Subtracting ascent with descent is correct. Descent is actually a
negative number, meaning that the glyph extends downward. So to get
the difference between the two (the text height) you can either do:
ascent + fabsf(descent)
or
ascent - descent (subtracting a negative is the same as adding)
On Mar 17, 2008, at 10:02 AM, Luigi Castelli wrote:
Hi there,
I am using Core Text to draw a line of text exactly centered in the
middle of a rectangle.
For reasons that I am not going to explain I can't/don't want to use
the image bounds of the line.
So, in order to retrieve the line metrics I am using the
CTLineGetTypographicBounds function.
The width returned by the function perfectly centers my line in the
rectangle and I am happy with it.
However, I still don't seem to find a way to retrieve the correct
height in order for the line to be perfectly centered.
In theory the correct way to get the line height is to add the
ascent and descent together (no leading).
In the majority of the cases this leaves the font too close to the
lower edge of my rectangle.
I also tried to use the font X-height, but that doesn't really
centers my line of text any better.
I found out that the method that - even though far from perfect -
works best is to subtract the descent to the ascent and use that
measure as the line height.
However that something I discovered by trial and error and doesn't
really make sense to me.
Now, I understand that different fonts have different ways of
adhering to the standard font metric rules. (some probably don't)
However is there a more accurate way to get the correct line height
to vertically center text, or is what I am after like a moving
target ?
Any help is highly appreciated.
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