Bounding box of character with diacritics using CoreText

I am trying to get the bounding box of a character in MacOS X/iOS using various techniques. I am now presenting all my attempts. Until now the code fails if I want to get the size of diacritic characters such as "Ä". Using `CTFontGetBoundingRectsForGlyphs` ``` -(void) resizeLayer1:(CATextLayer *)l toString:(NSString *)string { // need to set CGFont explicitly to convert font property to a CGFontRef CGFontRef layerFont = CGFontCreateWithFontName((CFStringRef)@"Helvetica"); l.font = layerFont; string = l.string; NSUInteger len = [string length]; // get characters from NSString UniChar *characters = (UniChar *)malloc(sizeof(UniChar)*len); CFStringGetCharacters((__bridge CFStringRef)l.string, CFRangeMake(0, [l.string length]), characters); // Get CTFontRef from CGFontRef CTFontRef coreTextFont = CTFontCreateWithGraphicsFont(layerFont, l.fontSize, NULL, NULL); // 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(coreTextFont, characters, glyphs, len); // get bounding boxes for glyphs CGRect *bb = (CGRect *)malloc(sizeof(CGRect)*len); CTFontGetBoundingRectsForGlyphs(coreTextFont, kCTFontDefaultOrientation, glyphs, bb, len); CFRelease(coreTextFont); l.position = CGPointMake(200.f, 100.f); l.bounds = bb[0]; l.backgroundColor = CGColorCreateGenericRGB(0.f, .5f, .9f, 1.f); free(characters); free(glyphs); free(bb); } ``` Result It kind of works, but there is some padding going on as the glyph is rendered by the CATextLayer Using `CTFramesetterSuggestFrameSizeWithConstraints` ``` -(void) resizeLayer2:(CATextLayer *)l toString:(NSString *)string { // need to set CGFont explicitly to convert font property to a CGFontRef CGFontRef layerFont = CGFontCreateWithFontName((CFStringRef)@"Helvetica"); l.font = layerFont; string = l.string; NSUInteger len = [string length]; // get characters from NSString UniChar *characters = (UniChar *)malloc(sizeof(UniChar)*len); CFStringGetCharacters((__bridge CFStringRef)l.string, CFRangeMake(0, [l.string length]), characters); // Get CTFontRef from CGFontRef CTFontRef coreTextFont = CTFontCreateWithGraphicsFont(layerFont, l.fontSize, NULL, NULL); CFMutableAttributedStringRef attrStr = CFAttributedStringCreateMutable(kCFAllocatorDefault, 0); CFAttributedStringReplaceString(attrStr, CFRangeMake(0, 0), (__bridge CFStringRef)string); CTTextAlignment alignment = kCTJustifiedTextAlignment; CTParagraphStyleSetting _settings[] = { {kCTParagraphStyleSpecifierAlignment, sizeof(alignment), &alignment} }; CTParagraphStyleRef paragraphStyle = CTParagraphStyleCreate(_settings, sizeof(_settings) / sizeof(_settings[0])); CFAttributedStringSetAttribute(attrStr, CFRangeMake(0, CFAttributedStringGetLength(attrStr)), kCTParagraphStyleAttributeName, paragraphStyle); CFAttributedStringSetAttribute(attrStr, CFRangeMake(0, CFAttributedStringGetLength(attrStr)), kCTFontAttributeName, coreTextFont); CFRelease(paragraphStyle); CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString(attrStr); CFRelease(attrStr); CFRange range; CGFloat maxWidth = CGFLOAT_MAX; CGFloat maxHeight = 10000.f; CGSize constraint = CGSizeMake(maxWidth, maxHeight); // checking frame sizes CGSize coreTextSize = CTFramesetterSuggestFrameSizeWithConstraints(framesetter, CFRangeMake(0, len), nil, constraint, &range); // 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(coreTextFont, characters, glyphs, len); // get bounding boxes for glyphs CGRect *bb = (CGRect *)malloc(sizeof(CGRect)*len); CTFontGetBoundingRectsForGlyphs(coreTextFont, kCTFontDefaultOrientation, glyphs, bb, len); CFRelease(coreTextFont); bb[0].origin = l.bounds.origin; coreTextSize.width = ceilf(coreTextSize.width); coreTextSize.height = ceilf(coreTextSize.height); bb[0].size = coreTextSize; l.position = CGPointMake(200.f, 100.f); // after setting the bounds the layer gets transparent l.bounds = bb[0]; l.opaque = YES; return; l.backgroundColor = CGColorCreateGenericRGB(0.f, .5f, .9f, 1.f); free(characters); free(glyphs); free(bb); } ``` Result The bounding box of the string is correct. It gets problematic with diacritics: the Ä is missing its dots, because the bounding box is not tall enough. Using `CTLineGetTypographicBounds` ``` -(void) resizeLayer3:(CATextLayer *)l toString:(NSString *)string { // need to set CGFont explicitly to convert font property to a CGFontRef CGFontRef layerFont = CGFontCreateWithFontName((CFStringRef)@"Helvetica"); l.font = layerFont; string = l.string; NSUInteger len = [string length]; // get characters from NSString UniChar *characters = (UniChar *)malloc(sizeof(UniChar)*len); CFStringGetCharacters((__bridge CFStringRef)l.string, CFRangeMake(0, [l.string length]), characters); // Get CTFontRef from CGFontRef CTFontRef coreTextFont = CTFontCreateWithGraphicsFont(layerFont, l.fontSize, NULL, NULL); CFMutableAttributedStringRef attrStr = CFAttributedStringCreateMutable(kCFAllocatorDefault, 0); CFAttributedStringReplaceString(attrStr, CFRangeMake(0, 0), (__bridge CFStringRef)string); CFAttributedStringSetAttribute(attrStr, CFRangeMake(0, CFAttributedStringGetLength(attrStr)), kCTFontAttributeName, coreTextFont); CTLineRef line = CTLineCreateWithAttributedString(attrStr); CGFloat ascent; CGFloat descent; CGFloat width = CTLineGetTypographicBounds(line, &ascent, &descent, NULL); CGFloat height = ascent+descent; CGSize coreTextSize = CGSizeMake(width,height); // get bounding boxes for glyphs CGRect *bb = (CGRect *)malloc(sizeof(CGRect)*len); CFRelease(coreTextFont); bb[0].origin = CGPointZero; coreTextSize.width = ceilf(coreTextSize.width); coreTextSize.height = ceilf(coreTextSize.height); bb[0].size = coreTextSize; l.position = CGPointMake(200.f, 100.f); // after setting the bounds the layer gets transparent l.bounds = bb[0]; l.opaque = YES; return; l.backgroundColor = CGColorCreateGenericRGB(0.f, .5f, .9f, 1.f); free(characters); free(bb); } ``` Result The bounding box of the string is correct. It gets problematic with diacritics: the Ä is missing its dots, because the bounding box is not tall enough. Using `CTFontGetBoundingRectsForGlyphs` ``` -(void) resizeLayer4:(CATextLayer *)l toString:(NSString *)string { // need to set CGFont explicitly to convert font property to a CGFontRef CGFontRef layerFont = CGFontCreateWithFontName((CFStringRef)@"Helvetica"); l.font = layerFont; string = l.string; NSUInteger len = [string length]; // get characters from NSString UniChar *characters = (UniChar *)malloc(sizeof(UniChar)*len); CFStringGetCharacters((__bridge CFStringRef)l.string, CFRangeMake(0, [l.string length]), characters); // Get CTFontRef from CGFontRef CTFontRef coreTextFont = CTFontCreateWithGraphicsFont(layerFont, l.fontSize, NULL, NULL); // 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(coreTextFont, characters, glyphs, len); CGPathRef glyphPath = CTFontCreatePathForGlyph(coreTextFont, glyphs[1], NULL); CGRect rect = CGPathGetBoundingBox(glyphPath); // get bounding boxes for glyphs CGRect *bb = (CGRect *)malloc(sizeof(CGRect)*len); CTFontGetBoundingRectsForGlyphs(coreTextFont, kCTFontDefaultOrientation, glyphs, bb, len); CFRelease(coreTextFont); l.position = CGPointMake(200.f, 100.f); l.bounds = rect; l.backgroundColor = CGColorCreateGenericRGB(0.f, .5f, .9f, 1.f); free(characters); free(glyphs); free(bb); } ``` Result The bounding box of the string is correct. It gets problematic with diacritics as the diacritics itself are a glyph and the character are another glyph meaning that Ä consists of two glyphs. How could one use that? Are there any other possibilities I have overlooked and are worthwhile trying? EDIT The third option `CTLineGetTypographicBounds` seems to work. I am running however in a different problem, that the first line in a `CATextLayer` is missing its diacritic marks. The first line is somehow just not tall enough. That would mean I am barking up the wrong tree here.