% $Id: svgout.w 1902 2013-05-22 14:44:36Z taco $
%
% Copyright 2008-2009 Taco Hoekwater.
%
% This program is free software: you can redistribute it and/or modify
% it under the terms of the GNU Lesser General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
%
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU Lesser General Public License for more details.
%
% You should have received a copy of the GNU Lesser General Public License
% along with this program.  If not, see <http://www.gnu.org/licenses/>.
%
% TeX is a trademark of the American Mathematical Society.
% METAFONT is a trademark of Addison-Wesley Publishing Company.
% PostScript is a trademark of Adobe Systems Incorporated.

% Here is TeX material that gets inserted after \input webmac

\font\tenlogo=logo10 % font used for the METAFONT logo
\font\logos=logosl10
\def\MF{{\tenlogo META}\-{\tenlogo FONT}}
\def\MP{{\tenlogo META}\-{\tenlogo POST}}
\def\<#1>{$\langle#1\rangle$}
\def\section{\mathhexbox278}
\def\[#1]{} % from pascal web
\def\(#1){} % this is used to make section names sort themselves better
\def\9#1{} % this is used for sort keys in the index via @@:sort key}{entry@@>

\def\title{MetaPost SVG output}
\def\topofcontents{\hsize 5.5in
  \vglue -30pt plus 1fil minus 1.5in
  \def\?##1]{\hbox to 1in{\hfil##1.\ }}
  }
\def\botofcontents{\vskip 0pt plus 1fil minus 1.5in}
\pdfoutput=1
\pageno=3

@ 
@d zero_t  ((math_data *)mp->math)->zero_t
@d number_zero(A)		       (((math_data *)(mp->math))->equal)(A,zero_t)		       
@d number_greater(A,B)		       (((math_data *)(mp->math))->greater)(A,B)		       
@d number_positive(A)		       number_greater(A, zero_t)		       
@d number_to_scaled(A)		       (((math_data *)(mp->math))->to_scaled)(A)		       
@d round_unscaled(A)		       (((math_data *)(mp->math))->round_unscaled)(A)		       
@d true 1
@d false 0
@d null_font 0
@d null 0
@d unity   1.0
@d incr(A)   (A)=(A)+1 /* increase a variable by unity */
@d decr(A)   (A)=(A)-1 /* decrease a variable by unity */
@d negate(A)   (A)=-(A) /* change the sign of a variable */

@c
#include <w2c/config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include "mplib.h"
#include "mplibps.h" /* external header */
#include "mplibsvg.h" /* external header */
#include "mpmp.h" /* internal header */
#include "mppsout.h" /* internal header */
#include "mpsvgout.h" /* internal header */
#include "mpmath.h" /* internal header */
@h
@<Types in the outer block@>
@<Declarations@>

@ There is a small bit of code from the backend that bleads through
to the frontend because I do not know how to set up the includes
properly. That is |typedef struct svgout_data_struct * svgout_data|.

@ @(mpsvgout.h@>=
#ifndef MPSVGOUT_H
#define MPSVGOUT_H 1
#include "mplib.h"
#include "mpmp.h"
#include "mplibps.h"
typedef struct svgout_data_struct {
  @<Globals@>
} svgout_data_struct ;
@<Exported function headers@>
#endif

@ @<Exported function headers@>=
void mp_svg_backend_initialize (MP mp) ;
void mp_svg_backend_free (MP mp) ;

@ @c 
void mp_svg_backend_initialize (MP mp) {
  mp->svg = mp_xmalloc(mp,1,sizeof(svgout_data_struct));
  @<Set initial values@>;
}
void mp_svg_backend_free (MP mp) {
  mp_xfree(mp->svg->buf);
  mp_xfree(mp->svg);
  mp->svg = NULL;
}

@ Writing to SVG files

This variable holds the number of characters on the current SVG file
line. It could also be a boolean because right now the only interesting
thing it does is keep track of whether or not we are start-of-line.

@<Globals@>=
size_t file_offset;

@ @<Set initial values@>=
mp->svg->file_offset = 0;

@ Print a newline.

@c
static void mp_svg_print_ln (MP mp) {
  (mp->write_ascii_file)(mp,mp->output_file,"\n");
  mp->svg->file_offset=0;
} 

@ Print a single character.

@c
static void mp_svg_print_char (MP mp, int s) {
  char ss[2]; 
  ss[0]=(char)s; ss[1]=0; 
  (mp->write_ascii_file)(mp,mp->output_file,(char *)ss); 
  mp->svg->file_offset ++;
}

@ Print a string.

In PostScript, this used to be done in terms of |mp_svg_print_char|,
but that is very expensive (in other words: slow). It should be ok
to print whole strings here because line length of an XML file should
not be an issue to any respectable XML processing tool.

@c
static void mp_svg_print (MP mp, const char *ss) {
  (mp->write_ascii_file)(mp,mp->output_file,ss); 
  mp->svg->file_offset += strlen(ss);
}


@ The procedure |print_nl| is like |print|, but it makes sure that the
string appears at the beginning of a new line.

@c
static void mp_svg_print_nl (MP mp, const char *s) { 
  if ( mp->svg->file_offset>0 )
    mp_svg_print_ln(mp);
  mp_svg_print(mp, s);
}


@ Many of the printing routines use a print buffer to store partial
strings in before feeding the attribute value to |mp_svg_attribute|.

@<Globals...@>=
char *buf;
unsigned loc;
unsigned bufsize;

@ Start with a modest size of 256. the buffer will grow automatically
when needed.

@<Set initial values@>=
mp->svg->loc = 0;
mp->svg->bufsize = 256;
mp->svg->buf = mp_xmalloc(mp,mp->svg->bufsize,1);
memset(mp->svg->buf,0,256);


@ How to append a character or a string of characters to 
the end of the buffer.

