static NSImage *topLeftCornerImage;
static NSImage *topEdgeImage;
static NSImage *topRightCornerImage;
static NSImage *leftEdgeImage;
static NSImage *centerImage;
static NSImage *rightEdgeImage;
static NSImage *bottomLeftCornerImage;
static NSImage *bottomEdgeImage;
static NSImage *bottomRightCornerImage;

+ (void)initialize;
{
  if (baseImage) return;

  NSRect tileRect = NSMakeRect(0,0,8,8);

  baseImage = [NSImage imageNamed:@"SoundPickerBackground"];

  topLeftCornerImage = [[NSImage alloc] initWithSize:tileRect.size];
  [topLeftCornerImage lockFocus];
  [baseImage drawInRect:tileRect
               fromRect:NSMakeRect(0.0,16.0,8.0,8.0)
              operation:NSCompositeCopy fraction:1.0];
  [topLeftCornerImage unlockFocus];

  topEdgeImage = [[NSImage alloc] initWithSize:tileRect.size];
  [topEdgeImage lockFocus];
  [baseImage drawInRect:tileRect
               fromRect:NSMakeRect(8.0,16.0,8.0,8.0)
              operation:NSCompositeCopy fraction:1.0];
  [topEdgeImage unlockFocus];

  topRightCornerImage = [[NSImage alloc] initWithSize:tileRect.size];
  [topRightCornerImage lockFocus];
  [baseImage drawInRect:tileRect
               fromRect:NSMakeRect(16.0,16.0,8.0,8.0)
              operation:NSCompositeCopy fraction:1.0];
  [topRightCornerImage unlockFocus];

  leftEdgeImage = [[NSImage alloc] initWithSize:tileRect.size];
  [leftEdgeImage lockFocus];
  [baseImage drawInRect:tileRect
               fromRect:NSMakeRect(0,8.0,8.0,8.0)
              operation:NSCompositeCopy fraction:1.0];
  [leftEdgeImage unlockFocus];

  centerImage = [[NSImage alloc] initWithSize:tileRect.size];
  [centerImage lockFocus];
  [baseImage drawInRect:tileRect
               fromRect:NSMakeRect(8.0,8.0,8.0,8.0)
              operation:NSCompositeCopy fraction:1.0];
  [centerImage unlockFocus];

  rightEdgeImage = [[NSImage alloc] initWithSize:tileRect.size];
  [rightEdgeImage lockFocus];
  [baseImage drawInRect:tileRect
               fromRect:NSMakeRect(16.0,8.0,8.0,8.0)
              operation:NSCompositeCopy fraction:1.0];
  [rightEdgeImage unlockFocus];

  bottomLeftCornerImage = [[NSImage alloc] initWithSize:tileRect.size];
  [bottomLeftCornerImage lockFocus];
  [baseImage drawInRect:tileRect
               fromRect:NSMakeRect(0,0,8.0,8.0)
              operation:NSCompositeCopy fraction:1.0];
  [bottomLeftCornerImage unlockFocus];

  bottomEdgeImage = [[NSImage alloc] initWithSize:tileRect.size];
  [bottomEdgeImage lockFocus];
  [baseImage drawInRect:tileRect
               fromRect:NSMakeRect(8.0,0,8.0,8.0)
              operation:NSCompositeCopy fraction:1.0];
  [bottomEdgeImage unlockFocus];

  bottomRightCornerImage = [[NSImage alloc] initWithSize:tileRect.size];
  [bottomRightCornerImage lockFocus];
  [baseImage drawInRect:tileRect
               fromRect:NSMakeRect(16.0,0,8.0,8.0)
              operation:NSCompositeCopy fraction:1.0];
  [bottomRightCornerImage unlockFocus];
}



- (void)drawRect:(NSRect)rect;
{
  NSDrawNinePartImage([self bounds],
                      topLeftCornerImage, topEdgeImage, topRightCornerImage,
                      leftEdgeImage, centerImage, rightEdgeImage,
                      bottomLeftCornerImage, bottomEdgeImage, bottomRightCornerImage,
                      NSCompositeSourceOver, 1.0, NO);
}

http://www.karlkraft.com/index.php/2007/11/14/nsdrawninepartimage/

Drawing scaled rectangles of arbitrary width and height that keeps the corner and sides properly scaled while growing the center.

Drawing Scaled Rectangles with NSDrawNinePartImage

osx

Objective C