/* Copyright (C) 2001-2006 Artifex Software, Inc.
   All Rights Reserved.
  
   This software is provided AS-IS with no warranty, either express or
   implied.

   This software is distributed under license and may not be copied, modified
   or distributed except as expressly authorized under the terms of that
   license.  Refer to licensing information at http://www.artifex.com/
   or contact Artifex Software, Inc.,  7 Mt. Lassen Drive - Suite A-134,
   San Rafael, CA  94903, U.S.A., +1(415)492-9861, for further information.
*/

/*$Id: gzspotan.c 11176 2010-05-04 18:47:12Z robin $ */
/* A spot analyzer device implementation. */
/*
    This implements a spot topology analyzis and 
    stem recognition for True Type grid fitting.
*/
#include "gx.h"
#include "gserrors.h"
#include "gsdevice.h"
#include "gzspotan.h"
#include "gxfixed.h"
#include "gxdevice.h"
#include "gxfdrop.h" /* Only for VD_* constants. */
#include "gzpath.h"
#include "memory_.h"
#include "math_.h"
#include "vdtrace.h"

#define VD_TRAP_N_COLOR RGB(128, 128, 0)
#define VD_TRAP_U_COLOR RGB(0, 0, 255)
#define VD_CONT_COLOR RGB(0, 255, 0)
#define VD_STEM_COLOR RGB(255, 255, 255)
#define VD_HINT_COLOR RGB(255, 0, 0)

public_st_device_spot_analyzer();
private_st_san_trap();
private_st_san_trap_contact();

static dev_proc_close_device(san_close);
static dev_proc_get_clipping_box(san_get_clipping_box);


/* --------------------- List management ------------------------- */
/* fixme : use something like C++ patterns to generate same functions for various types. */


static inline void
free_trap_list(gs_memory_t *mem, gx_san_trap **list)
{
    gx_san_trap *t = *list, *t1;

    for (t = *list; t != NULL; t = t1) {
	t1 = t->link;
	gs_free_object(mem, t, "free_trap_list");
    }
    *list = 0;
}

static inline void
free_cont_list(gs_memory_t *mem, gx_san_trap_contact **list)
{
    gx_san_trap_contact *t = *list, *t1;

    for (t = *list; t != NULL; t = t1) {
	t1 = t->link;
	gs_free_object(mem, t, "free_trap_list");
    }
    *list = 0;
}

static inline gx_san_trap *
trap_reserve(gx_device_spot_analyzer *padev)
{
    gx_san_trap *t = padev->trap_free;

    if (t != NULL) {
	padev->trap_free = t->link;
    } else {
	if (padev->trap_buffer_count > 10000)
	    return NULL;
	t = gs_alloc_struct(padev->memory, gx_san_trap, 
		&st_san_trap, "trap_reserve");
	if (t == NULL)
	    return NULL;
	t->link = NULL;
	if (padev->trap_buffer_last == NULL)
	    padev->trap_buffer = t;
	else
	    padev->trap_buffer_last->link = t;
	padev->trap_buffer_last = t;
	padev->trap_buffer_count++;
    }
    return t;
}

static inline gx_san_trap_contact *
cont_reserve(gx_device_spot_analyzer *padev)
{
    gx_san_trap_contact *t = padev->cont_free;

    if (t != NULL) {
	padev->cont_free = t->link;
    } else {
	if (padev->cont_buffer_count > 10000)
	    return NULL;
	t = gs_alloc_struct(padev->memory, gx_san_trap_contact, 
		&st_san_trap_contact, "cont_reserve");
	if (t == NULL)
	    return NULL;
	t->link = NULL;
	if (padev->cont_buffer_last == NULL)
	    padev->cont_buffer = t;
	else
	    padev->cont_buffer_last->link = t;
	padev->cont_buffer_last = t;
	padev->cont_buffer_count++;
    }
    return t;
}

static inline int
trap_unreserve(gx_device_spot_analyzer *padev, gx_san_trap *t)
{
    /* Assuming the last reserved one. */
    if (t->link != padev->trap_free)
	return_error(gs_error_unregistered); /* Must not happen. */
    padev->trap_free = t;
    return 0;
}

static inline int
cont_unreserve(gx_device_spot_analyzer *padev, gx_san_trap_contact *t)
{
    /* Assuming the last reserved one. */
    if (t->link != padev->cont_free)
	return_error(gs_error_unregistered); /* Must not happen. */
    padev->cont_free = t;
    return 0;
}

