CTRunGetImageBounds 返回不准确的结果

Question

我正在使用 Core Text 来绘制一些文本。我想获取各种运行边界，但是当我调用 CTRunGetImageBounds 时，返回的矩形大小正确，但位置错误。具体来说，行原点位于整个文本的末尾。

- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext();
    self.transform = CGAffineTransformMakeScale(1.0, -1.0);
    CGContextSetTextMatrix(context, CGAffineTransformIdentity);

    [[UIColor whiteColor] set];
    CGContextFillRect(context, self.bounds);

    NSMutableAttributedString* attrString = [[NSMutableAttributedString alloc] initWithString:@"Blue should be underlined."];
    NSRange blueRange = NSMakeRange(0, 4);
    [attrString beginEditing];
    //make all text size 20.0
    [attrString addAttribute:(NSString *)kCTFontAttributeName value:(id)CTFontCreateWithName((CFStringRef)@"Helvetica", 20.0, NULL) range:NSMakeRange(0, [attrString length])];
    //make the text appear in blue
    [attrString addAttribute:(NSString *)kCTForegroundColorAttributeName value:(id)[[UIColor blueColor] CGColor] range:blueRange];
    //next make the text appear with an underline
    [attrString addAttribute:(NSString *)kCTUnderlineStyleAttributeName value:[NSNumber numberWithInt:1] range:blueRange];
    [attrString endEditing];

    CGMutablePathRef path = CGPathCreateMutable();
    CGRect bounds = CGRectMake(10.0, 10.0, 200.0, 200.0);
    [[UIColor redColor] set];
    CGContextFillRect(context, bounds);
    CGPathAddRect(path, NULL, bounds);

    CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)attrString);
    CTFrameRef frame = CTFramesetterCreateFrame(framesetter, CFRangeMake(0, 0), path, NULL);
    CTFrameDraw(frame, context);

    for (id lineObj in (NSArray *)CTFrameGetLines(frame)) {
        CTLineRef line = (CTLineRef)lineObj;
        for (id runObj in (NSArray *)CTLineGetGlyphRuns(line)) {
            CTRunRef run = (CTRunRef)runObj;
            CGRect runBounds = CTRunGetImageBounds(run, context, CFRangeMake(0, 0));
            NSLog(@"bounds: %@", NSStringFromCGRect(runBounds));

            [[UIColor greenColor] set];
            CGContextFillRect(context, runBounds);
        }
    }

    CFRelease(framesetter);
    CFRelease(frame);
    [attrString release];
}

产生：

Answer 1

这是我想出的。这是完全准确的。

CTFrameRef frame = [self _frameWithRect:rect];

NSArray *lines = (NSArray *)CTFrameGetLines(frame);

CGPoint origins[[lines count]];//the origins of each line at the baseline
CTFrameGetLineOrigins(frame, CFRangeMake(0, 0), origins);

NSUInteger lineIndex = 0;
for (id lineObj in lines) {
    CTLineRef line = (CTLineRef)lineObj;

    for (id runObj in (NSArray *)CTLineGetGlyphRuns(line)) {
        CTRunRef run = (CTRunRef)runObj;
        CFRange runRange = CTRunGetStringRange(run);

        CGRect runBounds;

        CGFloat ascent;//height above the baseline
        CGFloat descent;//height below the baseline
        runBounds.size.width = CTRunGetTypographicBounds(run, CFRangeMake(0, 0), &ascent, &descent, NULL);
        runBounds.size.height = ascent + descent;

        CGFloat xOffset = CTLineGetOffsetForStringIndex(line, CTRunGetStringRange(run).location, NULL);
        runBounds.origin.x = origins[lineIndex].x + rect.origin.x + xOffset;
        runBounds.origin.y = origins[lineIndex].y + rect.origin.y;
        runBounds.origin.y -= descent;

        //do something with runBounds
    }
    lineIndex++;
}

Answer 2

在使用 CTRunGetImageBounds() 或 CTLineDraw() 之前，您需要在绘制或计算每条线之前通过调用 CGContextSetTextPosition() 设置起始文本位置。原因是 CTLine 不知道自己从哪里开始绘制（或计算），它使用最后一个文本位置，因此您需要给它一个 XY 起点。要获取帧的线数组的原点，请使用点数组调用 CTFrameGetLineOrigins()。然后，在绘制或计算每条线之前 - 通过 CGContextSetTextPosition() 设置该线的原点。

NSArray *lines = (NSArray *)CTFrameGetLines(frame);

CGPoint origins[[lines count]];                              // the origins of each line at the baseline
CTFrameGetLineOrigins(frame, CFRangeMake(0, 0), origins); 

int i, lineCount;

lineCount = [lines count];

for (i = 0; i < lineCount; i++) {
 CTLineRef line = (CTLineRef)[lines objectAtIndex:i];
 CGContextSetTextPosition(context, origins[i].x, origins[i].y);
 CTLineDraw(line, context);
 }