如何在iPhone上绘制透明笔划(或任何清晰的图像部分) [英] How to draw a transparent stroke (or anyway clear part of an image) on the iPhone
问题描述
我有一个小应用程序,允许用户用手指在屏幕上绘图。
我有一个 UIImageView
用户通过创建 CGContextRef
和各种<$ c $来绘制c> CG绘制函数。我主要使用函数 CGContextAddLineToPoint
I have a small app that allows the user to draw on the screen with the finger.
I have a UIImageView
where the user draws, by creating a CGContextRef
and the various CG draw
functions. I primarily draw strokes/lines with the function CGContextAddLineToPoint
绘制笔画/线条现在我的问题是:
用户可以画出各种颜色的线条。我想让他能够使用橡胶
工具用手指删除到目前为止绘制的图像的某些部分。我最初通过使用白色作为笔划(使用 CGContextSetRGBStrokeColor
函数设置)来做到这一点,但它没有用完...因为我后来发现<$ UIImageView
上的c $ c> UIImage 实际上有一个透明的背景,而不是白色...所以我最终会得到一个白色的透明图像就行了!
Now my issue is this:
The user can draw lines of various colors. I want to give him the ability to use a "rubber"
tool to delete some part of the image drawn so far, with the finger. I initially did this by using a white color for the stroke (set with the CGContextSetRGBStrokeColor
function) but it didn't work out...because I discovered later that the UIImage
on the UIImageView
actually had a transparent background, not white...so I would end up with a transparent image with white lines on it!
无论如何设置透明
笔触颜色还是有其他方法可以当他移动它时,在用户的手指下清除 CGContextRef
的内容?
谢谢
Is there anyway to set a "transparent"
stroke color or is there any other way to clear the content of the CGContextRef
under the user's finger, when he moves it?
Thanks
推荐答案
这样做可以解决问题:
CGContextSetBlendMode(context, kCGBlendModeClear)
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