实现将NSImage保持指定像素的拉伸

转自：http://www.tanhao.me/pieces/1408.html/

在UIKit中的UIImage有以下两个方法可以实现对图片的部分拉伸：

- (UIImage *)stretchableImageWithLeftCapWidth:(NSInteger)leftCapWidth topCapHeight:(NSInteger)topCapHeight- (UIImage *)resizableImageWithCapInsets:(UIEdgeInsets)capInsets

但在AppKit中的NSImage却没有类似的方法，于是手动写了类似这两个功能的函数:

//保持四周一定区域像素不拉伸，将图像扩散到一定的大小- (NSImage *)stretchableImageWithSize:(NSSize)size edgeInsets:(NSEdgeInsets)insets;//保持leftWidth,rightWidth这左右一定区域不拉伸，将图片宽度拉伸到(leftWidth+middleWidth+rightWidth)- (NSImage *)stretchableImageWithLeftCapWidth:(float)leftWidth middleWidth:(float)middleWidth rightCapWidth:(float)rightWidth;

详细代码如下：

/** * //保持四周一定区域像素不拉伸，将图像扩散到一定的大小 */- (NSImage *)stretchableImageWithSize:(NSSize)size edgeInsets:(NSEdgeInsets)insets{    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);//60        CGFloat h = NSHeight(srcRect);//62        CGFloat cw = w - insets.left - insets.right;//60 - 15 - 15 = 30        CGFloat ch = h - insets.top - insets.bottom; //62 - 20 -20 = 22                CGFloat x0 = NSMinX(srcRect);//0        CGFloat x1 = x0 + insets.left;//15        CGFloat x2 = NSMaxX(srcRect) - insets.right;//   60 - 15 = 45                CGFloat y0 = NSMinY(srcRect);//0        CGFloat y1 = y0 + insets.bottom;//20        CGFloat y2 = NSMaxY(srcRect) - insets.top;//62-20=42                *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);    };        NSRect rect = NSMakeRect(0, 0, size.width, size.height);        // 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);        NSRect srcRects[] = {srcTopL, srcTopC, srcTopR, srcMidL, srcMidC, srcMidR, srcBotL, srcBotC, srcBotR};    NSRect dstRects[] = {dstTopL, dstTopC, dstTopR, dstMidL, dstMidC, dstMidR, dstBotL, dstBotC, dstBotR};    NSMutableArray *partImgs = [NSMutableArray arrayWithCapacity:9];    for (int i=0;i<9;i++)    {        NSRect aSrcRect = srcRects[i];        NSRect aDstRect = dstRects[i];                NSImage *partImg = [[NSImage alloc] initWithSize:aSrcRect.size];        [partImg lockFocus];        [self drawAtPoint:NSZeroPoint fromRect:aSrcRect operation:NSCompositeSourceOver fraction:1.0];        [partImg setSize:aDstRect.size];        [partImg unlockFocus];        [partImgs addObject:partImg];    }        // Draw    NSImage *resultImg = [[NSImage alloc] initWithSize:rect.size];    [resultImg lockFocus];    NSDrawNinePartImage(rect,                        [partImgs objectAtIndex:0],                        [partImgs objectAtIndex:1],                        [partImgs objectAtIndex:2],                        [partImgs objectAtIndex:3],                        [partImgs objectAtIndex:4],                        [partImgs objectAtIndex:5],                        [partImgs objectAtIndex:6],                        [partImgs objectAtIndex:7],                        [partImgs objectAtIndex:8],                        NSCompositeSourceOver, 1, NO);    [resultImg unlockFocus];    return resultImg;}/** * //保持leftWidth,rightWidth这左右一定区域不拉伸，将图片宽度拉伸到(leftWidth+middleWidth+rightWidth) */- (NSImage *)stretchableImageWithLeftCapWidth:(float)leftWidth middleWidth:(float)middleWidth rightCapWidth:(float)rightWidth{    // Calculate the new images dimensions    float imageWidth = leftWidth + middleWidth + rightWidth;    float imageHeight = self.size.height;        // Generate the left image    NSRect rectLeft = NSMakeRect(0, 0, leftWidth, imageHeight);    NSImage *imageLeft = [[NSImage alloc] initWithSize:rectLeft.size];    if (imageLeft.size.width > 0) {        [imageLeft lockFocus];        [self drawInRect:rectLeft fromRect:rectLeft operation:NSCompositeCopy fraction:1.0];        [imageLeft unlockFocus];    }        // Generate the middle image    NSRect rectMiddle = NSMakeRect(0, 0, middleWidth, imageHeight);    NSImage *imageMiddle = [[NSImage alloc] initWithSize:rectMiddle.size];    if (imageMiddle.size.width > 0) {        [imageMiddle lockFocus];        [self drawInRect:rectMiddle fromRect:NSMakeRect(leftWidth, 0, self.size.width-rightWidth-leftWidth,imageHeight) operation:NSCompositeCopy fraction:1.0];        [imageMiddle unlockFocus];    }        // Generate the right image    NSRect rectRight = NSMakeRect(0, 0, rightWidth, imageHeight);    NSImage *imageRight = [[NSImage alloc] initWithSize:rectRight.size];    if (imageRight.size.width > 0) {        [imageRight lockFocus];        [self drawInRect:rectRight fromRect:NSMakeRect(self.size.width - rightWidth, 0, rightWidth, imageHeight) operation:NSCompositeCopy fraction:1.0];        [imageRight unlockFocus];    }        // Combine the images    NSImage *newImage = [[NSImage alloc] initWithSize:NSMakeSize(imageWidth,  imageHeight)];    if (newImage.size.width > 0) {        [newImage lockFocus];        NSDrawThreePartImage(NSMakeRect(0, 0, imageWidth, imageHeight), imageLeft, imageMiddle, imageRight, NO, NSCompositeSourceOver, 1, NO);        [newImage unlockFocus];    }        // Release the images and return the new image    return newImage;}