Geografic-Information-System/lib/cairodriver/cairodriver.html

<!-- meta page description: Cairo DISPLAY DRIVER -->

<em>Cairo display driver</em> for bitmap or vector output using the
Cairo graphics library.

<h2>DESCRIPTION</h2>

The Cairo driver generates PNG, BMP, PPM, PS, PDF or SVG images by
GRASS display commands, using the
<a href="http://www.cairographics.org/">Cairo graphics library</a>.
The image format is selected from the extension of the output file.

The Cairo driver is used for GRASS display commands by default if
available, otherwise <em><a href="pngdriver.html">PNG driver</a></em>
is used.

<h2>USAGE</h2>

<h3>Environment variables</h3>

The Cairo driver can be enabled by
setting <b>GRASS_RENDER_IMMEDIATE</b> variable, eg.

<div class="code"><pre>
export GRASS_RENDER_IMMEDIATE=cairo
</pre></div>

Several environment variables affect the operation of the Cairo driver:

<ul>
  <li><b>GRASS_RENDER_WIDTH=xxx</b><br>
    the width of the image map (default is 640).
  </li>
  <li><b>GRASS_RENDER_HEIGHT=yyy</b><br>
    the height of the image map (default is 480).
  </li>
  <li><b>GRASS_RENDER_BACKGROUNDCOLOR=RRGGBB</b><br>
    specifies the background color to use in RGB notation (hex or
    R:G:B values). Named colors are also supported. Default
    is <b>FFFFFF</b> (white).
  </li>
  <li><b>GRASS_RENDER_TRANSPARENT=[TRUE|FALSE]</b><br>
    sets transparent background on (TRUE) or off (FALSE, default).
  </li>
  <li><b>GRASS_RENDER_ANTIALIAS</b><br> can be <em>default</em>,
    <em>none</em>, <em>gray</em>, or <em>subpixel</em>, corresponding to
    <a href="http://www.cairographics.org/manual/cairo-cairo-t.html#cairo-antialias-t">cairo_antialias_t</a>
  </li>
  <li><b>GRASS_RENDER_FILE=filename</b><br>
     the name and format of the resulting image file, default is
     <tt>map.png</tt>.<br>
     The image format is determined from the file extension.<br>
     Supported bitmap formats:
     <ul>
       <li><b>.png</b> - Portable Network Graphics (PNG)</li>
       <li><b>.bmp</b> - Windows Bitmap (BMP, 32-bpp)
           (these are not readable by some older viewers)</li>
       <li><b>.ppm</b> - Portable Pixmap (PPM + PGM for alpha channel)</li>
     </ul>
     Supported vector formats:
     <ul>
       <li><b>.pdf</b> - Portable Document Format (PDF)</li>
       <li><b>.ps</b> - PostScript (PS)</li>
       <li><b>.svg</b> - Scalable Vector Graphics (SVG)</li>
     </ul>
     (Note: Some formats may not be available, depending on your platform and
     the Cairo library that GRASS was built with.)
  </li> 
  <li><b>GRASS_RENDER_FILE_READ</b><br>
     if <tt>TRUE</tt>, the Cairo driver will initialize the image from
    the contents of GRASS_RENDER_FILE.<br>
    (<em>Note: This is only supported for bitmap formats</em>)
  </li>
  <li><b>GRASS_RENDER_FILE_MAPPED</b><br>
    if <tt>TRUE</tt>, the Cairo driver will map GRASS_RENDER_FILE as its framebuffer,
    rather than using memory.<br>
    (<em>Note: This only works with BMP files.</em>)
  </li>
  <li><b>GRASS_RENDER_CAIRO_SCREEN</b><br>
    defines Cairo screen
  </li>
  <li><b>GRASS_RENDER_CAIRO_VISUAL</b><br>
    defines Cairo visual
  </li>
</ul>

<h2>EXAMPLES</h2>

<h3>PNG Example</h3>

Example: using the driver to generate a PNG file (bash-syntax):

<div class="code"><pre>
export GRASS_RENDER_IMMEDIATE=cairo
export GRASS_RENDER_FILE=nc_spm.png
export GRASS_RENDER_WIDTH=800
export GRASS_RENDER_HEIGHT=800
export GRASS_RENDER_FILE_READ=TRUE

g.region raster=elevation
d.rast map=elevation
d.vect map=streams width=1 color=blue fcolor=aqua type=area,line
d.vect map=roadsmajor width=2
</pre></div>

<h3>PDF Examples</h3>

Example: using the driver to generate a PDF vector file with a vector
map (bash-syntax):

<div class="code"><pre>
export GRASS_RENDER_IMMEDIATE=cairo
export GRASS_RENDER_FILE=nc_spm.pdf
export GRASS_RENDER_WIDTH=800
export GRASS_RENDER_HEIGHT=800

g.region vector=roadsmajor
# activate vector font
d.font Vera
d.vect map=roadsmajor layer=1 display=shape attrcolumn=ROAD_NAME lcolor=0:90:255
</pre></div>

<p>
Example: using the driver to generate a PDF raster file with a raster
map (bash-syntax):

<div class="code"><pre>
export GRASS_RENDER_IMMEDIATE=cairo
export GRASS_RENDER_FILE=nc_spm.pdf
export GRASS_RENDER_WIDTH=800
export GRASS_RENDER_HEIGHT=800

g.region raster=elevation
d.rast map=elevation
</pre></div>


<h3>SVG Example</h3>

Example: using the driver to generate a SVG vector file with a vector
map (bash-syntax):

<div class="code"><pre>
export GRASS_RENDER_IMMEDIATE=cairo
export GRASS_RENDER_FILE=vectormap.svg

g.region vector=roadsmajor
d.vect map=roadsmajor -c
</pre></div>


<h2>NOTES</h2> 

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

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

<p>The resolution of the output images is defined by current region
extents. Use <tt>g.region -p</tt> to get the number of rows and cols
and use the environment variables to set the image size. If you would
like a larger image, multiply both rows and cols by the same whole
number to preserve the aspect ratio.

<p>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.

<h2>SEE ALSO</h2>
<em>
<a href="pngdriver.html">PNG driver</a>,
<a href="psdriver.html">PS driver</a>,
<a href="htmldriver.html">HTML driver</a>,
<a href="variables.html">variables</a>
</em>
<p>
<em>
<a href="d.rast.html">d.rast</a>,
<a href="d.vect.html">d.vect</a>,
<a href="d.mon.html">d.mon</a>,
<a href="d.erase.html">d.erase</a>,
<a href="d.redraw.html">d.redraw</a>
</em>

<h2>AUTHOR</h2>
Lars Ahlzen &lt;<i>lars (at) ahlzen.com</i>&gt;<br>
and the GRASS Development Team.

<p>
<i>Last changed: $Date$</i>