title: CGContext scale to retina
body: <p>I have this code that renders a custom slidebar handle with a dynamic text inside.
  The problem is that I cannot get it to scale to retina resolution. It draws right on all devices and has the right size, but the resolution is low on retina.
  How do I change this code to double the end image resolution?</p>
  
  <pre><code>-(UIImage *)addText:(UIImage *)img{
      int w = img.size.width;
      int h = img.size.height;
  
  
  
      CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
      CGContextRef context = CGBitmapContextCreate(NULL, w, h, 8, 0, colorSpace,kCGImageAlphaPremultipliedFirst);
      CGContextDrawImage(context, CGRectMake(0, 0, w, h), img.CGImage);
  
      char* text= (char *)[[NSString stringWithFormat:@"$%d", (int)betSlider.value * 5] cStringUsingEncoding:NSASCIIStringEncoding];
      CGContextSetShouldAntialias(context, true);
      CGContextSelectFont(context, "TimesNewRomanPS-BoldMT",mainFrame.size.width/22, kCGEncodingMacRoman);
      CGContextSetTextDrawingMode(context, kCGTextFill);
      CGContextSetRGBFillColor(context,255,255,255, 1);
      CGContextShowTextAtPoint(context,(img.size.width-(strlen(text)*strlen(text)*(img.size.width/27)))/2.5,img.size.width/2.5,text, strlen(text));
      CGImageRef imgCombined = CGBitmapContextCreateImage(context);
  
  
      CGContextRelease(context);
      CGColorSpaceRelease(colorSpace);
  
      UIImage *retImage = [UIImage imageWithCGImage:imgCombined];
      CGImageRelease(imgCombined);
  
      return retImage;
  }
  </code></pre>