These are some notes I thought will come in handly as I work through the
  code and write new code.


Event handling
===============
* Each platform gets the events from the underlying graphics library.
* Events get caught and translated into a fpGUI message record.
* The fpGUI message record gets placed (using fpgPostMessage) in a custom
  fpGUI message queue (which is a linkedlist structure with 512 links).
* From there the fpGUI message records get delivered to the specific window.
* Certain messages traverse up the hierarchy to be processed by all parents.
* Messages get delivered up the hierarchy using the TObject.Dispatch method
* Messages get delivered down the hierarchy using the TComponent.Components
  property.
* The standard 'message' language feature of Object Pascal gets used to in
  the class interfaces section to capture a posted message (event). All
  standard FPGM_xxx messages get handled in the TfpgWidget and TfpgForm 
  classes.



Pen and Brush support (X11)
===========================
* They come from the GC
* They are seperate GC's and swapped around when needed in the different 
  Xlib drawing routines.  Both created with the XCreateGC() function
  eg:
    d->gc            = Pen
    d->gc_brush      = Brush

    XFillRectangle(dpy, screen, d->gc_brush, .....);
    XDrawRectangle(dpy, screen, d->gc, .....);

* Updating the Pen and Brush attributes are done with a call to XChangeGC(),
  passing in the relevant GC (d->gc or d->gc_brush).