Lars Ahlzen wrote: > My apologies if this has been done and/or discussed before, but a search > of grass-dev came up empty. > > Since the Cairo graphics library (http://www.cairographics.org, LGPL > licensed) provides very high-quality graphics output in several vector > and raster formats, I thought it would make sense to create a "pseudo" > monitor driver for it (similar to the PNG and PS drivers). So I did. > Cairo does all of the hard work, so it's really mostly simple "glue" code. > > It seems stable, and is fairly complete in terms of features. I've used > for most of my own work recently. > > Benefits include: > > * High quality antialiased output. See > http://lars.ahlzen.com/cairograss/ for a few simple examples and a > comparison with the PNG driver.
One thing to be careful of with anti-aliasing is tesselations. Issues with Ghostscript's anti-aliasing option are a regular topic on the GMT list. > * Several output format options, both vector and bitmap. The driver > currently supports PNG, PDF, PS and SVG. Output to X or Win32 windows > might be possible in the future, since Cairo supports such formats as well. > > Of course, such niceness comes at a price. It takes longer to draw > complex vector data, compared to the PNG driver. However, I imagine that > in most cases drawing is not the main bottleneck anyway. For d.vect, drawing usually is the bottleneck. > Also, it obviously pulls in Cairo as an additional dependency. Cairo is > probably found on most systems nowadays, though, since many other > applications (including some mapping and GIS software) already use it. > > Additionally, the fact that GRASS monitors (unfortunately) receive > integer data (screen coordinates, line widths, etc) somewhat limits the > effectiveness of the high-precision output from the CAIRO driver. For > example, in the "Massachusetts Counties and roads" example, the > antialiasing breaks down for certain lines because they are divided into > smaller segments whose coordinates are rounded before they are drawn. > Similarly, zooming in on vector output will also reveal this drawback. > > My main question is: Does all of this seem useful to anyone else? I do > realize that most of these things can be achieved in other ways, but > I've personally found this driver to produce high quality output in a > very convenient way. Feedback is appreciated! The main thing to bear in mind is that the graphics system is going to be completely re-written for 7.x. If Cairo is available for both Windows and MacOSX (natively, i.e. not requiring X11), and does an adequate job of PostScript generation (embedding a pre-rendered image in a PostScript file doesn't count), it could be a viable basis for the new graphics architecture. > I can of course post code too, if anyone would be interested in actually > trying it. The code would certainly be useful. -- Glynn Clements <[EMAIL PROTECTED]> _______________________________________________ grass-dev mailing list grass-dev@grass.itc.it http://grass.itc.it/mailman/listinfo/grass-dev
