Multi-line NSAttributedString with truncated text

http://stackoverflow.com/questions/7611816/multi-line-nsattributedstring-with-truncated-text/10172794#10172794

Multi-line NSAttributedString with truncated text

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I need a UILabel subcass with multiline attributed text with support for links, bold styles, etc. I also need tail truncation with an ellipsis. None of the open source code that supports attributed text inside UILabels (TTTAttributedLabel, OHAttribuedLabel, TTStyledTextLabel) seem to support tail truncation for multi-line text. Is there an easy way to get this?

ios core-text

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edited Oct 11 '11 at 3:41

asked Sep 30 '11 at 14:27 John Wright 1,18631627

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7 Answers

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up vote11down voteaccepted

Hi I am the developer of OHAttributedLabel.

There is no easy way to achieve this (as explained in the associated issue I opened on the github repository of my project), because CoreText does not offer such feature.

The only way to do this would be to implement the text layout yourself using CoreText objects (CTLine, etc) instead of using the CTFrameSetter that does this for you (but w/o managing line truncation). The idea would be to build all the CTLines to lay them out (depending on the glyphs in your NSAttributedString it contains and the word wrapping policy) one after the other and manage the ellipsis at the end yourself.

I would really appreciate if someone propose a solution to do this propery as it seems a bit of work to do and you have to manage a range of special/unusual cases too (emoji cases, fonts with odd metrics and unusual glyphs, vertical alignment, take into account the size of the ellipsis itself at the end to know when to stop).

So feel free to dig around and try to implement the framing of the lines yourself it would be really appreciated!

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edited Dec 2 '11 at 10:14

answered Sep 30 '11 at 14:49 AliSoftware 25.9k45565

Thanks so much for the response and the confirmation that this is the case as I had thought. Is there a problem with the simple and naive solution that would calculate whether truncation is needed and then simply remove 1 or 2 characters from the attributed string and add an ellipsis in their place? – John Wright Sep 30 '11 at 15:47

That could work even if you will have to determine which characters to remove (at what offset does the text gets troncated — well that's the easiers part) and how much (that's more complicated) depending on the font and size at the truncation point (3 letters 'i' in plain text won't be enough but 3 'w' in bold will be too much…), and especially if the trunction happens in the middle of a change of style (font, style, size, …) too! Also the "…" ellipsis single character won't be the same size depending on the font too…, so even if this is possible, be careful with all those tricky cases – AliSoftware Sep 30 '11 at 16:28 

1

I haven't tried this but also I noticed in the CoreText documentation on manual line breaking theCTTypesetterSuggestLineBreak function which will suggest a line break on an attributed string for a given width. This width could be calculated on the last CTLine by calculating the width of the ellipsis with the same attributed string and it seems like most of your above special cases would then be handled properly. – John Wright Oct 6 '11 at 11:19 

Thks for the tip, seems promising. Note: if you have a github account, don't hesitate to post a comment on the related issue (or do a fork to try some code and send a pull request then) – AliSoftware Oct 6 '11 at 12:02

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up vote7down vote

Based on what I found here and over at https://groups.google.com/forum/?fromgroups=#!topic/cocoa-unbound/Qin6gjYj7XU, I came up with the following which works very well.

- (void)drawString:(CFAttributedStringRef)attString inRect:(CGRect)frameRect inContext:    (CGContextRef)context
{
CGContextSaveGState(context);

// Flip the coordinate system
CGContextSetTextMatrix(context, CGAffineTransformIdentity);
CGContextTranslateCTM(context, 0, self.bounds.size.height);
CGContextScaleCTM(context, 1.0, -1.0);

CGFloat height = self.frame.size.height;
frameRect.origin.y = (height - frameRect.origin.y)  - frameRect.size.height ;

