ioscore-animationsubtractioncgpathcashapelayer

Trim/subtract CGPath from CGPath?


I have some CGPath (a poly with two circle) carried out on a CAShapeLayer.

Can I trim/subtract paths like this?

enter image description here


Solution

  • Instead of do the math, the result can be achieved at drawing time using kCGBlendModeClear.

    // Create the poly.
    CGContextBeginPath(context);
    CGContextMoveToPoint       (context, a_.x, a_.y);
    CGContextAddLineToPoint    (context, b_.x, b_.y);
    CGContextAddLineToPoint    (context, c_.x, c_.y);
    CGContextAddLineToPoint    (context, d_.x, d_.y);
    CGContextClosePath(context);
    
    // Draw with the desired color.
    CGContextSetFillColorWithColor(context, self.color.CGColor);
    CGContextFillPath(context);
    
    // Create a circle.
    CGContextBeginPath(context);
    CGContextAddEllipseInRect(context, (CGRect){
        b_.x - self.radius,
        b_.y - self.radius,
        self.radius * 2.0,
        self.radius * 2.0 });
    CGContextClosePath(context);
    
    // Draw with Clear (!) blend mode.
    CGContextSetBlendMode(context, kCGBlendModeClear);
    CGContextSetFillColorWithColor(context, self.color.CGColor);
    CGContextFillPath(context);