/*****************************************************************************
 * feynman.asy -- An Asymptote library for drawing Feynman diagrams.         *
 *                                                                           *
 * by:  Martin Wiebusch <martin.wiebusch@gmx.net>                            *
 * last change: 2007/04/13                                                   *
 *****************************************************************************/


/* default parameters ********************************************************/

// default ratio of width (distance between two loops) to amplitude for a gluon
// line. The gluon function uses this ratio, if the width parameter is
// negative.
real gluonratio;

// default ratio of width (distance between two crests) to amplitude for a
// photon  line. The photon function uses this ratio, if the width parameter is
// negative.
real photonratio;

// default gluon amplitude
real gluonamplitude;

// default photon amplitude
real photonamplitude;

// default pen for drawing the background. Usually white.
pen backgroundpen;

// default pen for drawing gluon lines
pen gluonpen;

// default pen for drawing photon lines
pen photonpen;

// default pen for drawing fermion lines
pen fermionpen;

// default pen for drawing scalar lines
pen scalarpen;

// default pen for drawing ghost lines
pen ghostpen;

// default pen for drawing double lines
pen doublelinepen;

// default pen for drawing vertices
pen vertexpen;

// default pen for drawing big vertices (drawVertexOX and drawVertexBoxX)
pen bigvertexpen;

// inner spacing of a double line
real doublelinespacing;

// default arrow for propagators
arrowbar currentarrow;

// if true, each of the drawSomething commands blots out the background
// (with pen backgroundpen) before drawing.
bool overpaint;

// margin around lines. If one line is drawn over anoter, a white margin
// of size linemargin is kept around the top one.
real linemargin;

// at vertices, where many lines join, the last line drawn should not blot
// out the others. By not erasing the background near the ends of lines,
// this is prevented for lines with an angle greater than minvertexangle to
// each other. Note, that small values for minvertexangle mean that the
// background is only erased behind a small segment of every line. Setting
// minvertexangle = 0 effectively disables background erasing for lines.
real minvertexangle;

// size (radius) of vertices
real vertexsize;

// size (radius) of big vertices (drawVertexOX and drawVertexBoxX)
real bigvertexsize;

/* defaults for momentum arrows **********************************************/

// (momentum arrows are small arrows parallel to particle lines indicating the
// direction of momentum)

// default size of the arrowhead of momentum arrows
arrowbar currentmomarrow;

// default length of momentum arrows
real momarrowlength;

// default pen for momentum arrows
pen momarrowpen;

// default offset between momentum arrow and related particle line
real momarrowoffset;

// default margin for momentum arrows
real momarrowmargin;

// factor for determining the size of momentum arrowheads. After changing it,
// you still have to update currentmomarrow manually.
real momarrowfactor;

// size function for momentum arrowheads
real momarrowsize(pen p=momarrowpen) { return momarrowfactor*linewidth(p); }


/* defaults for texshipout ***************************************************/

// tex command for including graphics. It takes one argument, which is the
// name of the graphics (eps or pdf) file.
string includegraphicscommand;

// Determines whether the suffix (.eps or .pdf) should be appended to the stem
// of the file name in the \includegraphics command.
bool appendsuffix;


/* helper functions **********************************************************/

// internal function for overpainting
private void do_overpaint(picture pic, path p, pen bgpen,
                          real halfwidth, real vertexangle)
{
  real tanvertexangle = tan(vertexangle*pi/180);
  if(tanvertexangle != 0) {
    real t1 = arctime(p, halfwidth/tanvertexangle+halfwidth);
    real t2 = arctime(p, arclength(p)-halfwidth/tanvertexangle-halfwidth);
    draw(pic, subpath(p, t1, t2),
         bgpen+linewidth(2*halfwidth));
  }
}

// returns the path of a gluon line along path p, with amplitude amp and width
// width (distance between two loops). If width is negative, the width is
// set to amp*gluonratio
path gluon(path p, real amp = gluonamplitude, real width=-1)
{
  if(width < 0) width = abs(gluonratio*amp);

  real pathlen = arclength(p);
  int ncurls = floor(pathlen/width);
  real firstlen = (pathlen - width*(ncurls-1))/2;
  real firstt = arctime(p, firstlen);
  pair firstv = dir(p, firstt);
  guide g = point(p, 0)..{firstv}( point(p, firstt)
                                   +amp*unit(rotate(90)*firstv));

  real t1;
  pair v1;
  real t2;
  pair v2;
  pathlen -= firstlen;
  for(real len = firstlen+width/2; len < pathlen; len += width) {
    t1 = arctime(p, len);
    v1 = dir(p, t1);
    t2 = arctime(p, len + width/2);
    v2 = dir(p, t2);

    g=g..{-v1}(point(p, t1)+amp*unit(rotate(-90)*v1))
                ..{+v2}(point(p, t2)+amp*unit(rotate(+90)*v2));
  }
  g = g..point(p, size(p));
  return g;
}

