用透明度繪製圖像

Question

我有幾個png，我將它們彼此重疊以在beginGraphicsContextWithOptions中形成單個圖像....但是，我想用透明度繪製一些這些圖像。我該怎麼做？

Answer 1

這裏是你將如何覆蓋與transparancy圖片：

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];