> Is there some way to enable double-buffering of some sort, or > something along those lines, in gschem so that the whole sheet isn't > redrawn over and over during panning with the scrollbars? > > I know X11 can do it (I've done it in Xt apps ages ago) but I don't > know how deeply that stuff is buried underneath gtk.
For those who don't know, there are a couple of ways to make redraws cleaner when scrolling or exposing. This is more of a primer than a gschem-specific solution, since I don't know what api gschem uses for its graphics. PCB uses the gdk or X11 level stuff, so it has access to the raw screen for these types of optimization. When scrolling, the key is to use a blit to copy the existing screen to the new location, and only redraw the new part. For exposures, the key is to only redraw the exposed part. Both of these are similar, in that you want to set up a clipping region for the new parts, clear that, and redraw that. That way you don't see the whole screen redraw, and it's potentially a lot faster if you can reduce the amount of data you have to scan through. However, if your scrollbars don't correspond to an exact number of pixels per increment, you may accumulate rounding errors, which would cause the occasional visual discontinuity on the screen (I see this in Firefox occasionally). Alternatively, you can do what the lesstif HID does, which is to redraw the whole screen when the system is idle (i.e. done changing things). It redraws the whole screen to a pixmap, then blits the pixmap to the screen. While you still redraw the whole screen, you don't have to erase it first, so there's no visible flicker. Also, this gives you a free backing store for exposures - when you get an exposure, you just blit that part of the pixmap (which you save for this purpose :) to the exposed part of the screen. The other advantage is that you don't ever have to wait for the screen to "catch up" to your actions, because if it's not trying to update the screen each time, *only* when there's nothing else to do. There's always the option of true double buffering, but that's not always faster than the other options since you always draw the whole screen each time you want to change anything. The other option is to use GLX to render your "wireframe" schematic on the screen. You're still updating the whole "screen" each time, but you've got dedicated hardware doing the heavy lifting for you. _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
