Hi
Michael Lawrence wrote: > On Feb 7, 2008 4:49 PM, Mark W Kimpel <[EMAIL PROTECTED]> wrote: > >> I'm doing some work on a potential patch to the Bioconductor package >> Rgraphviz and have some questions on code that is contained in engine.c. >> In particular, I am developing some custom shapes using polygon and need >> to make sure that, with rendering, the line connecting the centers of >> two polygons stops at the border of each polygon. The polygons can be >> transparent, so the option of just rendering the lines first won't work. >> >> Is there some help for me with an R internal or perhaps a higher level >> function? >> > > I have to admit I am not that familiar with R graphics, but a very common > way to achieve this in general is to use clipping. That is, you would set > the regions covered by your node polygons as the "clip" and then draw your > edges. Anything drawn onto the clip region is discarded. You would then > reset the clip and continue drawing. > > I'm pretty sure that base R does not support the complex clip regions you > would require. However, it would be possible to do this in R by rendering to That's right. R's graphics engine only copes with rectangular clipping regions. OTOH, the 'grid' package does have a facility to determine locations on the edges of objects (see grobX() abnd grobY()). This is not fully-featured, but for convex polygons it might give you what you want. There's an example or two in http://www.stat.auckland.ac.nz/~paul/Talks/rgraphs.pdf Paul > pixmaps in memory and then compositing the pixmaps. The first part is > supported by the cairoDevice package and the latter part by RGtk2 (in > particular its binding to GDK). I'm sure you'd rather not introduce such a > dependency on Rgraphviz, but it's an option. I think the graphviz developers > are moving towards GTK+/Cairo in terms of plugins and other work. > > I checked libgd (already a dependency of graphviz) but found that it only > supports a single rectangle for clipping. > > Anyway, I hope this helps a little and good luck, > Michael > > >> Thanks, >> Mark >> -- >> >> Mark W. Kimpel MD ** Neuroinformatics ** Dept. of Psychiatry >> Indiana University School of Medicine >> >> 15032 Hunter Court, Westfield, IN 46074 >> >> (317) 490-5129 Work, & Mobile & VoiceMail >> (317) 204-4202 Home (no voice mail please) >> >> mwkimpel<at>gmail<dot>com >> >> ______________________________________________ >> R-devel@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-devel >> > > [[alternative HTML version deleted]] > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel -- Dr Paul Murrell Department of Statistics The University of Auckland Private Bag 92019 Auckland New Zealand 64 9 3737599 x85392 [EMAIL PROTECTED] http://www.stat.auckland.ac.nz/~paul/ ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
