rsvg-path.c 13.8 KB
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/* 
   rsvg-path.c: Parse SVG path element data into bezier path.
 
   Copyright (C) 2000 Eazel, Inc.
  
   This program is free software; you can redistribute it and/or
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   modify it under the terms of the GNU Library General Public License as
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   published by the Free Software Foundation; either version 2 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
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   Library General Public License for more details.
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   You should have received a copy of the GNU Library General Public
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   License along with this program; if not, write to the
   Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.
  
   Author: Raph Levien <raph@artofcode.com>
*/

/* This is adapted from svg-path in Gill. */

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#include "config.h"
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#include "rsvg-path.h"

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#include <glib/gtypes.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>

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/* This module parses an SVG path element into an RsvgBpathDef.

   At present, there is no support for <marker> or any other contextual
   information from the SVG file. The API will need to change rather
   significantly to support these.

   Reference: SVG working draft 3 March 2000, section 8.
*/

#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif  /*  M_PI  */

typedef struct _RSVGParsePathCtx RSVGParsePathCtx;

struct _RSVGParsePathCtx {
  RsvgBpathDef *bpath;
  double cpx, cpy;  /* current point */
  double rpx, rpy;  /* reflection point (for 's' and 't' commands) */
  char cmd;         /* current command (lowercase) */
  int param;        /* parameter number */
  gboolean rel;     /* true if relative coords */
  double params[7]; /* parameters that have been parsed */
};

static void
rsvg_path_arc_segment (RSVGParsePathCtx *ctx,
		      double xc, double yc,
		      double th0, double th1,
		      double rx, double ry, double x_axis_rotation)
{
  double sin_th, cos_th;
  double a00, a01, a10, a11;
  double x1, y1, x2, y2, x3, y3;
  double t;
  double th_half;

  sin_th = sin (x_axis_rotation * (M_PI / 180.0));
  cos_th = cos (x_axis_rotation * (M_PI / 180.0)); 
  /* inverse transform compared with rsvg_path_arc */
  a00 = cos_th * rx;
  a01 = -sin_th * ry;
  a10 = sin_th * rx;
  a11 = cos_th * ry;

  th_half = 0.5 * (th1 - th0);
  t = (8.0 / 3.0) * sin (th_half * 0.5) * sin (th_half * 0.5) / sin (th_half);
  x1 = xc + cos (th0) - t * sin (th0);
  y1 = yc + sin (th0) + t * cos (th0);
  x3 = xc + cos (th1);
  y3 = yc + sin (th1);
  x2 = x3 + t * sin (th1);
  y2 = y3 - t * cos (th1);
  rsvg_bpath_def_curveto (ctx->bpath,
				  a00 * x1 + a01 * y1, a10 * x1 + a11 * y1,
				  a00 * x2 + a01 * y2, a10 * x2 + a11 * y2,
				  a00 * x3 + a01 * y3, a10 * x3 + a11 * y3);
}

/**
 * rsvg_path_arc: Add an RSVG arc to the path context.
 * @ctx: Path context.
 * @rx: Radius in x direction (before rotation).
 * @ry: Radius in y direction (before rotation).
 * @x_axis_rotation: Rotation angle for axes.
 * @large_arc_flag: 0 for arc length <= 180, 1 for arc >= 180.
 * @sweep: 0 for "negative angle", 1 for "positive angle".
 * @x: New x coordinate.
 * @y: New y coordinate.
 *
 **/
static void
rsvg_path_arc (RSVGParsePathCtx *ctx,
	      double rx, double ry, double x_axis_rotation,
	      int large_arc_flag, int sweep_flag,
	      double x, double y)
{
  double sin_th, cos_th;
  double a00, a01, a10, a11;
  double x0, y0, x1, y1, xc, yc;
  double d, sfactor, sfactor_sq;
  double th0, th1, th_arc;
  int i, n_segs;

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  /* Check that neither radius is zero, since its isn't either
     geometrically or mathematically meaningful and will
     cause divide by zero and subsequent NaNs.  We should
     really do some ranged check ie -0.001 < x < 000.1 rather
     can just a straight check again zero.
  */
  if ((rx == 0.0) || (ry == 0.0)) return;

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  sin_th = sin (x_axis_rotation * (M_PI / 180.0));
  cos_th = cos (x_axis_rotation * (M_PI / 180.0));
  a00 = cos_th / rx;
  a01 = sin_th / rx;
  a10 = -sin_th / ry;
  a11 = cos_th / ry;
  x0 = a00 * ctx->cpx + a01 * ctx->cpy;
  y0 = a10 * ctx->cpx + a11 * ctx->cpy;
  x1 = a00 * x + a01 * y;
  y1 = a10 * x + a11 * y;
  /* (x0, y0) is current point in transformed coordinate space.
     (x1, y1) is new point in transformed coordinate space.