@d append_char(A) do {
  if (mp->svg->loc==(mp->svg->bufsize-1)) {
    char *buffer;
    unsigned l;
    l = (unsigned)(mp->svg->bufsize+(mp->svg->bufsize>>4));
    if (l>(0x3FFFFFF)) {
      mp_confusion(mp,"svg buffer size");
    }
    buffer = mp_xmalloc(mp,l,1);
    memset (buffer,0,l);
    memcpy(buffer,mp->svg->buf,(size_t)mp->svg->bufsize);
    mp_xfree(mp->svg->buf);
    mp->svg->buf = buffer ;
    mp->svg->bufsize = l;    
  }
  mp->svg->buf[mp->svg->loc++] = (A);
} while (0)

@d append_string(A) do {
   const char *ss = (A);
   while (*ss != '\0') { append_char(*ss); ss++ ;}
} while (0)

@ This function resets the buffer in preparation of the next string.
The |memset| is an easy way to make sure that the old string is
forgotten completely and that the new string will be zero-terminated.

@c 
static void mp_svg_reset_buf(MP mp) {
   mp->svg->loc = 0;
   memset (mp->svg->buf,0,mp->svg->bufsize);
}

@ Printing the buffer is a matter of printing its string, then
it is reset.

@c
static void mp_svg_print_buf (MP mp) {
   mp_svg_print(mp, (char *)mp->svg->buf);
   mp_svg_reset_buf(mp);
}

@ The following procedure, which stores the decimal representation of
a given integer |n| in the buffer, has been written carefully so that
it works properly if |n=0| or if |(-n)| would cause overflow.

@c
static void mp_svg_store_int (MP mp, integer n) {
  unsigned char dig[23];  /* digits in a number, for rounding */
  integer m; /* used to negate |n| in possibly dangerous cases */
  int k = 0; /* index to current digit; we assume that $|n|<10^{23}$ */
  if ( n<0 ) { 
    append_char('-');
    if ( n>-100000000 ) {
	  negate(n);
    } else  { 
	  m=-1-n; n=m / 10; m=(m % 10)+1; k=1;
      if ( m<10 ) {
        dig[0]=(unsigned char)m;
      } else { 
        dig[0]=0; incr(n);
      }
    }
  }
  do {  
    dig[k]=(unsigned char)(n % 10); n=n / 10; incr(k);
  } while (n!=0);
  /* print the digits */
  while ( k-->0 ){ 
    append_char((char)('0'+dig[k]));
  }
}

@ \MP\ also makes use of a trivial procedure to output two digits. The
following subroutine is usually called with a parameter in the range |0<=n<=99|,
but the assignments makes sure that only the two least significant digits 
are printed, just in case.

@c 
static void mp_svg_store_dd (MP mp,integer n) {
  char nn=(char)abs(n) % 100; 
  append_char((char)('0'+(nn / 10)));
  append_char((char)('0'+(nn % 10)));
}

@ Conversely, here is a procedure analogous to |mp_svg_store_int|. 
A decimal point is printed only if the value is not an integer. If
there is more than one way to print the result with the optimum
number of digits following the decimal point, the closest possible
value is given.

The invariant relation in the \&{do while} loop is that a sequence of
decimal digits yet to be printed will yield the original number if and only if
they form a fraction~$f$ in the range $s-\delta\L10\cdot2^{16}f<s$.
We can stop if and only if $f=0$ satisfies this condition; the loop will
terminate before $s$ can possibly become zero.

@c
static void mp_svg_store_double (MP mp, double s) { 
  char *value, *c;
  value = mp_xmalloc(mp,1,32);
  mp_snprintf(value,32,"%f", s);
  c = value;
  while (*c) {
    append_char(*c); 
    c++;
  }
  free(value);
}


@ Output XML tags. 

In order to create a nicely indented output file, the current tag
nesting level needs to be remembered.

@<Globals...@>=
int level;

@ @<Set initial values@>=
mp->svg->level = 0;

@ Output an XML start tag. 

Because start tags may carry attributes, this happens in two steps.
The close function is trivial of course, but it looks nicer in the source.

@d mp_svg_starttag(A,B) { mp_svg_open_starttag (A,B); mp_svg_close_starttag(A); }

@c 
static void mp_svg_open_starttag (MP mp, const char *s) { 
  int l = mp->svg->level * 2;
  mp_svg_print_ln(mp);
  while (l-->0) {
     append_char(' ');
  }
  append_char('<');
  append_string(s);
  mp_svg_print_buf(mp);
  mp->svg->level++;
}
static void mp_svg_close_starttag (MP mp) { 
  mp_svg_print_char(mp,'>');
}

@ Output an XML end tag. 

If the |indent| is true, then the end tag will appear on the next line
of the SVG file, correctly indented for the current XML nesting
level. If it is false, the end tag will appear immediatelu after the
preceding output.

@c
static void mp_svg_endtag (MP mp, const char *s, boolean indent) { 
  mp->svg->level--;
  if (indent) {
    int l = mp->svg->level * 2;
    mp_svg_print_ln(mp);
    while (l-->0) {
      append_char(' ');
    }
  }
  append_string("</");
  append_string(s);
  append_char('>');
  mp_svg_print_buf(mp);
}

@ Attribute. Can't play with the buffer here becase it is likely
that that is the |v| argument.

@c
static void mp_svg_attribute (MP mp, const char *s, const char *v) { 
  mp_svg_print_char(mp, ' ');
  mp_svg_print(mp, s);
  mp_svg_print(mp,"=\"");
  mp_svg_print(mp, v);
  mp_svg_print_char(mp,'"');
}

@ This is a test to filter out characters that are illegal in XML.
 
@<Character |k| is illegal in SVG output@>=
 (k<=0x8)||(k==0xB)||(k==0xC)||(k>=0xE && k<=0x1F)||
 (k>=0x7F && k<=0x84)||(k>=0x86 && k<=0x9F)


@ This is test is used to switch between direct representation of characters
and character references. Just in case the input string is UTF-8, allow everything
except the characters that have to be quoted for XML well-formedness.

@<Character |k| is not allowed in SVG output@>=
 (k=='&')||(k=='>')||(k=='<')

@ We often need to print a pair of coordinates. 

Because of bugs in svg rendering software, it is necessary to 
change the point coordinates so that there are all in the "positive" 
quadrant of the SVG field. This means an shift and a vertical flip.