static inline gx_san_trap *
band_list_last(const gx_san_trap *list)
{
    /* Assuming a non-empty cyclic list, and the anchor points to the first element.  */
    return list->prev;
}

static inline gx_san_trap_contact *
cont_list_last(const gx_san_trap_contact *list)
{
    /* Assuming a non-empty cyclic list, and the anchor points to the first element.  */
    return list->prev;
}

static inline void
band_list_remove(gx_san_trap **list, gx_san_trap *t)
{
    /* Assuming a cyclic list, and the element is in it. */
    if (t->next == t) {
	*list = NULL;
    } else {
	if (*list == t)
	    *list = t->next;
	t->next->prev = t->prev;
	t->prev->next = t->next;
    }
    t->next = t->prev = NULL; /* Safety. */
}

static inline void
band_list_insert_last(gx_san_trap **list, gx_san_trap *t)
{
    /* Assuming a cyclic list. */
    if (*list == 0) {
	*list = t->next = t->prev = t;
    } else {
	gx_san_trap *last = band_list_last(*list);
	gx_san_trap *first = *list;

	t->next = first;
	t->prev = last;
	last->next = first->prev = t;
    }
}

static inline void
cont_list_insert_last(gx_san_trap_contact **list, gx_san_trap_contact *t)
{
    /* Assuming a cyclic list. */
    if (*list == 0) {
	*list = t->next = t->prev = t;
    } else {
	gx_san_trap_contact *last = cont_list_last(*list);
	gx_san_trap_contact *first = *list;

	t->next = first;
	t->prev = last;
	last->next = first->prev = t;
    }
}

static inline bool
trap_is_last(const gx_san_trap *list, const gx_san_trap *t)
{
    /* Assuming a non-empty cyclic list, and the anchor points to the first element.  */
    return t->next == list; 
}

/* ---------------------The device ---------------------------- */

/* The device descriptor */
/* Many of these procedures won't be called; they are set to NULL. */
static const gx_device_spot_analyzer gx_spot_analyzer_device =
{std_device_std_body(gx_device_spot_analyzer, 0, "spot analyzer",
		     0, 0, 1, 1),
 {san_open,
  NULL,
  NULL,
  NULL,
  san_close,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  gx_default_fill_path,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  san_get_clipping_box,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  gx_default_finish_copydevice,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL,
  NULL
 }
};

int
san_open(register gx_device * dev)
{
    gx_device_spot_analyzer * const padev = (gx_device_spot_analyzer *)dev;

    padev->trap_buffer = padev->trap_buffer_last = NULL;
    padev->cont_buffer = padev->cont_buffer_last = NULL;
    padev->trap_buffer_count = 0;
    padev->cont_buffer_count = 0;
    padev->xmin = 0;
    padev->xmax = -1;
    return 0;
}

static int
san_close(gx_device * dev)
{
    gx_device_spot_analyzer * const padev = (gx_device_spot_analyzer *)dev;

    free_trap_list(padev->memory, &padev->trap_buffer);
    free_cont_list(padev->memory, &padev->cont_buffer);
    padev->trap_buffer_last = NULL;
    padev->cont_buffer_last = NULL;
    padev->trap_free = NULL;
    padev->cont_free = NULL;
    padev->top_band = NULL;
    padev->bot_band = NULL;
    padev->bot_current = NULL;
    return 0;
}

void
san_get_clipping_box(gx_device * dev, gs_fixed_rect * pbox)
{
    pbox->p.x = min_int;
    pbox->p.y = min_int;
    pbox->q.x = max_int;
    pbox->q.y = max_int;
}

/* --------------------- Utilities ------------------------- */

static inline int
check_band_list(const gx_san_trap *list)
{
#ifdef DEBUG
    if (list != NULL) {
	const gx_san_trap *t = list;

	while (t->next != list) {
	    if (t->xrtop > t->next->xltop)
		return_error(gs_error_unregistered); /* Must not happen. */
	    t = t->next;
	}
    }
#endif
    return 0;
}

