Drawing an NSDrawNinePartImage from a single NSImage

gistfile1.m

static NSImage *croppedImageWithRect(NSImage *image, NSRect rect){
    NSImage *subImage = [[NSImage alloc] initWithSize:rect.size];
    NSRect drawRect = NSZeroRect;
    drawRect.size = rect.size;
    [subImage lockFocus];
    [image drawInRect:drawRect
             fromRect:rect
            operation:NSCompositeSourceOver
             fraction:1.0f];
    [subImage unlockFocus];
    return subImage;
}

- (void)drawRect:(NSRect)dirtyRect{
    NSSize cornerSize = NSMakeSize(8.0f, 8.0f);
    NSImage *wholeImage = [NSImage imageNamed:@"input"];
    
    static NSImage *topLeftCorner = nil;
    if(topLeftCorner == nil){
        NSRect imageRect = NSZeroRect;
        imageRect.size = cornerSize;
        imageRect.origin.y = wholeImage.size.height-cornerSize.height;
        topLeftCorner = croppedImageWithRect(wholeImage, imageRect);
    }
    
    static NSImage *topEdgeFill = nil;
    if(topEdgeFill == nil){
        NSRect imageRect = NSZeroRect;
        imageRect.size.width = wholeImage.size.width-cornerSize.width*2.0f;
        imageRect.size.height = cornerSize.height;
        imageRect.origin.x = cornerSize.width;
        imageRect.origin.y = wholeImage.size.height-cornerSize.height;
        topEdgeFill = croppedImageWithRect(wholeImage, imageRect);
    }
    
    static NSImage *topRightCorner = nil;
    if(topRightCorner == nil){
        NSRect imageRect = NSZeroRect;
        imageRect.size = cornerSize;
        imageRect.origin.x = wholeImage.size.width-cornerSize.width;
        imageRect.origin.y = wholeImage.size.height-cornerSize.height;
        topRightCorner = croppedImageWithRect(wholeImage, imageRect);
    }
    
    static NSImage *leftEdgeFill = nil;
    if(leftEdgeFill == nil){
        NSRect imageRect = NSZeroRect;
        imageRect.size.width = cornerSize.width;
        imageRect.size.height = wholeImage.size.height-cornerSize.height*2.0f;
        imageRect.origin.y = cornerSize.height;
        leftEdgeFill = croppedImageWithRect(wholeImage, imageRect);
    }
    
    static NSImage *centerFill = nil;
    if(centerFill == nil){
        NSRect imageRect = NSZeroRect;
        imageRect.size.width = wholeImage.size.width-cornerSize.width*2.0f;
        imageRect.size.height = wholeImage.size.height-cornerSize.height*2.0f;
        imageRect.origin.x = cornerSize.width;
        imageRect.origin.y = cornerSize.height;
        centerFill = croppedImageWithRect(wholeImage, imageRect);
    }
    
    static NSImage *rightEdgeFill = nil;
    if(rightEdgeFill == nil){
        NSRect imageRect = NSZeroRect;
        imageRect.size.width = cornerSize.width;
        imageRect.size.height = wholeImage.size.height-cornerSize.height*2.0f;
        imageRect.origin.y = cornerSize.height;
        imageRect.origin.x = wholeImage.size.width-cornerSize.width;
        rightEdgeFill = croppedImageWithRect(wholeImage, imageRect);
    } 
    
    static NSImage *bottomLeftCorner = nil;
    if(bottomLeftCorner == nil){
        NSRect imageRect = NSZeroRect;
        imageRect.size = cornerSize;
        bottomLeftCorner = croppedImageWithRect(wholeImage, imageRect);
    } 
    
    static NSImage *bottomEdgeFill = nil;
    if(bottomEdgeFill == nil){
        NSRect imageRect = NSZeroRect;
        imageRect.size.width = wholeImage.size.width-cornerSize.width*2.0f;
        imageRect.size.height = cornerSize.height;
        imageRect.origin.x = cornerSize.width;
        bottomEdgeFill = croppedImageWithRect(wholeImage, imageRect);
    }
    
    static NSImage *bottomRightCorner = nil;
    if(bottomRightCorner == nil){
        NSRect imageRect = NSZeroRect;
        imageRect.size = cornerSize;
        imageRect.origin.x = wholeImage.size.width-cornerSize.width;
        bottomRightCorner = croppedImageWithRect(wholeImage, imageRect);
    }   
    
    NSDrawNinePartImage(self.bounds, topLeftCorner, topEdgeFill, topRightCorner, 
        leftEdgeFill, centerFill, rightEdgeFill, bottomLeftCorner, bottomEdgeFill,
        bottomRightCorner, NSCompositeSourceOver, 1.0f, [self isFlipped]);
}