Description: The PLIB minimal Windowing Library (PW) is a portable interface that makes it as simple as possible to make an OpenGL application that can open a single window and read the mouse and keyboard. It is a wrapper to make the various underlying OS mechanisms look the same to application code.
Keywords: PW, PLIB, OpenGL, window, library, portable, interface, games, Baker, Steve, pwInit

# A PLIB Windowing Library.
by Steve Baker

## Introduction

PW is now just one component of PLIB.

The PLIB minimal Windowing Library (PW) is a portable interface that makes it as simple as possible to make an OpenGL application that can open a single window and read the mouse and keyboard. It is a wrapper to make the various underlying OS mechanisms look the same to application code.

You should include the PW header file '/usr/include/plib/pw.h' and link to the PW library '/usr/lib/libplibpw.a'.

Before using any other PW functions, you should initialise the library by calling either:

    void pwInit ( int multisample, int num_samples ) ;

...or:

    void pwInit ( int x, int y, int w, int h,
                  int multisample,
                  char *title, int border, int num_samples ) ;

The first version creates a full-screen window with no borders, titles, etc (or at least as close to that as your OS can manage). The second version creates a window with it's origin at (x,y) of dimensions w x h, with the specified title string, and optionally with or without a border.

The window that's created will have the maximum number of colours that your system supports - double-buffered plus a Z buffer.

Both forms allow you to specify whether you'd like multisampling to be enabled or not - and if so, with how many samples. If your system cannot produce the number of samples requested, pwInit will fall back to the best it can do.

Then, initialise other PLIB components such as PUI. When initialisation is complete, call this function:

    void pwCallbacks ( pwKeybdFunc    *kb = NULL, pwMouseFunc *ms = NULL,
                       pwMousePosFunc *mp = NULL, pwResizeCB *rcb = NULL,
                       pwExitCB      *ecb = NULL ) ;

These parameters are callback functions for (repectively) incoming keyboard keystrokes, incoming mouse button press or release events, mouse movements, window resize events and finally, a window close callback. (That's invoked by PW when the user attempts to close the window by pressing the exit button on the window border.) PW also calls the exit function when it detects a fatal error that occurs after the window has been successfully opened.

Your application has to be prepared for these callbacks to be invoked at any time after pwCallbacks. PW allows you to issue OpenGL calls any time after pwInit().

The specifications of these various callbacks are:

    typedef void pwResizeCB ( int w, int h ) ;
    typedef void pwExitCB   () ;
    typedef void pwKeybdFunc    ( int key, int updown, int x, int y ) ;
    typedef void pwMouseFunc    ( int button, int updown, int x, int y ) ;
    typedef void pwMousePosFunc ( int x, int y ) ;

The 'updown' parameter is set to PW_DOWN when a key or mouse button is pressed or to PW_UP when it's released. The 'key' parameter is either an ASCII character or one of:

     PW_KEY_F1       PW_KEY_F2       PW_KEY_F3       PW_KEY_F4
     PW_KEY_F5       PW_KEY_F6       PW_KEY_F7       PW_KEY_F8
     PW_KEY_F9       PW_KEY_F10      PW_KEY_F11      PW_KEY_F12

     PW_KEY_LEFT     PW_KEY_UP       PW_KEY_RIGHT    PW_KEY_DOWN

     PW_KEY_PAGE_UP  PW_KEY_PAGE_DOWN

     PW_KEY_HOME     PW_KEY_END      PW_KEY_INSERT

The 'button' parameter is one of:

     PW_LEFT_BUTTON  PW_MIDDLE_BUTTON  PW_RIGHT_BUTTON

These constants are chosen to be identical to the similarly named constants used in the PLIB PUI library so that it's easy to connect a PUI GUI to a PW window.

Once the window is initialised, you may call other PLIB graphics initialisations (puInit, ssgInit, etc).

So now you have your window open, you only need to do one thing - call this function once per frame:

    void pwSwapBuffers () ;

This function swaps the double-buffers, collects keystrokes, mouse events and resize events and calls whatever application-defined callbacks are needed. It is NOT LEGAL to call pwSwapBuffers() from inside a PW callback function.

When you wish to close the PW window, you should call:

    void pwCleanup () ;

Some applications need to know when the shift/control/alt keys are being held down by the user:

    int pwGetModifiers () ;

This returns the state of those three keys as the OR of the three constants:

     PW_SHIFT  PW_CTRL  PW_ALT

Note that the results are only valid inside of a callback called from pwSwapBuffers().

By default, PW disallows auto-repeat of keyboard keys. This is generally what you want for games. However, it's possible that you may want auto-repeat to be enabled:

       void pwSetAutoRepeatKey ( bool enable ) ;

If the user has told the windowing system that auto repeat should be off as some kind of a global preference then pwSetAutoRepeatKey(true) won't turn it back on again.

Finally, there are a number of functions for setting and getting the window position and dimensions - also to set the current cursor shape:

    void pwGetSize       ( int *w, int *h ) ;
    void pwSetSizeOrigin ( int x, int y, int w, int h ) ;
    void pwSetSize       ( int x, int y ) ;
    void pwSetOrigin     ( int w, int h ) ;
    void pwSetCursor     ( int c ) ;

The available cursor shapes for pwSetCursor are:

       PW_CURSOR_NONE    0
       PW_CURSOR_RIGHT   1
       PW_CURSOR_LEFT    2
       PW_CURSOR_QUERY   3
       PW_CURSOR_AIM     4
       PW_CURSOR_CIRCLE  5
       PW_CURSOR_WAIT    6
       PW_CURSOR_CROSS   7
       PW_CURSOR_CUSTOM  8