The two correction values are calculated by the function that writes
the initial |<svg>| tag, and  are stored in two globals:

@<Globals@>=
integer dx;
integer dy;

@ @c
void mp_svg_pair_out (MP mp,double x, double y) { 
  mp_svg_store_double(mp, (x+mp->svg->dx));
  append_char(' ');
  mp_svg_store_double(mp, (-(y+mp->svg->dy)));
}

@ @<Declarations@>=
void mp_svg_font_pair_out (MP mp,double x, double y) ;

@ @c
void mp_svg_font_pair_out (MP mp,double x, double y) { 
  mp_svg_store_double(mp, (x));
  append_char(' ');
  mp_svg_store_double(mp, -(y));
}

@ When stroking a path with an elliptical pen, it is necessary to distort
the path such that a circular pen can be used to stroke the path.  The path
itself is wrapped in another transformation to restore the points to their
correct location (but now with a modified pen stroke).

Because all the points in the path need fixing, it makes sense to 
have a specific helper to write such distorted pairs of coordinates out. 

@<Declarations@>=
void mp_svg_trans_pair_out (MP mp, mp_pen_info *pen, double x, double y) ;

@ @c 
void mp_svg_trans_pair_out (MP mp, mp_pen_info *pen, double x, double y) { 
  double sx,sy, rx,ry, px, py, retval, divider;
  sx = (pen->sx);
  sy = (pen->sy);
  rx = (pen->rx);
  ry = (pen->ry);
  px = ((x+mp->svg->dx));
  py = ((-(y+mp->svg->dy)));
  divider = (sx*sy - rx*ry);
  retval = (sy*px-ry*py)/divider;
  mp_svg_store_double(mp, (retval)); 
  append_char(' ');
  retval = (sx*py-rx*px)/divider;
  mp_svg_store_double(mp, (retval)); 
}



@ @<Declarations@>=
static void mp_svg_pair_out (MP mp,double x, double y) ;

@ 
@<Declarations@>=
static void mp_svg_print_initial_comment(MP mp,mp_edge_object *hh);

@ @c
void mp_svg_print_initial_comment(MP mp,mp_edge_object *hh) {
  double tx, ty;
  @<Print the MetaPost version and time @>;
  mp_svg_open_starttag(mp,"svg");
  mp_svg_attribute(mp,"version", "1.1");
  mp_svg_attribute(mp,"xmlns", "http://www.w3.org/2000/svg");
  mp_svg_attribute(mp, "xmlns:xlink", "http://www.w3.org/1999/xlink");
  if ( hh->minx>hh->maxx)  { 
    tx = 0;
    ty = 0;
    mp->svg->dx = 0;
    mp->svg->dy = 0;
 } else {
    tx = (hh->minx<0 ? -hh->minx : 0) + hh->maxx;
    ty = (hh->miny<0 ? -hh->miny : 0) + hh->maxy;
    mp->svg->dx = (hh->minx<0 ? -hh->minx : 0);
    mp->svg->dy = (hh->miny<0 ? -hh->miny : 0) - ty;
  }
  mp_svg_store_double(mp, tx);
  mp_svg_attribute(mp,"width", mp->svg->buf);
  mp_svg_reset_buf(mp);
  mp_svg_store_double(mp, ty);
  mp_svg_attribute(mp,"height", mp->svg->buf);
  mp_svg_reset_buf(mp);
  append_string("0 0 "); mp_svg_store_double(mp,tx); 
  append_char(' ');      mp_svg_store_double(mp,ty);
  mp_svg_attribute(mp,"viewBox", mp->svg->buf);
  mp_svg_reset_buf(mp);
  mp_svg_close_starttag(mp);
  mp_svg_print_nl(mp,"<!-- Original BoundingBox: ");
  mp_svg_store_double(mp, hh->minx); append_char(' ');
  mp_svg_store_double(mp, hh->miny); append_char(' ');
  mp_svg_store_double(mp, hh->maxx); append_char(' ');
  mp_svg_store_double(mp, hh->maxy);
  mp_svg_print_buf(mp);  
  mp_svg_print(mp," -->");
}

@ @<Print the MetaPost version and time @>=
{
  char *s;   
  int tt; /* scaled */
  mp_svg_print_nl(mp, "<!-- Created by MetaPost ");
  s = mp_metapost_version();
  mp_svg_print(mp, s);
  mp_xfree(s);
  mp_svg_print(mp, " on ");
  mp_svg_store_int(mp, round_unscaled(internal_value(mp_year))); 
  append_char('.');
  mp_svg_store_dd(mp, round_unscaled(internal_value(mp_month))); 
  append_char('.');
  mp_svg_store_dd(mp, round_unscaled(internal_value(mp_day))); 
  append_char(':');
  tt=round_unscaled(internal_value(mp_time));
  mp_svg_store_dd(mp, tt / 60); 
  mp_svg_store_dd(mp, tt % 60);
  mp_svg_print_buf(mp);
  mp_svg_print(mp, " -->");
}


@ Outputting a color specification.

@d set_color_objects(pq)
  object_color_model = pq->color_model;
  object_color_a = pq->color.a_val;
  object_color_b = pq->color.b_val;
  object_color_c = pq->color.c_val;
  object_color_d = pq->color.d_val; 

@c
static void mp_svg_color_out (MP mp, mp_graphic_object *p) {
  int object_color_model;
  double object_color_a, object_color_b, object_color_c, object_color_d ; 
  if (gr_type(p) == mp_fill_code) {
    mp_fill_object *pq = (mp_fill_object *)p;
    set_color_objects(pq);
  } else if (gr_type(p) == mp_stroked_code) {
    mp_stroked_object *pq = (mp_stroked_object *)p;
    set_color_objects(pq);
  } else {
    mp_text_object *pq = (mp_text_object *)p;
    set_color_objects(pq);
  }
  if ( object_color_model==mp_no_model ) {
    append_string("black");
  } else {
    if ( object_color_model==mp_grey_model ) {
       object_color_b = object_color_a;
       object_color_c = object_color_a;
    } else if ( object_color_model==mp_cmyk_model) {
      int c,m,y,k;
      c = object_color_a;
      m = object_color_b;
      y = object_color_c;
      k = object_color_d;
      object_color_a = unity - (c+k>unity ? unity : c+k);
      object_color_b = unity - (m+k>unity ? unity : m+k);
      object_color_c = unity - (y+k>unity ? unity : y+k);
    }
    append_string("rgb(");
    mp_svg_store_double(mp, (object_color_a * 100));
    append_char('%');
    append_char(',');
    mp_svg_store_double(mp, (object_color_b * 100));
    append_char('%');
    append_char(',');
    mp_svg_store_double(mp, (object_color_c * 100));
    append_char('%');
    append_char(')');
  }
}