     The arc fits a unit-radius circle in this space.
  */
  d = (x1 - x0) * (x1 - x0) + (y1 - y0) * (y1 - y0);
  sfactor_sq = 1.0 / d - 0.25;
  if (sfactor_sq < 0) sfactor_sq = 0;
  sfactor = sqrt (sfactor_sq);
  if (sweep_flag == large_arc_flag) sfactor = -sfactor;
  xc = 0.5 * (x0 + x1) - sfactor * (y1 - y0);
  yc = 0.5 * (y0 + y1) + sfactor * (x1 - x0);
  /* (xc, yc) is center of the circle. */

  th0 = atan2 (y0 - yc, x0 - xc);
  th1 = atan2 (y1 - yc, x1 - xc);

  th_arc = th1 - th0;
  if (th_arc < 0 && sweep_flag)
    th_arc += 2 * M_PI;
  else if (th_arc > 0 && !sweep_flag)
    th_arc -= 2 * M_PI;

  n_segs = ceil (fabs (th_arc / (M_PI * 0.5 + 0.001)));

  for (i = 0; i < n_segs; i++)
    rsvg_path_arc_segment (ctx, xc, yc,
			  th0 + i * th_arc / n_segs,
			  th0 + (i + 1) * th_arc / n_segs,
			  rx, ry, x_axis_rotation);

  ctx->cpx = x;
  ctx->cpy = y;
}


/* supply defaults for missing parameters, assuming relative coordinates
   are to be interpreted as x,y */
static void
rsvg_parse_path_default_xy (RSVGParsePathCtx *ctx, int n_params)
{
  int i;

  if (ctx->rel)
    {
      for (i = ctx->param; i < n_params; i++)
	{
	  if (i > 2)
	    ctx->params[i] = ctx->params[i - 2];
	  else if (i == 1)
	    ctx->params[i] = ctx->cpy;
	  else if (i == 0)
	    /* we shouldn't get here (usually ctx->param > 0 as
               precondition) */
	    ctx->params[i] = ctx->cpx;
	}
    }
  else
    {
      for (i = ctx->param; i < n_params; i++)
	ctx->params[i] = 0.0;
    }
}

static void
rsvg_parse_path_do_cmd (RSVGParsePathCtx *ctx, gboolean final)
{
  double x1, y1, x2, y2, x3, y3;

  switch (ctx->cmd)
    {
    case 'm':
      /* moveto */
      if (ctx->param == 2 || final)
	{
	  rsvg_parse_path_default_xy (ctx, 2);
	  rsvg_bpath_def_moveto (ctx->bpath,
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				 ctx->params[0], ctx->params[1]);
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	  ctx->cpx = ctx->rpx = ctx->params[0];
	  ctx->cpy = ctx->rpy = ctx->params[1];
	  ctx->param = 0;
	}
      break;
    case 'l':
      /* lineto */
      if (ctx->param == 2 || final)
	{
	  rsvg_parse_path_default_xy (ctx, 2);
	  rsvg_bpath_def_lineto (ctx->bpath,
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				 ctx->params[0], ctx->params[1]);
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	  ctx->cpx = ctx->rpx = ctx->params[0];
	  ctx->cpy = ctx->rpy = ctx->params[1];
	  ctx->param = 0;
	}
      break;
    case 'c':
      /* curveto */
      if (ctx->param == 6 || final)
	{
	  rsvg_parse_path_default_xy (ctx, 6);
	  x1 = ctx->params[0];
	  y1 = ctx->params[1];
	  x2 = ctx->params[2];
	  y2 = ctx->params[3];
	  x3 = ctx->params[4];
	  y3 = ctx->params[5];
	  rsvg_bpath_def_curveto (ctx->bpath,
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				  x1, y1, x2, y2, x3, y3);
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	  ctx->rpx = x2;
	  ctx->rpy = y2;
	  ctx->cpx = x3;
	  ctx->cpy = y3;
	  ctx->param = 0;
	}
      break;
    case 's':
      /* smooth curveto */
      if (ctx->param == 4 || final)
	{
	  rsvg_parse_path_default_xy (ctx, 4);
	  x1 = 2 * ctx->cpx - ctx->rpx;
	  y1 = 2 * ctx->cpy - ctx->rpy;
	  x2 = ctx->params[0];
	  y2 = ctx->params[1];
	  x3 = ctx->params[2];
	  y3 = ctx->params[3];
	  rsvg_bpath_def_curveto (ctx->bpath,
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				  x1, y1, x2, y2, x3, y3);
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	  ctx->rpx = x2;
	  ctx->rpy = y2;
	  ctx->cpx = x3;
	  ctx->cpy = y3;
	  ctx->param = 0;
	}
      break;
    case 'h':
      /* horizontal lineto */
      if (ctx->param == 1)
	{
	  rsvg_bpath_def_lineto (ctx->bpath,
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				 ctx->params[0], ctx->cpy);
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	  ctx->cpx = ctx->rpx = ctx->params[0];
	  ctx->param = 0;
	}
      break;
    case 'v':
      /* vertical lineto */
      if (ctx->param == 1)
	{
	  rsvg_bpath_def_lineto (ctx->bpath,
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				 ctx->cpx, ctx->params[0]);
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	  ctx->cpy = ctx->rpy = ctx->params[0];
	  ctx->param = 0;
	}
      break;
    case 'q':
      /* quadratic bezier curveto */

