Problem in saving the pixbuf to image when window is resized

suhasthejaswi · **Joined:** Sat Jun 11, 2011 4:30 am **Posts:** 7

Hi,
We are trying to save the pixbuf to an image.
We are facing an issue when we try to save the pixbuf after resizing the window.
Here is the code snippet.
I have also attached the screen shots of the window and the images that gets saved.

Code:

    _theCanvas= getWidget(GRAPH_CANVAS);// get the GtkDrawingArea from glade XML
    gtk_widget_set_app_paintable( _theCanvas, TRUE);
    gtk_widget_set_double_buffered( _theCanvas, FALSE);

    int canvasWidth= 0;
    int canvasHeight= 0;
    GError *error=NULL;

    gdk_drawable_get_size( gtk_widget_get_window( _theCanvas), &canvasWidth, &canvasHeight);
    std::cout<<"Height: "<<canvasHeight<<"Width: "<<canvasHeight<<std::endl;

    GdkPixbuf *pixbuf= gdk_pixbuf_get_from_drawable( NULL,
                                _theCanvas->window,
                                NULL,
                                0, 0, 0, 0,
                                canvasWidth,
                                canvasHeight);
    GdkPixbuf *rotatedPixbuf= gdk_pixbuf_rotate_simple( pixbuf, GDK_PIXBUF_ROTATE_COUNTERCLOCKWISE);
    gdk_pixbuf_save( rotatedPixbuf, "/suhas/png/temp.png", "png", &error, NULL, "100", NULL);

Normal Window without Resizing

Attachment:

File comment: This is a Gtk Window without resizing, I am able to successfully save the image.

normal_window.JPG [ 52.53 KiB | Viewed 165 times ]

This is how the image is saved.This is how we want even when the window is resized.

Attachment:

File comment: This is how the image gets saved.

normal_image.png [ 14.27 KiB | Viewed 165 times ]

Resized Gtk window and the corresponding saved image screen shot

Attachment:

resized.jpg [ 97.48 KiB | Viewed 165 times ]

Paul Childs · **Posted:** Fri Nov 04, 2011 3:10 am

Your trouble is you are only saving the window rather than the underlying image. Because you are using scrolled windows these are different sizes. If you check the documentation for gdk_pixmap_get_from_drawable http://developer.gnome.org/gdk/stable/gdk-Pixbufs.html#gdk-pixbuf-get-from-drawable you'll see that it is undefined in regions that are offscreen or obscured.

There are two approaches to solve your problem
1. Don't use scrollbars.
2. Save your image based on the data that generates the image on the screen rather than transferring the image on the screen to file.

Of course the second approach is better. If you draw from the screen you will always be limited in the size/resolution that the screen provides, but why should you have to be? You have a data set that creates a graph that is rendered to the screen at a specific size/resolution. Why not bypass the screen and render directly to file? GTK now uses cairo for rendering 2D graphics http://cairographics.org/ so you can almost forget about GDK. It's worth your while to learn it. With it you can directly render to SVG, PNG, etc images and specify a resolution/size.
To get a few ideas you could have a look at a plotting program I've been putting together https://github.com/pchilds/GtkPlot. It's fairly big but runs fast so it will run smoothly when churning through large data sets. If you compile it there's an example program that'll show you it working. (by the way I am interested in developing it for a wide range of scientific data presentation so if you are interested let me know any feedback on what features you need -- I notice that you've got a doubled y scale, I'll be working on incorporating that into the program in time)

Incidently don't use gdk_drawable_get_size. It's depreciated (http://developer.gnome.org/gdk/stable/gdk-Drawing-Primitives.html#gdk-drawable-get-size) so you'll run into trouble later on trying to maintain your code.

suhasthejaswi · **Joined:** Sat Jun 11, 2011 4:30 am **Posts:** 7

Thanks a lot for you help.

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Problem in saving the pixbuf to image when window is resized

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