@ @<Declarations@>=
static void mp_svg_color_out (MP mp, mp_graphic_object *p);

@ This is the information that comes from a pen

@<Types...@>=
typedef struct mp_pen_info {
  double tx, ty;
  double sx, rx, ry, sy; 
  double ww;
} mp_pen_info;


@ (Re)discover the characteristics of an elliptical pen

@<Declarations@>=
mp_pen_info *mp_svg_pen_info(MP mp, mp_gr_knot pp, mp_gr_knot p);

@ The next two constants come from the original web source. 
Together with the two helper functions, they will tell whether 
the |x| or the |y| direction of the path is the most important

@d aspect_bound   (10/65536.0)
@d aspect_default 1

@c
static double coord_range_x (mp_gr_knot h, double dz) {
  double z;
  double zlo = 0, zhi = 0;
  mp_gr_knot f = h; 
  while (h != NULL) {
    z = gr_x_coord(h);
    if (z < zlo) zlo = z; else if (z > zhi) zhi = z;
    z = gr_right_x(h);
    if (z < zlo) zlo = z; else if (z > zhi) zhi = z;
    z = gr_left_x(h);
    if (z < zlo) zlo = z; else if (z > zhi) zhi = z;
    h = gr_next_knot(h);
    if (h==f)
      break;
  }
  return (zhi - zlo <= dz ? aspect_bound : aspect_default);
}
static double coord_range_y (mp_gr_knot h, double dz) {
  double z;
  double zlo = 0, zhi = 0;
  mp_gr_knot f = h; 
  while (h != NULL) {
    z = gr_y_coord(h);
    if (z < zlo) zlo = z; else if (z > zhi) zhi = z;
    z = gr_right_y(h);
    if (z < zlo) zlo = z; else if (z > zhi) zhi = z;
    z = gr_left_y(h);
    if (z < zlo) zlo = z; else if (z > zhi) zhi = z;
    h = gr_next_knot(h);
    if (h==f)
      break;
  }
  return (zhi - zlo <= dz ? aspect_bound : aspect_default);
}

@ 
@c
mp_pen_info *mp_svg_pen_info(MP mp, mp_gr_knot pp, mp_gr_knot p) {
  double wx, wy; /* temporary pen widths, in either direction */
  struct mp_pen_info *pen; /* return structure */
  if (p == NULL)
     return NULL;
  pen = mp_xmalloc(mp, 1, sizeof(mp_pen_info));
  pen->rx = unity;
  pen->ry = unity;
  pen->ww = unity;
  if ((gr_right_x(p) == gr_x_coord(p)) 
       && 
      (gr_left_y(p) == gr_y_coord(p))) {
    wx = fabs(gr_left_x(p)  - gr_x_coord(p));
    wy = fabs(gr_right_y(p) - gr_y_coord(p));
  } else {
    mp_number arg1, arg2, ret;
    new_number(ret);
    new_number(arg1);
    new_number(arg2);
    mp_set_number_from_double (&arg1, gr_left_x(p)-gr_x_coord(p));
    mp_set_number_from_double (&arg2, gr_right_x(p)-gr_x_coord(p));
    mp_pyth_add(mp, &ret, arg1, arg2);
    wx = mp_number_to_double(ret);
    mp_set_number_from_double (&arg1, gr_left_y(p)-gr_y_coord(p));
    mp_set_number_from_double (&arg2, gr_right_y(p)-gr_y_coord(p));
    mp_pyth_add(mp, &ret, arg1, arg2);
    wy = mp_number_to_double(ret);
    free_number(ret);
    free_number(arg1);
    free_number(arg2);
  }
  if ((wy/coord_range_x(pp, wx)) >= (wx/coord_range_y(pp, wy)))
    pen->ww = wy;
  else
    pen->ww = wx;
  pen->tx = gr_x_coord(p); 
  pen->ty = gr_y_coord(p);
  pen->sx = gr_left_x(p) - pen->tx; 
  pen->rx = gr_left_y(p) - pen->ty; 
  pen->ry = gr_right_x(p) - pen->tx; 
  pen->sy = gr_right_y(p) - pen->ty;
  if (pen->ww != unity) {
    if (pen->ww == 0) {
      pen->sx = unity;
      pen->sy = unity;
    } else {
      /* this negation is needed because the svg coordinate system differs
         from postscript's. */
      pen->rx = -(pen->rx / pen->ww);
      pen->ry = -(pen->ry / pen->ww);
      pen->sx = pen->sx / pen->ww;
      pen->sy = pen->sy / pen->ww;
    }
  }
  return pen;
}

@ Two types of straight lines come up often in \MP\ paths:
cubics with zero initial and final velocity as created by |make_path| or
|make_envelope|, and cubics with control points uniformly spaced on a line
as created by |make_choices|.

