%D \module
%D   [       file=mp-sketch.mp
%D        version=2021.05.13
%D          title=\CONTEXT\ \METAPOST\ graphics,
%D       subtitle=Sketch drawing,
%D         author=Aditya Mahajan,
%D           date=\currentdate,
%D      copyright={Aditya Mahajan}]

%D This metapost module is inspired by a TeX.SE question:
%D http://tex.stackexchange.com/q/39296/323
%D
%D I thought that it would be fun to implement a similar feature in MetaPost.
%D
%D To use this package in MetaPost:
%D
%D \starttyping
%D    input mp-sketch;
%D
%D    beginfig(1)
%D      sketchypaths; % Make draw and fill sketchy
%D      ...
%D      naturalizepaths; % Restore the value of draw and fill
%D      ...
%D    endfig
%D \stoptyping
%D
%D The code is heavily inspired by Hans Hagen's Metafun macros.
%D
%D The macro \type{sketchypaths} is modeled after \type{visualizepaths} from
%D \filename{mp-tool}.

def sketchypaths =
    let draw = sketchdraw ;
    let fill = sketchfill ;
enddef ;

%D Check if \filename{mp-tool} is loaded
if not known context_tool :
  let normaldraw = draw;
  let normalfill = fill;

  def naturalizepaths =
      let fill = normalfill ;
      let draw = normaldraw ;
  enddef ;
fi

%D The variable \type{sketch_amount} determines the amount of randomness in the
%D drawing
numeric sketch_amount; sketch_amount := 0.75bp;

%D The variable \type{sketch_passes} determines the number of times the path
%D is drawn
numeric sketch_passes; sketch_passes := 1;

%D Based on \type{randomized}. Assumes p is path:
numeric sketch_segments; sketch_segments := 20;

%D Length (time) of line segments:
numeric sketch_length; sketch_length := 5mm;

primarydef p sketchrandomized s = (
    if path p :
        for t = 0 step 1/sketch_segments until 1-1/sketch_segments :
            ((point       (t*arclength(p))                     on p) randomshifted s) .. controls
            ((postcontrol (t*arclength(p))                     on p) randomshifted s) and
            ((precontrol  ((t+1/sketch_segments)*arclength(p)) on p) randomshifted s) ..
        endfor
        % TODO: beide Ansätze kombinieren. Eckpunkte erhalten!

%        for t = 0 step sketch_length until arclength p:
%          (point (arctime t of p) of p) randomshifted s ..
%        endfor
        if cycle p : % funktioniert nicht
          cycle
        else :
          ((point       (arclength(p))                     on p) randomshifted s)
          %(point (arctime t of p) of p) randomshifted s
        fi
    else :
        p
    fi
) enddef ;



%D The macro \type{sketchdraw} draws the randomized path. The
%D \type{expr} ... \type{text} trick is copied from the definition of
%D \type{drawarrow}
def sketchdraw expr p =
   do_sketchdraw(p)
enddef;

def do_sketchdraw(expr p) text t =
  if (path p) :
      for i = 1 upto max(1,sketch_passes) :
        normaldraw p
                   sketchrandomized sketch_amount
                   withtransparency ("multiply", 1/max(1,sketch_passes))
                   t ;
      endfor;
  else :
      normaldraw p t;
  fi
enddef;

%D The macro \type{sketchfill} randomizes the path before filling it.
def sketchfill expr p =
  do_sketchfill(p)
enddef ;

def do_sketchfill(expr p) text t =
  if (path p) :
      for i = 1 upto max(1,sketch_passes) :
        normalfill p
                   sketchrandomized sketch_amount
                   withtransparency ("multiply", 1/max(1,sketch_passes))
                   t ;
      endfor;
  else :
      normalfill p t;
  fi
enddef;

picture NoisePattern;
NoisePattern := image(
  pickup pencircle xyscaled 0.5bp;
  numeric pmax ; pmax := 7 ;
  numeric x ; numeric y ;
	for i = 1 upto pmax:
		for j = 1 upto pmax:
      % try to get more dots in the center
      x := (i - (pmax/2) * (uniformdeviate 2.5)); % we use a wide pen
      y := (j - (pmax/2)) * (uniformdeviate 1.25);
      draw (x, y) withcolor "LineColor" withtransparency ("normal", (uniformdeviate 0.33));
		endfor
	endfor
);

numeric brush_length ; brush_length := 20 ;
%numeric brush_width ; brush_width := 0.5 ;

picture BrushPattern;

def makeBrush(expr brush_width) =
  BrushPattern := image(
    naturalizepaths;
    pickup pensquare xyscaled 0.25bp;
    numeric xmax, ymax, dev ;
    ymax := 7 ;
    xmax := round(ymax/2 * brush_width);
    numeric x ; numeric y ;
  	for i = 1 upto xmax:
  		for j = 1 upto ymax:
        x := (i - (xmax/2));
        y := (j - (ymax/2)); % * (uniformdeviate 1.25);
        dev := (uniformdeviate 1)-0.5;
        draw (x-dev, y-(uniformdeviate brush_length))--(x+dev, y+(uniformdeviate brush_length)) withcolor "LineColor" withtransparency ("normal", (uniformdeviate 0.25));
  		endfor
  	endfor
  );
enddef;

numeric noise_steps ; noise_steps := 150;
numeric nrush_steps ; brush_steps := 30;

def noisify(expr p) =
  for i = 0 step 1/noise_steps until length p:
  	draw NoisePattern randomized 1 shifted point i of p ;
  endfor
enddef;

def brushify(expr p, w) =
  makeBrush(w);
  for i = 0 step 1/brush_steps until length p:
  	draw BrushPattern randomized 1 rotated (90 + angle direction i of p) shifted point i of p ;
  endfor
enddef;

endinput;

% Modified example from
% http://tex.loria.fr/prod-graph/zoonekynd/metapost/metapost.html

beginfig(1)
  pair A,B,C,O;
  A=(0,0); B=(3cm,0); C=(1cm,2cm);

  O - 1/2[B,C] = whatever * (B-C) rotated 90;
  O - 1/2[A,B] = whatever * (A-B) rotated 90;

  sketchypaths;
  sketch_amount := 5bp;
  draw A--B--C--cycle;

  draw O withpen pencircle scaled 4bp;

  sketch_amount := 2bp;
  draw fullcircle scaled 2abs(O-A) shifted O;
endfig