// returns the path of a photon line along path p, with amplitude amp and width
// width (distance between two crests). If width is negative, the width is
// set to amp*photonratio
path photon(path p, real amp = photonamplitude, real width=-1)
{
  if(width < 0)
    width = abs(photonratio*amp)/2;
  else
    width = width/2;

  real pathlen = arclength(p);
  int ncurls = floor(pathlen/width);
  real firstlen = (pathlen - width*ncurls)/2;
  real firstt = arctime(p, firstlen+width);
  guide g =   point(p, 0){unit(point(p, firstt)-point(p, 0))};

  real t;
  pair v;
  pathlen -= firstlen;
  for(real len = firstlen+width; len < pathlen; len += width) {
    t = arctime(p, len);
    v = dir(p, t);

    g=g..{v}(point(p, t)+amp*unit(rotate(90)*v));
    amp = -amp;
  }
  g = g..{unit(point(p, size(p))-point(p, t))}point(p, size(p));
  return g;
}

// returns the path of a momentum arrow along path p, with length length,
// an offset offset from the path p and at position position. position will
// usually be one of the predefined pairs left or right. Making adjust
// nonzero shifts the momentum arrow along the path.
path momArrowPath(path p,
                  align align,
                  position pos,
                  real offset = momarrowoffset,
                  real length = momarrowlength)
{
  real pathlen = arclength(p);

  real t1, t2;
  if(pos.relative) {
    t1 = arctime(p, (pathlen-length)*pos.position.x);
    t2 = arctime(p, (pathlen-length)*pos.position.x+length);
  } else {
    t1 = arctime(p, (pathlen-length)/2 + pos.position.x);
    t2 = arctime(p, (pathlen+length)/2+ pos.position.x);
  }

  pair v1 = dir(p, t1);
  pair v2 = dir(p, t2);

  pair p1, p2;
  if(align.relative) {
    p1 = point(p, t1) +  offset*abs(align.dir)
      *unit(rotate(degrees(align.dir)-90)*v1);
    p2 = point(p, t2) +  offset*abs(align.dir)
      *unit(rotate(degrees(align.dir)-90)*v2);
  } else {
    p1 = point(p, t1) + offset*align.dir;
    p2 = point(p, t2) + offset*align.dir;
  }

  return p1{v1}..{v2}p2;
}




/* drawing functions *********************************************************/

// draw a gluon line on picture pic, along path p, with amplitude amp, width
// width (distance between loops) and with pen fgpen. If erasebg is true,
// bgpen is used to erase the background behind the line and at a margin
// margin around it. The background is not erased at a certain distance to
// the endpoints, which is determined by vertexangle (see comments to the
// default parameter minvertexangle). For negative values of width, the width
// is set to gluonratio*amp.
void drawGluon(picture pic = currentpicture,
               path p,
               real amp = gluonamplitude,
               real width = -1,
               pen fgpen = gluonpen,
               bool erasebg = overpaint,
               pen bgpen = backgroundpen,
               real vertexangle = minvertexangle,
               real margin = linemargin)
{
  if(width < 0) width = abs(2*amp);

  if(erasebg) do_overpaint(pic, p, bgpen, amp+margin, vertexangle);
  draw(pic, gluon(p, amp, width), fgpen);
}

// draw a photon line on picture pic, along path p, with amplitude amp, width
// width (distance between loops) and with pen fgpen. If erasebg is true,
// bgpen is used to erase the background behind the line and at a margin
// margin around it. The background is not erased at a certain distance to
// the endpoints, which is determined by vertexangle (see comments to the
// default parameter minvertexangle). For negative values of width, the width
// is set to photonratio*amp.
void drawPhoton(picture pic = currentpicture,
                path p,
                real amp = photonamplitude,
                real width = -1,
                pen fgpen = currentpen,
                bool erasebg = overpaint,
                pen bgpen = backgroundpen,
                real vertexangle = minvertexangle,
                real margin = linemargin)
{
  if(width < 0) width = abs(4*amp);

  if(erasebg) do_overpaint(pic, p, bgpen, amp+margin, vertexangle);
  draw(pic, photon(p, amp, width), fgpen);
}

