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─────Run-Time Library───────────────────────────────────────────────────────
 
     There are three coordinate systems employed by the low-level
     graphics functions. The first is the physical screen coordinate
     system, where the origin (0,0) is located at the upper-left corner
     of the screen and the coordinates increase downward and to the
     right. All coordinates must be integral values. Only _setcliprgn,
     _setviewport, _setvieworg, _getviewcoord, and _getphyscoord
     require physical coordinates.
 
     The second is the viewport (or view) coordinate system. The
     graphics viewport is a clipping region with a coordinate system
     origin at its upper-left corner. The default viewport is the
     physical screen, until a new one is defined using _setviewport.
     The viewport origin can also be reset with _setvieworg. All
     coordinates must be integral values. Functions without a suffix
     use view coordinates, and take shorts for coordinate arguments.
 
     The third is the window coordinate system. The _setwindow function
     transforms the current graphics viewport into a window by mapping
     a real-valued coordinate system onto the viewport. Each coordinate
     can have an arbitrary range specified by the _setwindow arguments.
     The y coordinate can be either increasing downward or increasing
     upward. Functions ending with _w use window coordinates, and take
     doubles for coordinate arguments. Functions ending with _wxy take
     _wxycoord structures.
 
     For translating between the various coordinate systems, use the
     _getphyscoord, _getviewcoord, and _getwindowcoord functions.
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