绘制透明图像
我为按钮创建了一个自定义视图，因为我需要在鼠标悬停时实现一些突出显示。该类非常简单，我已经实现了 mouseEntered: 以及 mouseExited:。该视图已在 init 方法中注册用于跟踪（不确定它是否是最佳位置）。
问题是画图。我保留一个 ivar mouseOver，在鼠标进入时设置为 YES，在鼠标退出时设置为 NO。另一个 ivar 用于图像，称为 image。绘图时鼠标悬停与否的区别在于透明度。这是我的 drawRect:：
- (void)drawRect:(NSRect)dirtyRect
{
[image drawAtPoint:NSMakePoint(0.0,0.0)
fromRect:dirtyRect
operation:NSCompositeCopy
fraction:((mouseOver) ? 1.0 : 0.0)];
}
它工作得很好，但显然只有当鼠标第一次进入时。我想问题是在绘制其他图像之前没有清除视图。我尝试添加：
[[NSColor clearColor] set];
NSRectFillUsingOperation(dirtyRect, NSCompositeClear);
但没有成功。我该如何解决这个问题？
I created a custom view to a button, as I need to implement some highlighting when the mouse is over. The class is very simple, and I already implemented mouseEntered: as well as mouseExited:. The view was registered for tracking in the init method (not sure if it's the best place).
The problem is drawing. I keep an ivar mouseOver, set to YES on mouse enter and NO on mouse exited. The other ivar is for the image, called image. The difference between mouse over or not when it comes to drawing, is the transparency. Here is my drawRect::
- (void)drawRect:(NSRect)dirtyRect
{
[image drawAtPoint:NSMakePoint(0.0,0.0)
fromRect:dirtyRect
operation:NSCompositeCopy
fraction:((mouseOver) ? 1.0 : 0.0)];
}
It works nicely, but only when the mouse first entered, apparently. I guess the problem is that the view is not cleared before drawing the other image. I tried adding:
[[NSColor clearColor] set];
NSRectFillUsingOperation(dirtyRect, NSCompositeClear);
But without success. How can I fix this?
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[NSColor clearColor]是纯透明颜色。您可能想使用具有一定不透明度的颜色进行填充，例如[NSColor WhiteColor]。[NSColor clearColor]is a purely transparent color. You probably want to fill using a color with some opacity, like, say,[NSColor whiteColor].