This document explains unified coordinates as they're used within
the Nuclex User Interface library


Principle

  The idea of unified coordinates comes from CeGui.

  Unified coordinates contain a fractional part (called 'relative' in CeGui) that describes
  the position or size as a fraction of the dimensions of the parent coordinate frame. For
  example, a unified coordinate with a fractional part of 0.5 would always start out in the
  center of its parent coordinate frame.

  In addition to the fractional part, unified coordinates also have an offset part (called
  'absolute' in CeGui) which is the offset, in pixels, from the position indicated by the
  fractional part. This allows you to do things like place an object 10 pixels from the
  right of the parent coordinate frame (by setting the fractional part to 1.0 and the offset
  to -10).


Usage in Nuclex.UserInterface

  All controls in the Nuclex GUI library use unified coordinates. The final pixel positions
  and sizes of everything thus depend on the scale of the root coordinate frame that is
  hosting the GUI.

  This root coordinate frame here is the Screen class. A Screen manages the entire state of
  the GUI (eg. which control has input focus, where the cursor is currently) and knows the
  absolute pixel coordinates of the area the GUI can occupy.

  Any screen manages a single invisible control that forms the topmost element of any GUI
  control hierarchy: The desktop. This elegantly allows you to use the unified coordinate
  features for the size of the actual GUI area (eg. you could make the GUI always stay away
  10% from the screen's borders for TVs where these areas may be invisible).
  
  An example of this hierarchy:

  Screen  (Nuclex.UserInterface.Screen)
    Desktop  (Nuclex.UserInterface.Controls.Control)
      MyDialog1  (MyProject.Dialog)
        MyControl1  (Nuclex.UserInterface.Controls.ButtonControl)
        MyControl2  (Nuclex.UserInterface.Controls.ButtonControl)
      MyDialog2  (MyProject.Dialog)
        MyControl1  (Nuclex.UserInterface.Controls.ButtonControl)
        MyControl2  (Nuclex.UserInterface.Controls.ButtonControl)