@<Declarations@>=
static boolean mp_is_curved(mp_gr_knot p, mp_gr_knot q) ;


@ 
@d bend_tolerance (131/65536.0) /* allow rounding error of $2\cdot10^{-3}$ */

@c 
boolean mp_is_curved(mp_gr_knot p, mp_gr_knot q) {
  double d; /* a temporary value */
  if ( gr_right_x(p)==gr_x_coord(p) )
    if ( gr_right_y(p)==gr_y_coord(p) )
      if ( gr_left_x(q)==gr_x_coord(q) )
        if ( gr_left_y(q)==gr_y_coord(q) ) 
          return false;
  d=gr_left_x(q)-gr_right_x(p);
  if ( fabs(gr_right_x(p)-gr_x_coord(p)-d)<=bend_tolerance )
    if ( fabs(gr_x_coord(q)-gr_left_x(q)-d)<=bend_tolerance ) {
      d=gr_left_y(q)-gr_right_y(p);
      if ( fabs(gr_right_y(p)-gr_y_coord(p)-d)<=bend_tolerance )
        if ( fabs(gr_y_coord(q)-gr_left_y(q)-d)<=bend_tolerance )
           return false;
    }
  return true;
}


@ @c
static void mp_svg_path_out (MP mp, mp_gr_knot h) {
  mp_gr_knot p, q; /* for scanning the path */
  append_char('M');
  mp_svg_pair_out(mp, gr_x_coord(h),gr_y_coord(h));
  p=h;
  do {  
    if ( gr_right_type(p)==mp_endpoint ) { 
      if ( p==h ) {
        append_string("l0 0");
      }
      return;
    }
    q=gr_next_knot(p);
    if (mp_is_curved(p, q)){ 
      append_char('C');
      mp_svg_pair_out(mp, gr_right_x(p),gr_right_y(p));
      append_char(',');
      mp_svg_pair_out(mp, gr_left_x(q),gr_left_y(q));
      append_char(',');
      mp_svg_pair_out(mp, gr_x_coord(q),gr_y_coord(q));
    } else if ( q!=h ){ 
      append_char('L');
      mp_svg_pair_out(mp, gr_x_coord(q),gr_y_coord(q));
    }
    p=q;
  } while (p!=h);
  append_char('Z');
  append_char(0);
}

@ @c
static void mp_svg_path_trans_out (MP mp, mp_gr_knot h, mp_pen_info *pen) {
  mp_gr_knot p, q; /* for scanning the path */
  append_char('M');
  mp_svg_trans_pair_out(mp, pen, gr_x_coord(h),gr_y_coord(h));
  p=h;
  do {  
    if ( gr_right_type(p)==mp_endpoint ) { 
      if ( p==h ) {
        append_string("l0 0");
      }
      return;
    }
    q=gr_next_knot(p);
    if (mp_is_curved(p, q)){ 
      append_char('C');
      mp_svg_trans_pair_out(mp, pen, gr_right_x(p),gr_right_y(p));
      append_char(',');
      mp_svg_trans_pair_out(mp, pen,gr_left_x(q),gr_left_y(q));
      append_char(',');
      mp_svg_trans_pair_out(mp, pen,gr_x_coord(q),gr_y_coord(q));
    } else if ( q!=h ){ 
      append_char('L');
      mp_svg_trans_pair_out(mp, pen,gr_x_coord(q),gr_y_coord(q));
   }
    p=q;
  } while (p!=h);
  append_char('Z');
  append_char(0);
}


@ @c
static void mp_svg_font_path_out (MP mp, mp_gr_knot h) {
  mp_gr_knot p, q; /* for scanning the path */
  append_char('M');
  mp_svg_font_pair_out(mp, gr_x_coord(h),gr_y_coord(h));
  p=h;
  do {  
    if ( gr_right_type(p)==mp_endpoint ) { 
      if ( p==h ) {
        append_char('l');
        mp_svg_font_pair_out(mp, 0, 0);
      }
      return;
    }
    q=gr_next_knot(p);
    if (mp_is_curved(p, q)){ 
      append_char('C');
      mp_svg_font_pair_out(mp, gr_right_x(p),gr_right_y(p));
      append_char(',');
      mp_svg_font_pair_out(mp, gr_left_x(q),gr_left_y(q));
      append_char(',');
      mp_svg_font_pair_out(mp, gr_x_coord(q),gr_y_coord(q));
    } else if ( q!=h ){ 
      append_char('L');
      mp_svg_font_pair_out(mp, gr_x_coord(q),gr_y_coord(q));
    }
    p=q;
  } while (p!=h);
  append_char(0);
}

@ If |prologues:=3|, any glyphs in labels will be converted into paths.

@d do_mark(A,B) do {
   if (mp_chars == NULL) {
     mp_chars = mp_xmalloc(mp, mp->font_max+1, sizeof(int *));
     memset(mp_chars, 0, ((mp->font_max+1) * sizeof(int *)));
   }
   if (mp_chars[(A)] == NULL) {
     int *glfs =  mp_xmalloc(mp, 256, sizeof(int));
     memset(glfs, 0, (256 * sizeof(int)));
     mp_chars[(A)] = glfs;
   }
   mp_chars[(A)][(int)(B)] = 1;
} while (0)

@<Declarations@>=
void mp_svg_print_glyph_defs (MP mp, mp_edge_object *h);

@ @c
void mp_svg_print_glyph_defs (MP mp, mp_edge_object *h) {
  mp_graphic_object *p; /* object index */
  int k; /* general purpose index */
  size_t l; /* a string length */
  int **mp_chars = NULL; /* a twodimensional array of used glyphs */
  mp_ps_font *f = NULL; 
  mp_edge_object *ch;
  p = h->body;
  while ( p!=NULL ) {
    if ((gr_type(p) == mp_text_code) &&
        (gr_font_n(p)!=null_font) && 
        ((l = gr_text_l(p))>0) ) {
      unsigned char *s = (unsigned char *)gr_text_p(p);
      while (l-->0) {
        do_mark(gr_font_n(p), *s);
        s++;
      }
    }
    p=gr_link(p);
  }
  if (mp_chars != NULL) {
    mp_svg_starttag(mp,"defs");
    for (k=0;k<=(int)mp->font_max;k++) {
       if (mp_chars[k] != NULL ) {
          double scale; /* the next gives rounding errors */
          double ds,dx,sk;
          ds =(mp->font_dsize[k]+8) / 16;
          scale = (1/1000.0) * (ds);
          ds = (scale);
          dx = ds;
          sk = 0;
          for (l=0;l<256;l++) {
            if (mp_chars[k][l] == 1) {
               if (f == NULL) {
                  f = mp_ps_font_parse(mp, k);
                  if (f == NULL) continue;
                  if (f->extend != 0) {
                    dx = (((double)f->extend / 1000.0) * scale);
                  }
                  if (f->slant != 0) {
                    sk = (((double)f->slant / 1000.0) * 90);
                  } 
               }
               mp_svg_open_starttag(mp,"g");
               append_string("scale(");
               mp_svg_store_double(mp,dx/65536);
               append_char(',');
               mp_svg_store_double(mp,ds/65536);
               append_char(')');
               if (sk!=0) {
                  append_string(" skewX(");
                  mp_svg_store_double(mp,-sk);
                  append_char(')');
               }
               mp_svg_attribute(mp, "transform", mp->svg->buf);
               mp_svg_reset_buf(mp);

