Re: picture slide show flicker and previous image flush problem

[Jerry Wang <jerry wang beonic com>]

I'm wondering if the cario is the right solution.

Because there are window transparency based on image transparency. I
played a looped movie indefinitely in the X root window. And I need to
paint a picture on it, like logo. 

I still need to mask the image window background, right?

Jerry

On Wed, 2011-05-11 at 18:22 +1000, Maarten Bosmans wrote:
> 2011/5/11 Jerry Wang <jerry wang beonic com>:
> > Hi guys,
> >
> > I wrote some code with GTK lib to show the image consequently and here
> > is my situation.
> >
> >        use pixbuf to get data from files:
> >        -pixbuf=gdk_pixbuf_new_from_file(filename, NULL);
> >
> >        use pixmap to get the mask (for transparent consideration):
> >        -mask=gdk_pixmap_new(NULL, width, height, 1);
> >        -gdk_pixbuf_render_threshold_alpha(pixbuf, mask, 0, 0,
> >        0, 0, width, height, 1)
> >
> >        then combine the mask with shown window:
> >        gdk_window_shape_combine_mask(window->window, mask, 0, 0);
> >
> >        and crate the image from pixbuf:
> >        -image=gtk_image_new_from_pixbuf(pixbuf);
> >
> >        then add to window:
> >        gtk_container_add((GtkContainer*)window, image);
> >
> >
> >        before every image loading, remove the old one
> >        gtk_container_remove((GtkContainer*)window, image);
> >
> > My images are around 2M high definition PNG files. And my running
> > machine is a ATOM N270 1.6G. Every image will take about 0.3s to load.
> >
> > My problem is, there are one totally transparent image in my image
> > files. After showing the total transparent image, before pop out the
> > next image, it will show the previous image (before the transparent
> > image) for a very short of time, just like flushing the buffer.
> 
> I'm not sure it is the cause of the problem, but using adding a new
> widget to the hierarchy for every image seems like a wrong approach. A
> better way would be to use Cairo to draw the pixbufs directly in the
> draw event of a widget, for example a GtkDrawingArea.
> 
> This would require some rewriting of the code, but you gain a lot of
> flexibility, like e.g. the possibility for crossfading. Make sure you
> don't actually load the pixbuf in the draw(expose) event, but only do
> the gdk_cairo_set_source_pixbuf(), cairo_paint() there.
> 
> > I was considering the root cause is double buffering. But if I disable
> > the double buffering feature, the slide show will not be smooth, it
> > looks flick.
> >
> > Also I try to disable the X's double buffer extension, but still see
> > previous image.
> >
> > Need advice.
> >
> > Thanks,
> > Jerry
> 
> Maarten