[求助] 在绘制圆角图片时碰到个问题，某些颜色下会出现圆角不光滑的情形

[ahmiao]

代码

    extension UIImage {
      func thumbnails(with options: SomeDrawingOptions) -> UIImage? {
        // ...

        UIGraphicsBeginImageContextWithOptions(targetRect.size, false, 0)
        defer {
          UIGraphicsEndImageContext()
        }
        let context = UIGraphicsGetCurrentContext()!
        
        UIColor.white.setFill()
        context.fill(targetRect)

        UIBezierPath(roundedRect: targetRect, cornerRadius: 8).addClip()

        // Drawing image
        draw(in: targetRect)
        
        // Drawing a transparent mask
        UIColor.black.withAlphaComponent(0.4).setFill()
        context.fill(targetRect)

        // Drawing bar
        UIColor.white.setFill()
        context.fill(someBarRect)

        return UIGraphicsGetImageFromCurrentImageContext()
      }
    }

参见图片

[imhui]

看起来像是出现了锯齿问题。
试一下改成这样：
UIGraphicsBeginImageContextWithOptions(targetRect.size, false, [UIScreen mainScreen].scale)

[ahmiao]

@imhui 嗯，是锯齿，一直没想起这个词。不过传入 [UIScreen mainScreen].scale 和 传入 0 效果是一样的，文档里写了

> scale The scale factor to apply to the bitmap. If you specify a value of 0.0, the scale factor is set to the scale factor of the device ’ s main screen.