Shade and Width Example

Try it.

% Demonstrate shading and width in drawing lines and filling shapes

% Define an operator box which builds a path for a one inch square box
% Note that box does not draw or fill the box.

/box {
  moveto                                % Current point is on stack
  0 72 rlineto                          % Left
  72 0 rlineto                          % Top
  0 -72 rlineto                         % Right
  closepath                             % Bottom
} def

0 setgray                               % 100% black
1 setlinewidth                          % One point thick lines
72 72 moveto 72 144 lineto stroke       % Draw a one inch line

gsave                                   % Save a copy of the current settings
  0.5 setgray                           % 50% black
  10 setlinewidth                       % 10 point wide lines
  144 72 moveto 144 144 lineto stroke   % Draw a one inch wide line
  216 72 box                            % Build a square path...
  0.35 setgray                          %   make it a little darker...
  fill                                  %   and fill it.
grestore                                % Go back to the original settings

3 setlinewidth                          % Make the box lines wider
300 72 box stroke                       % Draw a black box


If you try this example, you should note a couple of things. Firstly, the black outlined box is a little larger than the gray filled one. This extra width comes from the 3 point wide lines used to draw it—they are centered about the path of the box. The ink filling the gray box, however, is completely within the path of the box. Also, when shading objects, you must be careful. PostScript makes shades through a process called halftoning. Basically, uniform dots are placed in various patterns to simulate different shades of grey. Unfortunately, various considerations limit how many shades a printer can produce. So some grey tones may come out the same. This may be the case with the filled box and the outlined box when viewed on your screen or printer.