GTK window motion animation?

Question

I want to move my GTK_WINDOW across the screen automatically. Currently I have it in a draw/move loop, but that's terribly choppy. I'm very new to GTK programming (and gui programming in general). What am I missing?

Answer 1

You haven't said what sort of path you want the window to follow. If the path is some simple function of time -- that is, if you have a way to compute where you want the window to be at any given time -- you could try the method illustrated in following code. For the quite-simple menu in the example, it works ok on my Linux system and produces fairly smooth motion.

The key to the method is that instead of moving the window a given distance per timer event, it finds out the current time and moves the window to the location it should be at, at that time. Thus, the time derivative of speed of motion should be constant, which avoids ragged or choppy motion even if timer events occur irregularly. (As noted in g-timeout-add() description, irregularity can easily occur.)

In this example, the path is from top left of window to bottom left and back, repeatedly. The constant 'HalfTime' in timerEvent() controls how long it takes to move from corner to corner. The constant 3 in the g_timeout_add() call sets the timer interval to 0.003 seconds, or about 333 moves per second (MPS). (You may want to try more-reasonable rates, such as 20, 30, 40, etc MPS; I used the number 3 because I didn't look up g-timeout-add() before using it, and assumed the delay was hundreths of seconds, for about 33 MPS, rather than milliseconds, for about 333 MPS.) If your window contents are quite complex, fewer MPS will be practical. Also, I tried some slower rates and got more of an impression of choppiness.

/* $Id: app12.c $
 Re: animating position of a top-level Gtk window
 jiw July 2011 -- Offered without warranty under GPL v3
 terms per http://www.gnu.org/licenses/gpl.html  */
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <gtk/gtk.h>
typedef struct DATA { GTimer *timer; GtkWidget *window; int w, h; }
  DataStruct;

gboolean timerEvent(void *dataset) {
  enum { HalfTime=8, CycTime=2*HalfTime };
  gulong micros;
  DataStruct *data =dataset;
  double t = fabs(fmod (g_timer_elapsed (data->timer, &micros), CycTime));
  int x = (t*data->w)/HalfTime, y = (t*data->h)/HalfTime;
  gtk_window_move (GTK_WINDOW(data->window),
       t<HalfTime? x : 2*data->w-x, t<HalfTime? y : 2*data->h-y);
  return TRUE; /* Keep timeout running */
}

int main(int argc, char **argv) {
  GtkWidget *vbox, *b;
  GdkScreen *gds;
  DataStruct data;
  data.timer = g_timer_new();
  gtk_init (&argc, &argv);
  data.window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_window_set_default_size (GTK_WINDOW(data.window), 200, 150);
  g_signal_connect (G_OBJECT(data.window), "destroy",
            G_CALLBACK(gtk_main_quit), NULL);
  vbox = gtk_vbox_new (FALSE, 0);
  gtk_container_add (GTK_CONTAINER(data.window), vbox);
  b = gtk_button_new_with_label ("Click to Exit");
  gtk_box_pack_start (GTK_BOX(vbox), b, TRUE, TRUE, TRUE);
  g_signal_connect (b, "clicked", G_CALLBACK(gtk_main_quit), NULL);
  gtk_widget_show_all (data.window);

  gds = gdk_screen_get_default ();  /* Get pointer to screen  */
  data.w = gdk_screen_get_width (gds);  /* Find out screen width  */
  data.h = gdk_screen_get_height (gds); /* Find out screen height */
  printf ("Screen size = %d by %d\n", data.w, data.h); fflush(stdout);
  g_timeout_add(3, timerEvent, &data);  /* Create .003 sec timer   */
  gtk_main();
  return (0);
}