Simple Xlib Example Program

Example 3-2 : Simple Xlib Example Program

/*
 * simplest - simple single buffered RGBA xlib program.
 */
/* compile: cc -o simplest simplest.c -lGL -lX11 */

#include <GL/glx.h>
#include <X11/keysym.h>
#include <stdlib.h>
#include <stdio.h>

static int attributeList[] = { GLX_RGBA, None };

static void
draw_scene(void) {
    glClearColor(0.5, 0.5, 0.5, 1.0);
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1.0,0.0,0.0);
    glRectf(-.5,-.5,.5,.5);
    glColor3f(0.0,1.0,0.0);
    glRectf(-.4,-.4,.4,.4);
    glColor3f(0.0,0.0,1.0);
    glRectf(-.3,-.3,.3,.3);
    glFlush();
}

static void
process_input(Display *dpy) {
    XEvent event;
    Bool redraw = 0;

    do {
        char buf[31];
        KeySym keysym;

        XNextEvent(dpy, &event);
        switch(event.type) {
        case Expose:
            redraw = 1;
            break;
        case ConfigureNotify:
            glViewport(0, 0, event.xconfigure.width, 
                    event.xconfigure.height);
            redraw = 1;
            break;
        case KeyPress:
            (void) XLookupString(&event.xkey, buf, sizeof(buf), 
                    &keysym, NULL);
            switch (keysym) {

            case XK_Escape:
                exit(EXIT_SUCCESS);
            default:
                break;
            }
        default:
            break;
        }
    } while (XPending(dpy));
    if (redraw) draw_scene();
}

static void
error(const char *prog, const char *msg) {
    fprintf(stderr, "%s: %s\n", prog, msg);
    exit(EXIT_FAILURE);
}
int
main(int argc, char **argv) {
    Display *dpy;
    XVisualInfo *vi;
    XSetWindowAttributes swa;
    Window win;
    GLXContext cx;

    /* get a connection */
    dpy = XOpenDisplay(0);
    if (!dpy) error(argv[0], "can't open display");

    /* get an appropriate visual */
    vi = glXChooseVisual(dpy, DefaultScreen(dpy), attributeList);
    if (!vi) error(argv[0], "no suitable visual");

    /* create a GLX context */
    cx = glXCreateContext(dpy, vi, 0, GL_TRUE);

    /* create a colormap */
    swa.colormap = XCreateColormap(dpy, RootWindow(dpy, vi->screen),
                                   vi->visual, AllocNone);
    /* create a window */
    swa.border_pixel = 0;
    swa.event_mask = ExposureMask | StructureNotifyMask | KeyPressMask;
    win = XCreateWindow(dpy, RootWindow(dpy, vi->screen), 0, 0, 300, 
                        300, 0, vi->depth, InputOutput, vi->visual,
                        CWBorderPixel|CWColormap|CWEventMask, &swa);
    XStoreName(dpy, win, "simplest");
    XMapWindow(dpy, win);

    /* connect the context to the window */
    glXMakeCurrent(dpy, win, cx);

    while (1) process_input(dpy);
}