drawRect绘制“透明”文本？ [英] drawRect drawing 'transparent' text?

问题描述

我希望绘制一个UILabel（最好是通过子类化）作为透明标签，但要有坚实的背景。我画了一个简单的示例（对不起，它很丑陋，但要点很清楚：）。）

I am looking to draw a UILabel (preferable through subclassing) as a transparent label, but with solid background. I draw up an quick example (sorry, it's ugly, but it gets the points across :)).

基本上我有一个UILabel，我希望背景是固定的颜色，并且文本应该是透明的。我不想使用视图背景为文本着色，而是使文本具有100％的透明度，因为我在背景中有一个纹理，我想确保标签内外的线条对齐。

Basically I have a UILabel and I would like the background to be a set colour, and the text should be transparent. I do not want to colour the text with the views background, but instead have it be 100% transparent, since I have a texture in the background that I want to make sure lines up inside and outside of the label.

我一直在过夜浏览SO并在Google上进行搜索，但是我没有找到有用的消息来源。我对CG绘图没有太多的经验，所以我将不胜感激任何链接，帮助，教程或示例代码（也许Apple需要一些我看一下？）。

I've been spending the night browsing SO and searching on Google, but I have found no helpful sources. I don't have much experience with CG drawing, so I would appreciate any links, help, tutorial or sample code (maybe Apple has some I need to have a look at?).

感谢一堆！

推荐答案

我几乎使用任何代码将其重写为UILabel子类，并将其发布在 GitHub

I've rewritten it as a UILabel subclass using barely any code and posted it on GitHub

要点是您重写drawRect但调用 [super drawRect：rect] 以使UILabel正常渲染。使用白色标签颜色可以使您轻松地将标签本身用作遮罩。

The gist of it is you override drawRect but call [super drawRect:rect] to let the UILabel render as normal. Using a white label color lets you easily use the label itself as a mask.

- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext();

    // let the superclass draw the label normally
    [super drawRect:rect];

    CGContextConcatCTM(context, CGAffineTransformMake(1, 0, 0, -1, 0, CGRectGetHeight(rect)));

    // create a mask from the normally rendered text
    CGImageRef image = CGBitmapContextCreateImage(context);
    CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(image), CGImageGetHeight(image), CGImageGetBitsPerComponent(image), CGImageGetBitsPerPixel(image), CGImageGetBytesPerRow(image), CGImageGetDataProvider(image), CGImageGetDecode(image), CGImageGetShouldInterpolate(image));

    CFRelease(image); image = NULL;

    // wipe the slate clean
    CGContextClearRect(context, rect);

    CGContextSaveGState(context);
    CGContextClipToMask(context, rect, mask);

    CFRelease(mask);  mask = NULL;

    [self RS_drawBackgroundInRect:rect];

    CGContextRestoreGState(context);

}

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