// draw a fermion line on picture pic, along path p with pen fgpen and an
// arrowhead arrow. If erasebg is true, bgpen is used to erase the background
// at a margin margin around the line. The background is not erased at a
// certain distance to the endpoints, which is determined by vertexangle
// (see comments to the default parameter minvertexangle).
void drawFermion(picture pic = currentpicture,
                 path p,
                 pen fgpen = currentpen,
                 arrowbar arrow = currentarrow,
                 bool erasebg = overpaint,
                 pen bgpen = backgroundpen,
                 real vertexangle = minvertexangle,
                 real margin = linemargin)
{
  if(erasebg) do_overpaint(pic, p, bgpen,
                           linewidth(fgpen)+margin, vertexangle);
  draw(pic, p, fgpen, arrow);
}

// draw a scalar line on picture pic, along path p with pen fgpen and an
// arrowhead arrow. If erasebg is true, bgpen is used to erase the background
// at a margin margin around the line. The background is not erased at a
// certain distance to the endpoints, which is determined by vertexangle
// (see comments to the default parameter minvertexangle).
void drawScalar(picture pic = currentpicture,
                path p,
                pen fgpen = scalarpen,
                arrowbar arrow = currentarrow,
                bool erasebg = overpaint,
                pen bgpen = backgroundpen,
                real vertexangle = minvertexangle,
                real margin = linemargin)
{
  if(erasebg) do_overpaint(pic, p, bgpen,
                           linewidth(fgpen)+margin, vertexangle);
  draw(pic, p, fgpen, arrow);
}

// draw a ghost line on picture pic, along path p with pen fgpen and an
// arrowhead arrow. If erasebg is true, bgpen is used to erase the background
// at a margin margin around the line. The background is not erased at a
// certain distance to the endpoints, which is determined by vertexangle
// (see comments to the default parameter minvertexangle).
void drawGhost(picture pic = currentpicture,
               path p,
               pen fgpen = ghostpen,
               arrowbar arrow = currentarrow,
               bool erasebg = overpaint,
               pen bgpen = backgroundpen,
               real vertexangle = minvertexangle,
               real margin = linemargin)
{
  if(erasebg) do_overpaint(pic, p, bgpen,
                           linewidth(fgpen)+margin, vertexangle);
  draw(pic, p, fgpen, arrow);
}

// draw a double line on picture pic, along path p with pen fgpen, an inner
// spacing of dlspacint and an arrowhead arrow. If erasebg is true, bgpen is
// used to erase the background at a margin margin around the line. The
// background is not erased at a certain distance to the endpoints, which is
// determined by vertexangle (see comments to the default parameter
// minvertexangle).
void drawDoubleLine(picture pic = currentpicture,
                    path p,
                    pen fgpen = doublelinepen,
                    real dlspacing = doublelinespacing,
                    arrowbar arrow = currentarrow,
                    bool erasebg = overpaint,
                    pen bgpen = backgroundpen,
                    real vertexangle = minvertexangle,
                    real margin = linemargin)
{
  if(erasebg) do_overpaint(pic, p, bgpen,
                           linewidth(fgpen)+margin, vertexangle);

  real htw = linewidth(fgpen)+dlspacing/2;
  draw(pic, p, fgpen+2*htw);
  draw(pic, p, bgpen+(linewidth(dlspacing)));
  path rect = (-htw,-htw)--(-htw,htw)--(0,htw)--(0,-htw)--cycle;
  fill(shift(point(p,0))*rotate(degrees(dir(p,0)))*rect, bgpen);
  fill(shift(point(p,size(p)))*scale(-1)*rotate(degrees(dir(p,size(p))))*
       rect,bgpen);
  draw(pic, p, invisible, arrow);
}

// draw a vertex dot on picture pic, at position xy with radius r and pen
// fgpen
void drawVertex(picture pic = currentpicture,
                pair xy,
                real r = vertexsize,
                pen fgpen = vertexpen)
{
  fill(pic, circle(xy, r), fgpen);
}