      /* non-normative reference:
	 http://www.icce.rug.nl/erikjan/bluefuzz/beziers/beziers/beziers.html
      */
      if (ctx->param == 4 || final)
	{
	  rsvg_parse_path_default_xy (ctx, 4);
	  /* raise quadratic bezier to cubic */
	  x1 = (ctx->cpx + 2 * ctx->params[0]) * (1.0 / 3.0);
	  y1 = (ctx->cpy + 2 * ctx->params[1]) * (1.0 / 3.0);
	  x3 = ctx->params[2];
	  y3 = ctx->params[3];
	  x2 = (x3 + 2 * ctx->params[0]) * (1.0 / 3.0);
	  y2 = (y3 + 2 * ctx->params[1]) * (1.0 / 3.0);
	  rsvg_bpath_def_curveto (ctx->bpath,
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				  x1, y1, x2, y2, x3, y3);
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	  ctx->rpx = ctx->params[0];
	  ctx->rpy = ctx->params[1];
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	  ctx->cpx = x3;
	  ctx->cpy = y3;
	  ctx->param = 0;
	}
      break;
    case 't':
      /* Truetype quadratic bezier curveto */
      if (ctx->param == 2 || final)
	{
	  double xc, yc; /* quadratic control point */

	  xc = 2 * ctx->cpx - ctx->rpx;
	  yc = 2 * ctx->cpy - ctx->rpy;
	  /* generate a quadratic bezier with control point = xc, yc */
	  x1 = (ctx->cpx + 2 * xc) * (1.0 / 3.0);
	  y1 = (ctx->cpy + 2 * yc) * (1.0 / 3.0);
	  x3 = ctx->params[0];
	  y3 = ctx->params[1];
	  x2 = (x3 + 2 * xc) * (1.0 / 3.0);
	  y2 = (y3 + 2 * yc) * (1.0 / 3.0);
	  rsvg_bpath_def_curveto (ctx->bpath,
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				  x1, y1, x2, y2, x3, y3);
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	  ctx->rpx = xc;
	  ctx->rpy = yc;
	  ctx->cpx = x3;
	  ctx->cpy = y3;
	  ctx->param = 0;
	}
      else if (final)
	{
	  if (ctx->param > 2)
	    {
	      rsvg_parse_path_default_xy (ctx, 4);
	      /* raise quadratic bezier to cubic */
	      x1 = (ctx->cpx + 2 * ctx->params[0]) * (1.0 / 3.0);
	      y1 = (ctx->cpy + 2 * ctx->params[1]) * (1.0 / 3.0);
	      x3 = ctx->params[2];
	      y3 = ctx->params[3];
	      x2 = (x3 + 2 * ctx->params[0]) * (1.0 / 3.0);
	      y2 = (y3 + 2 * ctx->params[1]) * (1.0 / 3.0);
	      rsvg_bpath_def_curveto (ctx->bpath,
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				      x1, y1, x2, y2, x3, y3);
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              ctx->rpx = ctx->params[0];
              ctx->rpy = ctx->params[1];
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	      ctx->cpx = x3;
	      ctx->cpy = y3;
	    }
	  else
	    {
	      rsvg_parse_path_default_xy (ctx, 2);
	      rsvg_bpath_def_lineto (ctx->bpath,
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				     ctx->params[0], ctx->params[1]);
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	      ctx->cpx = ctx->rpx = ctx->params[0];
	      ctx->cpy = ctx->rpy = ctx->params[1];
	    }
	  ctx->param = 0;
	}
      break;
    case 'a':
      if (ctx->param == 7 || final)
	{
	  rsvg_path_arc (ctx,
			ctx->params[0], ctx->params[1], ctx->params[2],
			ctx->params[3], ctx->params[4],
			ctx->params[5], ctx->params[6]);
	  ctx->param = 0;
	}
      break;
    default:
      ctx->param = 0;
    }
}

static void
rsvg_parse_path_data (RSVGParsePathCtx *ctx, const char *data)
{
  int i = 0;
  double val = 0;
  char c = 0;
  gboolean in_num = FALSE;
  gboolean in_frac = FALSE;
  gboolean in_exp = FALSE;
  gboolean exp_wait_sign = FALSE;
  int sign = 0;
  int exp = 0;
  int exp_sign = 0;
  double frac = 0.0;

