Re: [GtkGLExt] off-screen rendering

["Christophe Dehais" <christophe dehais gmail com>]

Hi Jean,

You can use a GdkPixmap as the "support" for offline rendering (thus
no window at all need to be opened).
With the combo Nvidia card/proprietary drivers, direct rendering
contexts (ie accelerated) are available for GdkPixmap. I don't know
how well this works with other cards and drivers.

I use the following function that returns a GdkGLDrawable * wrapping a
GdkDrawable of the specified size:

GdkGLDrawable * init_offline_context (int width, int height)
{

    GdkGLConfig *glconfig;
    GdkPixmap *pixmap;
    GdkGLPixmap *glpixmap;
    GdkGLContext *context;
    g_print ("configuring GL viewport\n");

    /* try double-buffered visual */
    glconfig = gdk_gl_config_new_by_mode (GDK_GL_MODE_RGBA |
                                          GDK_GL_MODE_DEPTH |
                                          GDK_GL_MODE_DOUBLE);
    if (glconfig == NULL) {
      g_print ("*** Cannot find the double-buffered visual.\n");
      g_print ("*** Trying single-buffered visual.\n");

      /* try single-buffered visual */
      glconfig = gdk_gl_config_new_by_mode (GDK_GL_MODE_RGBA   |
                                            GDK_GL_MODE_DEPTH);
      if (glconfig == NULL) {
          g_print ("*** No appropriate OpenGL-capable visual found.\n");
          exit (EXIT_FAILURE);
        }
    }

    pixmap = gdk_pixmap_new (NULL, width, height, 24);
    if (pixmap == NULL) {
        g_print ("*** Could not create the GdkPixmap\n");
        exit (EXIT_FAILURE);
    }
    glpixmap = gdk_pixmap_set_gl_capability (pixmap, glconfig, NULL);
    if (glpixmap == NULL) {
        g_print ("*** Could not create the GdkGLPixmap\n");
        exit (EXIT_FAILURE);
    }

    context = gdk_gl_context_new (GDK_GL_DRAWABLE (glpixmap), NULL,
TRUE, GDK_GL_RGBA_TYPE);
    if (context == NULL) {
        g_print ("*** Could not create a direct context for the pixmap\n");
        exit (EXIT_FAILURE);
    }

    if (!gdk_gl_drawable_make_current (GDK_GL_DRAWABLE (glpixmap), context)) {
        g_print ("*** Could not attach the context to the pixmap\n");
        exit (EXIT_FAILURE);
    }

    return GDK_GL_DRAWABLE (glpixmap);
}

Then something like this in my main() does what I need:

    context = gdk_gl_context_get_current();
    if (!gdk_gl_drawable_gl_begin (pixmap, context)) {
        printf ("*** problem beginning OpenGL operations\n");
        return 0;
    }
    printf ("Direct rendering ?: %d\n", gdk_gl_context_is_direct (context));

    do_some_processing_or_drawing_using_opengl ();

    gdk_gl_drawable_gl_end (pixmap);


hope this helps,
Christophe


On Nov 30, 2007 4:40 PM, Jean Bréfort <jean brefort normalesup org> wrote:
> Hi,
>
> Does anybody knows if and how it is possible to do off-screen rendering
> using gtkglext? I tested using a pixbuf as a drawable, but seems it
> crashes during gdk_gl_drawable_gl_begin with some video cards.
>
> Best regards,
> Jean Brefort
>
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