GPUTPIXEL()
 Draw a pixel on the screen
------------------------------------------------------------------------------
 Syntax

     GPUTPIXEL(<nX>, <nY>, <nColor>, <nMode>) --> NIL

 Arguments

     <nX> and <nY> define pixel coordinates for row and column on the
     screen.

     <nColor> is a numeric value representing the display color of the
     pixel.

     The range of values is limited to the number of colors available in the
     selected video mode.  In 16-color modes, valid values are between 0 and
     15.  In 256-color modes, valid values are between 0 and 255.

     <nMode> is the numeric value representing the video mode.  The
     following are valid <nMode> values.  They are all # defines in Llibg.ch.

     Video Mode Constants
     ------------------------------------------------------------------------
     Constant       Description
     ------------------------------------------------------------------------
     LLG_MODE_SET   Display in SET mode (ignores any pixels present under the
                    line displayed).  This is the most common display mode.
     LLG_MODE_AND   Display in AND mode (executes an AND on pixels present
                    under the line at display time and on the display color).
     LLG_MODE_OR    Display in OR mode (executes an OR on pixels present
                    under the line at display time and on the display color).
     LLG_MODE_XOR   Display in XOR mode (executes an XOR on pixels present
                    under the line at display time and on the display color).
                    See note.
     ------------------------------------------------------------------------

     Note:  This method allows you to move objects around on the screen
     without damaging the background.  To retrieve the initial background,
     just repeat the call for display in XOR mode.  If the display mode
     parameter is missing, the last mode specified in a call to a CA-Clipper
     graphic function is used.

 Returns

     GPUTPIXEL() always returns NIL.

 Description

     This function can be used to change the color of a specific pixel on the
     screen.

 Examples

     .  The following example will put a white pixel at X-coordinate
        200 and Y-coordinate 100:

        GPUTPIXEL (200, 100, 15, LLG_MODE_SET)

 Files   Library is LLIBG.LIB, header file is Llibg.ch.