  in_num = FALSE;
  for (i = 0; ; i++)
    {
      c = data[i];
      if (c >= '0' && c <= '9')
	{
	  /* digit */
	  if (in_num)
	    {
	      if (in_exp)
		{
		  exp = (exp * 10) + c - '0';
		  exp_wait_sign = FALSE;
		}
	      else if (in_frac)
		val += (frac *= 0.1) * (c - '0');
	      else
		val = (val * 10) + c - '0';
	    }
	  else
	    {
	      in_num = TRUE;
	      in_frac = FALSE;
	      in_exp = FALSE;
	      exp = 0;
	      exp_sign = 1;
	      exp_wait_sign = FALSE;
	      val = c - '0';
	      sign = 1;
	    }
	}
      else if (c == '.')
	{
	  if (!in_num)
	    {
	      in_num = TRUE;
	      val = 0;
	    }
	  in_frac = TRUE;
	  frac = 1;
	}
      else if ((c == 'E' || c == 'e') && in_num)
	{
	  in_exp = TRUE;
	  exp_wait_sign = TRUE;
	  exp = 0;
	  exp_sign = 1;
	}
      else if ((c == '+' || c == '-') && in_exp)
	{
	  exp_sign = c == '+' ? 1 : -1;
	}
      else if (in_num)
	{
	  /* end of number */

	  val *= sign * pow (10, exp_sign * exp);
	  if (ctx->rel)
	    {
	      /* Handle relative coordinates. This switch statement attempts
		 to determine _what_ the coords are relative to. This is
		 underspecified in the 12 Apr working draft. */
	      switch (ctx->cmd)
		{
		case 'l':
		case 'm':
		case 'c':
		case 's':
		case 'q':
		case 't':
#ifndef RSVGV_RELATIVE
		  /* rule: even-numbered params are x-relative, odd-numbered
		     are y-relative */
		  if ((ctx->param & 1) == 0)
		    val += ctx->cpx;
		  else if ((ctx->param & 1) == 1)
		    val += ctx->cpy;
		  break;
#else
		  /* rule: even-numbered params are x-relative, odd-numbered
		     are y-relative */
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		  if (ctx->param == 0 || (ctx->param % 2 == 0))
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		    val += ctx->cpx;
		  else 
		    val += ctx->cpy;
		  break;
#endif
		case 'a':
		  /* rule: sixth and seventh are x and y, rest are not
		     relative */
		  if (ctx->param == 5)
		    val += ctx->cpx;
		  else if (ctx->param == 6)
		    val += ctx->cpy;
		  break;
		case 'h':
		  /* rule: x-relative */
		  val += ctx->cpx;
		  break;
		case 'v':
		  /* rule: y-relative */
		  val += ctx->cpy;
		  break;
		}
	    }
	  ctx->params[ctx->param++] = val;
	  rsvg_parse_path_do_cmd (ctx, FALSE);
	  in_num = FALSE;
	}

      if (c == '\0')
	break;
      else if ((c == '+' || c == '-') && !exp_wait_sign)
	{
	  sign = c == '+' ? 1 : -1;;
	  val = 0;
	  in_num = TRUE;
	  in_frac = FALSE;
	  in_exp = FALSE;
	  exp = 0;
	  exp_sign = 1;
	  exp_wait_sign = FALSE;
	}
      else if (c == 'z' || c == 'Z')
	{
	  if (ctx->param)
	    rsvg_parse_path_do_cmd (ctx, TRUE);
	  rsvg_bpath_def_closepath (ctx->bpath);
	}
      else if (c >= 'A' && c <= 'Z' && c != 'E')
	{
	  if (ctx->param)
	    rsvg_parse_path_do_cmd (ctx, TRUE);
	  ctx->cmd = c + 'a' - 'A';
	  ctx->rel = FALSE;
	}
      else if (c >= 'a' && c <= 'z' && c != 'e')
	{
	  if (ctx->param)
	    rsvg_parse_path_do_cmd (ctx, TRUE);
	  ctx->cmd = c;
	  ctx->rel = TRUE;
	}
      /* else c _should_ be whitespace or , */
    }
}

RsvgBpathDef *
rsvg_parse_path (const char *path_str)
{
  RSVGParsePathCtx ctx;

  ctx.bpath = rsvg_bpath_def_new ();
  ctx.cpx = 0.0;
  ctx.cpy = 0.0;
  ctx.cmd = 0;
  ctx.param = 0;

  rsvg_parse_path_data (&ctx, path_str);

  if (ctx.param)
    rsvg_parse_path_do_cmd (&ctx, TRUE);

  return ctx.bpath;
}