绘制透明图像

Question

我有几个png，我在beginGraphicsContextWithOptions中相互叠加形成一个图像。但是，我想用透明度绘制一些这些图像。我该怎么办呢？

Answer 1

以下是如何使用透明度叠加图像：

NSString* file1 = "your images file path";

NSRect largerect = NSRectMake(10,10,300,300);

NSString* file2 = "your images file path";

NSString* file3 = "your images file path";

NSString* file4 = "your images file path";

NSImage* img1 = [[NSImage alloc] initWithContentsOfFile:file1];

NSImage* img2 = [[NSImage alloc] initWithContentsOfFile:file1];

NSImage* img3 = [[NSImage alloc] initWithContentsOfFile:file1];

NSImage* img4 = [[NSImage alloc] initWithContentsOfFile:file1];

//the fraction parameter is just how transparent you want it so 1.0 is opaque and 0.0      you will not see the image

[image1 drawInRect: largeRect
      fromRect: NSZeroRect
     operation: NSCompositeSourceOver
      fraction: 0.8];

[image2 drawInRect: largeRect
      fromRect: NSZeroRect
     operation: NSCompositeSourceOver
      fraction: 0.6];

[image1 drawInRect: smallRect1
      fromRect: NSZeroRect
     operation: NSCompositeSourceOver
      fraction: 0.40];

[image2 drawInRect: smallRect2
      fromRect: NSZeroRect
     operation: NSCompositeSourceOver
      fraction: 0.40];