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(groff)Drawing Requests

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Drawing Requests
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   `gtroff' provides a number of ways to draw lines and other figures
on the page.  Used in combination with the page motion commands (see
Note: Page Motions, for more info), a wide variety of figures can be
drawn.  However, for complex drawings these operations can be quite
cumbersome, and it may be wise to use graphic preprocessors like `gpic'
or `ggrn'.  Note: gpic, and Note: ggrn, for more information.

   All drawing is done via escapes.

 - Escape: \l'L C'
     Draws a line rightwards from the current location.  The full
     syntax for this escape is:


          \l'LC'

     where L is the length of the line to be drawn, starting at the
     current location; positive numbers draw to the right, and negative
     numbers draw towards the left.  This can also be specified
     absolutely (i.e. with a leading `|') which draws back to the
     beginning of the line.

     The optional second parameter C is a character to draw the line
     with.  If this second argument is not specified, `gtroff' uses the
     underscore character.

     To separate the two arguments (to prevent `gtroff' from
     interpreting a drawing character as a scaling indicator) use `\&'.

     Here a small useful example:


          .de box
          \(br\\$*\(br\l'|0\(rn'\l'|0\(ul'
          ..

     Note that this works by outputting a box rule (a vertical line),
     then the text given as an argument and then another box rule.
     Then the line drawing escapes both draw from the current location
     to the beginning of the _input_ line.

 - Escape: \L'L C'
     Draws vertical lines.  Its parameters are similar to the `\l'
     escape.  The movement is downwards for positive values, and
     upwards for negative values.  The default character is the box
     rule character.  As with the vertical motion escapes, text
     processing blindly continues where the line ends.


 - Escape: \D'COMMAND ARG ...'
     The `\D' escape provides a variety of drawing functions.  While
     the previous escapes work on a character device, these escapes do
     not.

    `\D'l DX DY''
          Draw a line from the current location to the relative point
          specified by (DX,DY).

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

    `\D'C D''
          Draw a solid circle with the same parameters as an outlined
          circle.

    `\D'e DX DY''
          Draw an ellipse with a horizontal diameter of DX and a
          vertical diameter of DY with the leftmost point at the
          current position.

    `\D'E DX DY''
          Draw a solid ellipse with the same parameters as an outlined
          ellipse.

    `\D'a DX1 DY1 DX2 DY2''
          Draw an arc clockwise from the current location through the
          two specified locations (DX1,DY1) and (DX2,DY2).

    `\D'~ DX1 DY1 DX2 DY2 ...''
          Draw a spline from the current location to (DX1,DY1) and then
          to (DX2,DY2), and so on.

    `\D'f 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.

    `\D'p DX1 DY1 DX2 DY2 ...''
          Draw a polygon from the current location to (DX1,DY1) and
          then to (DX2,DY2) and so on.  When the specified data points
          are exhausted, a line is drawn back to the starting point.

    `\D'P DX1 DY1 DX2 DY2 ...''
          Draw a solid polygon with the same parameters as an outlined
          polygon.

    `\D't N''
          Set the current line thickness to N machine units.  A value of
          zero selects the smallest available line thickness.  A
          negative value makes the line thickness proportional to the
          current point size (this is the default behaviour of
          `ditroff').

 - Escape: \b'STRING'
     "Piles" a sequence of characters vertically, and centers it
     vertically on the current line.  Use it to build large brackets
     and braces.


          \b'\(lt\(bv\(lk\(bv\(lb'


   Note: Drawing Functions.