               append_string("GLYPH");
               append_string(mp->font_name[k]);
               append_char('_');
               mp_svg_store_int(mp, (int)l);
               mp_svg_attribute(mp, "id", mp->svg->buf);
               mp_svg_reset_buf(mp);
               mp_svg_close_starttag(mp);
               if (f != NULL) {
                 ch = mp_ps_font_charstring(mp,f,(int)l);
                 if (ch != NULL) {
                   p = ch->body;
                   mp_svg_open_starttag(mp,"path");
                   mp_svg_attribute(mp, "style", "fill-rule: evenodd;");
                   while (p!=NULL) {
                     if (mp->svg->loc>0) mp->svg->loc--; /* drop a '\0' */
                     mp_svg_font_path_out(mp, gr_path_p((mp_fill_object *)p));
                     p=p->next;
                   }
                   mp_svg_attribute(mp, "d", mp->svg->buf);
                   mp_svg_reset_buf(mp);
                   mp_svg_close_starttag(mp);
                   mp_svg_endtag(mp,"path",false);
                 }
                 mp_gr_toss_objects(ch);
               }
               mp_svg_endtag(mp,"g",true);
            }
          }
          if (f!=NULL) { mp_ps_font_free(mp, f); f = NULL; }
       }
    }
    mp_svg_endtag(mp,"defs", true);
    
    /* cleanup */
    for (k=0;k<(int)mp->font_max;k++) {
      mp_xfree(mp_chars[k]);
    }
    mp_xfree(mp_chars);
  }
}


@ Now for outputting the actual graphic objects. 

@<Declarations@>=
static void mp_svg_text_out (MP mp, mp_text_object *p, int prologues) ;

@ @c
void mp_svg_text_out (MP mp, mp_text_object *p, int prologues) {
  /* -Wunused: char *fname; */
  unsigned char *s;
  int k; /* a character */
  size_t l; /* string length */
  boolean transformed ;
  double ds; /* design size and scale factor for a text node */
  /* clang: never read: fname = mp->font_ps_name[gr_font_n(p)]; */
  s = (unsigned char *)gr_text_p(p);
  l = gr_text_l(p);
  transformed=(gr_txx_val(p)!=unity)||(gr_tyy_val(p)!=unity)||
              (gr_txy_val(p)!=0)||(gr_tyx_val(p)!=0);
  mp_svg_open_starttag(mp, "g");
  if ( transformed ) {
    append_string("matrix(");
    mp_svg_store_double(mp,gr_txx_val(p)); append_char(',');
    mp_svg_store_double(mp,-gr_tyx_val(p)); append_char(',');
    mp_svg_store_double(mp,-gr_txy_val(p)); append_char(',');
    mp_svg_store_double(mp,gr_tyy_val(p)); append_char(',');
  } else { 
    append_string("translate(");
  }
  mp_svg_pair_out(mp,gr_tx_val(p),gr_ty_val(p)); 
  append_char(')');
  
  mp_svg_attribute(mp, "transform", mp->svg->buf);
  mp_svg_reset_buf(mp);

  append_string("fill: ");
  mp_svg_color_out(mp,(mp_graphic_object *)p);
  append_char(';');
  mp_svg_attribute(mp, "style", mp->svg->buf);
  mp_svg_reset_buf(mp);

  mp_svg_close_starttag(mp);
   
  if (prologues == 3 ) {
     
    double charwd;
    double wd = 0.0; /* this is in PS design units */
    while (l-->0) {
      k=(int)*s++;
      mp_svg_open_starttag(mp, "use");
      append_string("#GLYPH");
      append_string(mp->font_name[gr_font_n(p)]);
      append_char('_');
      mp_svg_store_int(mp,k);
      mp_svg_attribute(mp,"xlink:href", mp->svg->buf);
      mp_svg_reset_buf(mp);
      charwd = ((wd/100));
      if (charwd!=0) {
        mp_svg_store_double(mp,charwd);
        mp_svg_attribute(mp,"x", mp->svg->buf);
        mp_svg_reset_buf(mp);
      }
      wd += mp_get_char_dimension (mp, mp->font_name[gr_font_n(p)], k, 'w');
      mp_svg_close_starttag(mp);
      mp_svg_endtag(mp, "use", false);
   }
  }  else {
    mp_svg_open_starttag(mp, "text");
    ds=(mp->font_dsize[gr_font_n(p)]+8) / 16 / 65536.0;
    mp_svg_store_double(mp,ds);
    mp_svg_attribute(mp, "font-size", mp->svg->buf);
    mp_svg_reset_buf(mp);
    mp_svg_close_starttag(mp);
  
    while (l-->0) {
      k=(int)*s++;
      if (@<Character |k| is illegal in SVG output@>) {
        char S[100];
        mp_snprintf(S,99,"The character %d cannot be output in SVG "
                         "unless prologues:=3;",k);
        mp_warn(mp,S);
      } else if ( (@<Character |k| is not allowed in SVG output@>) ) {
        append_string("&#");
        mp_svg_store_int(mp,k);
        append_char(';');
      } else {
        append_char((char)k);
      }
    }
    mp_svg_print_buf(mp);
    mp_svg_endtag(mp, "text", false);
  }
  mp_svg_endtag(mp, "g", true);
}

@ When stroking a path with an elliptical pen, it is necessary to transform
the coordinate system so that a unit circular pen will have the desired shape.
To keep this transformation local, we enclose it in a $$\&{<g>}\ldots\&{</g>}$$
block. Any translation component must be applied to the path being stroked
while the rest of the transformation must apply only to the pen.
If |fill_also=true|, the path is to be filled as well as stroked so we must
insert commands to do this after giving the path.

