Cairo animation example with timing

/**
 * A simple animation using cairo and GTK+
 *
 * This program shows high /usr/libexec/Xorg load while running full screen on Linux
 *
 * Compile with:
 *   gcc `pkg-config --cflags --libs gtk+-3.0` -lm main.c
 */

#include <gtk/gtk.h>
#include <math.h>
#include <time.h>

#define NUM_WINDOWS (1u)
#define NUM_POINTS (1000u)
#define PERIOD (100u)

/* Local function prototypes */
static gboolean invalidate_cb(void *);
static gboolean drawing_area_draw_cb(GtkWidget *, cairo_t *, void *);

int main(int argc, char **argv)
{
    int i;
    gtk_init(&argc, &argv);

    for (i = 0; i < NUM_WINDOWS; i++)
    {
        GtkWidget *main_window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
        gtk_window_set_title(GTK_WINDOW(main_window), "Drawing example");
        gtk_window_set_default_size(GTK_WINDOW(main_window), 400, 400);
        GtkWidget *drawing_area = gtk_drawing_area_new();

        gtk_container_add(GTK_CONTAINER(main_window), drawing_area);
        gtk_widget_show_all(main_window);

        /* Create a  timer to invalidate our window at 60Hz */
        g_timeout_add(1000 / 60, invalidate_cb, drawing_area);

        /* Connect our redraw callback */
        g_signal_connect(drawing_area, "draw", G_CALLBACK(drawing_area_draw_cb), NULL);

        /* Connect the destroy signal */
        g_signal_connect(main_window, "destroy", G_CALLBACK(gtk_main_quit), NULL);
    }
    gtk_main();
}

static gboolean invalidate_cb(void *ptr)
{
    if (GTK_IS_WIDGET(ptr))
    {
        gtk_widget_queue_draw(GTK_WIDGET(ptr));
        return TRUE;
    }
    return FALSE;
}

static inline float sine_to_point(int x, int width, int height)
{

    return (height / 2.0) * sin(x * 2 * M_PI / (PERIOD)) + height / 2.0;
}

static gboolean drawing_area_draw_cb(GtkWidget *widget, cairo_t *context, void *ptr)
{
    static int redraw_number = 0;
    static double average_time = 0;
    clock_t start = clock();
    int width, height, i;

    width = gtk_widget_get_allocated_width(widget);
    height = gtk_widget_get_allocated_height(widget);

    /* Draw the background */
    cairo_set_source_rgb(context, 1, 1, 1);
    cairo_rectangle(context, 0, 0, width, height);
    cairo_fill(context);

    /* Draw a moving sine wave */
    cairo_set_source_rgb(context, 0.5, 0.5, 0);
    cairo_move_to(context, 0, sine_to_point(0 + redraw_number, width, height));
    for (i = 1; i < NUM_POINTS; i++)
    {
        cairo_line_to(context,  i, sine_to_point(i + redraw_number, width, height));
    }
    cairo_stroke(context);


    redraw_number++;

    clock_t end = clock();
    average_time += (double) (end - start) / CLOCKS_PER_SEC;
    if (redraw_number % 60 == 0)
    {
        printf("Average time: %fms, Max FPS: %d\n", 1000.0 * average_time / 60, (int) (1.0 / (average_time / 60)));
        average_time = 0;
    }
}