TargetView.m

/*
     File: TargetView.m 
 Abstract: A simple NSImageView subclass that draws little green circles where the user clicks on top of the image.
  
  Version: 1.1 
  
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 */
 
#import "TargetView.h"
 
@implementation TargetView
 
- (id)initWithFrame:(NSRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        self.image = [NSImage imageNamed:@"bullseye"];
        [self setAutoresizingMask: (NSViewMinYMargin | NSViewMinXMargin)];
    }
    return self;
}
 
- (void)dealloc {
    [_path release];
    [super dealloc];
}
 
 
#pragma mark NSResponder
 
- (void)mouseDown:(NSEvent *)event {
    // We use an NSBezierPath to store and draw the clicked points. We create it lazily on the first click in the view.
    if (!_path){
        _path = [[NSBezierPath bezierPath] retain];
    }
    
    // Convert the clicked point into the views coordinate space and add the green circle to the bezierPath. Any point within the bounds of the view is considered a hit.
    NSPoint cursorLocation = [event locationInWindow];
    cursorLocation = [self convertPoint:cursorLocation fromView:nil];
    
    // Test if the hit occured in the opaque part of the image.  We create a 1x1 rectange at the click point and test for intersection with a non-transparent section of the image.
    NSRect cursorLocationRect = { cursorLocation, {1, 1} };
    if ( [self.image hitTestRect:cursorLocationRect withImageDestinationRect:self.bounds 
                       context:nil hints:nil flipped:NO] == NO ) {
        // If the click missed then we ignore it here.
        [super mouseDown:event];
        return;
    }
    
    static const CGFloat kHoleRadius = 6.0f;
    CGFloat kHoleDiameter = kHoleRadius * 2.0f;
    
    NSRect holeFrame = NSMakeRect(cursorLocation.x - kHoleRadius, cursorLocation.y - kHoleRadius, kHoleDiameter, kHoleDiameter);
    [_path appendBezierPath:[NSBezierPath bezierPathWithOvalInRect:holeFrame]];
    
    [self setNeedsDisplayInRect:holeFrame];
}
 
 
#pragma mark NSView
 
- (void)drawRect:(NSRect)dirtyRect {
    // Let super handle drawing of the image.
    [super drawRect:dirtyRect];
    
    // All we need to draw are the green circles where the user clicked.
    [[NSColor greenColor] set];
    [_path fill];
}
 
@end