drawInRect：失去图像分辨率的质量 [英] drawInRect: losing Quality of Image resolution

问题描述

我想使用以下代码清除图片

  CGColorRef strokeColor = [UIColor whiteColor] .CGColor; 
 
 UIGraphicsBeginImageContext（imgForeground.frame.size）; 
 
 CGContextRef context = UIGraphicsGetCurrentContext（）; 
 [imgForeground.image drawInRect：CGRectMake（0，0，imgForeground.frame.size.width，imgForeground.frame.size.height）]; 
 
 CGContextSetLineCap（context，kCGLineCapRound）; 
 CGContextSetLineWidth（context，10）; 
 
 CGContextSetStrokeColorWithColor（context，strokeColor）; 
 CGContextSetBlendMode（context，kCGBlendModeClear）; 
 
 CGContextBeginPath（context）; 
 CGContextMoveToPoint（context，lastPoint.x，lastPoint.y）; 
 CGContextAddLineToPoint（context，currentPoint.x，currentPoint.y）; 
 CGContextStrokePath（context）; 
 
 imgForeground.image = UIGraphicsGetImageFromCurrentImageContext（）; 
 UIGraphicsEndImageContext（）; 
  

但我只是发现图像由于 drawInRect / p>

解决方案

$ c> UIGraphicsBeginImageContextWithOptions 而不是 UIGraphicsBeginImageContext ，以便可以指定比例因子。

例如，这将使用设备主屏幕的缩放系数：

  UIGraphicsBeginImageContextWithOptions（imgForeground.frame.size，NO，0）; 
  

I am trying to erase image using following code

 CGColorRef strokeColor = [UIColor whiteColor].CGColor;

 UIGraphicsBeginImageContext(imgForeground.frame.size);

 CGContextRef context = UIGraphicsGetCurrentContext();
 [imgForeground.image drawInRect:CGRectMake(0, 0, imgForeground.frame.size.width, imgForeground.frame.size.height)];

 CGContextSetLineCap(context, kCGLineCapRound);
 CGContextSetLineWidth(context, 10);

 CGContextSetStrokeColorWithColor(context, strokeColor);
 CGContextSetBlendMode(context, kCGBlendModeClear);

 CGContextBeginPath(context);
 CGContextMoveToPoint(context, lastPoint.x, lastPoint.y);
 CGContextAddLineToPoint(context, currentPoint.x, currentPoint.y);
 CGContextStrokePath(context);

 imgForeground.image  = UIGraphicsGetImageFromCurrentImageContext();
 UIGraphicsEndImageContext();

But I just find out Image losing its resolution due to drawInRect.

解决方案

You should go with UIGraphicsBeginImageContextWithOptions instead of UIGraphicsBeginImageContext, so that a scale factor can be specified.

For example, this will use the scale factor of the device's main screen:

UIGraphicsBeginImageContextWithOptions(imgForeground.frame.size, NO, 0);

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