Also, it would be also useful to have a command line option that specifies a particular layer for output.
[ellson] You can generate multiple layer images into any output format that allows multiple images. At the moment this is -Tps and -Tswf (if graphviz is built with libming). I think SVG could support multiple pages, but thats not implemented yet.
-Tpng doesn't support multiple images in a single file, AFAIK. Some possibilies:
All these options just require some coding. All the hooks are in place at the plugin interface to provide layers to any format that can handle them.
- extend funtionality of -O to generate a uniquely named png image file for each layer. - add support for -Tmng - add support for the animated GIF format (what is it called?) - extend SVG support to multiple pages.
For now I recommend that you use -Tps for layered, or other multipage, graphs.