NSImage透明度

Question

我想設置一個自定義的拖動圖標在NSTableView中使用。一切似乎都奏效，但由於我對Quartz缺乏經驗，我遇到了一個問題。

- (NSImage *)dragImageForRowsWithIndexes:(NSIndexSet *)dragRows tableColumns:(NSArray *)tableColumns event:(NSEvent *)dragEvent offset:(NSPointPointer)dragImageOffset 
{ 
NSImage *dragImage = [NSImage imageNamed:@"icon.png"]; 
NSString *count = [NSString stringWithFormat:@"%d", [dragRows count]]; 

[dragImage lockFocus]; 
[dragImage compositeToPoint:NSZeroPoint fromRect:NSZeroRect operation:NSCompositeSourceOver fraction:0.5]; 
[count drawAtPoint:NSZeroPoint withAttributes:nil]; 

[dragImage unlockFocus]; 
return dragImage; 
} 

基本上就是我希望做的是渲染透明度爲50％我的icon.png文件與一個NSString這顯示當前正在拖行數一起。我看到的問題是我的NSString呈現低透明度，但不是我的圖標。

Answer 1

問題是你正在繪製自己的圖標。你可能想要的是這樣的：

- (NSImage *)dragImageForRowsWithIndexes:(NSIndexSet *)dragRows tableColumns:(NSArray *)tableColumns event:(NSEvent *)dragEvent offset:(NSPointPointer)dragImageOffset 
{ 
NSImage *icon = [NSImage imageNamed:@"icon.png"]; 
NSString *count = [NSString stringWithFormat:@"%lu", [dragRows count]]; 

NSImage *dragImage = [[[NSImage alloc] initWithSize:[icon size]] autorelease]; 

[dragImage lockFocus]; 
[icon drawAtPoint:NSZeroPoint fromRect:NSZeroRect operation:NSCompositeSourceOver fraction:0.5]; 
[count drawAtPoint:NSZeroPoint withAttributes:nil]; 

[dragImage unlockFocus]; 
return dragImage; 
}