CAShapeLayer strokeColor从图像图案UIColor到CGColor上下颠倒

Question

I'm using CABasicAnimation to draw all UIBezierPaths i have in an Array using CAShapeLayer

CAShapeLayer *shapeLayer = [CAShapeLayer layer];    
shapeLayer.path = [path CGPath];
shapeLayer.strokeColor = path.color.CGColor;

My path.color is a UIColor from image pattern. When it is converted to CGColor the image pattern is upside down. I know that is because iOS and core graphics use different starting points for drawing.

I have tried

shapeLayer.transform = CATransform3DMakeRotation(M_PI, 0.0, 0.0, 1.0);

and

shapeLayer.geometryFlipped = YES;

But none of them worked.

How do I flip the strokeColor image pattern 180 degree to match with the origin UIColor ?

Answer 1

As you have correctly suspected, the coordinate system differs. In this case, the origin is at the bottom left at (0, 0) .

So what you could do to compensate that is to either flip the image yourself using an image editor or do it in code like so:

UIImage *flippedPatternImage = [UIImage imageWithCGImage:patternImage.CGImage scale:1.0f orientation:UIImageOrientationLeftMirrored];

UIColor *colorWithImagePattern = [UIColor colorWithPatternImage:flippedPatternImage];

And finally assign it to the strokeColor :

shapeLayer.strokeColor = path.color.CGColor;