% Copyright 2012 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 PNG 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 "mplibpng.h" /* external header */
#include "mpmp.h" /* internal header */
#include "mppsout.h" /* internal header */
#include "mppngout.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 pngout_data_struct * pngout_data|.

@ @(mppngout.h@>=
#ifndef MPPNGOUT_H
#define MPPNGOUT_H 1
#include "cairo.h"
const char *COMPILED_CAIRO_VERSION_STRING = CAIRO_VERSION_STRING;
#include "pixman.h"
const char *COMPILED_PIXMAN_VERSION_STRING = PIXMAN_VERSION_STRING;
#define PNG_SKIP_SETJMP_CHECK 1
#include "png.h"
#include "mplib.h"
#include "mpmp.h"
#include "mplibps.h"
typedef struct pngout_data_struct {
  @<Globals@>
} pngout_data_struct ;
@<Exported function headers@>
#endif

@ @<Exported function headers@>=
void mp_png_backend_initialize (MP mp) ;
void mp_png_backend_free (MP mp) ;

@ @c 
void mp_png_backend_initialize (MP mp) {
  mp->png = mp_xmalloc(mp,1,sizeof(pngout_data_struct));
  memset(mp->png,0,sizeof(pngout_data_struct));
}
void mp_png_backend_free (MP mp) {
  mp_xfree(mp->png);
  mp->png = NULL;
}

@ Writing to PNG files

@<Globals@>=
cairo_surface_t *surface;
cairo_t *cr;

@ We often need to print a pair of coordinates, and these need to
offset so that all coordinates are positive.

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

@ 
@<Declarations@>=
static void mp_png_start(MP mp,mp_edge_object *hh, double hppp, double vppp, int colormodel, int antialias);

@ 
@c
void mp_png_start(MP mp,mp_edge_object *hh, double hppp, double vppp, int colormodel, int antialias) {
  double w, h;
  if ( hh->minx>hh->maxx)  { 
    w = 1;
    h = 1;
    mp->png->dx = 0;
    mp->png->dy = 0;
 } else {
    w = (ceil(hh->maxx) - floor(hh->minx)) / hppp;
    h = (ceil(hh->maxy) - floor(hh->miny)) / vppp;
    mp->png->dx = -floor(hh->minx);
    mp->png->dy = -floor(hh->miny);
  }
  mp->png->surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, w, h);
  mp->png->cr = cairo_create (mp->png->surface);
  /* if there is no alpha channel, a white background is needed */
  if (colormodel == PNG_COLOR_TYPE_RGB ||
      colormodel == PNG_COLOR_TYPE_GRAY) {
     cairo_save(mp->png->cr);
     cairo_set_source_rgb(mp->png->cr, 1.0, 1.0, 1.0);
     cairo_rectangle(mp->png->cr, 0, 0, w, h);
     cairo_fill(mp->png->cr);
     cairo_restore(mp->png->cr);
  }
  cairo_scale(mp->png->cr, 1/hppp, -1/vppp);
  cairo_translate(mp->png->cr, 0, -(h*vppp));
  cairo_translate(mp->png->cr, mp->png->dx, mp->png->dy);
  cairo_set_antialias(mp->png->cr, antialias);
}

@ 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_png_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 ) {
    cairo_set_source_rgb (mp->png->cr, 0, 0, 0);
  } 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);
    }
    cairo_set_source_rgb (mp->png->cr, object_color_a, object_color_b, object_color_c);
  }
}

@ @<Declarations@>=
static void mp_png_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_png_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_png_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 {
    double arg1, arg2;
    arg1 = gr_left_x(p)-gr_x_coord(p);
    arg2 = gr_right_x(p)-gr_x_coord(p);
    wx = sqrt(arg1*arg1 + arg2*arg2);
    arg1 = gr_left_y(p)-gr_y_coord(p);
    arg2 = gr_right_y(p)-gr_y_coord(p);
    wy = sqrt(arg1*arg1 + arg2*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 {
      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;
}


