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(groff)Drawing Functions

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Drawing Functions
-----------------

   The `D' drawing command has been extended.  These extensions are
used by GNU `pic' only if the `-x' option is given.

   Note: Drawing Requests.

`Df N'
     Set the shade of gray to be used for filling solid objects to N;
     N must be an integer between 0 and 1000, where 0 corresponds solid
     white and 1000 to solid black, and values in between correspond to
     intermediate shades of gray.  This applies only to solid circles,
     solid ellipses and solid polygons.  By default, a level of 1000 is
     used.  Whatever color a solid object has, it should completely
     obscure everything beneath it.  A value greater than 1000 or less
     than 0 can also be used: this means fill with the shade of gray
     that is currently being used for lines and text.  Normally this is
     black, but some drivers may provide a way of changing this.

`DC D'
     Draw a solid circle with a diameter of D with the leftmost point
     at the current position.

`DE DX DY'
     Draw a solid ellipse with a horizontal diameter of DX and a
     vertical diameter of DY with the leftmost point at the current
     position.

`Dp DX1 DY1 DX2 DY2 ... DXN DYN'
     Draw a polygon with automatic closure.  The first vertex is at the
     current position, the second vertex at an offset (DX1,DY1) from
     the current position, the second vertex at an offset (DX2,DY2)
     from the first vertex, and so on up to the Nth vertex.  At the
     moment, GNU `pic' only uses this command to generate triangles and
     rectangles.

`DP DX1 DY1 DX2 DY2 ... DXN DYN'
     Like `Dp' but draw a solid rather than outlined polygon.

`Dt N'
     Set the current line thickness to N machine units.  Traditionally,
     UNIX `troff' drivers use a line thickness proportional to the
     current point size; drivers should continue to do this if no `Dt'
     command has been given, or if a `Dt' command has been given with a
     negative value of N.  A zero value of N selects the smallest
     available line thickness.

   A difficulty arises in how the current position should be changed
after the execution of these commands.  This is not of great importance
since the code generated by GNU `pic' does not depend on this.  Given a
drawing command of the form


     \D'C X1 Y1 X2 Y2 ... XN YN'

where C is not one of `c', `e', `l', `a' or `~', UNIX `troff' treats
each x value as a horizontal quantity, and each y value as a vertical
quantity; it assumes that the width of the drawn object is the sum of
all x values, and that the height is the sum of all y values.  (The
assumption about the height can be seen by examining the `st' and `sb'
registers after using such a `D' command in a `\w' escape sequence.)
This rule also holds for all the original drawing commands with the
exception of `De'.  For the sake of compatibility GNU `troff' also
follows this rule, even though it produces an ugly result in the case
of the `Df', `Dt', and, to a lesser extent, `DE' commands.  Thus after
executing a `D' command of the form


     DC X1 Y1 X2 Y2 ... XN YN

the current position should be increased horizontally by the sum of all
x values and vertically by the sum of all y values.