// Create a path to render text in
// don't set any line break modes, etc, just let the frame draw as many full lines as will fit
CGMutablePathRef framePath = CGPathCreateMutable();
CGPathAddRect(framePath, nil, frameRect);
CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString(attString);
CFRange fullStringRange = CFRangeMake(0, CFAttributedStringGetLength(attString));
CTFrameRef aFrame = CTFramesetterCreateFrame(framesetter, fullStringRange, framePath, NULL);
CFRelease(framePath);

CFArrayRef lines = CTFrameGetLines(aFrame);
CFIndex count = CFArrayGetCount(lines);
CGPoint *origins = malloc(sizeof(CGPoint)*count);
CTFrameGetLineOrigins(aFrame, CFRangeMake(0, count), origins);

// note that we only enumerate to count-1 in here-- we draw the last line separately
for (CFIndex i = 0; i < count-1; i++)
{
    // draw each line in the correct position as-is
    CGContextSetTextPosition(context, origins[i].x + frameRect.origin.x, origins[i].y + frameRect.origin.y);
    CTLineRef line = (CTLineRef)CFArrayGetValueAtIndex(lines, i);
    CTLineDraw(line, context);
}

// truncate the last line before drawing it
if (count) {
    CGPoint lastOrigin = origins[count-1];
    CTLineRef lastLine = CFArrayGetValueAtIndex(lines, count-1);

    // truncation token is a CTLineRef itself
    CFRange effectiveRange;
    CFDictionaryRef stringAttrs = CFAttributedStringGetAttributes(attString, 0, &effectiveRange);

    CFAttributedStringRef truncationString = CFAttributedStringCreate(NULL, CFSTR("\u2026"), stringAttrs);
    CTLineRef truncationToken = CTLineCreateWithAttributedString(truncationString);
    CFRelease(truncationString);

    // now create the truncated line -- need to grab extra characters from the source string,
    // or else the system will see the line as already fitting within the given width and
    // will not truncate it.

    // range to cover everything from the start of lastLine to the end of the string
    CFRange rng = CFRangeMake(CTLineGetStringRange(lastLine).location, 0);
    rng.length = CFAttributedStringGetLength(attString) - rng.location;

    // substring with that range
    CFAttributedStringRef longString = CFAttributedStringCreateWithSubstring(NULL, attString, rng);
    // line for that string
    CTLineRef longLine = CTLineCreateWithAttributedString(longString);
    CFRelease(longString);

    CTLineRef truncated = CTLineCreateTruncatedLine(longLine, frameRect.size.width, kCTLineTruncationEnd, truncationToken);
    CFRelease(longLine);
    CFRelease(truncationToken);

    // if 'truncated' is NULL, then no truncation was required to fit it
    if (truncated == NULL)
        truncated = (CTLineRef)CFRetain(lastLine);

    // draw it at the same offset as the non-truncated version
    CGContextSetTextPosition(context, lastOrigin.x + frameRect.origin.x, lastOrigin.y + frameRect.origin.y);CTLineDraw(truncated, context);CFRelease(truncated);}
free(origins);CGContextRestoreGState(context);

}

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answered Feb 7 '13 at 16:30 naughton 21144

Excellent solution! – mydogisbox Jun 24 '13 at 21:59

2

Could you explain, which class did you subclass? – dig Jan 15 '14 at 15:13

@naughton this code is leaking for me... should the CTFrameRef be released also? – mga Jun 30 '14 at 20:49

@naughton adding CFRelease(aFrame); CFRelease(framesetter); at the end after free(origins) did the trick... no leaks! – mga Jun 30 '14 at 20:56

1

Can we add Image to truncationToken string ? i mean attribute string with NSTextAttachment .? – Nanda Sep 8 '14 at 12:15

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up vote3down vote

Maybe I'm missing something, but whats wrong with? :

NSMutableAttributedString *text = [[NSMutableAttributedString alloc] initWithString:@"test"];

NSMutableParagraphStyle *style = [[NSMutableParagraphStyle alloc] init];
style.lineBreakMode = NSLineBreakByTruncatingTail;
[text addAttribute:NSParagraphStyleAttributeName
                      value:style
                      range:NSMakeRange(0, text.length)];

label.attributedText = text;

This works perfectly and will add a ellipsis to the end.

