CGFontGetGlyphBBoxes wrong result

Question

I have been trying to measure glyph bounds precisely but this code prints out 916!!! The real width of this is 69.

- (void)drawRect:(NSRect)dirtyRect {
        CGContextRef main = [[NSGraphicsContext currentContext] graphicsPort];
        CGContextSetTextMatrix(main, CGAffineTransformIdentity);
        CGGlyph g;
        CGPoint p  = CGPointMake(100, 100);
        CGRect rect = CGRectMake(0, 0, 0, 0);
        CGFontRef font = CGFontCreateWithFontName((CFStringRef)@"Arial");
        g = CGFontGetGlyphWithGlyphName(font, CFSTR("L"));
        CGContextSetFont(main, font);
        CGContextSetTextPosition(main, 0, 0);
        CGContextSetFontSize(main, 200);
        CGContextSetRGBFillColor(main, 0, 0, 1, 1);
        CGContextShowGlyphsAtPositions(main, &g, &p, 1);
        CGFontGetGlyphBBoxes(font, &g, 1, &rect);
        printf("%f", rect.size.width);
    }

Answer 1

You are using CGFontGetGlyphBBoxes, which returns the size in glyph space units. To use this, you need to scale it with the units per em and the font size.

CGRect rect;
CGFontRef font = CGFontCreateWithFontName((CFStringRef)@"Arial");
CGFloat fontSize = 200.0;
CGGlyph g = CGFontGetGlyphWithGlyphName(font, CFSTR("L"));
CGFontGetGlyphBBoxes(font, &g, 1, &rect);
CGFloat width = rect.size.Width / CGFontGetUnitsPerEm(font) * fontSize;

An alternate way to do it to use [NSFont boundingRectForCGGlyph:].

NSFont *font = [NSFont fontWithName:@"Arial" size:200];
NSRect rect = [font boundingRectForCGGlyph:g];

boundingRectForCGGlyph
Returns the bounding rectangle for the specified glyph, scaled to the receiver’s size.