Stretchable NSImage

NSImage+Stretchable.m

@implementation NSImage (Resizable)

- (void)drawStretchableInRect:(NSRect)rect edgeInsets:(NSEdgeInsets)insets operation:(NSCompositingOperation)op fraction:(CGFloat)delta {
  NSRect srcRect = (NSRect){NSZeroPoint, self.size};
  
  NSRect topLeft = NSMakeRect(NSMinX(srcRect), NSMaxY(srcRect) - insets.top, insets.left, insets.top);
  NSRect centerLeft = NSMakeRect(NSMinX(srcRect), NSMinY(srcRect) + insets.bottom, insets.left, NSHeight(srcRect) - insets.top - insets.bottom);
  NSRect bottomLeft = NSMakeRect(NSMinX(srcRect), NSMinY(srcRect), insets.left, insets.bottom);
  
  NSRect topCenter = NSMakeRect(NSMaxX(topLeft),
                                NSMaxY(srcRect) - insets.top,
                                NSWidth(srcRect) - insets.left - insets.right,
                                insets.top);
  NSRect centerCenter = NSMakeRect(NSMaxX(centerLeft),
                                   NSMinY(srcRect) + insets.bottom,
                                   NSWidth(srcRect) - insets.left - insets.right,
                                   NSHeight(srcRect) - insets.top - insets.bottom);
  NSRect bottomCenter = NSMakeRect(NSMaxX(bottomLeft),
                                   NSMinY(srcRect),
                                   NSWidth(srcRect) - insets.left - insets.right,
                                   insets.bottom);
  
  NSRect topRight = NSMakeRect(NSMaxX(srcRect) - insets.right,
                               NSMaxY(srcRect) - insets.top,
                               insets.right,
                               insets.top);
  NSRect centerRight = NSMakeRect(NSMaxX(srcRect) - insets.right,
                                  NSMinY(srcRect) + insets.bottom,
                                  insets.right,
                                  NSHeight(srcRect) - insets.top - insets.bottom);
  NSRect bottomRight = NSMakeRect(NSMaxX(srcRect) - insets.right,
                                  NSMinY(srcRect),
                                  insets.right,
                                  insets.bottom);
  
  [self drawInRect:NSMakeRect(NSMinX(rect), NSMaxY(rect) - insets.top, insets.left, insets.top)
          fromRect:topLeft operation:op fraction:delta];
  
  [self drawInRect:NSMakeRect(NSMinX(rect), NSMinY(rect) + insets.bottom, insets.left, NSHeight(rect) - insets.top - insets.bottom)
          fromRect:centerLeft operation:op fraction:delta];
  
  [self drawInRect:NSMakeRect(NSMinX(rect), NSMinY(rect), insets.left, insets.bottom)
          fromRect:bottomLeft operation:op fraction:delta];
  
  [self drawInRect:NSMakeRect(NSMinX(rect) + insets.left, NSMaxY(rect) - insets.top, NSWidth(rect) - insets.left - insets.right, insets.top)
          fromRect:topCenter operation:op fraction:delta];
  
  [self drawInRect:NSMakeRect(NSMinX(rect) + insets.left, NSMinY(rect) + insets.bottom, NSWidth(rect) - insets.left - insets.right, NSHeight(rect) - insets.top - insets.bottom) fromRect:centerCenter operation:op fraction:delta];
  
  [self drawInRect:NSMakeRect(NSMinX(rect) + insets.left, NSMinY(rect), NSWidth(rect) - insets.left - insets.right, insets.bottom)
          fromRect:bottomCenter operation:op fraction:delta];
  
  [self drawInRect:NSMakeRect(NSMaxX(rect) - insets.right, NSMaxY(rect) - insets.top, insets.right, insets.top)
          fromRect:topRight operation:op fraction:delta];
  
