On 2010.06.10 22:44:40 +0530, Jeenu V wrote: > On Thu, Jun 10, 2010 at 8:23 PM, David Ripton <drip...@ripton.net> wrote: > > Yes, of course you can just use PyCairo rather than a canvas. It's just > > more work that way. I ended up having to go this route at work because > > we're stuck on RHEL 5 which has ancient versions of GTK+ and Cairo, and > > all the nice new canvases I tried require newer versions. > > Alright. If you've anything that can be shared about how you took the > long(er) route, please consider doing so.
Cairo is basically immediate mode. Which means you need to redraw everything in the exposed area every time. A canvas is retained mode. Meaning you build some objects that know how to redraw themselves every time they are exposed, with support for placing them and possibly overlapping them and only drawing what's on top. If your drawing is simple enough then it's easier to just use Cairo; the more objects you throw onto the screen, the more sense it makes to use a full canvas to subdivide the work so you don't end up with a gigantic unmaintainable draw method. I needed a canvas that would work well with the old versions of libraries on RHEL 5 and not have license problems, and couldn't find one (GnomeCanvas didn't let me rescale things well, GooCanvas didn't work well for me for some reason I've forgotten and was also a pain to build, the one from OLPC was GPL licensed), so I wrote my own. Basically inherits from DrawingArea and does Cairo calls in the draw methods. The canvas is only 850 lines of Python, but it's the kind of fiddly lower-level GUI code that's a pain to write. There are classes for rectangles, lines with arrows on the ends of them (which require some trig to draw correctly), SVG images (rsvg module), text (pango and pangocairo). A general-purpose canvas library would have more stuff, but that's all I needed. Performance is fine for a small number of displayed objects but doesn't scale well to hundreds of objects. I'd like to obsolete this code when we can switch to RHEL 6. I highly recommend reusing one of the existing canvases rather than writing your own if at all possible. -- David Ripton drip...@ripton.net _______________________________________________ pygtk mailing list pygtk@daa.com.au http://www.daa.com.au/mailman/listinfo/pygtk Read the PyGTK FAQ: http://faq.pygtk.org/
