NSImage透明度 [英] NSImage transparency

问题描述

我正在尝试设置一个自定义拖动图标用于NSTableView。一切似乎工作，但我遇到了一个问题，由于我没有经验Quartz。

I'm trying to set a custom drag icon for use in an NSTableView. Everything seems to work but I've run into a problem due to my inexperience with Quartz.

- (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;
}

基本上我要做的是render my icon.png文件50％不透明度以及显示当前被拖动的行数的NSString。我看到的问题是，我的NSString呈现低不透明度，但不是我的图标。

Essentially what I'm looking to do is render my icon.png file with 50% opacity along with an NSString which shows the number of rows currently being dragged. The issue I'm seeing is that my NSString renders with a low opacity, but not my icon.

推荐答案

问题是，你在自己的顶部绘制你的图标。你可能想要的是这样：

The issue is that you’re drawing your icon on top of itself. What you probably want is something like this:

- (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;
}

这篇关于NSImage透明度的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！