NSImage透明度

Question

我想设置一个自定义的拖动图标在NSTableView中使用。一切似乎都奏效，但由于我对Quartz缺乏经验，我遇到了一个问题。

- (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为50％我的icon.png文件与一个NSString这显示当前正在拖行数一起。我看到的问题是我的NSString呈现低透明度，但不是我的图标。

Answer 1

问题是你正在绘制自己的图标。你可能想要的是这样的：

- (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; 
}