From: Glynn Clements <glynn.clements@virgin.net>
To: Somesh Agarwal <agarwal_somesh@yahoo.com>
Cc: grass5 developers list <grass5@geog.uni-hannover.de>
Subject: Re: [GRASS5] grass .. how does write on display

Somesh Agarwal wrote:

> I am new to grass and while looking at grass code I found this find io.c
> in which
> to write a text to display (from paint dir) we write the whole of
> $GISBASE/font/fontname  file contents to the display socket ,
> I did not understand what is happening exactly , can someone throw
> more light into the issue ,

The current mechanism is this (all files are in the directory
src/display/devices/lib unless stated otherwise):

1. A client calls R_font(), which sends the filename
($GISBASE/fonts/font_name) to the display driver using the FONT
command. See src/libes/raster/Font.c.

2. The display driver receives the FONT command and the filename. See
command.c.

3. It passes the filename to Font_get() (Font_get.c), which passes it
to init_font() (font.c), which reads the file into memory.

4. A client draws text by calling R_text (src/libes/raster/Text.c),
which sends the string to the display driver using the TEXT command.

5. The display driver receives the TEXT command and the string. See
command.c (again).

6. It passes the string to Text() (Text.c) which calls soft_text()
with the string and several stored parameters.

7. soft_text() (Text2.c) calls drawchar() (same file), to draw each
character.

8. drawchar() calls get_char_vects() (font.c) to retrieve the actual
vector definitions. It then draws the character using text_move() and
text_draw() (same file), which use the Move_abs() and Cont_abs()
functions (these are implemented separately by each display driver,
e.g. XDRIVER).

-- 
Glynn Clements <glynn.clements@virgin.net>
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