Hi
strheight(), which is based GEStrHeight(), is pretty crude, not only
ignoring descenders, but also only considering the ascent of the overall
font (capital "M").
There is a GEStrMetric(), which returns character-specific ascent and
descent, but that is only currently exposed via grid::stringAscent() and
grid::stringDescent(). There is also grid::stringHeight(), which is as
unsubtle as strheight().
For example, these are all the same (just font ascent) ...
> strheight("y", "in")
[1] 0.1248031
> strheight("x", "in")
[1] 0.1248031
> strheight("M", "in")
[1] 0.1248031
... and these are all the same ...
> convertHeight(stringHeight("y"), "in")
[1] 0.124803149606299inches
> convertHeight(stringHeight("x"), "in")
[1] 0.124803149606299inches
> convertHeight(stringAscent("M"), "in")
[1] 0.124803149606299inches
... but these have more detail ...
> convertHeight(stringAscent("y"), "in")
[1] 0.0936023622047244inches
> convertHeight(stringDescent("y"), "in")
[1] 0.0416010498687664inches
> convertHeight(stringAscent("x"), "in")
[1] 0.0936023622047244inches
> convertHeight(stringDescent("x"), "in")
[1] 0inches
> convertHeight(stringHeight("M"), "in")
[1] 0.124803149606299inches
> convertHeight(stringDescent("M"), "in")
[1] 0inches
In theory, it should not be difficult to add a graphics::strascent() and
graphics::strdescent() if that would help.
Paul
On 26/09/23 08:06, Duncan Murdoch wrote:> I've mentioned in previous messages that I'm trying to redo rgl
text.
>
> Part of what I need is to measure the size of strings in pixels when
> they are drawn by base graphics.
>
> It appears that
>
> strwidth(texts, "user", cex = cex, font = font, family = family)
>
> gives accurate measurements of the width in user coordinates. I've got
> those set up to match pixels, so I'm fine here.
>
> However, the equivalent call for strheight() only measures height above
> the baseline according to the docs, and indeed the number is smaller
> than the size of what's displayed. Descenders (e.g. the tail of
"y")
> aren't counted.
>
> Is there a way to measure how far a character might descend? Is it
> valid to assume it won't descend more than a line height below the top
> of the char?
>
> I have a partial solution -- textshaping::shape_text gives a
"height"
> value that includes lots of space below the character, and a
> "top_border" value that measures from the top of the textbox to
the
> baseline. So I think `height - top_border` would give me what I'm
> asking for. But this only works with graphics devices in the ragg
> package. Is there a general solution?
>
> Duncan Murdoch
>
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--
Dr Paul Murrell
Te Kura Tatauranga | Department of Statistics
Waipapa Taumata Rau | The University of Auckland
Private Bag 92019, Auckland 1142, New Zealand
64 9 3737599 x85392
paul at stat.auckland.ac.nz
www.stat.auckland.ac.nz/~paul/