// draw an empty vertex dot on picture pic, at position xy with radius r
// and pen fgpen. If erasebg is true, the background is erased in the inside
// of the circle.
void drawVertexO(picture pic = currentpicture,
                 pair xy,
                 real r = vertexsize,
                 pen fgpen = vertexpen,
                 bool erasebg = overpaint,
                 pen bgpen = backgroundpen)
{
  if(erasebg)
    filldraw(pic, circle(xy, r), bgpen, fgpen);
  else
    draw(pic, circle(xy, r), fgpen);
}

// draw a vertex triangle on picture pic, at position xy with radius r and pen
// fgpen
void drawVertexTriangle(picture pic = currentpicture,
                        pair xy,
                        real r = vertexsize,
                        pen fgpen = vertexpen)
{
  real cospi6 = cos(pi/6);
  real sinpi6 = sin(pi/6);
  path triangle = (cospi6,-sinpi6)--(0,1)--(-cospi6,-sinpi6)--cycle;
  fill(pic, shift(xy)*scale(r)*triangle, fgpen);
}

// draw an empty vertex triangle on picture pic, at position xy with size r
// and pen fgpen. If erasebg is true, the background is erased in the inside
// of the triangle.
void drawVertexTriangleO(picture pic = currentpicture,
                         pair xy,
                         real r = vertexsize,
                         pen fgpen = vertexpen,
                         bool erasebg = overpaint,
                         pen bgpen = backgroundpen)
{
  real cospi6 = cos(pi/6);
  real sinpi6 = sin(pi/6);
  path triangle = (cospi6,-sinpi6)--(0,1)--(-cospi6,-sinpi6)--cycle;

  if(erasebg)
    filldraw(pic, shift(xy)*scale(r)*triangle, bgpen, fgpen);
  else
    draw(pic, shift(xy)*scale(r)*triangle, fgpen);
}

// draw a vertex box on picture pic, at position xy with radius r and pen
// fgpen
void drawVertexBox(picture pic = currentpicture,
                   pair xy,
                   real r = vertexsize,
                   pen fgpen = vertexpen)
{
  path box = (1,1)--(-1,1)--(-1,-1)--(1,-1)--cycle;
  fill(pic, shift(xy)*scale(r)*box, fgpen);
}

// draw an empty vertex box on picture pic, at position xy with size r
// and pen fgpen. If erasebg is true, the background is erased in the inside
// of the box.
void drawVertexBoxO(picture pic = currentpicture,
                    pair xy,
                    real r = vertexsize,
                    pen fgpen = vertexpen,
                    bool erasebg = overpaint,
                    pen bgpen = backgroundpen)
{
  path box = (1,1)--(-1,1)--(-1,-1)--(1,-1)--cycle;
  if(erasebg)
    filldraw(pic, shift(xy)*scale(r)*box, bgpen, fgpen);
  else
    draw(pic, shift(xy)*scale(r)*box, fgpen);
}

// draw an X on picture pic, at position xy with size r and pen
// fgpen
void drawVertexX(picture pic = currentpicture,
                 pair xy,
                 real r = vertexsize,
                 pen fgpen = vertexpen)
{
  draw(pic, shift(xy)*scale(r)*((-1,-1)--(1,1)), fgpen);
  draw(pic, shift(xy)*scale(r)*((1,-1)--(-1,1)), fgpen);
}

// draw a circle with an X in the middle on picture pic, at position xy with
// size r and pen fgpen. If erasebg is true, the background is erased in the
// inside of the circle.
void drawVertexOX(picture pic = currentpicture,
                  pair xy,
                  real r = bigvertexsize,
                  pen fgpen = vertexpen,
                  bool erasebg = overpaint,
                  pen bgpen = backgroundpen)
{
  if(erasebg)
    filldraw(pic, circle(xy, r), bgpen, fgpen);
  else
    draw(pic, circle(xy, r), fgpen);
  draw(pic, shift(xy)*scale(r)*(NW--SE), fgpen);
  draw(pic, shift(xy)*scale(r)*(SW--NE), fgpen);
}