@<Declarations@>=
static void mp_svg_stroke_out (MP mp,  mp_graphic_object *h, 
                               mp_pen_info *pen, boolean fill_also) ;


@ @c
void mp_svg_stroke_out (MP mp,  mp_graphic_object *h, 
                              mp_pen_info *pen, boolean fill_also) {
  boolean transformed = false;
  if (pen != NULL) {
    transformed = true;
    if ((pen->sx==unity) &&
        (pen->rx==0) &&
        (pen->ry==0) &&
        (pen->sy==unity) &&
        (pen->tx==0) && 
        (pen->ty==0)) {
      transformed = false;
    }
  }
  if (transformed) {
    mp_svg_open_starttag(mp, "g");
    append_string("matrix(");
    mp_svg_store_double(mp,pen->sx);  append_char(',');
    mp_svg_store_double(mp,pen->rx);  append_char(',');
    mp_svg_store_double(mp,pen->ry);  append_char(',');
    mp_svg_store_double(mp,pen->sy);  append_char(',');
    mp_svg_store_double(mp,pen->tx);  append_char(',');
    mp_svg_store_double(mp,pen->ty);
    append_char(')');
    mp_svg_attribute(mp, "transform", mp->svg->buf);
    mp_svg_reset_buf(mp);
    mp_svg_close_starttag(mp);
  }
  mp_svg_open_starttag(mp, "path");

  if (false) {
    if (transformed) 
      mp_svg_path_trans_out(mp, gr_path_p((mp_fill_object *)h), pen);
    else
      mp_svg_path_out(mp, gr_path_p((mp_fill_object *)h));
    mp_svg_attribute(mp, "d", mp->svg->buf);
    mp_svg_reset_buf(mp);
    append_string("fill: ");
    mp_svg_color_out(mp,h);
    append_string("; stroke: none;");
    mp_svg_attribute(mp, "style", mp->svg->buf);
    mp_svg_reset_buf(mp);
  } else {
    if (transformed) 
      mp_svg_path_trans_out(mp, gr_path_p((mp_stroked_object *)h), pen);
    else
      mp_svg_path_out(mp, gr_path_p((mp_stroked_object *)h));
    mp_svg_attribute(mp, "d", mp->svg->buf);
    mp_svg_reset_buf(mp);
    append_string("stroke:");
    mp_svg_color_out(mp,h);
    append_string("; stroke-width: ");
    if (pen != NULL) {
      mp_svg_store_double(mp, pen->ww);
    } else {
      append_char('0');
    }
    append_char(';');
    if (gr_lcap_val(h)!=0) {
      append_string("stroke-linecap: ");
      switch (gr_lcap_val(h)) {
        case 1: append_string("round"); break;
        case 2: append_string("square"); break;
        default: append_string("butt"); break;
      }
      append_char(';');
    }
    if (gr_type(h)!=mp_fill_code) {
      mp_dash_object *hh;
      hh =gr_dash_p(h);
      if (hh != NULL && hh->array != NULL) {
         int i;
         append_string("stroke-dasharray: "); 
         /* svg doesn't accept offsets */
         for (i=0; *(hh->array+i) != -1;i++) {
           mp_svg_store_double(mp, *(hh->array+i)); 
           append_char(' ')	;
         }
         append_char(';');
      }

    if (gr_ljoin_val((mp_stroked_object *)h)!=0) {
      append_string ("stroke-linejoin: ");
      switch (gr_ljoin_val((mp_stroked_object *)h)) {
        case 1:  append_string("round"); break;
        case 2:  append_string("bevel"); break;
        default: append_string("miter"); break;
      }
      append_char(';');
    }
  
    if (gr_miterlim_val((mp_stroked_object *)h) != 4*unity) {
      append_string("stroke-miterlimit: ");
      mp_svg_store_double(mp, gr_miterlim_val((mp_stroked_object *)h)); 
      append_char(';');
    }
    }

    append_string("fill: ");
    if (fill_also) {
      mp_svg_color_out(mp,h);
    } else {
      append_string("none");
    }
    append_char(';');
    mp_svg_attribute(mp, "style", mp->svg->buf);
    mp_svg_reset_buf(mp);
  }
  mp_svg_close_starttag(mp);
  mp_svg_endtag(mp, "path", false);
  if (transformed) {
    mp_svg_endtag(mp, "g", true);
  }
}

@ Here is a simple routine that just fills a cycle.

@<Declarations@>=
static void mp_svg_fill_out (MP mp, mp_gr_knot p, mp_graphic_object *h);

@ @c
void mp_svg_fill_out (MP mp, mp_gr_knot p, mp_graphic_object *h) {
  mp_svg_open_starttag(mp, "path");
  mp_svg_path_out(mp, p);
  mp_svg_attribute(mp, "d", mp->svg->buf);
  mp_svg_reset_buf(mp);
  append_string("fill: ");
  mp_svg_color_out(mp,h);
  append_string(";stroke: none;");
  mp_svg_attribute(mp, "style", mp->svg->buf);
  mp_svg_reset_buf(mp);
  mp_svg_close_starttag(mp); /* path */
  mp_svg_endtag(mp, "path", false);
}

@ Clipping paths use IDs, so an extra global is needed:

@<Globals...@>=
int clipid;

@
@<Set initial values@>=
mp->svg->clipid = 0;

@ @<Declarations@>=
static void mp_svg_clip_out (MP mp, mp_clip_object *p);

