R help - Jul 2003 - metapost device in R (again ;-)

Hi,

I read the 2000 thread on a MetaPost device in R. If I understand
correctly, the main problem with the concept is that R wants the device
driver to give back information on the size of strings/labels.

To the bet of my knowledge, MetaPost _does_ make it possible to
measure the bounding box of text (see section 7.3: Measuring text in
the MetaPost manual). For example, one could get the size of the
bounding box of btex $\int_a^b x^2$ etex -- would that be enough to
make an implementation possible? Or are the size of individual
characters and kerning information necessary?

Another question: can graphics devices be implemented solely in R (ie
without writing C code)? I realize that it will be much slower, but
first I would like to see how it works before writing in C. What
source files should I be looking at?

You may ask why I should bother about using Metapost. Well, I'd like
my TeX documents to be more consistent typographically, and MP has
quite a lot of useful features (such as the possibility to include its
eps output in LaTeX directly, EVEN when generating PDF files with
latexpdf). But the biggest bonus would clearly be the ability to
typeset math formulas nicely. (I realize that this would require one
to start a MetaPost process, but IMO the benefits would be worth the
overhead).

Is anyone else interested in a MetaPost device?

Thanks,

Tamas

-- 
Tam?s K. Papp
E-mail: tpapp at axelero.hu (preferred, especially for large messages)
        tpapp at westel900.net
Please try to send only (latin-2) plain text, not HTML or other garbage.

Hi


Tamas Papp wrote:
> Hi,
> 
> I read the 2000 thread on a MetaPost device in R. If I understand
> correctly, the main problem with the concept is that R wants the device
> driver to give back information on the size of strings/labels.
> 
> To the bet of my knowledge, MetaPost _does_ make it possible to
> measure the bounding box of text (see section 7.3: Measuring text in
> the MetaPost manual). For example, one could get the size of the
> bounding box of btex $\int_a^b x^2$ etex -- would that be enough to
> make an implementation possible? Or are the size of individual
> characters and kerning information necessary?

Kerning information is not required, but a device driver does need to 
provide information on the size of individual characters (or return 
zeroes which in some cases will prompt a warning that such information 
is not available, but most stuff will still work it just may look a bit 
nastier).

> Another question: can graphics devices be implemented solely in R (ie
> without writing C code)? I realize that it will be much slower, but
> first I would like to see how it works before writing in C. What
> source files should I be looking at?

Unfortunately, you can't write a device driver solely in R -- all the 
hooks are at the C-level.  You need to look at ...

R/src/include/R_ext/GraphicsDevice.h

... for a description of the device structures and function calls you 
have to fill in, and see one of the existing device drivers, e.g., ...

R/src/modules/X11/devX11.c

... for an example of how an existing device does the filling in.

> You may ask why I should bother about using Metapost. Well, I'd like
> my TeX documents to be more consistent typographically, and MP has
> quite a lot of useful features (such as the possibility to include its
> eps output in LaTeX directly, EVEN when generating PDF files with
> latexpdf). But the biggest bonus would clearly be the ability to
> typeset math formulas nicely. (I realize that this would require one
> to start a MetaPost process, but IMO the benefits would be worth the
> overhead).

I assume that you know about the mathematical annotation facilities in R 
-- help(plotmath) -- and want something "nicer" ...

Paul
-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
paul at stat.auckland.ac.nz