Animating GTK+ Windows - c

Question

I am trying to create a smoothly animated window in GTK+
Here is the code I came up with:
#include <gtk/gtk.h>
typedef struct {
GtkWindow *window;
int timePassed;
int fromX;
int fromY;
int toX;
int toY;
int time;
int step;
void (*callback)(void*);
void *data;
} AnimationStructure;
double coolBezier(double t) {
double register one_minus_t_powered;
double register one_minus_t_;
one_minus_t_ = 1 - t;
one_minus_t_powered = one_minus_t_ * one_minus_t_;
return one_minus_t_powered * 0.0 + one_minus_t_ * 2.0 * t * -1.00 + t * t * 1.0;
}
gboolean animate_window_timeout(AnimationStructure *ani) {
double time = coolBezier((double) ani->timePassed / ani->time);
if (time >= 1.0) {
gtk_window_move(ani->window, ani->fromX + ani->toX, ani->fromY + ani->toY);
ani->callback(ani->data);
g_free(ani);
return FALSE;
}
printf("FromX: %d; FromY: %d\n", ani->fromX, ani->fromY);
gtk_window_move(ani->window, ani->fromX + (ani->toX * time), ani->fromY + (ani->toY * time));
ani->timePassed += ani->step;
return TRUE;
}
void animate_window(GtkWindow *window, int x, int y, int time, int step_time, void (*callback)(void*), void* data) {
AnimationStructure *ani = g_new(AnimationStructure, 1);
ani->window = window;
ani->toX = x;
ani->toY = y;
ani->timePassed = 0;
ani->time = time;
ani->step = step_time;
ani->callback = callback;
ani->data = data;
gtk_window_get_position(window, &(ani->fromX), &(ani->fromY));
g_timeout_add(step_time, (GSourceFunc) animate_window_timeout, ani);
}
int main (int argc, char *argv[]) {
GtkWindow *window;
gtk_init(&argc, &argv);
window = (GtkWindow*) gtk_window_new(GTK_WINDOW_TOPLEVEL);
gtk_window_set_position(window, GTK_WIN_POS_CENTER);
gtk_window_set_default_size(window, 300, 300);
g_signal_connect_swapped(window, "destroy", gtk_main_quit, NULL);
animate_window(window, 300, 0, 1000, 15, NULL, NULL);
gtk_widget_show_all(GTK_WIDGET(window));
gtk_main();
return 0;
}
This works and when I applied it to the notification window the effect was like on this gif:
But the window is not smooth as I would like it to be, you can notice that at the end the window almost jumps 50px from left to right.