangleBorderRect];
[rectangleNegativePath appendPath: rectanglePath];
rectangleNegativePath.usesEvenOddFillRule = YES;
CGContextSaveGState(context);
{
CGFloat xOffset = shadowOffset.width + round(rectangleBorderRect.size.width);
CGFloat yOffset = shadowOffset.height;
CGContextSetShadowWithColor(context,
CGSizeMake(xOffset + copysign(0.1, xOffset), yOffset + copysign(0.1, yOffset)),
shadowBlurRadius,
shadow.CGColor);
[rectanglePath addClip];
CGAffineTransform transform = CGAffineTransformMakeTranslation(-round(rectangleBorderRect.size.width), 0);
[rectangleNegativePath applyTransform: transform];
[[UIColor grayColor] setFill];
[rectangleNegativePath fill];
}
CGContextRestoreGState(context);