Re: Brainy person needed for scrolling canvas problem!
On 3 Jul 2010, at 09:43, jcup...@gmail.com wrote: You'd link to the configure event to build the offscreen pixmap. The scribble example in the tutorial uses pixmaps to improve drawing: I downloaded the Scribble example but interestingly, it seems to have been written for an older version of gtk/gdk. It uses some gdk types (e.g. GdkDeviceInfo) which seem to be missing from gtk-2.0 but which look as though they used to be present in gtk-1.2. I guess I could temporarily rename my gtk-2.0 include folders to make gtk-2.0 inaccessible to the compiler but I'm curious to know if there's a better way to revert to the older version? John ___ gtk-app-devel-list mailing list gtk-app-devel-list@gnome.org http://mail.gnome.org/mailman/listinfo/gtk-app-devel-list
Re: Brainy person needed for scrolling canvas problem!
On 3 Jul 2010, at 15:33, John Emmas wrote: I downloaded the Scribble example but interestingly, it seems to have been written for an older version of gtk/gdk. It uses some gdk types (e.g. GdkDeviceInfo) which seem to be missing from gtk-2.0 but which look as though they used to be present in gtk-1.2. I guess I could temporarily rename my gtk-2.0 include folders to make gtk-2.0 inaccessible to the compiler but I'm curious to know if there's a better way to revert to the older version? Actually, it's slightly simpler than I thought. The Scribble project has two source files (scribble.c and scribble-xinput.c). Further investigation reveals that they actually compile to two different executables (At first, I thought they were both part of the same project which would have been worrying - because scribble.c needs gtk-2.0, whereas scribble-xinput.c needs gtk-1.2). ___ gtk-app-devel-list mailing list gtk-app-devel-list@gnome.org http://mail.gnome.org/mailman/listinfo/gtk-app-devel-list
Brainy person needed for scrolling canvas problem!
A program I'm working on uses a GTK main window to view an underlying gnome canvas object. The canvas is wider than the part of it that's visible at any given time, so a horizontal scrollbar can be used to scroll the canvas, leftwards or rightwards. The effect is similar to a multitrack audio tape. Like the tape analogy, the user needs to be able to fast-forward and rewind (by dragging the scrollbar) but also, the canvas needs to scroll continuously in time (i.e. programatically) to simulate time-based movement (like a tape that's playing). There are two ways to achieve the playing effect:- 1) Every 1/30th second or thereabouts, erase all the objects on the canvas and redraw them, slightly to the left of their former positions. This works quite well if the canvas only contains a small number of objects but if too many objects need to be redrawn, it soon becomes unwieldy and the movement ends up looking very jerky. 2) Draw all the objects onto a very wide canvas. Every 1/30th second, reposition the viewport so that it's slightly to the right of its previous position (analogous to programatically setting the current position of the scrollbar). This also works and gives a much smoother scrolling effect. Now for the problem when in playback mode, I'd like the viewport to have a vertical now line (similar to the play head on a tape recorder). At the moment, this is drawn onto the canvas. Therefore every 1/30th second, it needs to be erased, then the viewport needs to be adjusted, then the now line needs to be redrawn. This produces a very flickery now line. In an ideal world, I'd like the now line to be a viewport object, rather than a canvas object. The viewport would ideally contain some kind of transparent pane (with the now line drawn on it) and the canvas would be viewable through the pane's transparent part. The pane would be treated like a foreground object (so as to be permanently visible) with a fixed position, relative to the viewport, whereas the canvas would have a variable position, relative to the viewport. Off the top of my head, I can't think of any gtk widget that's designed for this purpose. Has anyone ever seen a project with this kind of feature? Or can anyone suggest a feasible strategy I could try? Thanks, John ___ gtk-app-devel-list mailing list gtk-app-devel-list@gnome.org http://mail.gnome.org/mailman/listinfo/gtk-app-devel-list
Re: Brainy person needed for scrolling canvas problem!
Hi John, On 2 July 2010 16:04, John Emmas john...@tiscali.co.uk wrote: Now for the problem when in playback mode, I'd like the viewport to have a vertical now line (similar to the play head on a tape recorder). I doubt I count as brainy, but one simple technique would be to render the screen in layers. You would have an offscreen pixbuf with the current view, minus the now line. On an expose event, you copy the relevant parts of the offscreen buffer to the display, then draw the now line over that. Because of gtk's double-buffering, this will be flicker-free. To scroll 100 pixels to the right, you blit your offscreen buffer by 100 pixels, draw just the objects in the exposed area of pixels, then queue an expose for the whole widget. This means you have to handle all the scrolling yourself, but it's not so hard. Just connect your 'scroll by x pixels' function to the adjust signal on a scrollbar. If you need more speed (though I think it'd be quick enough on most machines) you'd probably need to use opengl. John ___ gtk-app-devel-list mailing list gtk-app-devel-list@gnome.org http://mail.gnome.org/mailman/listinfo/gtk-app-devel-list
Re: Brainy person needed for scrolling canvas problem!
Thanks for the suggestion John. Can I assume that you're referring to the functionality of gdk-pixbuf? It didn't occur to me to look there, though I suppose it's the most obvious place to find a solution. I'd been looking for layering API's or blitting API's within gtk :-( So the obvious question is what would I use to obtain a pixbuf object from the current viewport / viewable area of a canvas? Are there some handy API's available or would I need to roll my own? John ___ gtk-app-devel-list mailing list gtk-app-devel-list@gnome.org http://mail.gnome.org/mailman/listinfo/gtk-app-devel-list
