iOS : UIImage created by UIBezierPath not smooth

Question

我从触摸屏获取点，缩放点，然后我把点放到UIBezierPath，

这是我的代码

let bezierPath = UIBezierPath()

for var i:Int = 0 ; i < newPoints.count ; i++ {
   var indexCount = 0
   let point = newPoints[i][j]
   if point.count > 0{
      let newPointX = point[0] - originRectX // reset the point start with CGPointZero
      let newPointY = point[1] - originRectY
      let scalePointX = newPointX * heightScale  //scale the point with heightScale 0.25
      let scalePointY = newPointY * heightScale
      let scalePoint = CGPointMake(scalePointX, scalePointY)
      if indexCount == 0 {
         bezierPath.moveToPoint(scalePoint)
      }else{
         bezierPath.addLineToPoint(scalePoint)
      }
      indexCount++
   }
}

然后我将路径转换为 ​​UIImage

var tempImage = UIImage()
UIGraphicsBeginImageContextWithOptions(size, false, 1)
stokeColor.setStroke()
bezierPath.lineWidth = lineWidth
bezierPath.lineCapStyle = CGLineCap.Round
bezierPath.lineJoinStyle = CGLineJoin.Round
bezierPath.stroke()
tempImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

然后我在屏幕上绘制 UIImage

 let context = UIGraphicsGetCurrentContext();
 CGContextSaveGState(context)
 let rect = CGRect(x: drawObj.points![0].x,y: drawObj.points![0].y,width: drawObj.image.size.width,height: drawObj.image.size.height)
 drawObj.image?.drawInRect(rect)
 CGContextRotateCTM(context,CGFloat(Double(drawObj.angle!)*M_PI/180))
 CGContextRestoreGState(context)

这是效果

你会发现它不平滑

Answer 1

阅读documentation对于您调用的函数。

UIGraphicsBeginImageContextWithOptions(size, false, 1)

第三个参数是scale。您传递的是 1，这是 1x 显示的比例，如原始 iPhone。在 2016 年，您几乎肯定会使用主屏幕为 2 倍或 3 倍的设备。最简单的修复方法是将参数更改为 0，这将自动使用主屏幕的比例:

UIGraphicsBeginImageContextWithOptions(size, false, 0)

此外，当我们在这里时，这一行实际上什么也没做:

CGContextRotateCTM(context,CGFloat(Double(drawObj.angle!)*M_PI/180))

如果你想让它应用于图像的绘制，你需要先调用它，在你调用drawObj.image?.drawInRect(rect)之前。