[GRASS-dev] Re: windows binaries

[Glynn Clements]

Glynn Clements wrote:

> Here's an idea: if direct rendering had an option to initialise the
> framebuffer from an image file (or PPM/PGM pair), building up an image
> by having multiple d.* commands render on top of each other would
> work, in the same way that it does with persistent drivers.

I've added this feature to libpngdriver (so it affects both the
standalone PNG driver and direct rendering).

If you set GRASS_PNG_READ to TRUE, it will read $GRASS_PNGFILE (either
a PNG file or PPM/PGM pair) into the framebuffer at startup. This
allows you to build up a rendered image by overlaying multiple d.*
commands.

The file(s) must exist, and match the various PNG driver environment
variables in all respects, otherwise a fatal error occurs. So long as
the file was generated from a previous invocation with the same
settings, there shouldn't be any problems.

Note that GRASS_PNG_READ mustn't be set for the first command, as the
file(s) won't exist yet.

This feature is useful primarily for scripts (e.g. d.vect.thematic)
which run multiple d.* commands to generate a final result. It should
be simpler than managing and compositing the various layers manually. 
It also works with PNG files as well as PPM/PGM pairs (we don't have a
PNG version of g.pnmcomp).

-- 
Glynn Clements <glynn at gclements.plus.com>