[Rd] proposal: 'dev.capabilities()' can also query Unicode capabilities of current graphics device

[Trevor Davis]

> However, pdf()   *does*  support  Unicode.

When I run a simple Unicode example like:

```
f <- tempfile(fileext = ".pdf")
pdf(f)
# U+2655 ♥ is found in most (all?) "sans" fonts like Arial, Dejavu Sans,
Arimo, etc.
# However, it is not in the Latin-1 encoding
grid::grid.text("\u2665")
dev.off()
```

I observe the following output:

```
Warning in grid.Call.graphics(C_text, as.graphicsAnnot(x$label), x$x, x$y,
 :
  conversion failure on '♥' in 'mbcsToSbcs': dot substituted for <e2>
Warning in grid.Call.graphics(C_text, as.graphicsAnnot(x$label), x$x, x$y,
 :
  conversion failure on '♥' in 'mbcsToSbcs': dot substituted for <99>
Warning in grid.Call.graphics(C_text, as.graphicsAnnot(x$label), x$x, x$y,
 :
  conversion failure on '♥' in 'mbcsToSbcs': dot substituted for <a5>
Warning in grid.Call.graphics(C_text, as.graphicsAnnot(x$label), x$x, x$y,
 :
  conversion failure on '♥' in 'mbcsToSbcs': dot substituted for <e2>
Warning in grid.Call.graphics(C_text, as.graphicsAnnot(x$label), x$x, x$y,
 :
  conversion failure on '♥' in 'mbcsToSbcs': dot substituted for <99>
Warning in grid.Call.graphics(C_text, as.graphicsAnnot(x$label), x$x, x$y,
 :
  conversion failure on '♥' in 'mbcsToSbcs': dot substituted for <a5>
```

When I open up the pdf file I just see three dots and not a heart as I
expected even if I open it up with `xpdf`.

In contrast the pdf generated by `cairo_pdf()` has a heart without
generating any warnings.

Avoiding such WARNINGs on certain CRAN check machines when I have a Unicode
graphics example that is worth including in a package's examples (if
protected by an appropriate if statement) is my main use case for such a
new feature.  However, a new feature like `dev.capabilities()$unicode`
could certainly return something more sophisticated than a crude `TRUE` and
`FALSE` to distinguish between levels of Unicode support provided by
different graphics devices.

Thanks,

Trevor

On Wed, Sep 20, 2023 at 3:39 AM Martin Maechler <maechler using stat.math.ethz.ch>
wrote:

> >>>>> Trevor Davis
> >>>>>     on Thu, 31 Aug 2023 13:49:03 -0700 writes:
>
>     > Hi,
>
>     > It would be nice if `grDevices::dev.capabilities()` could also be
> used to
>     > query whether the current graphics device supports Unicode.  In such
> a case
>     > I'd expect it to return `FALSE` if `pdf()` is the current graphics
> device
>     > and something else for the Cairo or Quartz devices.
>
>     > Thanks,
>     > Trevor
>
> I agree in principle that this would be useful new feature for
> dev.capabilities()
>
> However, pdf()   *does*  support  Unicode.
>
> The problem is that some pdf *viewers*,
> notably `evince` on Fedora Linux, for several years now,
> do *not* show *some* of the UTF-8 glyphs because they do not use
> the correct fonts {which *are* on the machine; good old `xpdf`
> does in that case show the glyphs}.
>
> Martin
>

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