@ Cairo does not want to draw a path that consists of only a moveto,
so make sure there is some kind of line even for single-pair paths.
@c
static void mp_png_path_out (MP mp, mp_gr_knot h) {
  mp_gr_knot p, q; /* for scanning the path */
  int steps = 0;
  cairo_move_to (mp->png->cr, gr_x_coord(h),gr_y_coord(h));
  p=h;
  do {  
    if ( gr_right_type(p)==mp_endpoint ) { 
      if (steps==0) {
         cairo_line_to (mp->png->cr, gr_x_coord(p),gr_y_coord(p));
      }
      return;
    }
    q=gr_next_knot(p);
    if (mp_is_curved(p, q)){ 
      cairo_curve_to (mp->png->cr, gr_right_x(p),gr_right_y(p), 
                                   gr_left_x(q),gr_left_y(q),
                                   gr_x_coord(q),gr_y_coord(q));
    } else { 
      cairo_line_to (mp->png->cr, gr_x_coord(q),gr_y_coord(q));
    }
    p=q;
    steps++;
  } while (p!=h);
  if ((gr_x_coord(p) == gr_x_coord(h)) && (gr_y_coord(p) == gr_y_coord(h)) &&
      gr_right_type(p)!=mp_endpoint) {
     cairo_close_path(mp->png->cr);
  }
}

@ Now for outputting the actual graphic objects. 

@<Declarations@>=
static double mp_png_choose_scale (MP mp, mp_graphic_object *p) ;

@ @c double mp_png_choose_scale (MP mp, mp_graphic_object *p) {
  /* |p| should point to a text node */
  double a,b,c,d,ad,bc; /* temporary values */
  double ret1, ret2;
  a=gr_txx_val(p);
  b=gr_txy_val(p);
  c=gr_tyx_val(p);
  d=gr_tyy_val(p);
  if ( a<0 ) negate(a);
  if ( b<0 ) negate(b);
  if ( c<0 ) negate(c);
  if ( d<0 ) negate(d);
  ad=(a-d)/2.0;
  bc=(b-c)/2.0;
  ret1 = sqrt((d+ad)*(d+ad) + ad*ad);
  ret2 = sqrt((c+bc)*(c+bc) + bc*bc);
  return sqrt(ret1*ret1 + ret2*ret2);
}

@ 
@d xrealloc(P,A,B) mp_xrealloc(mp,P,(size_t)A,B)
@d XREALLOC(a,b,c) a = xrealloc(a,(b+1),sizeof(c));

@c
void mp_reallocate_psfonts (MP mp, int l) {
  if (l>=mp->png->font_max) {
    int f;
    mp->png->last_fnum = mp->png->font_max;
    XREALLOC (mp->png->psfonts, l, mp_edge_object *);
    for (f = (mp->png->last_fnum + 1); f <= l; f++) {
    	mp->png->psfonts[f] = NULL;
    }
    mp->png->font_max = l;
  }
}

@ @<Declarations@>=
void mp_reallocate_psfonts (MP mp, int l);

@ @<Globals@>=
mp_edge_object **psfonts;
int font_max;
int last_fnum;