  [self drawInRect:NSMakeRect(NSMaxX(rect) - insets.right, NSMinY(rect) + insets.bottom, insets.right, NSHeight(rect) - insets.top - insets.bottom)
          fromRect:centerRight operation:op fraction:delta];
  
  [self drawInRect:NSMakeRect(NSMaxX(rect) - insets.right, NSMinY(rect), insets.right, insets.bottom)
          fromRect:bottomRight operation:op fraction:delta];
}

@end

NSImageStretchable.m

@implementation NSImage (Resizable)

- (void)drawStretchableInRect:(NSRect)rect edgeInsets:(NSEdgeInsets)insets operation:(NSCompositingOperation)op fraction:(CGFloat)delta {
  void (^makeAreas)(NSRect, NSRect *, NSRect *, NSRect *, NSRect *, NSRect *, NSRect *, NSRect *, NSRect *, NSRect *) = ^(NSRect srcRect, NSRect *tl, NSRect *tc, NSRect *tr, NSRect *ml, NSRect *mc, NSRect *mr, NSRect *bl, NSRect *bc, NSRect *br) {
    CGFloat w = NSWidth(srcRect);
    CGFloat h = NSHeight(srcRect);
    CGFloat cw = w - insets.left - insets.right;
    CGFloat ch = h - insets.top - insets.bottom;
    
    CGFloat x0 = NSMinX(srcRect);
    CGFloat x1 = x0 + insets.left;
    CGFloat x2 = NSMaxX(srcRect) - insets.right;
    
    CGFloat y0 = NSMinY(srcRect);
    CGFloat y1 = y0 + insets.bottom;
    CGFloat y2 = NSMaxY(srcRect) - insets.top;
    
    *tl = NSMakeRect(x0, y2, insets.left, insets.top);
    *tc = NSMakeRect(x1, y2, cw, insets.top);
    *tr = NSMakeRect(x2, y2, insets.right, insets.top);
    
    *ml = NSMakeRect(x0, y1, insets.left, ch);
    *mc = NSMakeRect(x1, y1, cw, ch);
    *mr = NSMakeRect(x2, y1, insets.right, ch);
    
    *bl = NSMakeRect(x0, y0, insets.left, insets.bottom);
    *bc = NSMakeRect(x1, y0, cw, insets.bottom);
    *br = NSMakeRect(x2, y0, insets.right, insets.bottom);
  };
  
  // Source rects
  NSRect srcRect = (NSRect){NSZeroPoint, self.size};
  NSRect srcTopL, srcTopC, srcTopR, srcMidL, srcMidC, srcMidR, srcBotL, srcBotC, srcBotR;
  makeAreas(srcRect, &srcTopL, &srcTopC, &srcTopR, &srcMidL, &srcMidC, &srcMidR, &srcBotL, &srcBotC, &srcBotR);
  
  // Destinations rects
  NSRect dstTopL, dstTopC, dstTopR, dstMidL, dstMidC, dstMidR, dstBotL, dstBotC, dstBotR;
  makeAreas(rect, &dstTopL, &dstTopC, &dstTopR, &dstMidL, &dstMidC, &dstMidR, &dstBotL, &dstBotC, &dstBotR);
  
  // Draw
  [self drawInRect:dstTopL fromRect:srcTopL operation:op fraction:delta];
  [self drawInRect:dstTopC fromRect:srcTopC operation:op fraction:delta];
  [self drawInRect:dstTopR fromRect:srcTopR operation:op fraction:delta];
  
  [self drawInRect:dstMidL fromRect:srcMidL operation:op fraction:delta];
  [self drawInRect:dstMidC fromRect:srcMidC operation:op fraction:delta];
  [self drawInRect:dstMidR fromRect:srcMidR operation:op fraction:delta];
  
  [self drawInRect:dstBotL fromRect:srcBotL operation:op fraction:delta];
  [self drawInRect:dstBotC fromRect:srcBotC operation:op fraction:delta];
  [self drawInRect:dstBotR fromRect:srcBotR operation:op fraction:delta];
}

@end