Xlib demo - X11 X Windows System

CMakeLists.txt

cmake_minimum_required(VERSION 3.9)
project(Simple_Cmake_Project)

#========== Global Configurations =============#
#----------------------------------------------#

set(CMAKE_CXX_STANDARD 17)     
set(CMAKE_VERBOSE_MAKEFILE ON)

find_package(X11 REQUIRED)

#========== Targets Configurations ============#

       add_executable( xlib-demo xlib-demo.cpp )
target_link_libraries( xlib-demo ${X11_LIBRARIES} )

# add_executable(app2 application2.cpp)

xlib-demo.cpp

#include <iostream>
#include <string> 
#include <cstring>
#include <cassert> 

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

void abort_on_failure(bool predicate, const char* message = "Abort runtime.")
{
	if(predicate) return;
	std::fprintf(stderr, " [ABORT] %s", message);
	abort();
}

int main(int argc, char** argv)
{
	/** If the value passed to XOpenDisplay is null, the XClient (Xlib) attempts 
	 * to connect to the display server designated by the environment variable  
	 * $DISPLAY, which is often set to the :1.0 or the local machine. 
	 *------------------------------------------------------------------------*/
	Display* dpy = XOpenDisplay(nullptr);
	abort_on_failure(dpy != nullptr, "Cannot open display.");

	/** ----- Query Information about display server ------------------------*/

	int version = XProtocolVersion(dpy);
	std::cout << " [INFO] X11 protocol version = " << version << '\n';

	const char* vendor = XServerVendor(dpy);
	std::cout << " [INFO] X11 XServer vendor = " << vendor << '\n';

	const char* disp_str = XDisplayString(dpy);
	std::cout << " [INFO] X11 Display string = " << disp_str << '\n';

	int n_screen = XScreenCount(dpy);
	std::cout << " [INFO] Number of screens = " << n_screen << '\n';

	/** ----- Draw Screen ------------------------------------------------*/

	int screen = DefaultScreen(dpy);

	Window wnd = XCreateSimpleWindow(
					  dpy                         // Display 
					, RootWindow(dpy, screen)     // Parent Window 
					, 10, 20                      // Position (x - horizontal, y - vertical) from top-left corner 
					, 400, 500                    // Dimensions (width, height)
					, 1                           // Border width 
					, BlackPixel(dpy, screen)     // Border 
					, WhitePixel(dpy, screen)     // Background color 
					);

	/* Casting void means that the return value (type int) is being ignored. */
	(void) XStoreName(dpy, wnd, "X Windows-System X11");
	// Makes window visible 
	XMapWindow(dpy, wnd);
	XFlush(dpy);

	XEvent event;

	// Select events that the application is interested in. 
	// Only those events will notify the application. (XClient)
	auto mask  =   ExposureMask        
				 | ButtonPressMask     // Event: mouse button press
				 | KeyPressMask        // Event: key press (keyboard)
				 | KeyReleaseMask      // Event: key release (keyboard)
				 //| PointerMotionMask   // Event: Mouse Move
				 ;
	XSelectInput(dpy, wnd, mask);

	// Process window close event in X11 event loop for(;;)
	Atom wnd_del = XInternAtom(dpy, "WM_DELETE_WINDOW", 0);
	XSetWMProtocols(dpy, wnd, &wnd_del, 1);

	const char* message = "Draw some string on X11 - X windows system.";

	/* ------- X11 (X Windows System) - Event loop ------------ */

	for(;;)
	{
		std::fprintf(stderr, "\n [TRACE] Waiting event. \n");;

		// Get next X11 event 		
		XNextEvent(dpy, &event);

		if(event.type == ClientMessage){
			fprintf(stderr, " [Event] User closed window. => Shutdown \n");
			break;
		}

		if(event.type == Expose)    
			fprintf(stderr,  " [Event] Expose event. \n");

		if(event.type == KeyPress)    
			fprintf(stderr,  " [Event] Key pressed. \n");
		
		if(event.type == ButtonPress) 
			fprintf(stderr,  " [Event] Mouse button pressed. \n");

		if(event.type == PointerMotionMask) 
			fprintf(stderr,  " [Event] Mouse button pressed. \n");		

		// X11 Graphics context, useful for drawing 
		GC gctx = DefaultGC(dpy, screen);
		
		XFillRectangle( dpy, wnd, gctx
		               , 20, 50    // (x, y) position from top-left corner origin 
					   , 100, 200  // width and height 
					   );

		GC gctx2 = DefaultGC(dpy, screen);					   

		XDrawString(  dpy     // Pointer to display object 
					, wnd     // Pointer to window 
					, gctx    // Graphics context 
					, 90, 300 // (x, y) Position where string will be drawn (from top-left corner)
                  	, message
				  	, strlen(message) ); 
		
	} // ----- End of event loop -------- // 

	fprintf(stderr, " [TRACE] User closed window. Shutdown application. Ok \n");

	XDestroyWindow(dpy, wnd);

	// Always close display 
	XCloseDisplay(dpy);

	return 0;
}