// draw a box with an X in the middle on picture pic, at position xy with
// size r and pen fgpen. If erasebg is true, the background is erased in the
// inside of the box.
void drawVertexBoxX(picture pic = currentpicture,
                    pair xy,
                    real r = bigvertexsize,
                    pen fgpen = vertexpen,
                    bool erasebg = overpaint,
                    pen bgpen = backgroundpen)
{
  path box = (1,1)--(-1,1)--(-1,-1)--(1,-1)--cycle;
  box = shift(xy)*scale(r)*box;
  if(erasebg)
    filldraw(pic, box, bgpen, fgpen);
  else
    draw(pic, box, fgpen);
  draw(pic, shift(xy)*scale(r)*((-1,-1)--(1,1)), fgpen);
  draw(pic, shift(xy)*scale(r)*((1,-1)--(-1,1)), fgpen);
}

// draw a momentum arrow on picture pic, along path p, at position position
// (use one of the predefined pairs left or right), with an offset offset
// from the path, a length length, a pen fgpen and an arrowhead arrow. Making
// adjust nonzero shifts the momentum arrow along the path. If erasebg is true,
// the background is erased inside a margin margin around the momentum arrow.
// Make sure that offset and margin are chosen in such a way that the momentum
// arrow does not overdraw the particle line.
void drawMomArrow(picture pic = currentpicture,
                  path p,
                  align align,
                  position pos = MidPoint,
                  real offset = momarrowoffset,
                  real length = momarrowlength,
                  pen fgpen = momarrowpen,
                  arrowbar arrow = currentmomarrow,
                  bool erasebg = overpaint,
                  pen bgpen = backgroundpen,
                  real margin = momarrowmargin)
{
  path momarrow = momArrowPath(p, align, pos, offset, length);
  if(erasebg) do_overpaint(pic, momarrow, bgpen,
                           linewidth(fgpen)+margin, 90);
  draw(pic, momarrow, fgpen, arrow);
}


/* initialisation ************************************************************/

// The function fmdefaults() tries to guess reasonable values for the
// default parameters above by looking at the default parameters of plain.asy
// (essentially, currentpen, arrowfactor and dotfactor). After customising the
// default parameters of plain.asy, you may call fmdefaults to adjust the
// parameters of feynman.asy.
void fmdefaults()
{
  real arrowsize=arrowsize(currentpen);
  real linewidth=linewidth(currentpen);

  gluonratio = 2;
  photonratio = 4;
  gluonamplitude = arrowsize/3;
  photonamplitude = arrowsize/4;

  backgroundpen = white;
  gluonpen = currentpen;
  photonpen = currentpen;
  fermionpen = currentpen;
  scalarpen = dashed+linewidth;
  ghostpen = dotted+linewidth;
  doublelinepen = currentpen;
  vertexpen = currentpen;
  bigvertexpen = currentpen;
  currentarrow = MidArrow;

  doublelinespacing = 2*linewidth;
  linemargin = 0.5*arrowsize;
  minvertexangle = 30;
  overpaint = true;
  vertexsize = 0.5*dotfactor*linewidth;
  bigvertexsize = 0.4*arrowsize;

  momarrowfactor = 1.5*arrowfactor;
  momarrowlength = 2.5*arrowsize;
  momarrowpen = currentpen+0.5*linewidth;
  momarrowoffset = 0.8*arrowsize;
  momarrowmargin = 0.25*arrowsize;
  currentmomarrow = EndArrow(momarrowsize());

  includegraphicscommand = "\includegraphics";
  appendsuffix = false;
}

// We call fmdefaults once, when the module is loaded.
fmdefaults();


/* shipout *******************************************************************/

bool YAlign = false;
bool XYAlign = true;

// texshipout("filename", pic) creates two files: filename.eps holding the
// picture pic and filename.tex holding some LaTeX code that includes the
// picture from filename.eps and shifts it vertically in such a way that the
// point (0,0) lies on the baseline.
void texshipout(string stem,
                picture pic = currentpicture,
                bool xalign = YAlign)
{
  file tf = output(stem + ".tex");
  pair min=pic.min();
  real depth = min.y;
  real xoffset = min.x;
  if(xalign) {
    write(tf, "\makebox[0pt][l]{\kern");
    write(tf, xoffset);
    write(tf, "bp\relax");
  }
  write(tf, "\raisebox{");
  write(tf, depth);
  write(tf, "bp}{"+includegraphicscommand+"{");
  write(tf, stem);
  string suffix="."+nativeformat();
  if(appendsuffix)
    write(tf, suffix);
  write(tf, "}}");
  if(xalign)
    write(tf, "}");
  close(tf);
  shipout(stem+suffix, pic);
}