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answered Feb 18 at 15:27 Toydor 4341824

Verified. Works perfectly, iOS 8.3 here. – Matt Quiros Apr 16 at 15:13

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up vote2down vote

I haven't tried this in all cases, but something like this could work for truncation:

NSAttributedString *string = self.attributedString;
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetTextMatrix(context, CGAffineTransformIdentity);

CFAttributedStringRef attributedString = (__bridge CFTypeRef)string;
CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString(attributedString);
CGPathRef path = CGPathCreateWithRect(self.bounds, NULL);
CTFrameRef frame = CTFramesetterCreateFrame(framesetter, CFRangeMake(0, 0), path, NULL);

BOOL needsTruncation = CTFrameGetVisibleStringRange(frame).length < string.length;
CFArrayRef lines = CTFrameGetLines(frame);
NSUInteger lineCount = CFArrayGetCount(lines);
CGPoint *origins = malloc(sizeof(CGPoint) * lineCount);
CTFrameGetLineOrigins(frame, CFRangeMake(0, 0), origins);

for (NSUInteger i = 0; i < lineCount; i++) {
    CTLineRef line = CFArrayGetValueAtIndex(lines, i);
    CGPoint point = origins[i];
    CGContextSetTextPosition(context, point.x, point.y);

    BOOL truncate = (needsTruncation && (i == lineCount - 1));
    if (!truncate) {
        CTLineDraw(line, context);
    }
    else {
        NSDictionary *attributes = [string attributesAtIndex:string.length-1 effectiveRange:NULL];
        NSAttributedString *token = [[NSAttributedString alloc] initWithString:@"\u2026" attributes:attributes];
        CFAttributedStringRef tokenRef = (__bridge CFAttributedStringRef)token;
        CTLineRef truncationToken = CTLineCreateWithAttributedString(tokenRef);
        double width = CTLineGetTypographicBounds(line, NULL, NULL, NULL) - CTLineGetTrailingWhitespaceWidth(line);
        CTLineRef truncatedLine = CTLineCreateTruncatedLine(line, width-1, kCTLineTruncationEnd, truncationToken);

        if (truncatedLine) { CTLineDraw(truncatedLine, context); }
        else { CTLineDraw(line, context); }

        if (truncationToken) { CFRelease(truncationToken); }
        if (truncatedLine) { CFRelease(truncatedLine); }
    }
}

free(origins);
CGPathRelease(path);
CFRelease(frame);
CFRelease(framesetter);

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edited Jan 30 '13 at 20:07

answered Jan 30 '13 at 20:00 wbyoung 14.7k22035

This seems to be working, but text is drawn upside-down. To prevent this the following lines of code need to be added after CGContextSetTextMatrix(context, CGAffineTransformIdentity); :CGContextTranslateCTM(context, 0.0f, rect.size.height); CGContextScaleCTM(context, 1.0f, -1.0f); – Julia May 31 at 9:45 

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up vote1down vote

You may be able to use follow code to have a more simple solution.

    // last line.
    if (_limitToNumberOfLines && count == _numberOfLines-1)
    {
        // check if we reach end of text.
        if (lineRange.location + lineRange.length < [_text length])
        {
            CFDictionaryRef dict = ( CFDictionaryRef)attributes;
            CFAttributedStringRef truncatedString = CFAttributedStringCreate(NULL, CFSTR("\u2026"), dict);

            CTLineRef token = CTLineCreateWithAttributedString(truncatedString);

            // not possible to display all text, add tail ellipsis.
            CTLineRef truncatedLine = CTLineCreateTruncatedLine(line, self.bounds.size.width - 20, kCTLineTruncationEnd, token);
            CFRelease(line); line = nil;
            line = truncatedLine;
        }
    }

I'm using MTLabel in my project and it's a really nice solution for my project.

