How to render stretched text in iOS?

Given a rectangular area, I want to render some text using a specific font and have the rendered text fill out the rectangle. As in the image below:

1. This is not the same as just changing font size
2. Rendering it as a bitmap and then scale it is not an option 开发者_如何学Go(it looks horrible)
3. Vector graphics is the way to do it

Solution

I came up with the following which seems to work for my purposes. The code draws a single line of text scaling to fill the bounds. Subclass UIView and replace drawRect as follows.

- (void)drawRect:(CGRect)rect 
{
    [self drawScaledString:@"Abcde"]; 
}

- (void)drawScaledString:(NSString *)string
{
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetTextMatrix(context, CGAffineTransformIdentity);

    NSAttributedString *attrString = [self generateAttributedString:string];

    CFAttributedStringSetAttribute((CFMutableAttributedStringRef)attrString, CFRangeMake(0, string.length), 
                                   kCTForegroundColorAttributeName, [UIColor redColor].CGColor);

    CTLineRef line = CTLineCreateWithAttributedString((CFAttributedStringRef) attrString);

    // CTLineGetTypographicBounds doesn't give correct values, 
    // using GetImageBounds instead
    CGRect imageBounds = CTLineGetImageBounds(line, context);
    CGFloat width = imageBounds.size.width;
    CGFloat height = imageBounds.size.height;

    CGFloat padding = 0;

    width += padding;
    height += padding;

    float sx = self.bounds.size.width / width;
    float sy = self.bounds.size.height / height;

    CGContextSetTextMatrix(context, CGAffineTransformIdentity);

    CGContextTranslateCTM(context, 1, self.bounds.size.height);
    CGContextScaleCTM(context, 1, -1);
    CGContextScaleCTM(context, sx, sy);

    CGContextSetTextPosition(context, -imageBounds.origin.x + padding/2, -imageBounds.origin.y + padding/2);

    CTLineDraw(line, context);
    CFRelease(line);
}

- (NSAttributedString *)generateAttributedString:(NSString *)string
{

    CTFontRef helv = CTFontCreateWithName(CFSTR("Helvetica-Bold"),20, NULL);
    CGColorRef color = [UIColor blackColor].CGColor;

    NSDictionary *attributesDict = [NSDictionary dictionaryWithObjectsAndKeys:
                                    (id)helv, (NSString *)kCTFontAttributeName,
                                    color, (NSString *)kCTForegroundColorAttributeName,
                                    nil];

    NSAttributedString *attrString = [[[NSMutableAttributedString alloc]
                                   initWithString:string
                                        attributes:attributesDict] autorelease];

    return attrString;
}

Example usage:

CGRect rect = CGRectMake(0, 0, 50, 280);
MyCTLabel *label = [[MyCTLabel alloc] initWithFrame:rect];
label.backgroundColor = [UIColor whiteColor]; 
[self addSubview:label];

You can set the UILabel transform property and scale the width:

[myLabel sizeToFit];
myLabel.transform = CGAffineTransformMakeScale(0.5, 1.0);

You could try CoreText. Get a CTFramesetter, calculate its rect, then calculate the affine transform necessary to compress that rect into the bounds you want and set that as the CTM. Then when you draw the text, it should stretch it appropriately at full quality.

you can also try with the UILabel's @property(nonatomic) BOOL adjustsFontSizeToFitWidth and @property minimumFontSize

Initially you can set the much higher value for font property and also initialize the minimumFontSize with a minimum font value.