Question

I’m trying to draw a custom-shaped shadow using CALayer:

#import <QuartzCore/QuartzCore.h>

@implementation ZKSBAppDelegate

@synthesize window = _window;

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    NSView *view = self.window.contentView;
    view.wantsLayer = YES;

    CALayer *shadowLayer = [CALayer layer];
    shadowLayer.shadowOpacity = 1;
    shadowLayer.shadowRadius = 1;
    shadowLayer.shadowOffset = NSMakeSize(0, 0);

    CGMutablePathRef shadowPath = CGPathCreateMutable();
    // setting the following rect's width to 100 fixes everything.
    // setting it to 130 screws the shadow even more.
    CGPathAddRect(shadowPath, NULL, CGRectMake(4, 0, 120, 48));
    CGPathAddRect(shadowPath, NULL, CGRectMake(120, 50, 116, 48));
    shadowLayer.shadowPath = shadowPath;
    CGPathRelease(shadowPath);

    [view.layer addSublayer:shadowLayer];
}
@end

You can create an empty Cocoa project in Xcode, replace your app.delegate’s .m file content with the above code and try it yourself.

It looks like specific shadow path geometry causes CALayer to go nuts.

For example:

CGPathAddRect(shadowPath, NULL, CGRectMake(4, 0, 100, 48));
CGPathAddRect(shadowPath, NULL, CGRectMake(120, 50, 116, 48));

This one looks perfectly okay:

Now I’m going to make the 1st rectangle wider by 20 points:

CGPathAddRect(shadowPath, NULL, CGRectMake(4, 0, 120, 48));
CGPathAddRect(shadowPath, NULL, CGRectMake(120, 50, 116, 48));

…doesn’t look so good anymore. Plus 10 points:

CGPathAddRect(shadowPath, NULL, CGRectMake(4, 0, 130, 48));
CGPathAddRect(shadowPath, NULL, CGRectMake(120, 50, 116, 48));

Now that is plain wrong, isn’t it?

So, the question is: what the hell is going on, am I doing it wrong or something? Do you think it’s a bug and I should file a report?

Answer 1

Yes, that sounds like a bug. Even if it’s not, by filing a bug report Apple should respond and give you useful information.