[matplotlib-devel] Mixed-mode rendering

[Eric B. <eri...@gm...>]

Hi,

On trunk, there is mixed-mode rendering support built in to (at least) the
SVG and PDF backends, though there are no calls to start/stop_rasterizing()
that utilize the raster mode. I've implemented mode switching for
those backends,
and would appreciate feedback on what I've done.

There are two modes that might drive a switch to raster for some artists:
1. User-driven specification of known complex artitsts.
2. Automatic detection of artist complexity (by type or vertex count).
The first mode is what I coded up, so I'll discuss it below.

A list of artists to rasterize is passed as a draw_raster kwarg to savefig,
which percolates down into print_* in the backend-specific figure canvas.
When the backend's canvas creates a renderer, the draw_raster list is placed
as an attribute on the renderer instance. I figured that the renderer should
be responsible for transporting the list of artists needing rasterization,
since it's at the renderer level that pixel vs. vector matters.

The switch to/from raster mode was made in Axes.draw, where the artists for
each axes are looped over. In the artist loop, I check if the artist to be
rendered is listed in the draw_raster attribute on the renderer instance. If
so, the appropriate calls are made to start and stop rasterizing.

Sample usage:
f=pyplot.figure()
ax=f.add_subplot(111)
p,=ax.plot(range(10))
f.savefig('test.pdf', draw_raster=(p,))

svn diff at
http://www.deeplycloudy.com/20080503-matplotlib-mixed-mode-r5110.diff

Thanks,
Eric Bruning
Graduate Research Assistant, Meteorology, Univ. Oklahoma
As of 6/1/2008, Research Assoc., Univ. Maryland/CICS and NOAA/NESDIS/STAR