ios - 包裹的 CATextLayer 中的字符被部分截断

Question

我有创建 CATextLayer 并将其绘制到 UIView 上的代码:

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    CGRect viewRect = CGRectMake(50.0f, 50.0f, 345.0f, 120.0f);

    CATextLayer *textLayer = [CATextLayer layer];
    textLayer.contentsScale = [[UIScreen mainScreen] scale];
    textLayer.wrapped = YES;
    textLayer.truncationMode = kCATruncationNone;
    UIFont *font = [UIFont fontWithName:@"SnellRoundhand" size:20.0f];
    textLayer.string = @"Lorem Lipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat.";
    textLayer.alignmentMode = kCAAlignmentLeft;
    textLayer.fontSize = font.pointSize;
    CTFontRef fontRef = CTFontCreateWithName((__bridge CFStringRef)font.fontName, font.pointSize, nil);
    textLayer.font = fontRef;
    CFRelease(fontRef);

    textLayer.backgroundColor = [[UIColor lightGrayColor] CGColor];
    textLayer.foregroundColor = [[UIColor blackColor] CGColor];
    textLayer.frame = viewRect;


    UIGraphicsBeginImageContextWithOptions(textLayer.frame.size, NO, 0);
    [textLayer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *textImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    UIImageView *textImageView = [[UIImageView alloc] initWithImage:textImage];
    textImageView.frame = viewRect;
    [self.view addSubview:textImageView];
}

不幸的是，一些字符在渲染 View 时被截断了。在我发布的示例中，开头的“L”缺少最左边的像素，第二个末尾的“d”缺少最右边的像素。

有没有办法在不改变文本换行方式的情况下防止这种截断的发生？

Answer 1

我没有使用 CATextLayer 的默认行为，而是编写了一个从 CATextLayer 获取数据并手动将其绘制到 CGContext 中的函数。我为填充添加了一个参数来解决截止问题。

-(UIImage *)imageFromCATextLayer:(CATextLayer *)layer andPaddingSize:(CGSize)paddingSize
{
    CGFloat paddingWidth = paddingSize.width;
    CGFloat paddingHeight = paddingSize.height;
    CGRect textBounds = layer.frame;
    CGRect paddedImageBounds = CGRectMake(0.0f, 0.0f, textBounds.size.width + 2 * paddingWidth, textBounds.size.height + 2 * paddingHeight);
    UIGraphicsBeginImageContextWithOptions(paddedImageBounds.size, NO, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextTranslateCTM(context, 0.0f, paddedImageBounds.size.height);
    CGContextScaleCTM(context, 1, -1);

    CGContextSetFillColorWithColor(context, layer.backgroundColor);
    CGContextFillRect(context, paddedImageBounds);

    CTTextAlignment alignment;
    if ([layer.alignmentMode isEqualToString: kCAAlignmentLeft]) {
        alignment = kCTLeftTextAlignment;
    }
    else if ([layer.alignmentMode isEqualToString: kCAAlignmentCenter]) {
        alignment = kCTCenterTextAlignment;
    }
    else if ([layer.alignmentMode isEqualToString: kCAAlignmentRight]) {
        alignment = kCTRightTextAlignment;
    }
    else {
        alignment = kCTLeftTextAlignment;
    }

    CTParagraphStyleSetting paragraphSettings = {kCTParagraphStyleSpecifierAlignment, sizeof(alignment), &alignment};
    CTParagraphStyleRef paragraphStyle = CTParagraphStyleCreate(&paragraphSettings, 1);

    NSDictionary *attributes = [NSDictionary dictionaryWithObjectsAndKeys:layer.font, (NSString*)kCTFontAttributeName, paragraphStyle, kCTParagraphStyleAttributeName, layer.foregroundColor, kCTForegroundColorAttributeName, nil];
    NSAttributedString *attrString = [[NSAttributedString alloc] initWithString:layer.string attributes:attributes];
    CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((__bridge_retained CFAttributedStringRef)attrString);
    CGMutablePathRef p = CGPathCreateMutable();
    CGPathAddRect(p, NULL, CGRectMake(10.0f, 2 * paddingHeight - 10.0f, textBounds.size.width, textBounds.size.height));
    CTFrameRef frame = CTFramesetterCreateFrame(framesetter, CFRangeMake(0,0), p, NULL);
    CTFrameDraw(frame, context);

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return image;
}