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

@ @c
void mp_png_text_out (MP mp, mp_text_object *p) {
  double ds; /* design size and scale factor for a text node */
  unsigned char *s = (unsigned char *)gr_text_p(p);
  size_t l = gr_text_l(p); /* string length */
  boolean transformed= (gr_txx_val(p)!=unity)||(gr_tyy_val(p)!=unity)||
                       (gr_txy_val(p)!=0)||(gr_tyx_val(p)!=0);
  int fn = gr_font_n(p);
  mp_ps_font *f;
  double scf;
  ds =(mp->font_dsize[fn]+8) / (16*65536.0);
  scf = mp_png_choose_scale (mp,(mp_graphic_object *)p);
  cairo_save(mp->png->cr);
  if ( transformed ) {
    cairo_matrix_t matrix = {0,0,0,0,0,0};
    cairo_matrix_init(&matrix, (gr_txx_val(p)/scf),  (gr_tyx_val(p)/scf), 
                               (gr_txy_val(p)/scf), (gr_tyy_val(p)/scf), 
                               gr_tx_val(p),gr_ty_val(p));
    cairo_transform (mp->png->cr, &matrix);
    cairo_move_to(mp->png->cr, 0, 0);
  } else { 
    cairo_translate (mp->png->cr,gr_tx_val(p),gr_ty_val(p));
  }
  cairo_scale(mp->png->cr, ((ds/1000.0)*scf), ((ds/1000.0)*scf));
  mp_png_color_out(mp,(mp_graphic_object *)p);
  while (l-->0) {
      mp_edge_object *ch;
      int k = (int)*s++;
      double wd = 0.0; /* this is in PS design units */
      mp_reallocate_psfonts(mp, ((fn+1) * 256));
      ch = mp->png->psfonts[(fn*256)+k];
      if (ch == NULL) {
         f = mp_ps_font_parse(mp, fn);
	 if (f == NULL) return;
         ch = mp_ps_font_charstring(mp,f,k);
         mp->png->psfonts[(fn*256)+k] = ch;
      }
      if (ch != NULL) {
         mp_graphic_object *pp = ch->body;
         while (pp!=NULL) {
           mp_png_path_out(mp, gr_path_p((mp_fill_object *)pp));
           pp=pp->next;
         }
         cairo_fill(mp->png->cr);
       }
      wd = mp_get_char_dimension (mp, mp->font_name[fn], k, 'w');
/* $wd/100$ is the size in PS point , i.e, $wd =100\cdot real\_wd$   
        but without considering scaling.
       We have a scale factor of                             
       $(ds/1000.0)\cdot scf$                                
        so to match the scale wd should be                   
        $1000\cdot real_wd\cdot scf /(ds\cdot scf)$          
       i.e. $wd = 10\cdot wd/ds$.
*/
      wd *= 10.0/ds;
      cairo_translate(mp->png->cr,wd,0);
  }
  cairo_restore(mp->png->cr);
}

@ 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_png_stroke_out (MP mp,  mp_graphic_object *h, 
                               mp_pen_info *pen, boolean fill_also) ;


@ @c
void mp_png_stroke_out (MP mp,  mp_graphic_object *h, 
                              mp_pen_info *pen, boolean fill_also) {
  boolean transformed = false;
  if (fill_also) {
    cairo_save(mp->png->cr);
    mp_png_path_out(mp, gr_path_p((mp_stroked_object *)h));
    cairo_close_path (mp->png->cr); 
    cairo_fill (mp->png->cr);
    cairo_restore(mp->png->cr);
  }
  cairo_save(mp->png->cr);
  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 (pen != NULL) {
    cairo_set_line_width(mp->png->cr, pen->ww);
  } else {
    cairo_set_line_width(mp->png->cr, 0);
  }
  if (gr_lcap_val(h)!=0) {
    switch (gr_lcap_val(h)) {
      case 1: cairo_set_line_cap(mp->png->cr,CAIRO_LINE_CAP_ROUND); break;
      case 2: cairo_set_line_cap(mp->png->cr,CAIRO_LINE_CAP_SQUARE); break;
      default:cairo_set_line_cap(mp->png->cr,CAIRO_LINE_CAP_BUTT); break;
    }
  }
  if (gr_type(h)!=mp_fill_code) {
    mp_dash_object *hh= gr_dash_p(h);
    if (hh != NULL && hh->array != NULL) {
       int i;
       for (i=0; *(hh->array+i) != -1;i++)
         ;
       cairo_set_dash (mp->png->cr, hh->array, i, hh->offset);
    }
  }
  if (gr_ljoin_val((mp_stroked_object *)h)!=0) {
    switch (gr_ljoin_val((mp_stroked_object *)h)) {
      case 1:  cairo_set_line_join(mp->png->cr,CAIRO_LINE_JOIN_ROUND); break;
      case 2:  cairo_set_line_join(mp->png->cr,CAIRO_LINE_JOIN_BEVEL); break;
      default: cairo_set_line_join(mp->png->cr,CAIRO_LINE_JOIN_MITER); break;
    }
  }
  cairo_set_miter_limit(mp->png->cr,gr_miterlim_val((mp_stroked_object *)h)); 
  mp_png_path_out(mp, gr_path_p((mp_stroked_object *)h));
  if (transformed) {
    cairo_matrix_t matrix = {0,0,0,0,0,0};
    cairo_save(mp->png->cr);
    cairo_matrix_init(&matrix, pen->sx, pen->rx, pen->ry, pen->sy, pen->tx, pen->ty);
    cairo_transform (mp->png->cr, &matrix);
    cairo_stroke (mp->png->cr);
    cairo_restore(mp->png->cr);
  } else {
    cairo_stroke (mp->png->cr);
  } 
  cairo_restore(mp->png->cr);
}

