gistfile1.c

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <unistd.h>
#include <cairo-xlib.h>

#ifndef M_PI
#define M_PI 3.1415926535
#endif

const int gWidth = 500;
const int gHeight = 500;

int main(int argc, char *argv[]) {
    cairo_surface_t* cs;
    cairo_t *cr;

    Display *xDpy;
    Window window;

    double angle;
    struct timeval start, now;

    xDpy = XOpenDisplay(NULL);
    window = XCreateSimpleWindow(xDpy, XDefaultRootWindow(xDpy), 0, 0, gWidth, gHeight, 0, 0, 0);
    XMapWindow(xDpy, window);

    cs = cairo_xlib_surface_create(xDpy, window, DefaultVisual(xDpy, 0), gWidth, gHeight);

    gettimeofday(&start, NULL);

    for(;;) {
        cr = cairo_create(cs);

        gettimeofday(&now, NULL);
        angle = (now.tv_sec - start.tv_usec + (now.tv_usec-start.tv_usec)*1e-6) * M_PI/2;

        cairo_set_source_rgba(cr, 1., 1., 1., 1.);
        cairo_paint(cr);

        cairo_set_source_rgba(cr, 0., 0., 0., 1.);
        cairo_set_line_width (cr, 10.);
        cairo_arc (cr, gWidth/2., gHeight/2., 100., angle, angle + M_PI/4);
        cairo_stroke (cr);

        cairo_destroy(cr);
    }

    return 0;
}