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edited Apr 16 '12 at 18:12 arrowd 9,94612550

answered Apr 16 '12 at 10:56 user1333359 112

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up vote0down vote

I integrated wbyoung's solution into OHAttributedLabel drawTextInRect: method if anyone is interested:

- (void)drawTextInRect:(CGRect)aRect
{
    if (_attributedText)
    {
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGContextSaveGState(ctx);

    // flipping the context to draw core text
    // no need to flip our typographical bounds from now on
    CGContextConcatCTM(ctx, CGAffineTransformScale(CGAffineTransformMakeTranslation(0, self.bounds.size.height), 1.f, -1.f));

    if (self.shadowColor)
    {
        CGContextSetShadowWithColor(ctx, self.shadowOffset, 0.0, self.shadowColor.CGColor);
    }

    [self recomputeLinksInTextIfNeeded];
    NSAttributedString* attributedStringToDisplay = _attributedTextWithLinks;
    if (self.highlighted && self.highlightedTextColor != nil)
    {
        NSMutableAttributedString* mutAS = [attributedStringToDisplay mutableCopy];
        [mutAS setTextColor:self.highlightedTextColor];
        attributedStringToDisplay = mutAS;
        (void)MRC_AUTORELEASE(mutAS);
    }
    if (textFrame == NULL)
    {
        CFAttributedStringRef cfAttrStrWithLinks = (BRIDGE_CAST CFAttributedStringRef)attributedStringToDisplay;
        CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString(cfAttrStrWithLinks);
        drawingRect = self.bounds;
        if (self.centerVertically || self.extendBottomToFit)
        {
            CGSize sz = CTFramesetterSuggestFrameSizeWithConstraints(framesetter,CFRangeMake(0,0),NULL,CGSizeMake(drawingRect.size.width,CGFLOAT_MAX),NULL);
            if (self.extendBottomToFit)
            {
                CGFloat delta = MAX(0.f , ceilf(sz.height - drawingRect.size.height))+ 10 /* Security margin */;
                drawingRect.origin.y -= delta;
                drawingRect.size.height += delta;
            }
            if (self.centerVertically) {
                drawingRect.origin.y -= (drawingRect.size.height - sz.height)/2;
            }
        }
        CGMutablePathRef path = CGPathCreateMutable();
        CGPathAddRect(path, NULL, drawingRect);
        CFRange fullStringRange = CFRangeMake(0, CFAttributedStringGetLength(cfAttrStrWithLinks));
        textFrame = CTFramesetterCreateFrame(framesetter,fullStringRange, path, NULL);
        CGPathRelease(path);
        CFRelease(framesetter);
    }

    // draw highlights for activeLink
    if (_activeLink)
    {
        [self drawActiveLinkHighlightForRect:drawingRect];
    }

    BOOL hasLinkFillColorSelector = [self.delegate respondsToSelector:@selector(attributedLabel:fillColorForLink:underlineStyle:)];
    if (hasLinkFillColorSelector) {
        [self drawInactiveLinkHighlightForRect:drawingRect];
    }

    if (self.truncLastLine) {
        CFArrayRef lines = CTFrameGetLines(textFrame);
        CFIndex count = MIN(CFArrayGetCount(lines),floor(self.size.height/self.font.lineHeight));

