/* Copyright (C) 1989, 1992 Aladdin Enterprises.  All rights reserved.
  
  This file is part of Aladdin Ghostscript.
  
  Aladdin Ghostscript is distributed with NO WARRANTY OF ANY KIND.  No author
  or distributor accepts any responsibility for the consequences of using it,
  or for whether it serves any particular purpose or works at all, unless he
  or she says so in writing.  Refer to the Aladdin Ghostscript Free Public
  License (the "License") for full details.
  
  Every copy of Aladdin Ghostscript must include a copy of the License,
  normally in a plain ASCII text file named PUBLIC.  The License grants you
  the right to copy, modify and redistribute Aladdin Ghostscript, but only
  under certain conditions described in the License.  Among other things, the
  License requires that the copyright notice and this notice be preserved on
  all copies.
*/

/* gsimpath.c */
/* Image to outline conversion for Ghostscript library */
#include "gx.h"
#include "gserrors.h"
#include "gsmatrix.h"
#include "gsstate.h"
#include "gspath.h"

/* Define the state of the conversion process. */
typedef struct {
	/* The following are set at the beginning of the conversion. */
	gs_state *pgs;
	const byte *data;		/* image data */
	int width, height, raster;
	/* The following are updated dynamically. */
	int dx, dy;			/* X/Y increment of current run */
	int count;			/* # of steps in current run */
} status;

/* Define the scaling for the path tracer. */
/* It must be even. */
#define outline_scale 4
/* Define the length of the short strokes for turning corners. */
#define step 1

/* Forward declarations */
private int near get_pixel(P3(const status *, int, int));
private int near trace_from(P4(status *, int, int, int));
private int near add_dxdy(P4(status *, int, int, int));
#define add_deltas(s, dx, dy, n)\
  if ( (code = add_dxdy(s, dx, dy, n)) < 0 ) return code
/* Append an outline derived from an image to the current path. */
int
gs_imagepath(gs_state *pgs, int width, int height, const byte *data)
{	status stat;
	status *out = &stat;
	int code, x, y;
	/* Initialize the state. */
	stat.pgs = pgs;
	stat.data = data;
	stat.width = width;
	stat.height = height;
	stat.raster = (width + 7) / 8;
	/* Trace the cells to form an outline.  The trace goes in clockwise */
	/* order, always starting by going west along a bottom edge. */
	for ( y = height - 1; y >= 0; y-- )
	  for ( x = width - 1; x >= 0; x-- )
	   {	if ( get_pixel(out, x, y) && !get_pixel(out, x, y - 1) &&
		     (!get_pixel(out, x + 1, y) || get_pixel(out, x + 1, y - 1)) &&
		     !trace_from(out, x, y, 1)
		   )
		   {	/* Found a starting point */
			stat.count = 0;
			stat.dx = stat.dy = 0;
			if ( (code = trace_from(out, x, y, 0)) < 0 )
				return code;
			add_deltas(out, 0, 0, 1); /* force out last segment */
			if ( (code = gs_closepath(pgs)) < 0 )
				return code;
		   }
	   }
	return 0;
}

/* Get a pixel from the data.  Return 0 if outside the image. */
private int near
get_pixel(register const status *out, int x, int y)
{	if ( x < 0 || x >= out->width || y < 0 || y >= out->height )
		return 0;
	return (out->data[y * out->raster + (x >> 3)] >> (~x & 7)) & 1;
}

/* Trace a path.  If detect is true, don't draw, just return 1 if we ever */
/* encounter a starting point whose x,y follows that of the initial point */
/* in x-then-y scan order; if detect is false, actually draw the outline. */
private int near
trace_from(register status *out, int x0, int y0, int detect)
{	int x = x0, y = y0;
	int dx = -1, dy = 0;		/* initially going west */
	int part;			/* how far along edge we are */
	int code;
	if ( !detect )
	{	part = (get_pixel(out, x + 1, y - 1) ?
			outline_scale - step : step);
		code = gs_moveto(out->pgs,
				 x + 1 - part / (float)outline_scale,
				 (float)y);
		if ( code < 0 ) return code;
	}
	while ( 1 )
	   {	/* Relative to the current direction, */
		/* -dy,dx is at +90 degrees (counter-clockwise); */
		/* tx,ty is at +45 degrees; */
		/* ty,-tx is at -45 degrees (clockwise); */
		/* dy,-dx is at -90 degrees. */
		int tx = dx - dy, ty = dy + dx;
		if ( get_pixel(out, x + tx, y + ty) )
		{	/* Cell at 45 degrees is full, */
			/* go counter-clockwise. */
			if ( !detect )
			{	/* If this is a 90 degree corner set at a */
				/* 45 degree angle, avoid backtracking. */
				if ( out->dx == ty && out->dy == -tx )
				{
#define half_scale (outline_scale / 2 - step)
					out->count -= half_scale;
					add_deltas(out, tx, ty, outline_scale / 2);
#undef half_scale
				}
				else
				{	add_deltas(out, dx, dy, step - part);
					add_deltas(out, tx, ty, outline_scale - step);
				}
				part = outline_scale - step;
			}
			x += tx, y += ty;
			dx = -dy, dy += tx;
		}
		else if ( !get_pixel(out, x + dx, y + dy) )
		{	/* Cell straight ahead is empty, go clockwise. */
			if ( !detect )
			{	add_deltas(out, dx, dy, outline_scale - step - part);
				add_deltas(out, ty, -tx, step);
				part = step;
			}
			dx = dy, dy -= ty;
		}
		else
		{	/* Neither of the above, go in same direction. */
			if ( !detect )
			{	add_deltas(out, dx, dy, outline_scale);
			}
			x += dx, y += dy;
		}
		if ( dx == -step && dy == 0 && !(tx == -step && ty == -step) )
		{	/* We just turned a corner and are going west, */
			/* so the previous pixel is a starting point pixel. */
			if ( x == x0 && y == y0 ) return 0;
			if ( detect && (y > y0 || (y == y0 && x > x0)) )
				return 1;
		}
	   }
}

/* Add a (dx, dy) pair to the path being formed. */
/* Accumulate successive segments in the same direction. */
private int near
add_dxdy(register status *out, int dx, int dy, int count)
{	if ( count != 0 )
	   {	if ( dx == out->dx && dy == out->dy )
			out->count += count;
		else
		   {	if ( out->count != 0 )
			   {	int code = gs_rlineto(out->pgs,
				   out->dx * out->count / (float)outline_scale,
				   out->dy * out->count / (float)outline_scale);
				if ( code < 0 ) return code;
			   }
			out->dx = dx, out->dy = dy;
			out->count = count;
		   }
	   }
	return 0;
}
