How to delete a rect in a UIImage on iOS?

Question

How can i delete a rect area in a UIImage? My idea is i got a Solid colour image and a CGRect rectangle and i would like to deleted the CGrect in the UIImage so that the CGRect area will be transparent. Please refer to the image below. The Semi-red is my uiimage and i would like to deleted the middle rect so that it is transparent for me to view the background image.

Answer 1

CGContextClearRect（上下文，your_rect）

Answer 2

UIImage *yourImage;
CGRect imageRect = CGRectMake(0, 0, yourImage.size.width, yourImage.size.height);
CGRect grayRect = CGRectMake(20, 20, 20, 20);
CGRect rects[2] = {
  imageRect,
  grayRect
};
CGContextClipToRects(context, rects, 2);
[yourImage drawInRect:imageRect];