        CGPoint *origins = malloc(sizeof(CGPoint)*count);
        CTFrameGetLineOrigins(textFrame, CFRangeMake(0, count), origins);// note that we only enumerate to count-1 in here-- we draw the last line separatelyfor(CFIndex i =0; i < count-1; i++){// draw each line in the correct position as-isCGContextSetTextPosition(ctx, origins[i].x + drawingRect.origin.x, origins[i].y + drawingRect.origin.y);CTLineRef line =(CTLineRef)CFArrayGetValueAtIndex(lines, i);CTLineDraw(line, ctx);}// truncate the last line before drawing itif(count){CGPoint lastOrigin = origins[count-1];CTLineRef lastLine =CFArrayGetValueAtIndex(lines, count-1);// truncation token is a CTLineRef itselfCFRange effectiveRange;CFDictionaryRef stringAttrs =CFAttributedStringGetAttributes((BRIDGE_CAST CFAttributedStringRef)_attributedTextWithLinks,0,&effectiveRange);CFAttributedStringRef truncationString =CFAttributedStringCreate(NULL, CFSTR("\u2026"), stringAttrs);CTLineRef truncationToken =CTLineCreateWithAttributedString(truncationString);CFRelease(truncationString);// now create the truncated line -- need to grab extra characters from the source string,// or else the system will see the line as already fitting within the given width and// will not truncate it.// range to cover everything from the start of lastLine to the end of the stringCFRange rng =CFRangeMake(CTLineGetStringRange(lastLine).location,0);
            rng.length =CFAttributedStringGetLength((BRIDGE_CAST CFAttributedStringRef)_attributedTextWithLinks)- rng.location;// substring with that rangeCFAttributedStringRef longString =CFAttributedStringCreateWithSubstring(NULL,(BRIDGE_CAST CFAttributedStringRef)_attributedTextWithLinks, rng);// line for that stringCTLineRef longLine =CTLineCreateWithAttributedString(longString);CFRelease(longString);CTLineRef truncated =CTLineCreateTruncatedLine(longLine, drawingRect.size.width, kCTLineTruncationEnd, truncationToken);CFRelease(longLine);CFRelease(truncationToken);// if 'truncated' is NULL, then no truncation was required to fit itif(truncated == NULL){
                truncated =(CTLineRef)CFRetain(lastLine);}// draw it at the same offset as the non-truncated versionCGContextSetTextPosition(ctx, lastOrigin.x + drawingRect.origin.x, lastOrigin.y + drawingRect.origin.y);CTLineDraw(truncated, ctx);CFRelease(truncated);}
        free(origins);}else{CTFrameDraw(textFrame, ctx);}CGContextRestoreGState(ctx);}else{[super drawTextInRect:aRect];}}

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answered Mar 20 '14 at 10:09 KingBabar 1,6491526

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up vote-1down vote

I used as sample MTLabel. It allows to manage line height. I needed the draw method exactly, so i just put away most stuff i did not need. This method allows me to draw multilined text in rect with tail truncation.

CGRect CTLineGetTypographicBoundsAsRect(CTLineRef line, CGPoint lineOrigin)
{
CGFloat ascent = 0;
CGFloat descent = 0;
CGFloat leading = 0;
CGFloat width = CTLineGetTypographicBounds(line, &ascent, &descent, &leading);
CGFloat height = ascent + descent;

return CGRectMake(lineOrigin.x,
                  lineOrigin.y - descent,
                  width,
                  height);
}
- (void)drawText:(NSString*) text InRect:(CGRect)rect withFont:(UIFont*)aFont inContext:(CGContextRef)context {

if (!text) {
    return;
}

BOOL _limitToNumberOfLines = YES;
int _numberOfLines = 2;
float _lineHeight = 22;

//Create a CoreText font object with name and size from the UIKit one
CTFontRef font = CTFontCreateWithName((CFStringRef)aFont.fontName ,
                                      aFont.pointSize,
                                      NULL);

//Setup the attributes dictionary with font and color
NSDictionary *attributes = [NSDictionary dictionaryWithObjectsAndKeys:
                            (id)font, (id)kCTFontAttributeName,
                            [UIColor lightGrayColor].CGColor, kCTForegroundColorAttributeName,
                            nil];

NSAttributedString *attributedString = [[[NSAttributedString alloc]
                                         initWithString:text
                                         attributes:attributes] autorelease];

CFRelease(font);

//Create a TypeSetter object with the attributed text created earlier on
CTTypesetterRef typeSetter = CTTypesetterCreateWithAttributedString((CFAttributedStringRef)attributedString);

//Start drawing from the upper side of view (the context is flipped, so we need to grab the height to do so)
CGFloat y = self.bounds.origin.y + self.bounds.size.height - rect.origin.y - aFont.ascender;

