I'll test it this evening when I am back home. The animated-canvas class actually keeps two bitmaps - one for painting from and one for drawing to. The swap-bitmaps methods swaps those and repaints the canvas. I'm not sure which of those the new canvas backing store would replace.
Doug On Mon, Nov 1, 2010 at 9:07 AM, Matthew Flatt <mfl...@cs.utah.edu> wrote: > At Sun, 31 Oct 2010 16:29:08 -0600, Doug Williams wrote: > > The animated-canvas library that I have on PLaneT has two examples. The > > histogram-test.rkt example works as expected. The lines.rkt example draws > a > > few lines and then locks up. Adding a (yield) after (send canvas > > swap-bitmaps) in line 55 gets it to run - sort of. The animation is > fairly > > smooth for 10 sets of lines, but is really strange at 50 (for example) - > > with this machine on the old GRacket it would be smooth at 100. And, my > stop > > button implementation doesn't work will - it just sets a global and the > > graphics routines exit when they see it set - it eventually stops, but > may > > require 10 to 15 seconds or so. I suspect that the animated-canvas > > functionality for double-buffering may not be needed anymore and the > 'flush' > > operations are what I need to look at. > > > > The interactions.ss file in the simulation package on PLaneT also > required a > > (yield) after line 107 to give the animation effect - there is no double > > buffering or anything here. But, with that added, it seems to run fine. > > I've pushed changes to make the canvas refresh without `yield'. Can you > check with the latest version? > > > You're right that double-buffering usually should not be needed > anymore, since all canvases now have a backing buffer. As an example, > text editors (like the ones in DrRacket) used to have their own backing > buffer, and they don't anymore. > > There are cases where you need precise control over the timing of > flushes. The new `suspend-flush' and `resume-flush' methods on `dc<%>' > give you extra control over the timing of flushes, and often that extra > control is enough. (Text editors use those methods to group a refresh > of the editor.) Since `suspend-flush' doesn't absolutely prevent > flushes, however, an extra backing buffer would be needed if it's > important to never show an intermediate drawing state. > > Finally, you might still want an explicit backing buffer to stage a > complex drawing so that it can be moved onscreen quickly. Slideshow, > for example, still draws a next slide offscreen (when it is otherwise > idle) so that it can display the slide instantly when you advance the > show. > >
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