Function:     GgiDial

Purpose:      Create a dial analog valuator Ggi element

Category:     USER-INTERFACE

File:         ggi.src

Author:       J.P. Terlouw

Use:          
              #include "ggi.h"
              ident dial;
              char  *keyword, *message;
              int   radius, min_angle, max_angle, intervals;
              float arrow_width, inner_length, outer_length, low_val, high_val;

              dial = GgiDial( keyword,
                              message,
                              radius,
                              min_angle,
                              max_angle,
                              intervals,
                              arrow_width,
                              inner_length,
                              outer_length,
                              low_val,
                              high_val )

               dial         -  'handle' by which element can be referenced.
               keyword      -  user input keyword.
               message      -  help text which pops up when the pointer stays
                               in the dial for some time.
               radius       -  dial's radius in pixels.
               min_angle    -  the dial's minimum angle, measured in degrees
                               in clockwise direction from the lowest
                               (6 o'clock) position.
               max_angle    -  the dial's maximum angle.
               intervals    -  the number if tick-intervals around the dial.
               arrow_width  -  arrow width expressed as a fraction of radius.
               inner_length -  'inner' arrow length (fraction of radius).
               outer_length -  'outer' arrow length (fraction of radius).
               low_val      -  output value corresponding with min_angle.
               high_val     -  output value corresponding with max_angle.


Description:  GgiDial creates an analog valuator element based on the
              rheostat widget.
              On the screen is consists of a label field and the actual
              dial. By default the supplied keyword is taken as the
              label's value. 

              When it is manipulated, it writes its value to the keyword by
              calling wkey_c(). This can be read by any number reading
              routine e.g. userreal_c().

              The use of the layout parameters is illustrated in the html
              document $gip_htm/GgiDial/index.html .

Related documents: 
              GgiSetCircular.dc2, GgiSetFormat.dc2, GgiSetRange.dc2

Updates:      Jan 14, 1999: JPT, Document created.
              Jan 28, 1999: JPT, GgiSetFormat and GgiSetCircular added.