Multiple Coordinates in System

Multiple Coordinates in System

       In a display windowing system, an arithmetic sign used to
determine the coordinate axis of reference.  For positive x, y
coordinates refer to left hand and edges and negative coordinates to
right hand and top  This permits fixing positions of display items to
edges of a viewport which are independent of of size of viewport.

      A viewport in a window is a rectangular area through an
underlying scene, called a panel, is displayed.  A acts as a matrix
upon which fields are embedded.  The coordinate system defines the
positioning of these on the panel. Coordinate Systems

      In most windowing systems a panel will have either a based
coordinate system (in a row and column or a graphic coordinate system
in world coordinate units.  The screen-cell- based coordinate system
is as follows:
   The top-left cell is a row 1 column 1.
   Row coordinate values increase downwards.
   Column coordinate values increase to the right.
   The graphic coordinate system normally specifies that
   position
   x=0, y=0 is at the bottom-left of the panel.
   X-coordinate values increase to the right.
   Y-coordinate values increase upwards.
   Multiple Coordinate Systems (Fig. 1)

      The above coordinate systems do not use negative values,
negative values could be used to position fields the axes.  However,
negative values can be exploited another way.  Fig. 1 shows that a
positive x coordinate related to the left, whereas a negative x
coordinate is to the right.  If a positive x coordinate increases,
the corresponding position moves to the right, being displaced from
the left-hand axis.

      If a negative x coordinate decreases, then the postion moves to
the left, being further from the right-hand axis.  Similarly a
positive y relates to the bottom, and a negative y relates to the
top.

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