Cairo driver

## NAME

Cairo driver - driver for bitmap or vector output using the Cairo graphics library.
(drivers)

## DESCRIPTION

The Cairo driver generates PNG, BMP, PPM, PS, PDF or SVG images from GRASS display commands, using the Cairo graphics library. The image format is selected from the extension of the output file.

It is started as 'pseudo' monitor (output to an image file) and when stopped, all output from previously used display commands are written to the output file.

## USAGE

### Environment variables

Several environment variables affect the operation of the Cairo driver:

- GRASS_WIDTH=xxx
  the width of the image.
- GRASS_HEIGHT=yyy
  the height of the image.
- GRASS_CAIROFILE=filename
  the name and format of the resulting image file, default is `map.png`.
  The image format is determined from the file extension.
  Supported bitmap formats:
  - .png - Portable Network Graphics (PNG)
  - .bmp - Windows Bitmap (BMP, 32-bpp) (these are not readable by some older viewers)
  - .ppm - Portable Pixmap (PPM + PGM for alpha channel)
  Supported vector formats:
  - .pdf - Portable Document Format (PDF)
  - .ps - PostScript (PS)
  - .svg - Scalable Vector Graphics (SVG)
  (Note: Some formats may not be available, depending on your platform and the Cairo library that GRASS was built with.)
- GRASS_BACKGROUNDCOLOR=RRGGBB
  specifies the background color to use in RGB notation (hex values). Default is FFFFFF (white).
- GRASS_TRANSPARENT=[TRUE|FALSE]
  sets transparent background on (TRUE) or off (FALSE, default).
- GRASS_AUTO_WRITE=[TRUE|FALSE]
  if set to `TRUE`, the image file will be written after each operation (i.e. whenever a client disconnects), rather than only being written out when the driver terminates.
  (Note: This only applies to bitmap formats - vector formats are always written directly to file).
- GRASS_CAIRO_READ
  if `TRUE`, the Cairo driver will initialize the image from the contents of GRASS_CAIROFILE.
  (Note: This is only supported for bitmap formats)
- GRASS_CAIRO_MAPPED
  if `TRUE`, the Cairo driver will map GRASS_CAIROFILE as its framebuffer, rather than using memory. This only works with BMP files.

### Examples

Example using the driver directly (bash-syntax):

    export GRASS_CAIROFILE=spearfish.png
    export GRASS_WIDTH=800
    export GRASS_HEIGHT=800

    d.mon start=cairo
    d.rast map=elevation.10m
    d.vect map=streams width=1 color=blue fcolor=aqua type=area,line
    d.vect map=roads width=2
    d.mon stop=cairo

Example using d.out.file:

    d.mon x0
    d.rast map=elevation.10m
    d.vect map=streams width=1 color=blue fcolor=aqua type=area,line
    d.vect map=roads width=2

    d.out.file -c sf_cairo format=png size=800,800

A more complicated example using d.out.file:

    r.shaded.relief map=elevation.dem
    r.watershed elev=elevation.dem basin=watershed.basin thresh=10000

    d.mon x1
    d.shadedmap rel=elevation.dem.shade drape=watershed.basin bright=30
    d.vect streams color=aqua fcolor=aqua type=area,line
    d.vect roads where="label ~ 'light-duty road'" color=grey
    d.vect roads where="label ~ 'unimproved'" color=orange
    d.vect roads where="label ~ 'secondary highway'" color=100:100:100 width=2
    d.vect roads where="label ~ 'primary highway'" color=50:50:50 width=2
    d.vect railroads col=red width=2
    d.vect roads where="label = 'interstate'" color=black width=3

    d.vect archsites icon=basic/star size=25 fcolor=yellow

    d.font Andale_Mono
    echo "Spearfish, SD" | d.text color=black at=28,53 -b

    d.out.file -c sf_cairo2 format=png

## NOTES

The driver is still in development. Enable it by specifying `--with-cairo` when configuring GRASS. This requires a reasonably recent version of the Cairo libraries and a working pkg-config.

Antialiasing is enabled by default for bitmap formats. There is currently no way of disabling this.

Cairo supports true vector format output whenever possible. However, if the selected format doesn't support a necessary feature, Cairo may fall back on rendering a bitmap representation of the image wrapped in the selected vector format.

Cairo driver output via d.out.file is supported via the -c flag.

## SEE ALSO

HTMLMAP driver, PNG driver, PostScript driver, XDRIVER
d.frame, d.mon, d.rast, d.vect d.out.file

## AUTHOR

Lars Ahlzen <lars (at) ahlzen.com>
and the GRASS Development Team.