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

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

@ @c
void mp_png_fill_out (MP mp, mp_gr_knot p, mp_graphic_object *h) {
  cairo_save(mp->png->cr);
  mp_png_path_out(mp, p);
  cairo_close_path (mp->png->cr);
  cairo_fill (mp->png->cr);
  cairo_restore(mp->png->cr);
}

@ The main output function

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

@<Exported function ...@>=
int mp_png_gr_ship_out (mp_edge_object *hh, const char *options, int standalone) ;

@ This is a structure to ship data from cairo to our png writer. |width| and
|height| could have been stored in our private |mp| instance, but this is just
as easy.

@<Types...@>=
typedef struct {
    unsigned char * data;
    int height;
    int width;
} bitmap_t;

@ This is a small structure that is needed so that the png writer callbacks
can actually access the |mp| object instance.

@<Types...@>=
typedef struct {
   void *fp;
   MP mp;
} mp_png_io;

@ Output a png chunk: the libpng callbacks
@c
static void mp_write_png_data(png_structp png_ptr, png_bytep data, png_size_t length)
{ 
   mp_png_io *ioptr = (mp_png_io *)png_get_io_ptr(png_ptr);
   MP mp = ioptr->mp;
   (mp->write_binary_file)(mp,ioptr->fp, (void *)data, (size_t)length);
}
static void mp_write_png_flush(png_structp png_ptr)
{
   /* nothing to do */
}


@  Write |bitmap| to a PNG file specified by |path|; returns 0 on
success, non-zero on error.  The original of this function was 
borrowed from an internet post, and extended as needed.

@<Declarations@>=
int mp_png_save_to_file (MP mp, const bitmap_t * bitmap, const char *path, int colormodel);

@ @c
int mp_png_save_to_file (MP mp, const bitmap_t * bitmap, const char *path, int colormodel)
{
    mp_png_io io;
    png_structp png_ptr = NULL;
    png_infop info_ptr = NULL;
    size_t y;
    png_byte ** row_pointers = NULL;
    int status = -1;
    int depth = 8;
    int dpi = 72;
    int ppm_x;
    int ppm_y; /* pixels per metre */
    
    io.mp = mp;
    io.fp = (mp->open_file)(mp, path, "wb", mp_filetype_bitmap);
    if (!io.fp) {
        goto fopen_failed;
    }

    png_ptr = png_create_write_struct (PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if (png_ptr == NULL) {
        goto png_create_write_struct_failed;
    }
    
    info_ptr = png_create_info_struct (png_ptr);
    if (info_ptr == NULL) {
        goto png_create_info_struct_failed;
    }
    
    /* Set up error handling. */

    if (setjmp (png_jmpbuf (png_ptr))) {
        goto png_failure;
    }
    
    /* Set image attributes. */

    png_set_IHDR (png_ptr,
                  info_ptr,
                  bitmap->width,
                  bitmap->height,
                  depth,
                  colormodel,
                  PNG_INTERLACE_NONE,
                  PNG_COMPRESSION_TYPE_DEFAULT,
                  PNG_FILTER_TYPE_DEFAULT);
    
    /* Compression level |3| appears the best tradeoff between 
       disk size and compression speed */
    png_set_compression_level(png_ptr, 3); 
    png_set_filter(png_ptr,0,PNG_FILTER_NONE);
    /* setup some information */
    if (1) {
        png_text  text[2];
	char *a, *b, *c, *d; /* to get rid of a typecast warning */
        a = xstrdup("Title"); 
        b = xstrdup(path);    
        c = xstrdup("Software");
	d = xstrdup("Generated by Metapost version " metapost_version);
  
        text[0].compression = PNG_TEXT_COMPRESSION_NONE;
	text[0].key = a;
	text[0].text = b;
        text[1].compression = PNG_TEXT_COMPRESSION_NONE;
	text[1].key = c;
        text[1].text = d;
        png_set_text(png_ptr, info_ptr, text, 2);

	free(a); 
	free(b); 
	free(c); 
	free(d);
    }

    /* The original plan was to add |hppp| and |vppp| values in here,
       but that seems to have negative effects on various bits of 
       software. Better keep the DPI at 72 */
    ppm_x = dpi / 0.0254;
    ppm_y = dpi / 0.0254;
    png_set_pHYs(png_ptr, info_ptr, ppm_x, ppm_y, PNG_RESOLUTION_METER);
    
