CGContextShowTextAtPoint producing non-Retina output on Retina device - iphone

Question

I'm trying to add a text to an UIImage and I'm getting a pixelated drawing.
I have tried some other answers with no success:
Drawing on the retina display using CoreGraphics - Image pixelated
Retina display core graphics font quality
Drawing with Core Graphics looks chunky on Retina display
My code:
-(UIImage *)addText:(UIImage *)imgV text:(NSString *)text1
{
int w = self.frame.size.width * 2;
int h = self.frame.size.height * 2;
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate
(NULL, w, h, 8, 4 * w, colorSpace, kCGImageAlphaPremultipliedFirst);
CGContextDrawImage(context, CGRectMake(0, 0, w, h), imgV.CGImage);
CGContextSetRGBFillColor(context, 0.0, 0.0, 1.0, 1);
char* text = (char *)[text1 cStringUsingEncoding:NSASCIIStringEncoding];
CGContextSelectFont(context, "Arial", 24, kCGEncodingMacRoman);
// Adjust text;
CGContextSetTextDrawingMode(context, kCGTextInvisible);
CGContextShowTextAtPoint(context, 0, 0, text, strlen(text));
CGPoint pt = CGContextGetTextPosition(context);
float posx = (w/2 - pt.x)/2.0;
float posy = 54.0;
CGContextSetTextDrawingMode(context, kCGTextFill);
CGContextSetRGBFillColor(context, 255, 255, 255, 1.0);
CGContextShowTextAtPoint(context, posx, posy, text, strlen(text));
CGImageRef imageMasked = CGBitmapContextCreateImage(context);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
return [UIImage imageWithCGImage:imageMasked];
}

Answer 1

Like Peter said, use UIGraphicsBeginImageContextWithOptions. You might want to pass image.scale to the scale attribute (where image.scale is the scale of one of the images you're drawing), or simply use [UIScreen mainScreen].scale.
This code can be made simpler overall. Try something like:
// Create the image context
UIGraphicsBeginImageContextWithOptions(_baseImage.size, NO, _baseImage.scale);
// Draw the image
CGRect rect = CGRectMake(0, 0, _baseImage.size.width, _baseImage.size.height);
[_baseImage drawInRect:rect];
// Get a vertically centered rect for the text drawing
rect.origin.y = (rect.size.height - FONT_SIZE) / 2 - 2;
rect = CGRectIntegral(rect);
rect.size.height = FONT_SIZE;
// Draw the text
UIFont *font = [UIFont boldSystemFontOfSize:FONT_SIZE];
[[UIColor whiteColor] set];
[text drawInRect:rect withFont:font lineBreakMode:NSLineBreakByClipping alignment:NSTextAlignmentCenter];
// Get and return the new image
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
Where text is an NSString object.

Answer 2

I was facing the exact same problem and posted a question last night to which no-one replied. I have combined fnf's suggested changes with Clif Viegas's answer in the following question:
CGContextDrawImage draws image upside down when passed UIImage.CGImage
to come up with the solution. My addText method is slightly different from yours:
+(UIImage *)addTextToImage:(UIImage *)img text:(NSString *)text1{
int w = img.size.width;
int h = img.size.height;
CGSize size = CGSizeMake(w, h);
if (UIGraphicsBeginImageContextWithOptions != NULL) {
UIGraphicsBeginImageContextWithOptions(size, NO, 0.0);
} else {
UIGraphicsBeginImageContext(size);
}
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, 0,h);
CGContextScaleCTM(context, 1.0, -1.0);
CGContextDrawImage(context, CGRectMake(0, 0, w, h), img.CGImage);
CGContextSetRGBFillColor(context, 0.0, 0.0, 1.0, 1);
char* text = (char *)[text1 cStringUsingEncoding:NSASCIIStringEncoding];// \"05/05/09\";
CGContextSelectFont(context, "Times New Roman", 14, kCGEncodingMacRoman);
CGContextSetTextDrawingMode(context, kCGTextFill);
CGContextSetRGBFillColor(context, 0, 0, 0, 1);
//rotate text
CGContextSetTextMatrix(context, CGAffineTransformMakeRotation( -M_PI/8 ));
CGContextShowTextAtPoint(context, 70, 88, text, strlen(text));
CGColorSpaceRelease(colorSpace);
UIGraphicsEndImageContext();
return newImg;
}
In summary, what I have done is add
if (UIGraphicsBeginImageContextWithOptions != NULL) {
UIGraphicsBeginImageContextWithOptions(size, NO, 0.0);
} else {
UIGraphicsBeginImageContext(size);
}
Remove
// CGContextRef context = CGBitmapContextCreate(NULL, w, h, 8, 4 * w, colorSpace, kCGImageAlphaPremultipliedFirst);
and put
CGContextRef context = UIGraphicsGetCurrentContext();
instead. But this causes the image to be upside down. Hence I put
CGContextTranslateCTM(context, 0,h);
CGContextScaleCTM(context, 1.0, -1.0);
just before
CGContextDrawImage(context, CGRectMake(0, 0, w, h), img.CGImage);
This way you can use CG functions instead of using drawInRect etc.
Don't forget
UIGraphicsEndImageContext
at the end. Hope this helps.