Writing Sellable Software - Part 1

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4 - Onward to Implementation

With the game details firmly in mind, we're ready to go to implementation. Basically, we need to monitor only three messages:

MSG_KEY, to see if we need to display the menu (the K_MENU key code).
MSG_MENU_SELECT, to determine what menu item was selected.
MSG_PEN_DOWN, to handle X or O placement, and check game status.

From these messages, we can create the all-important message loop:

  S32 paTicTacToe::MsgHandler( MSG_TYPE type, 
                               CViewable *from, 
                               S32 data )
  {
    switch (type)
    {
      case MSG_KEY:
        if (data == K_MENU)
          m_menu->Show();
        return 1; // ignore all other keys!
      case MSG_MENU_SELECT:
        HandleMenu(from,data);
        return 1;
      case MSG_PEN_DOWN:
        HandlePen(from,data);
        return 1;
      default:
        break;
    }
    return CWindow::MsgHandler(type, from, data);
  }

Three items of note: we include a default case handler to handle all other messages (via falling through to CWindow::MsgHandler). As well, we indicate that a message has been processed by returning 1. This is especially important to note in the case of MSG_KEY - since we return 1, all other keys except for menuing are ignored, including the keyboard and cursor keys. If your program needs more key control, remember to add more tests here.

Finally, notice how small the code is - unlike most of this site's tutorials, the messages are processed in other functions. For anything but tutorial code, this is what I recommend. Filling up the message loop with handling code can make debugging and analyzing difficult, while placing the code in subroutines makes everything easier to work with. In this case, we have a function to handle the menu items, and one to handle the pen message (the MSG_KEY processing is too trivial to move).

Setting Up

Remember when beginning any programming project:

Create a new project directory.
Copy in the basic files: initial.mom, libraries.link, makefile, os1.def, os.def, os.link, <program>.atts,
Rename the atts file to your program name, and edit the _PUB, _NAME, and _ITXT entries.
Edit the makefile to your project name and add the code source you're including in the APPNAME and SRCS_CPP entries.
Create an icon by renaming and modifying the default bmp.
Include a default Forms Editor file to make initial design easier.

Consider keeping this skeleton code package handy to make new projects easier to set up.

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