    /* Initialize rows of PNG. */

    row_pointers = malloc (bitmap->height * sizeof (png_byte *));
    for (y = 0; y < bitmap->height; ++y) {
       if (colormodel == PNG_COLOR_TYPE_GRAY) {
         row_pointers[y] = bitmap->data + bitmap->width * y;
       } else if (colormodel == PNG_COLOR_TYPE_GRAY_ALPHA) {
         row_pointers[y] = bitmap->data + bitmap->width * 2 * y;
       } else {
         row_pointers[y] = bitmap->data + bitmap->width * 4 * y;
       }
    }

    /* Write the image data to |io| */
    png_set_write_fn(png_ptr, &io, mp_write_png_data, mp_write_png_flush);

    png_set_rows (png_ptr, info_ptr, row_pointers);
    if (colormodel == PNG_COLOR_TYPE_RGB) {
        /* Unfortunately, |png_write_png| does not have enough |PNG_TRANSFORM| options
	   to do this properly, so we have to modify the bitmap data */
        int i;
        for (i = 0; i < bitmap->width*bitmap->height*4; i+=4) {
	   unsigned char b = bitmap->data[i];
	   unsigned char g = bitmap->data[i+1];
	   bitmap->data[i]   = bitmap->data[i+3];
	   bitmap->data[i+1] = bitmap->data[i+2];
	   bitmap->data[i+2] = g;
	   bitmap->data[i+3] = b;
        }
        png_write_png (png_ptr, info_ptr, PNG_TRANSFORM_STRIP_FILLER, NULL);
    } else if (colormodel == PNG_COLOR_TYPE_RGB_ALPHA) {
        png_write_png (png_ptr, info_ptr, PNG_TRANSFORM_BGR, NULL);
    } else if (colormodel == PNG_COLOR_TYPE_GRAY ||
               colormodel == PNG_COLOR_TYPE_GRAY_ALPHA) {
        int i, j;
	j = 0;
        for (i = 0; i < bitmap->width*bitmap->height*4; i+=4) {
	   unsigned char b = bitmap->data[i];
	   unsigned char g = bitmap->data[i+1];
	   unsigned char r = bitmap->data[i+2];
    	   bitmap->data[j++] = ((r==g && r==b) ? r : 0.2126*r + 0.7152*g + 0.0722*b);
	   if (colormodel == PNG_COLOR_TYPE_GRAY_ALPHA)
	     bitmap->data[j++] = bitmap->data[i+3];
        }
        png_write_png (png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, NULL);
    }
    status = 0;
    
    free (row_pointers);
    
 png_failure:
 png_create_info_struct_failed:
    png_destroy_write_struct (&png_ptr, &info_ptr);
 png_create_write_struct_failed:
    (mp->close_file)(mp, io.fp);
 fopen_failed:
    return status;
}


@ 
@d number_to_double(A)		       (((math_data *)(mp->math))->to_double)(A)		       

