X11 simple paint app

This C program is a simple graphical application using the X11 library, which is a standard for creating graphical user interfaces in Unix-like operating systems. Here's a breakdown of what each part of the code does:

1. Include X11 Library:

   This line includes the X11 library header, which provides functions and definitions for interacting with the X Window System.

2. Define main Function: The main function is the entry point of the program.

3. Variable Declarations:

   • Display *dpy; - A pointer to a Display structure, representing the connection to the X server.
   • Window root, win; - Variables to store the root window and the application's window.
   • GC gc; - A 'Graphics Context' used for drawing.
   • XEvent ev; - A structure to hold X events.
   • int x_prev, y_prev; int x_cur, y_cur; - Variables to track the previous and current mouse coordinates.

4. Initialize X11 Display:

   • dpy = XOpenDisplay(NULL); - Opens a connection to the X server.
   • root = DefaultRootWindow(dpy); - Gets the root window of the screen.

5. Create a Window:

   • win = XCreateSimpleWindow(...); - Creates a simple window with specified dimensions and background color.
   • XSelectInput(...); - Selects which events the program is interested in (exposure, button presses, motion, etc.).
   • XMapWindow(dpy, win); - Makes the window visible on the screen.

6. Create Graphics Context:

   • gc = XCreateGC(dpy, win, 0, NULL); - Creates a graphics context for drawing in the window.

7. Event Loop:

   • The while (1) loop is an infinite loop that continually processes events.
   • XNextEvent(dpy, &ev); - Waits for the next event.
   • The switch statement handles different types of events:
     • Expose event: When part of the window needs to be redrawn. It sets the foreground color and fills the rectangle (the window).
     • ButtonPress event: Triggered when a mouse button is pressed. Records the mouse position.
     • MotionNotify event: Triggered when the mouse moves. If the left mouse button is pressed (Button1Mask), it draws a line from the previous to the current position.

8. Cleanup:

   • XFreeGC(dpy, gc); - Frees the graphics context.
   • XDestroyWindow(dpy, win); - Destroys the window.
   • XCloseDisplay(dpy); - Closes the connection to the X server.

The program effectively creates a window where you can draw with the mouse. When you move the mouse with the button pressed, it draws lines following the mouse movement.

Other versions

Project also includes c++, java and python code.

How to compile?

Compile/build instructions are in the source file.

Have fun!