在上篇里面介绍了缩放NSImage的方法,几天测试下来发现有个问题,就是在Retina屏下,发现总是比想要的尺寸大了一倍,经研究了,发现使用lockFocus方法,在Retina屏下会自动绘制两倍的大小,挺烦人,不过有个简单的解决方法,拿上篇的例子来说,代码如下:
需要使用NSScreen来获取是否是Retina,有个属性backingScaleFactor,Retina屏下是2.
可以这样干:
NSImage* sourceImage = ...;
NSSize size = ...;
CGFloat scaleFactor = [NSScreen mainScreen].backingScaleFactor;
size.width = size.width / scaleFactor;
size.height = size.height / scaleFactor;
NSRect targetFrame = NSMakeRect(0, 0, size.width, size.height);
NSImage* targetImage = nil;
NSImageRep *sourceImageRep =
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[sourceImage bestRepresentationForRect:targetFrame
context:nil
hints:nil];
targetImage = [[NSImage alloc] initWithSize:size];
[targetImage lockFocus];
[sourceImageRep drawInRect: targetFrame];
[targetImage unlockFocus];