static int
try_unite_last_trap(gx_device_spot_analyzer *padev, fixed xlbot)
{
    if (padev->bot_band != NULL && padev->top_band != NULL) {
	gx_san_trap *last = band_list_last(padev->top_band);
	gx_san_trap *t = padev->bot_current;
	/* If the last trapezoid is a prolongation of its bottom contact, 
	   unite it and release the last trapezoid and the last contact. */
	if (t != NULL && t->upper != NULL && last->xrbot < xlbot && 
		(last->prev == last || last->prev->xrbot < last->xlbot)) {
	    if ((t->next == NULL || t->xrtop < t->next->xltop) &&
	        (t->upper->next == t->upper &&
		    t->l == last->l && t->r == last->r)) {
		int code;

		if (padev->bot_current == t)
		    padev->bot_current = (t == band_list_last(padev->bot_band) ? NULL : t->next);
		if (t->upper->upper != last)
		    return_error(gs_error_unregistered); /* Must not happen. */
		band_list_remove(&padev->top_band, last);
		band_list_remove(&padev->bot_band, t);
		band_list_insert_last(&padev->top_band, t);
		t->ytop = last->ytop;
		t->xltop = last->xltop;
		t->xrtop = last->xrtop;
		t->rightmost &= last->rightmost;
		t->leftmost &= last->leftmost;
		vd_quad(t->xlbot, t->ybot, t->xrbot, t->ybot, 
			t->xrtop, t->ytop, t->xltop, t->ytop, 1, VD_TRAP_U_COLOR);
		code = trap_unreserve(padev, last);
		if (code < 0)
		    return code;
		code = cont_unreserve(padev, t->upper);
		if (code < 0)
		    return code;
		t->upper = NULL;
	    }
	}
    }
    return 0;
}

static inline double 
trap_area(gx_san_trap *t)
{
    return (double)(t->xrbot - t->xlbot + t->xrtop - t->xltop) * (t->ytop - t->ybot) / 2;
}

static inline double 
trap_axis_length(gx_san_trap *t)
{
    double xbot = (t->xlbot + t->xrbot) / 2.0;
    double xtop = (t->xltop + t->xrtop) / 2.0;

    return hypot(xtop - xbot, (double)t->ytop - t->ybot); /* See Bug 687238 */
}

static inline bool
is_stem_boundaries(gx_san_trap *t, int side_mask)
{
    double dx, norm, cosine;
    const double cosine_threshold = 0.9; /* Arbitrary */
    double dy = t->ytop - t->ybot;

    if (side_mask & 1) {
	dx = t->xltop - t->xlbot;
	norm = hypot(dx, dy);
	cosine = dx / norm;
	if (any_abs(cosine) > cosine_threshold)
	    return false;
    }
    if (side_mask & 2) {
	dx = t->xrtop - t->xrbot;
	norm = hypot(dx, dy);
	cosine = dx / norm;
	if (any_abs(cosine) > cosine_threshold)
	    return false;
    }
    return true;
}

/* --------------------- Accessories ------------------------- */

/* Obtain a spot analyzer device. */
int
gx_san__obtain(gs_memory_t *mem, gx_device_spot_analyzer **ppadev)
{
    gx_device_spot_analyzer *padev;
    int code;

    if (*ppadev != 0) {
	(*ppadev)->lock++;
	return 0;
    }
    padev = gs_alloc_struct(mem, gx_device_spot_analyzer, 
		&st_device_spot_analyzer, "gx_san__obtain");
    if (padev == 0)
	return_error(gs_error_VMerror);
    gx_device_init((gx_device *)padev, (const gx_device *)&gx_spot_analyzer_device,
		   mem, false);
    code = gs_opendevice((gx_device *)padev);
    if (code < 0) {
	gs_free_object(mem, padev, "gx_san__obtain");
	return code;
    }
    padev->lock = 1;
    *ppadev = padev;
    return 0;
}

void
gx_san__release(gx_device_spot_analyzer **ppadev)
{
    gx_device_spot_analyzer *padev = *ppadev;

    if (padev == NULL) {
        /* Can't use emprintf here! */
	eprintf("Extra call to gx_san__release.");
	return;
    }
    if(--padev->lock < 0) {
	emprintf(padev->memory, "Wrong lock to gx_san__release.");
	return;
    }
    if (padev->lock == 0) {
	*ppadev = NULL;
	rc_decrement(padev, "gx_san__release");
    }
}

/* Start accumulating a path. */
void 
gx_san_begin(gx_device_spot_analyzer *padev)
{
    padev->bot_band = NULL;
    padev->top_band = NULL;
    padev->bot_current = NULL;
    padev->trap_free = padev->trap_buffer;
    padev->cont_free = padev->cont_buffer;
}

