CMPS-3600 - Fall 2025 - Semester Project


Phase-4 - Show passes and collisions in a child window
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Start with your bblab9.c program.

Name your program: 3600/f/bbphase4.c

You may move all project phases to Odin directory 3600/f

    $ cd 3600/f
	$ cp ../4/myxwindow.c .
	$ cp ../6/bbphase2.c .
	$ cp ../9/bbphase3.c .
	$ cp ../9/bblab9.c bbphase4.c

Compile like this...

   gcc bbphase4.c -Wall -lX11 -lXext -pthread




What to do...

1. Press 'W' to get a child window.
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   The child will show the statistics for each car.
   Show the passes for each car.
   Show the total number of collisions.


2. In the parent window, add a feature to pause the action.
-----------------------------------------------------------
   Now we can easily see the statistics.


3. If the parent window is moved, the child follows.
----------------------------------------------------
   See the animation.


4. Inter process communication.
-------------------------------

   Use a System-V message queue to send the child the data.
   You may also use a pipe.

   recommended:
   Use a message queue to send car data.
   Use a pipe to send the parent window position when it moves.

   When a car passes through the intersection, send a message to the
   child updating that one car.


Tips:

   Your child process should be the bbphase4.c executable, but without...
      - the cars
	  - the intersection graphics
	  - the car thread

   You cannot run the car thread inside your child process.

   Pass these things to the child on the command-line...
      - message-queue ID
      - pipe file descriptors

   Allow multiple child windows.

   See the code below for child window movement.


Please allow for multiple child windows.






Code samples
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Update your main() function event loop
--------------------------------------

    // Add this to your event loop.
    check_resize(&e);


Add this function
-----------------

void check_resize(XEvent *e)
{
    //ConfigureNotify is sent when the window is resized or moved.
    if (e->type != ConfigureNotify)
        return;
    XConfigureEvent xce = e->xconfigure;
    g.xres = xce.width;
    g.yres = xce.height;
    //The following line removed courtesy: student Michael Kausch
    //init();
    if (child) {
        //store the child's position
        g.child_pos[0] = xce.x;
        g.child_pos[1] = xce.y;
    }
    if (!child) {
        // Translate the position coordinates.
        // Translating the window coordinates is documented here:
        //    https://stackoverflow.com/questions/25391791/
        //    x11-configurenotify-always-returning-x-y-0-0
        //
        Window root = DefaultRootWindow(g.dpy);
        Window chld;
        int x, y;
        XTranslateCoordinates(g.dpy, g.win, root, 0, 0, &x, &y, &chld);
        g.parent_pos[0] = x;
        g.parent_pos[1] = y;
        g.parent_dim[0] = xce.width;
        g.parent_dim[1] = xce.height;
        //parent sends its new position to the child.
        if (g.nchildren > 0) {
            // Send a message to the child here


        }
    }
    set_window_title();
    usleep(4000);
}

Use this function in your child window
--------------------------------------

// When the parent window moves, it will send the child a message.
// The child process will call this function. 

void moveWindow(int x, int y)
{
    XMoveWindow(g.dpy, g.win, x, y);
}