/*! \page rastergraphicslib GRASS Raster Graphics Library

\section intro Introduction

The <i>Raster Graphics Library</i> provides the programmer with access to 
the GRASS graphics devices. <b>All video graphics calls are made 
through this library (directly or indirectly)</b>. No 
standard/portable GRASS video graphics module drives any video display 
directly. This library provides a powerful, but limited number of graphics 
capabilities to the programmer. The tremendous benefit of this approach is 
seen in the ease with which GRASS graphics applications modules port to new 
machines or devices. Because no device-dependent code exists in application 
programs, virtually all GRASS graphics modules port without modification. 
Each graphics device must be provided a driver (or translator program). At 
run-time, GRASS graphics modules rendezvous with a user-selected driver 
module. Two significant prices are paid in this approach to graphics: 1) 
graphics displays run significantly slower, and 2) the programmer does not 
have access to fancy (and sometimes more efficient) resident library 
routines that have been specially created for the device.

This library uses a couple of simple concepts. First, there is the idea of a 
current screen location. There is nothing which appears on the graphics 
monitor to indicate the current location, but many graphic commands begin 
their graphics at this location. It can, of course, be set explicitly. 
Second, there is always a current color. Many graphic commands will do their 
work in the currently chosen color. The programmer always works in the 
screen coordinate system. Unlike many graphics libraries developed to 
support CAD, there is no concept of a world coordinate system. The 
programmer must address graphics requests to explicit screen locations. This 
is necessary, especially in the interest of fast raster graphics.

The upper left hand corner of the screen is the origin. The actual pixel 
rows and columns which define the edge of the video surface are returned 
with calls to <i>R_screen_left()</i>, <i>R_screen_rite(), 
R_screen_bot(), and R_screen_top().</i>

<b>Note.</b> All routines and global variables in this library, documented 
or undocumented, start with the prefix <b>R_.</b> To avoid name 
conflicts, programmers should not create variables or routines in their own 
modules which use this prefix.


\section conn Connecting to the Driver

Before any other graphics calls can be made, a successful connection to a 
running and selected graphics driver must be made.

- R_open_driver()

- R_close_driver()

\section col Colors

GRASS is highly dependent on color for distinguishing between different 
categories. No graphic patterning is supported in any automatic way. There 
are two color modes. Fixed color refers to set and immutable color look-up 
tables on the hardware device. In some cases this is necessary because the 
graphics device does not contain programmer definable color look-up tables 
(LUT). Floating colors use the LUTs of the graphics device often in an 
interactive mode with the user. The basic impact on the user is that under 
the fixed mode, multiple maps can be displayed on the device with apparently 
no color interference between maps. Under float mode, the user may 
interactively manipulate the hardware color tables (using modules such as 
<i>d.colors</i>). Other than the fact that in float mode no more colors 
may be used than color registers available on the user's chosen driver, 
there are no other programming repercussions.

- R_color_table_fixed()

- R_color_table_float()

Colors are set using integer values in the range of 0-255 to set the
<b>red, green</b>, and <b>blue</b> intensities. In float mode, these values
are used to directly modify the hardware color look-up tables and
instantaneously modify the appearance of colors on the monitor. In fixed mode,
these values modify secondary look-up tables in the devices driver module so
that the colors involved point to the closest available color on the device.

- R_reset_color()

- R_reset_colors()

- R_color()

- R_standard_color()

- R_RGB_color()

\section basic Basic Graphics

- R_screen_bot()

- R_screen_top()

- R_screen_left()

- R_screen_rite()

- R_move_abs()

- R_move_rel()

- R_cont_abs()

- R_cont_rel()

- R_box_abs()

- R_box_rel()

- R_erase()

- R_flush()

- R_stabilize()

\section poly Poly Calls

In many cases strings of points are used to describe a complex line, a series of
dots, or a solid polygon. Absolute and relative calls are provided for each of
these operations.

- R_polydots_abs()

- R_polydots_rel()

- R_polygon_abs()

- R_polygon_rel()

- R_polyline_abs()

- R_polyline_rel()

\section raster Raster Calls

GRASS requires efficient drawing of raster information to the display device.
These calls provide that capability.

- R_raster()

- R_raster_char()

- R_set_RGB_color()

- R_RGB_raster()

\section text Text

These calls provide access to built-in vector fonts which may be sized and
clipped to the programmer's specifications.

- R_set_window()

- R_font()

- R_text_size()

- R_text()

- R_get_text_box()

\section font GRASS font support

The current mechanism of GRASS font support is this (all files are in the
directory display/drivers/lib unless stated otherwise):

<ul>
<li> A client calls R_font(), which sends the filename
  ($GISBASE/fonts/font_name) to the display driver using the FONT command. See
  lib/raster/Font.c.
  
<li> The display driver receives the FONT command and the filename. See
  command.c.
  
<li> It passes the filename to Font_get() (Font_get.c), which passes it to
  init_font() (font.c), which reads the file into memory.
  
<li> A client draws text by calling R_text (lib/raster/Text.c), which
  sends the string to the display driver using the TEXT command.
  
<li> The display driver receives the TEXT command and the string. See command.c
  (again).
  
<li> It passes the string to Text() (Text.c) which calls soft_text() with the
  string and several stored parameters.
  
<li> soft_text() (Text2.c) calls drawchar() (same file), to draw each
  character.
  
<li> 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).
</ul>

\section user User Input

The raster library provides mouse (or other pointing device) input from the
user. This can be accomplished with a pointer, a rubber-band line or a
rubber-band box. Upon pressing one of three mouse buttons, the current mouse
location and the button pressed are returned.

- R_get_location_with_pointer()

- R_get_location_with_line()

- R_get_location_with_box()

\section load Loading the Raster Graphics Library

The library is loaded by specifying $ (RASTERLIB) in the Makefile.

<b>Note.</b> This library must be loaded with $(GISLIB) since it uses 
routines from that library. See \ref GIS_Library for details on that 
library. This library is usually loaded with the $(DISPLAYLIB). See 
\ref Display_Graphics_Library for details on that library.

See \ref Compiling_and_Installing_GRASS_Modules for a complete 
discussion of Makefiles.

*/
