[Gtk-sharp-list] DrawingArea flickering - how to stop erasing background

[Nicholas Frechette]

Have you tried playing with the following properties?
mDrawingArea.AppPaintable = true;
mDrawingArea.DoubleBuffered = false;

I set these values since I handle the drawing manually on a Cairo
surface followed by painting that on a pixmap (which is equivalent to
manually handling the double buffering).

My expose event looks like the following:
private void HandleDrawingAreaExposeEvent(object o, ExposeEventArgs args)
{
	var lArea = args.Event.Area;
	args.Event.Window.DrawDrawable(mDrawingArea.Style.BlackGC,
mCompositePixmap, lArea.X, lArea.Y, lArea.X, lArea.Y, lArea.Width,
lArea.Height);
	args.RetVal = false;
}

Hope this helps,
Nicholas

On Wed, Jun 13, 2012 at 8:20 AM, eskimobob <martin at berriman.co.uk> wrote:
> I've searched and searched on DoubleBuffering with Gdk# but am still stuck...
> I'm writing a test linux app in Monodevelop using Gdk# and Cairo.
> I have on my form a DrawingArea widget onto which I draw.
>
> In order to avoid flickering, I am creating a Cairo.ImageSurface where I do
> the actual drawing.  This is then painted onto the DrawingArea during the
> Expose event handler.
>
> I am finding that it is flickering badly but fail to understand why.  In a
> previous app on Windows, I had a similar problem because Windows tries to
> erase the background before each paint.  Since I am painting the entire
> image from memory, there is no need to erase first.  This was solved by
> handling the WM_ERASEBKGND message - i.e. intercept the message and ignore
> it so that the attempted erase does not occur.
>
> It seems likely that the same thing is happening here (automatic erase
> before my paint) however I don't know how to stop it.
>
> I've included example code below (although can't see any way to use code
> tags) and would appreciate any suggestions.
>
>        private Cairo.ImageSurface viewSurface; //surface used to double buffer
> drawing to prevent flicker
>        private System.Timers.Timer timer;              //used to cause a redraw
>
>        public MainWindow (): base (Gtk.WindowType.Toplevel)
>        {
>                Build ();
>                timer = new System.Timers.Timer(10);
>                timer.Enabled = false;
>                timer.Elapsed += HandleTimerElapsed;
>        }
>
>        void HandleTimerElapsed (object sender, System.Timers.ElapsedEventArgs e)
>        {
>                UpdateViewSurface();
>                mainDrawingArea.QueueDraw();
>        }
>
>        protected void eDrawingAreaConfigure (object o, Gtk.ConfigureEventArgs
> args)
>        {
>                //we get here we we have a resize event
>                //create our sufrace in memory for later use
>                viewSurface = new ImageSurface(Format.ARGB32,
> mainDrawingArea.Allocation.Width, mainDrawingArea.Allocation.Height);
>        }
>
>        protected void eDrawingAreaExpose (object sender, Gtk.ExposeEventArgs args)
>        {
>                //we get here when we need to redraw the screen
>                DrawingArea viewArea = (DrawingArea)sender;
>                using (Context cr = Gdk.CairoHelper.Create(viewArea.GdkWindow))
>                {
>                        cr.SetSourceSurface(viewSurface, 0, 0);
>                        cr.Paint();
>                }
>        }
>
>        private void UpdateViewSurface()
>        {
>                //whenever we want
>                //draw onto our surface in memory
>                //white background with a blue circle which has a red border
>                using (Context cr = new Context(viewSurface))
>                {
>                        int width, height;
>                        width = Allocation.Width;
>                        height = Allocation.Height;
>
>                        cr.Rectangle(0, 0, width, height);
>                        cr.SetSourceRGB(1, 1, 1);
>                        cr.Fill();
>
>                        cr.LineWidth = 9;
>                        cr.SetSourceRGB(1, 0, 0);
>
>                        cr.Translate(width/2, height/2);
>                        cr.Arc(0, 0, (width < height ? width : height) / 2 - 10, 0, 2*Math.PI);
>                        cr.StrokePreserve();
>
>                        cr.SetSourceRGB(0, 0, 1);
>                        cr.Fill();
>                }
>        }
>
> --
> View this message in context: http://mono.1490590.n4.nabble.com/DrawingArea-flickering-how-to-stop-erasing-background-tp4649911.html
> Sent from the Mono - Gtk# mailing list archive at Nabble.com.
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