我需要为 NSAttributedString(核心文本)中的每个字符(字形)计算精确的边界框。 将一些用于解决类似问题的代码(核心文本选择等)放在一起，结果相当不错，但只有几帧(红色)被正确计算:

大多数帧在水平或垂直方向上(一点点)都错位了。这是什么原因？如何完善此代码？:

-(void)recalculate{

    // get characters from NSString
    NSUInteger len = [_attributedString.string length];
    UniChar *characters = (UniChar *)malloc(sizeof(UniChar)*len);
    CFStringGetCharacters((__bridge CFStringRef)_attributedString.string, CFRangeMake(0, [_attributedString.string length]), characters);

    // allocate glyphs and bounding box arrays for holding the result
    // assuming that each character is only one glyph, which is wrong
    CGGlyph *glyphs = (CGGlyph *)malloc(sizeof(CGGlyph)*len);
    CTFontGetGlyphsForCharacters(_font, characters, glyphs, len);

    // get bounding boxes for glyphs
    CTFontGetBoundingRectsForGlyphs(_font, kCTFontDefaultOrientation, glyphs, _characterFrames, len);
    free(characters); free(glyphs);

    // Measure how mush specec will be needed for this attributed string
    // So we can find minimun frame needed
    CFRange fitRange;
    CGSize s = CTFramesetterSuggestFrameSizeWithConstraints(_framesetter, rangeAll, NULL, CGSizeMake(W, MAXFLOAT), &fitRange);

    _frameRect = CGRectMake(0, 0, s.width, s.height);
    CGPathRef framePath = CGPathCreateWithRect(_frameRect, NULL);
    _ctFrame = CTFramesetterCreateFrame(_framesetter, rangeAll, framePath, NULL);
    CGPathRelease(framePath);


    // Get the lines in our frame
    NSArray* lines = (NSArray*)CTFrameGetLines(_ctFrame);
    _lineCount = [lines count];

    // Allocate memory to hold line frames information:
    if (_lineOrigins != NULL)free(_lineOrigins);
    _lineOrigins = malloc(sizeof(CGPoint) * _lineCount);

    if (_lineFrames != NULL)free(_lineFrames);
    _lineFrames = malloc(sizeof(CGRect) * _lineCount);

    // Get the origin point of each of the lines
    CTFrameGetLineOrigins(_ctFrame, CFRangeMake(0, 0), _lineOrigins);

    // Solution borrowew from (but simplified):
    // https://github.com/twitter/twui/blob/master/lib/Support/CoreText%2BAdditions.m


    // Loop throught the lines
    for(CFIndex i = 0; i < _lineCount; ++i) {

        CTLineRef line = (__bridge CTLineRef)[lines objectAtIndex:i];

        CFRange lineRange = CTLineGetStringRange(line);
        CFIndex lineStartIndex = lineRange.location;
        CFIndex lineEndIndex = lineStartIndex + lineRange.length;

        CGPoint lineOrigin = _lineOrigins[i];
        CGFloat ascent, descent, leading;
        CGFloat lineWidth = CTLineGetTypographicBounds(line, &ascent, &descent, &leading);


        // If we have more than 1 line, we want to find the real height of the line by measuring the distance between the current line and previous line. If it's only 1 line, then we'll guess the line's height.
        BOOL useRealHeight = i < _lineCount - 1;
        CGFloat neighborLineY = i > 0 ? _lineOrigins[i - 1].y : (_lineCount - 1 > i ? _lineOrigins[i + 1].y : 0.0f);
        CGFloat lineHeight = ceil(useRealHeight ? abs(neighborLineY - lineOrigin.y) : ascent + descent + leading);

        _lineFrames[i].origin = lineOrigin;
        _lineFrames[i].size = CGSizeMake(lineWidth, lineHeight);

        for (int ic = lineStartIndex; ic < lineEndIndex; ic++) {

            CGFloat startOffset = CTLineGetOffsetForStringIndex(line, ic, NULL);
            _characterFrames[ic].origin = CGPointMake(startOffset, lineOrigin.y);
        }
    }
}


#pragma mark - Rendering Text:

-(void)renderInContext:(CGContextRef)context contextSize:(CGSize)size{

    CGContextSaveGState(context);

    // Draw Core Text attributes string:
    CGContextSetTextMatrix(context, CGAffineTransformIdentity);
    CGContextTranslateCTM(context, 0, CGRectGetHeight(_frameRect));
    CGContextScaleCTM(context, 1.0, -1.0);

    CTFrameDraw(_ctFrame, context);

    // Draw line and letter frames:
    CGContextSetStrokeColorWithColor(context, [UIColor colorWithRed:0.0 green:0.0 blue:1.0 alpha:0.5].CGColor);
    CGContextSetLineWidth(context, 1.0);

    CGContextBeginPath(context);
    CGContextAddRects(context, _lineFrames, _lineCount);
    CGContextClosePath(context);
    CGContextStrokePath(context);

    CGContextSetStrokeColorWithColor(context, [UIColor colorWithRed:1.0 green:0.0 blue:0.0 alpha:0.5].CGColor);
    CGContextBeginPath(context);
    CGContextAddRects(context, _characterFrames, _attributedString.string.length);
    CGContextClosePath(context);
    CGContextStrokePath(context);

    CGContextRestoreGState(context);

}

最佳答案

你在你的问题上做了很多令人印象深刻的工作，并且如此靠你自己接近。您遇到的问题来自这行代码，您在其中放置了每帧的边界框:

_characterFrames[ic].origin = CGPointMake(startOffset, lineOrigin.y);

问题在于，您覆盖了框架已有的任何偏移量。

如果您要注释掉该行，您会看到所有框架或多或少位于同一个位置但您也会看到它们不是定位在完全相同的位置。有些更靠左或靠右，有些更靠上或靠下。这意味着字形的框架有自己的位置。

解决问题的方法是在将框架移动到线上的正确位置时考虑框架的当前位置。您可以通过分别添加 x 和 y 来做到这一点:

_characterFrames[ic].origin.x += startOffset;
_characterFrames[ic].origin.y += lineOrigin.y;

或通过偏移矩形:

_characterFrames[ic] = CGRectOffset(_characterFrames[ic],
                                    startOffset, lineOrigin.y);

现在边界框将有正确的位置:

你应该看到它适用于一些更极端的字体

https://stackoverflow.com/questions/21443625/