-[NSWindow _cornerMask] implementation for hosting NSVisualEffectView

gistfile1.m

- (NSImage *)_cornerMask
{
    CGFloat radius = 4.0;
    CGFloat dimension = 2 * radius + 1;
    NSSize size = NSMakeSize(dimension, dimension);
    NSImage *image = [NSImage imageWithSize:size flipped:NO drawingHandler:^BOOL(NSRect dstRect) {
        NSBezierPath *bezierPath = [NSBezierPath bezierPathWithRoundedRect:dstRect xRadius:radius yRadius:radius];
        [[NSColor blackColor] set];
        [bezierPath fill];
        return YES;
    }];
    image.capInsets = NSEdgeInsetsMake(radius, radius, radius, radius);
    image.resizingMode = NSImageResizingModeStretch;
    return image;
}

- (NSImage *)cornerMask
{
    return [self _cornerMask];
}