iphone - 模拟NSImage绘制矩形:fromRect:operation:fraction with UIImage

Question

我真的需要使用 UIImage 模拟 NSImage 的 drawInRect:fromRect:operation:fraction 的行为，我想知道什么是最好的方法或(更好)，如果有人已经这样做并愿意分享代码。

我尝试使用 CGImageCreateWithImageInRect 执行此操作(请参阅最后的代码)，但我没有得到预期的结果。请注意，代码实际上是在 mac 上测试的(我现在无法在 iPhone 上运行整个代码)，所以我在从 NSImage 获取 CGImage 时可能会遇到一些问题

- (void)drawInRect:(CGRect)rect fromRect:(CGRect)fromRect alpha:(float)alpha {
      CGContextRef context;
       CGImageRef originalImageRef;
       CGImageRef subimageRef;

#if ERMac
       context=[[NSGraphicsContext currentContext] graphicsPort];

       CGImageSourceRef source;

       source = CGImageSourceCreateWithData((CFDataRef)[self TIFFRepresentation], NULL);
       originalImageRef =  CGImageSourceCreateImageAtIndex(source, 0, NULL);
       CFRelease(source);
#else
       context=UIGraphicsGetCurrentContext();
       originalImageRef=CGImageRetain([self CGImage]);
#endif

       subimageRef = CGImageCreateWithImageInRect (originalImageRef, fromRect);


       CGContextDrawImage(context, rect, subimageRef);


       if (subimageRef)
           CGImageRelease(subimageRef);
       if (originalImageRef)
           CGImageRelease(originalImageRef);
 }

Answer 1

我就是这样做的...

- (void)drawInRect:(CGRect)drawRect fromRect:(CGRect)fromRect operation:(CGBlendMode)blendMode fraction:(CGFloat)alpha
{
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSaveGState(context);
    CGContextClipToRect(context, drawRect);

    CGFloat xScale = (drawRect.size.width/fromRect.size.width);
    CGFloat yScale = (drawRect.size.height/fromRect.size.height);

    CGFloat scale = 1;
    if([self respondsToSelector:@selector(scale)])
    {
        scale = self.scale;
    }

    CGFloat actualWidth = (xScale * self.size.width)*scale;
    CGFloat actualHeight = (yScale * self.size.height)*scale;
    CGFloat xInset = fromRect.origin.x * xScale;
    CGFloat yInset = fromRect.origin.y * yScale;

    // Take care of Y-axis inversion problem by translating the context on the y axis
    CGContextTranslateCTM(context, 0, drawRect.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);
    CGContextDrawImage(context, CGRectMake(-xInset + drawRect.origin.x, -yInset + drawRect.origin.y, actualWidth, actualHeight), self.CGImage);

    CGContextRestoreGState(context);
}