如何在iOS中渲染拉伸文本？

Question

给定一个矩形区域,我想使用特定字体渲染一些文本,并使渲染文本填充矩形.如下图所示:

1. 这与仅更改字体大小不同
2. 将其渲染为位图然后缩放它不是一个选项(它看起来很糟糕)
3. 矢量图形是这样做的方式

解

我提出了以下似乎适用于我的目的.代码绘制一行文本缩放以填充边界.子类UIView和替换drawRect如下.

- (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;
}

用法示例:

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

Answer 1

您可以设置UILabel变换属性并缩放宽度:

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

Answer 2

你可以试试CoreText。获取 a CTFramesetter，计算其矩形，然后计算将该矩形压缩到所需范围所需的仿射变换，并将其设置为 CTM。然后，当您绘制文本时，它应该以最高质量适当拉伸。