@c
int mp_png_gr_ship_out (mp_edge_object *hh, const char *options, int standalone) {
  char *ss;
  mp_graphic_object *p;
  mp_pen_info *pen = NULL;
  MP mp = hh->parent;
  bitmap_t bitmap;
  const char *currentoption = options;
  int colormodel = PNG_COLOR_TYPE_RGB_ALPHA;
  int antialias = CAIRO_ANTIALIAS_FAST;
  int c;
  while (currentoption && *currentoption) {
    if (strncmp(currentoption,"format=",7)==0) {
      currentoption += 7;
      if (strncmp(currentoption,"rgba",4)==0) {
        colormodel = PNG_COLOR_TYPE_RGB_ALPHA;
        currentoption += 4;
      } else if (strncmp(currentoption,"rgb",3)==0) {
        colormodel = PNG_COLOR_TYPE_RGB;
        currentoption += 3;
      } else if (strncmp(currentoption,"graya",5)==0) {
        colormodel = PNG_COLOR_TYPE_GRAY_ALPHA;
        currentoption += 5;
      } else if (strncmp(currentoption,"gray",4)==0) {
        colormodel = PNG_COLOR_TYPE_GRAY;
        currentoption += 4;
      }
    } else if (strncmp(currentoption,"antialias=",10)==0) {
      currentoption += 10;
      if (strncmp(currentoption,"none",4)==0) {
        antialias = CAIRO_ANTIALIAS_NONE;
        currentoption += 4;
      } else if (strncmp(currentoption,"fast",4)==0) {
        antialias = CAIRO_ANTIALIAS_FAST;
        currentoption += 4;
      } else if (strncmp(currentoption,"good",4)==0) {
        antialias = CAIRO_ANTIALIAS_GOOD;
        currentoption += 4;
      } else if (strncmp(currentoption,"best",4)==0) {
        antialias = CAIRO_ANTIALIAS_BEST;
        currentoption += 4;
      }
    }
    currentoption = strchr(currentoption,' ');
    if (currentoption) {
      while (*currentoption == ' ')
        currentoption++;
    }
  }
  c = round_unscaled(internal_value (mp_char_code));
  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_png_start(mp, hh, number_to_double(internal_value(mp_hppp)), number_to_double(internal_value(mp_vppp)),
               colormodel, antialias);
  p = hh->body;
  while ( p!=NULL ) { 
    if (gr_has_color (p))
      mp_png_color_out (mp, p);
    switch (gr_type(p)) {
    case mp_fill_code: 
      {
        mp_fill_object *ph = (mp_fill_object *)p;
        if ( gr_pen_p(ph)==NULL ) {
          mp_png_fill_out(mp, gr_path_p(ph), p);
        } else if ( pen_is_elliptical(gr_pen_p(ph)) )  {
            pen = mp_png_pen_info(mp, gr_path_p(ph), gr_pen_p(ph));
            mp_png_stroke_out(mp, p, pen, true);
            mp_xfree(pen);
        } else { 
          mp_png_fill_out(mp, gr_path_p(ph), p);
          mp_png_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_png_pen_info(mp, gr_path_p(ph), gr_pen_p(ph));
	    mp_png_stroke_out(mp, p, pen, false);
            mp_xfree(pen);
        } else { 
          mp_png_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_png_text_out(mp, (mp_text_object *)p);
      }
      break;
    case mp_start_clip_code: 
      cairo_save(mp->png->cr);
      mp_png_path_out(mp, gr_path_p((mp_clip_object *)p));
      cairo_clip(mp->png->cr);
      cairo_new_path(mp->png->cr);
      break;
    case mp_stop_clip_code: 
      cairo_restore(mp->png->cr);
      break;
    case mp_start_bounds_code:
    case mp_stop_bounds_code:
      break;
    case mp_special_code:  
      break;
    } /* all cases are enumerated */
    p=gr_link(p);
  }
  (void)mp_set_output_file_name (mp, c);
  mp_store_true_output_filename (mp, c);
  ss = xstrdup(mp->name_of_file);
  cairo_surface_flush (mp->png->surface);
  cairo_destroy (mp->png->cr);
  bitmap.data = cairo_image_surface_get_data (mp->png->surface);
  bitmap.width = cairo_image_surface_get_width (mp->png->surface);
  bitmap.height = cairo_image_surface_get_height (mp->png->surface);
  mp_png_save_to_file (mp, &bitmap, ss, colormodel);
  cairo_surface_destroy (mp->png->surface);
  free(ss);
  return 1;
}

@ @(mplibpng.h@>=
#ifndef MPLIBPNG_H
#define MPLIBPNG_H 1
int mp_png_ship_out (mp_edge_object *hh, const char *options) ;
#endif

@ @c
int mp_png_ship_out (mp_edge_object *hh, const char *options) {
  return mp_png_gr_ship_out (hh, options, (int)true);
}