在Objective-C iPhone中将文字写在图像上，模拟器的字体大小与iPhone本身不同

Question

I'm having something really weird going, I'm adding caption to an image and everything works fine on simulator but on the device itself the font is really small...

I have a problem when using this code :

-(UIImage*) drawTextOnPic:(NSString*) bottomText
         inImage:(UIImage*)  image
{

UIFont *font = [UIFont boldSystemFontOfSize:48];
UIGraphicsBeginImageContext(image.size);
[image drawInRect:CGRectMake(0,0,image.size.width,image.size.height)];

CGRect = CGRectMake(10.0f,10.0f,image.size.width-20.0f, image.size.height);

CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetShadow(context, CGSizeMake(2.5f, 2.5f), 5.0f);


[[UIColor whiteColor] set];
[bottomText drawInRect:CGRectIntegral(rect) withFont:font lineBreakMode:UILineBreakModeClip alignment:UITextAlignmentCenter];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

return newImage;
}

Does someone know why it works only on simulator as I expected? BTW, I'm using the SDK for iOS6, Can it be something there? Is it something with the retina display? How to fix that?

Answer 1

When you call UIGraphicsBeginImageContext , you should be using the extended call to pass in screen scale, like this:

UIGraphicsBeginImageContextWithOptions(image.size, YES, [[UIScreen mainScreen] scale]);

That will create the image context at the scale of your screen. Note that the second argument, here YES , is whether or not you need the image to be opaque. If there's transparency in your image, set this to NO .

Answer 2

I choose the default font size (on my case it's 48) and then checked the image size according to some ref size (in my case 640x480), I did that by sqrtf(area(a)/area(ref)) then multiply this result on font size. That's the only way it works for me.

Hope that would help others...

Answer 3

//  Drawing text on image
+ (UIImage*) drawText:(NSString*)text withColor:(UIColor *) textColor inImage:(UIImage*)image atPoint:(CGPoint)point {

    UIFont *font = [UIFont boldSystemFontOfSize:12];
    UIGraphicsBeginImageContext(image.size);
    [image drawInRect:CGRectMake(0,0,image.size.width,image.size.height)];
    CGRect rect = CGRectMake(point.x, point.y, image.size.width, image.size.height);
    [textColor set];
    [text drawInRect:CGRectIntegral(rect) withFont:font];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return newImage;
}