@ @c
void mp_svg_clip_out (MP mp, mp_clip_object *p) {
  mp->svg->clipid++;
  mp_svg_starttag(mp, "g"); 
  mp_svg_starttag(mp, "defs"); 
  mp_svg_open_starttag(mp, "clipPath"); 

  append_string("CLIP");
  mp_svg_store_int(mp, mp->svg->clipid);
  mp_svg_attribute(mp, "id", mp->svg->buf);
  mp_svg_reset_buf(mp);

  mp_svg_close_starttag(mp); 
  mp_svg_open_starttag(mp, "path"); 
  mp_svg_path_out(mp, gr_path_p(p));
  mp_svg_attribute(mp,"d", mp->svg->buf);
  mp_svg_reset_buf(mp);
  mp_svg_attribute(mp, "style", "fill: black; stroke: none;");
  mp_svg_close_starttag(mp);  /* path */
  mp_svg_endtag(mp, "path", false); 
  mp_svg_endtag(mp, "clipPath", true); 
  mp_svg_endtag(mp, "defs", true); 
  mp_svg_open_starttag(mp, "g"); 

  append_string("url(#CLIP");
  mp_svg_store_int(mp, mp->svg->clipid);
  append_string(");");
  mp_svg_attribute(mp, "clip-path", mp->svg->buf);
  mp_svg_reset_buf(mp);

  mp_svg_close_starttag(mp); 
}



@ The main output function

@d gr_has_scripts(A) (gr_type((A))<mp_start_clip_code)
@d pen_is_elliptical(A) ((A)==gr_next_knot((A)))

@<Exported function ...@>=
int mp_svg_gr_ship_out (mp_edge_object *hh, int prologues, int standalone) ;

@ @c 
int mp_svg_gr_ship_out (mp_edge_object *hh, int qprologues, int standalone) {
  mp_graphic_object *p;
  mp_pen_info *pen = NULL;
  MP mp = hh->parent;
  if (standalone) {
     mp->jump_buf = malloc(sizeof(jmp_buf));
     if (mp->jump_buf == NULL || setjmp(*(mp->jump_buf)))
       return 0;
  }
  if (mp->history >= mp_fatal_error_stop ) return 1;
  mp_open_output_file(mp);
  if ( (qprologues>=1) && (mp->last_ps_fnum==0) && mp->last_fnum>0)
    mp_read_psname_table(mp);
  /* The next seems counterintuitive, but calls from |mp_svg_ship_out|
   * set standalone to true, and because embedded use is likely, it is 
   * better not to output the XML declaration in that case.
   */
  if (!standalone)
    mp_svg_print(mp, "<?xml version=\"1.0\"?>");
  mp_svg_print_initial_comment(mp, hh); 
  if (qprologues == 3) {
    mp_svg_print_glyph_defs(mp, hh);
  }
  p = hh->body;
  while ( p!=NULL ) { 
    if ( gr_has_scripts(p) ) {
      @<Write |pre_script| of |p|@>;
    }
    switch (gr_type(p)) {
    case mp_fill_code: 
      {
        mp_fill_object *ph = (mp_fill_object *)p;
        if ( gr_pen_p(ph)==NULL ) {
          mp_svg_fill_out(mp, gr_path_p(ph), p);
        } else if ( pen_is_elliptical(gr_pen_p(ph)) )  {
          pen = mp_svg_pen_info(mp, gr_path_p(ph), gr_pen_p(ph));
          mp_svg_stroke_out(mp, p, pen, true);
          mp_xfree(pen);
        } else { 
          mp_svg_fill_out(mp, gr_path_p(ph), p);
          mp_svg_fill_out(mp, gr_htap_p(ph), p);
        }
      }
      break;
    case mp_stroked_code:
      {
        mp_stroked_object *ph = (mp_stroked_object *)p;
        if ( pen_is_elliptical(gr_pen_p(ph))) {
          pen = mp_svg_pen_info(mp, gr_path_p(ph), gr_pen_p(ph));
	      mp_svg_stroke_out(mp, p, pen, false);
          mp_xfree(pen);
        } else { 
          mp_svg_fill_out(mp, gr_path_p(ph), p);
        }
      }
      break;
    case mp_text_code: 
      if ( (gr_font_n(p)!=null_font) && (gr_text_l(p)>0) ) {
        mp_svg_text_out(mp, (mp_text_object *)p, qprologues);
      }
      break;
    case mp_start_clip_code: 
       mp_svg_clip_out(mp, (mp_clip_object *)p);
      break;
    case mp_stop_clip_code: 
      mp_svg_endtag(mp, "g", true); 
      mp_svg_endtag(mp, "g", true); 
      break;
    case mp_start_bounds_code:
    case mp_stop_bounds_code:
	  break;
    case mp_special_code:  
      {
        mp_special_object *ps = (mp_special_object *)p;
        mp_svg_print_nl (mp, gr_pre_script(ps)); 
 	    mp_svg_print_ln (mp);
      }
      break;
    } /* all cases are enumerated */
    if ( gr_has_scripts(p) ) {
      @<Write |post_script| of |p|@>;
    }
    p=gr_link(p);
  }
  mp_svg_endtag(mp, "svg", true); 
  mp_svg_print_ln(mp);
  (mp->close_file)(mp,mp->output_file);
  return 1;
}

@ @(mplibsvg.h@>=
#ifndef MPLIBSVG_H
#define MPLIBSVG_H 1
#include "mplibps.h"
int mp_svg_ship_out (mp_edge_object *hh, int prologues) ;
#endif

@ @c
int mp_svg_ship_out (mp_edge_object *hh, int prologues) {
  return mp_svg_gr_ship_out (hh, prologues, (int)true);
}

@ 
@d do_write_prescript(a,b) {
  if ( (gr_pre_script((b *)a))!=NULL ) {
    mp_svg_print_nl (mp, gr_pre_script((b *)a)); 
    mp_svg_print_ln(mp);
  }
}

@<Write |pre_script| of |p|@>=
{
  if (gr_type(p)==mp_fill_code) { do_write_prescript(p,mp_fill_object); }
  else if (gr_type(p)==mp_stroked_code) { do_write_prescript(p,mp_stroked_object); }
  else if (gr_type(p)==mp_text_code) { do_write_prescript(p,mp_text_object); }
}


@ 
@d do_write_postscript(a,b) {
  if ( (gr_post_script((b *)a))!=NULL ) {
    mp_svg_print_nl (mp, gr_post_script((b *)a)); 
    mp_svg_print_ln(mp);
  }
}

@<Write |post_script| of |p|@>=
{
  if (gr_type(p)==mp_fill_code) { do_write_postscript(p,mp_fill_object); }
  else if (gr_type(p)==mp_stroked_code) { do_write_postscript(p,mp_stroked_object); }
  else if (gr_type(p)==mp_text_code) { do_write_postscript(p,mp_text_object); }
}