问如何在NSView中实现放大镜

EN

NSPoint mouseLoc;
BubbleNSImage * magImg;
BubbleNSImage * magGlass;
mouseLoc = [self convertPoint:[event locationInWindow] fromView:nil];

// Setup the magnifying glass image
magGlass = [[NSImage alloc] initWithData:
               [[NSImage imageNamed:@"magnifierCursor.png"] TIFFRepresentationUsingCompression:NSTIFFCompressionNone factor:0]];

// Get a 4x zoomed verion of a selection around where the mouse is
// set the image for the image view
if( 0 == _zoomMode ){
    magImg = [BubbleNSImage getPixelMultipliedNSImageRegionFromImage:self.image
                                                      withMultiplier:4
                                                        andSubRegion:NSMakeRect(mouseLoc.x - 17, 
                                                                                self.image.size.height - mouseLoc.y - 17, 
                                                                                34,
                                                                                34)]; 
}else{
    magImg = [BubbleNSImage getAppleMultipliedNSImageRegionNSImage:self.image
                                                    withMultiplier:4                                    
                                            andInterpolationMethod:_zoomMode     
                                                      andSubRegion:NSMakeRect(mouseLoc.x - 17,
                                                                              mouseLoc.y - 17,
                                                                              34,
                                                                              34)];
}


// Mask the 4x zoomed version with a mask made for the zoomer
[magImg maskWithImage:[NSImage imageNamed:@"magnifierCursorMask.png"]
        andMaskOffset:NSMakePoint(0, 0)
         andMaskColor:[NSColor colorWithRed:0 green:0 blue:0 alpha:1]];

// Add the 4x zoomed image behind the magnifying glass image
[magGlass addImageBehind:(NSImage *)magImg
              withOffset:NSMakePoint(16, 16)
       clipToOrigImgSize:NO];

// Preseent the full image as the cursor
[[[NSCursor alloc] initWithImage:(NSImage *)magGlass hotSpot:NSMakePoint(83, 83)] set];

-(void)mouseExited:(NSEvent *)event{
    [[NSCursor arrowCursor] set];
}