Run animated GIF with black background using Gtk

gtk-gif.c

#include <gtk/gtk.h>
#include <gdk/gdkscreen.h>
#include <cairo.h>
#include <gdk-pixbuf/gdk-pixbuf.h>

#include <unistd.h>
#include <stdlib.h>

/*
 * This program shows you how to create semi-transparent windows,
 * without any of the historical screenshot hacks. It requires
 * a modern system, with a compositing manager. I use xcompmgr
 * and the nvidia drivers with RenderAccel, and it works well.
 *
 * I'll take you through each step as we go. Minimal GTK+ knowledge is
 * assumed.
 *
 * gcc alphademo.c -o alphademo $( pkg-config --cflags --libs gtk+-2.0 )
 *
 * https://web.archive.org/web/20121027002505/http://plan99.net/~mike/files/alphademo.c
 */

static gboolean expose(GtkWidget *widget, GdkEventExpose *event, gpointer user_data);
static GdkPixbufAnimation *pixbuf_animation;
static GdkPixbufAnimationIter *iter;
static GtkWidget *window;

static gboolean timer(gpointer user_data)
{
    GTimeVal time;
    g_get_current_time(&time);
    gdk_pixbuf_animation_iter_advance(iter, &time);
    g_timeout_add(gdk_pixbuf_animation_iter_get_delay_time(iter), timer, NULL);
    gtk_widget_queue_draw(window);
    return FALSE;
}

int main(int argc, char **argv)
{
    /* boilerplate initialization code */
    gtk_init(&argc, &argv);

    const char *imgpath = "/tmp/giphy.gif";
    if (imgpath == NULL) {
        fprintf(stderr, "usage: see image.png\n");
        exit(1);
    }
    pixbuf_animation = gdk_pixbuf_animation_new_from_file (imgpath, NULL);

    GTimeVal time;
    g_get_current_time(&time);

    iter = gdk_pixbuf_animation_get_iter (pixbuf_animation, &time);
    timer(NULL);


    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title(GTK_WINDOW(window), "Alpha Demo");
    g_signal_connect(G_OBJECT(window), "delete-event", gtk_main_quit, NULL);


    /* Tell GTK+ that we want to draw the windows background ourself.
     * If we don't do this then GTK+ will clear the window to the
     * opaque theme default color, which isn't what we want.
     */
    gtk_widget_set_app_paintable(window, TRUE);

    /* We need to handle two events ourself: "expose-event" and "screen-changed".
     *
     * The X server sends us an expose event when the window becomes
     * visible on screen. It means we need to draw the contents.  On a
     * composited desktop expose is normally only sent when the window
     * is put on the screen. On a non-composited desktop it can be
     * sent whenever the window is uncovered by another.
     *
     * The screen-changed event means the display to which we are
     * drawing changed. GTK+ supports migration of running
     * applications between X servers, which might not support the
     * same features, so we need to check each time.
     */

    g_signal_connect(G_OBJECT(window), "expose-event", G_CALLBACK(expose), NULL);

    /* Run the program */
    gtk_widget_show_all(window);
    gtk_main();

    return 0;
}


/* This is called when we need to draw the windows contents */
static gboolean expose(GtkWidget *widget, GdkEventExpose *event, gpointer userdata)
{
    cairo_t *cr = gdk_cairo_create(widget->window);


    /* draw the background */
    cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
    //cairo_paint (cr);

    /* draw a circle */
    int width, height;
    gtk_window_get_size(GTK_WINDOW(widget), &width, &height);

    int imgw, imgh;

    GdkPixbuf *pixbuf;
    /* load image and get dimantions */
    //format = (gdk_pixbuf_get_has_alpha (pixbuf)) ? CAIRO_FORMAT_ARGB32 : CAIRO_FORMAT_RGB24;
    imgw = gdk_pixbuf_animation_get_width (pixbuf_animation);
    imgh = gdk_pixbuf_animation_get_height (pixbuf_animation);

    gtk_window_resize(GTK_WINDOW(widget), imgw, imgh);

            pixbuf = gdk_pixbuf_animation_iter_get_pixbuf(iter);
            //g_timeout_add(1000, pixbuf, NULL);
            gdk_cairo_set_source_pixbuf (cr, pixbuf, 0, 0);
            cairo_paint (cr);


    //gdk_cairo_set_source_pixbuf (cr, pixbuf, 0, 0);

    //cairo_paint (cr);

    cairo_destroy(cr);
    return FALSE;
}