The key is to not draw directly, but to invalidate one or more rectangles needed to for changing the image from the old to the new one.
I worked on this problem some years ago and I think my solution is very relevant to your question. See the gtk3 branch at: https://github.com/dov/dovtk-lasso . Regards, Dov On Mon, Mar 20, 2017 at 9:25 PM, Marcin Kolny <marcin.ko...@gmail.com> wrote: > Hi everyone, > I'd like to write very simple application for drawing lines. > 1) User press button - app saves x and y coordinates > 2) User moves the mouse - app dynamically draws potential line on each > mouse move event > 3) User releases button - app "saves" the line on the canvas. > > I've tried to modify slightly the GTK example drawing application [1]. > 1) On button press event I paint the current state to the "base_surface" > surface. > 2) On each mouse move I paint to the "tmp_surface" surface "base_surface" > and after that the actual line, so I avoid multiple lines on mouse move. > 3) On mouse release event I paint "tmp_surface" surface to "base_surface". > > This works, and full code can be found on my gist [2]. However, I don't > think it's the right approach, since I have to re-paint a whole image for > each mouse-move, and latter on, on "draw" event application is doing almost > the same, so I'm doing the re-paint twice per each mouse move. I'm afraid > that for huge surfaces it might be very inefficient. > > Do you know what would be the right approach to solve this sort of > problems? > > Thank you for help, > Marcin > > [1] https://developer.gnome.org/gtk3/stable/ch01s05.html > [2] https://gist.github.com/loganek/156b6b9ce2333fd7d389f74c093a92b4 > _______________________________________________ > gtk-app-devel-list mailing list > gtk-app-devel-list@gnome.org > https://mail.gnome.org/mailman/listinfo/gtk-app-devel-list > _______________________________________________ gtk-app-devel-list mailing list gtk-app-devel-list@gnome.org https://mail.gnome.org/mailman/listinfo/gtk-app-devel-list
