Most Basic X11 Program: hello_x11.c

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/*
*                               Basic X program:
*
*       This is a very simple X program.  It shows the basics needed to get the
*       simplest X program working.   Compile as:
*               cc hello_x11.c -lX11 -o hello_x11
*
*       When run, pops up a window with Hello World written in it.
*       When the mouse is clicked, the word Hi! appears at the spot.
*       If the window is covered, then uncovered ("exposed"), the
*       Hello World is redrawn - but not the various Hi! items.
*       If a key is pressed nothing happens except if it is q in which
*       case the program quits.
*
*/


#include <X11/Xlib.h>
#include <X11/Xutil.h>


main(argc,argv)
int argc; char **argv;
{
    Display *mydisplay;
    Window mywindow;
    GC mygc;
    XEvent myevent;
    KeySym mykey;
    XSizeHints myhint;
    int myscreen;
    unsigned long myforeground, mybackground;
    int i;
    char text[10];
    int done;
    char *hello = "Hello World", *hi = "Hi!";

    mydisplay = XOpenDisplay("");
    myscreen = DefaultScreen(mydisplay);
    mybackground = WhitePixel(mydisplay,myscreen);
    myforeground = BlackPixel(mydisplay,myscreen);

        /* Suggest where to position the window: */
    myhint.x = 200;
    myhint.y = 200;
    myhint.width = 300;
    myhint.height = 300;
    myhint.flags = PPosition | PSize;

        /* Create a window - not displayed yet however: */
    mywindow = XCreateSimpleWindow(mydisplay,DefaultRootWindow(mydisplay),

    myhint.x,myhint.y,myhint.width,myhint.height,5,myforeground,mybackground);


XSetStandardProperties(mydisplay,mywindow,hello,hello,None,argv,argc,&myhint
);

        /* Create a Graphics Context (GC) for the window: */
    mygc = XCreateGC(mydisplay,mywindow,0,0);
    XSetBackground(mydisplay,mygc,mybackground);
    XSetForeground(mydisplay,mygc,myforeground);
        /* Select input devices to listen to: */
    XSelectInput(mydisplay,mywindow,ButtonPressMask|KeyPressMask|ExposureMask);
        /* Actually display the window: */
    XMapRaised(mydisplay,mywindow);

        /* Main Event Loop: This is the core of any X program: */
    done = 0;
    while (done==0) {
        XNextEvent(mydisplay,&myevent);
        switch(myevent.type) {
        case Expose: /* Repaint window on expose */
            if (myevent.xexpose.count==0)
                XDrawImageString(myevent.xexpose.display,myevent.xexpose.window,
                        mygc,50,50,hello,strlen(hello));
            break;
        case MappingNotify: /* Process keyboard mapping changes: */
            XRefreshKeyboardMapping(&myevent);
            break;
        case ButtonPress: /* Process mouse click - output Hi! at mouse: */

	    XDrawImageString(myevent.xbutton.display,myevent.xbutton.window,
		mygc,myevent.xbutton.x,myevent.xbutton.y,hi,strlen(hi));
            break;
        case KeyPress: /* Process key press - quit on q: */
            i = XLookupString(&myevent,text,10,&mykey,0);
            if (i==1 && text[0]=='q') done = 1;
            break;
        }
    }

    XFreeGC(mydisplay,mygc);
    XDestroyWindow(mydisplay,mywindow);
    XCloseDisplay(mydisplay);
    exit(0);
}
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