BOOL shouldDrawAlong = YES;
int count = 0;
CFIndex currentIndex = 0;

float _textHeight = 0;

CGContextSaveGState(context);

CGContextSetTextMatrix(context, CGAffineTransformIdentity);
CGContextTranslateCTM(context, 0, self.bounds.size.height);
CGContextScaleCTM(context, 1.0, -1.0);

//Start drawing lines until we run out of text
while (shouldDrawAlong) {

    //Get CoreText to suggest a proper place to place the line break
    CFIndex lineLength = CTTypesetterSuggestLineBreak(typeSetter,
                                                      currentIndex,
                                                      rect.size.width);

    //Create a new line with from current index to line-break index
    CFRange lineRange = CFRangeMake(currentIndex, lineLength);
    CTLineRef line = CTTypesetterCreateLine(typeSetter, lineRange);

    //Check to see if our index didn't exceed the text, and if should limit to number of lines
    if (currentIndex + lineLength >= [text length])
    {
        shouldDrawAlong = NO;
    }
    else
    {
        if (!(_limitToNumberOfLines && count < _numberOfLines-1))
        {
            int i = 0;
            if ([[[text substringWithRange:NSMakeRange(currentIndex, lineLength)] stringByAppendingString:@"…"] sizeWithFont:aFont].width > rect.size.width)
            {
                i--;
                while ([[[text substringWithRange:NSMakeRange(currentIndex, lineLength + i)] stringByAppendingString:@"…"] sizeWithFont:aFont].width > rect.size.width)
                {
                    i--;}}else{
                i++;while([[[text substringWithRange:NSMakeRange(currentIndex, lineLength + i)] stringByAppendingString:@"…"] sizeWithFont:aFont].width < rect.size.width){
                    i++;}
                i--;}
            attributedString =[[[NSAttributedString alloc] initWithString:[[text substringWithRange:NSMakeRange(currentIndex, lineLength + i)] stringByAppendingString:@"…"] attributes:attributes] autorelease];CFRelease(typeSetter);

            typeSetter =CTTypesetterCreateWithAttributedString((CFAttributedStringRef)attributedString);CFRelease(line);CFRange lineRange =CFRangeMake(0,0);
            line =CTTypesetterCreateLine(typeSetter, lineRange);

            shouldDrawAlong = NO;}}CGFloat x = rect.origin.x;//Setup the line positionCGContextSetTextPosition(context, x, y);CTLineDraw(line, context);

    count++;CFRelease(line);

    y -= _lineHeight;

    currentIndex += lineLength;
    _textHeight += _lineHeight;}CFRelease(typeSetter);CGContextRestoreGState(context);}

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answered Mar 5 '12 at 16:31 mashe 7917

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if (true&&self.lineHeights>0 && CFArrayGetCount(lines)>=2) {
NSUInteger lineCount = CFArrayGetCount(lines);
CGPoint *origins = malloc(sizeof(CGPoint) * lineCount);
CTFrameGetLineOrigins(frame, CFRangeMake(0, 0), origins);
CTLineRef line0 = (CTLineRef)CFArrayGetValueAtIndex(lines, 0);
CTLineRef line1 = (CTLineRef)CFArrayGetValueAtIndex(lines, 1);

NSAttributedString *truncatedString = [[NSAttributedString alloc]initWithString:@"\u2026"];
CTLineRef token = CTLineCreateWithAttributedString((__bridge CFAttributedStringRef)truncatedString);
CTLineTruncationType ltt = kCTLineTruncationEnd;
CTLineRef line = CTLineCreateTruncatedLine(line1, self.width-10, ltt, token);
CGPoint point = origins[0];
CGContextSetTextPosition(context, point.x, point.y);
CTLineDraw(line0, context);
point = origins[1];
CGContextSetTextPosition(context, point.x, point.y);
CTLineDraw(line, context);
//CTFrameDraw(frame, context);
free(origins);

}