CALayer setNeedsDisplayInRect - InRect 的意义是什么？或者在drawInContext中更快地绘制

发布于 2024-10-20 01:53:27 字数 1092 浏览 1 评论 0原文

我有一个 CALayer (imageLayer)，以及一个充当 CALayer (maskLayer) 上的掩模的子类 CALayer。

我用手指在 maskLayer 上绘画，以便可以暂时擦除 imageLayer 的一部分。

我通过保留一个位图上下文 (maskContext) 并在 TouchMoved 中向其添加笔划来实现此目的。所以我的 maskContext 只保存我画的所有笔画。在touchesMoved中，我执行[maskLayer setNeedsDisplay];

在我的子类 maskLayer 中，我有 drawInContext 方法：

-(void)drawInContext:(CGContextRef)ctx
{
    CGImageRef image = CGBitmapContextCreateImage(maskContext);
    CGContextDrawImage(ctx, CGRectMake(0,0,self.frame.size.width, self.frame.size.height), image);
}

这一切都运行得很好，但速度非常慢，因为它为每个 TouchMoved 事件绘制整个视图。

我想过使用 [maskLayer setNeedsDisplayInRect:rect] 但我想知道重点是什么，因为 drawInContext 不查看矩形。我可以将矩形传递给 drawInContext，但我只需使用 setNeedsDisplay 即可做到这一点。

对于 CALayer 来说，是否有 setNeedsDisplayInRect 能做而 setNeedsDisplay 不能做的事情？

（我知道如果我使用 drawRect ，它将接受定义的矩形，但 CALayer 的 drawInContext 不会）

另外，有没有更好的方法来完成这个用手指绘画遮盖？主要问题是 CGContext 不是画布，不记得以前的笔划，因此必须始终重绘它们。

原文

I have a CALayer (imageLayer), and a subclassed CALayer that acts as a mask on the CALayer (maskLayer).

I am painting with a finger onto the maskLayer so that I can temporarily erase out part of the imageLayer.

I am accomplishing this by keeping one Bitmap Context (maskContext), and adding a stroke to it in touchesMoved. So my maskContext just holds all the strokes I have painted. In touchesMoved, I do [maskLayer setNeedsDisplay];

in my subclassed maskLayer, I have the drawInContext method:

-(void)drawInContext:(CGContextRef)ctx
{
    CGImageRef image = CGBitmapContextCreateImage(maskContext);
    CGContextDrawImage(ctx, CGRectMake(0,0,self.frame.size.width, self.frame.size.height), image);
}

This all works out really well, but is very slow as it's drawing the whole view for each touchesMoved event.

I thought of using [maskLayer setNeedsDisplayInRect:rect] but I wondered what the point is, as drawInContext does not look at the rect. I could pass the rect to drawInContext, but I could do that with just setNeedsDisplay.

Is there something that setNeedsDisplayInRect does that setNeedsDisplay doesn't for a CALayer?

(I am aware that if I were using drawRect, that would accept the defined rect, but a CALayer's drawInContext doesn't)

Also, is there any better way of accomplishing this masking by painting with a finger? The main problem is that the CGContext is not a canvas and does not remember previous strokes, so they have to be redrawn all the time.

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