[GRASS-dev] why d.vect.thematic won't run on WinGRASS - d.mon problem

[Glynn Clements]

Michael Barton wrote:

> Does d.erase work if there are no monitors?

It works with direct rendering.

d.erase just fills a rectangle in a specific colour. "d.erase -e" is
different in that it uses the R_erase() function (as does
"d.frame -e"), which corresponds to the ERASE opcode.

The PNG driver library (used by both the standalone driver and direct
rendering) responds to this opcode by clearing the image, making it
transparent if GRASS_TRANSPARENT=TRUE.

The only program which fundamentally doesn't work with direct
rendering is d.mon.

A few other programs aren't much use with direct rendering as they
rely upon operations which aren't implemented.

The main issue with direct rendering is that there is no persistence
between commands. This makes d.font useless, and d.frame mostly
useless ("d.frame -e" works to erase the screen, but you can't create
persistent frames).

Obviously, mouse interaction doesn't work, but that's also true of the
PNG driver (and all drivers except XDRIVER). Panels (the ability to
save and restore regions of the screen) don't work with either the PNG
driver or direct rendering, but they're only ever used in conjunction
with mouse interaction.

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