How to compensate the flipped coordinate system of core graphics for easy drawing?

Question

It\'s really a pain, but always when I draw an UIImage in -drawRect:, it\'s upside-down.

When I flip the coordinates, the image draws correctly, but at the cost of a

Answer 1

You can do that by apply affinetransform on the point you want to convert in UIKit related coordinates. Following is example.

// Create a affine transform object
CGAffineTransform transform = CGAffineTransformMakeScale(1, -1);
// First translate your image View according to transform
transform = CGAffineTransformTranslate(transform, 0, - imageView.bounds.size.height);
// Then whenever you want any point according to UIKit related coordinates apply this transformation on the point or rect.
// To get tranformed point
CGPoint newPointForUIKit = CGPointApplyAffineTransform(oldPointInCGKit, transform);
// To get transformed rect
CGRect newRectForUIKit = CGRectApplyAffineTransform(oldPointInCGKit, transform);