A window drawing area is the only graphic zone
in GAMGI, where all the rendering takes place.
Although this drawing area is unique, it is logically formed as the superposition
of unlimited layers, which are totally independent: they have independent lights,
types of projection, viewing referentials, transparency properties, etc.
Each window has always a currently working layer, where objects are handled
and action occurs. The objects in the current layer are always on top, and 
the viewport background color is always the color of the current layer.
Multiple side-by-side viewports, or superimposed lateraly filtered 
viewports, in a single drawing area, are currently not supported.
Dragging the mouse over the drawing area is an effective way to change the currently 
selected object: 1) pressing the left button rotates the object around its geometric 
center along the three x,y,z axes: dragging horizontally rotates the object along the 
vertical axis, dragging vertically rotates the object along the horizontal axis, and 
dragging along a circular arc far from the center rotates the object along the axis 
perpendicular to the screen; 2) pressing the center button moves the object in the 
dragging direction; 3) pressing the right button and dragging up and down scales the 
object up and down respectively. To change these defaults select 
Gamgi->Config.