/** animation.c **/
#include <gnome.h>
#include <math.h>

static struct ballStruct {
    double x;
    double y;
    double xVelocity;
    double yVelocity;
} ball[5];

gint eventDelete(GtkWidget *widget,
        GdkEvent *event,gpointer data);
gint eventDestroy(GtkWidget *widget,
        GdkEvent *event,gpointer data);
gint nextFrame(gpointer data);
void newBall(struct ballStruct *b);
void nextBall(struct ballStruct *b);
gint nextFrame(gpointer data);

#define WIDTH 400
#define HEIGHT 300
#define GRAVITY 0.8
#define RADIUS 5
#define DIAMETER (RADIUS * 2)
#define INTERVAL 30

int main(int argc,char *argv[])
{
    int i;
    GtkWidget *app;
    GtkWidget *area;

    gnome_init("animation","1.0",argc,argv);
    app = gnome_app_new("animation",
                    "Drawing Area Animation");
    gtk_container_set_border_width(GTK_CONTAINER(app),20);
    gtk_signal_connect(GTK_OBJECT(app),"delete_event",
            GTK_SIGNAL_FUNC(eventDelete),NULL);
    gtk_signal_connect(GTK_OBJECT(app),"destroy",
            GTK_SIGNAL_FUNC(eventDestroy),NULL);

    area = gtk_drawing_area_new();
    gtk_widget_set_usize(area,WIDTH,HEIGHT);
    gnome_app_set_contents(GNOME_APP(app),area);

    gtk_timeout_add(INTERVAL,nextFrame,area);
    for(i=0; i<5; i++)
        newBall(&ball[i]);

    gtk_widget_show_all(app);
    gtk_main();
    exit(0);
}
gint nextFrame(gpointer data)
{
    int i;
    static GdkPixmap *pixmap = NULL;
    GtkWidget *widget = (GtkWidget *)data;

    if(pixmap == NULL) {
        pixmap = gdk_pixmap_new(widget->window,
                    WIDTH,HEIGHT,-1);
    }

    gdk_draw_rectangle(pixmap,
            widget->style->white_gc,
            TRUE,
            0,0,
            WIDTH,HEIGHT);

    for(i=0; i<5; i++) {
        nextBall(&ball[i]);
        gdk_draw_arc(pixmap,
                widget->style->black_gc,
                TRUE,
                (int)ball[i].x,(int)ball[i].y,
                DIAMETER,DIAMETER,
                0,360*64);
    }

    gdk_draw_pixmap(widget->window,
            widget->style->black_gc,
            pixmap,
            0,0,
            0,0,
            WIDTH,HEIGHT);

    return(TRUE);
}
void newBall(struct ballStruct *b)
{
    b->x = (((double)rand()*WIDTH)/RAND_MAX);
    b->y = (((double)rand()*HEIGHT)/RAND_MAX) - HEIGHT;
    do {
        b->xVelocity = (((double)rand()*10)/RAND_MAX) - 5;
        b->yVelocity = (((double)rand()*10)/RAND_MAX) - 5;
    } while(fabs(b->xVelocity) < 0.5);
}
void nextBall(struct ballStruct *b)
{
    if((b->x < -DIAMETER) || (b->x > WIDTH)) {
        newBall(b);
        return;
    }
    if((b->y + DIAMETER) >= HEIGHT) {
        if(b->yVelocity > 0)
            b->yVelocity = -b->yVelocity;
        b->yVelocity *= 0.9;
    } else {
        b->yVelocity += GRAVITY;
    }
    b->x += b->xVelocity;
    b->y += b->yVelocity;
}
gint eventDelete(GtkWidget *widget,
        GdkEvent *event,gpointer data) {
    return(FALSE);
}
gint eventDestroy(GtkWidget *widget,
        GdkEvent *event,gpointer data) {
    gtk_main_quit();
    return(0);
}