/* Store a tarpezoid. */
/* Assumes an Y-band scanning order with increasing X inside a band. */
int
gx_san_trap_store(gx_device_spot_analyzer *padev, 
    fixed ybot, fixed ytop, fixed xlbot, fixed xrbot, fixed xltop, fixed xrtop,
    const segment *l, const segment *r, int dir_l, int dir_r)
{
    gx_san_trap *last;
    int code;

    if (padev->top_band != NULL && padev->top_band->ytop != ytop) {
	code = try_unite_last_trap(padev, max_int);
	if (code < 0)
	    return code;
	/* Step to a new band. */
	padev->bot_band = padev->bot_current = padev->top_band;
	padev->top_band = NULL;
    }
    if (padev->bot_band != NULL && padev->bot_band->ytop != ybot) {
	/* The Y-projection of the spot is not contiguous. */
	padev->top_band = NULL;
    }
    if (padev->top_band != NULL) {
	code = try_unite_last_trap(padev, xlbot);
	if (code < 0)
	    return code;
    }
    code = check_band_list(padev->bot_band);
    if (code < 0)
	return code;
    code =check_band_list(padev->top_band);
    if (code < 0)
	return code;
    /* Make new trapezoid. */
    last = trap_reserve(padev);
    if (last == NULL)
	return_error(gs_error_VMerror);
    last->ybot = ybot;
    last->ytop = ytop;
    last->xlbot = xlbot;
    last->xrbot = xrbot;
    last->xltop = xltop;
    last->xrtop = xrtop;
    last->l = l;
    last->r = r;
    last->dir_l = dir_l;
    last->dir_r = dir_r;
    last->upper = 0;
    last->fork = 0;
    last->visited = false;
    last->leftmost = last->rightmost = true;
    vd_quad(last->xlbot, last->ybot, last->xrbot, last->ybot, 
	    last->xrtop, last->ytop, last->xltop, last->ytop, 1, VD_TRAP_N_COLOR);
    if (padev->top_band != NULL) {
	padev->top_band->rightmost = false;
	last->leftmost = false;
    }
    band_list_insert_last(&padev->top_band, last);
    code = check_band_list(padev->top_band);
    if (code < 0)
	return code;
    while (padev->bot_current != NULL && padev->bot_current->xrtop < xlbot)
	padev->bot_current = (trap_is_last(padev->bot_band, padev->bot_current)
				    ? NULL : padev->bot_current->next);
    if (padev->bot_current != 0) {
	gx_san_trap *t = padev->bot_current;
	gx_san_trap *bot_last = band_list_last(padev->bot_band);

	while(t->xltop <= xrbot) {
	    gx_san_trap_contact *cont = cont_reserve(padev);

	    if (cont == NULL)
		return_error(gs_error_VMerror);
	    cont->lower = t;
	    cont->upper = last;
	    vd_bar((t->xltop + t->xrtop + t->xlbot + t->xrbot) / 4, (t->ytop + t->ybot) / 2,
		   (last->xltop + last->xrtop + last->xlbot + last->xrbot) / 4, 
		   (last->ytop + last->ybot) / 2, 0, VD_CONT_COLOR);
	    cont_list_insert_last(&t->upper, cont);
	    last->fork++;
	    if (t == bot_last)
		break;
	    t = t->next;
	}
    }
    if (padev->xmin > padev->xmax) {
	padev->xmin = min(xlbot, xltop);
	padev->xmax = max(xrbot, xrtop);
    } else {
	padev->xmin = min(padev->xmin, min(xlbot, xltop));
	padev->xmax = max(padev->xmax, max(xrbot, xrtop));
    }
    return 0;
}


/* Finish accumulating a path. */
void 
gx_san_end(const gx_device_spot_analyzer *padev)
{
}

static int
hint_by_trap(gx_device_spot_analyzer *padev, int side_mask,
    void *client_data, gx_san_trap *t0, gx_san_trap *t1, double ave_width,
    int (*handler)(void *client_data, gx_san_sect *ss))
{   gx_san_trap *t;
    double w, wd, best_width_diff = ave_width * 10;
    gx_san_trap *best_trap = NULL;
    bool at_top = false;
    gx_san_sect sect;
    int code;

    for (t = t0; ; t = t->upper->upper) {
	w = t->xrbot - t->xlbot;
	wd = any_abs(w - ave_width);
	if (w > 0 && wd < best_width_diff) {
	    best_width_diff = wd;
	    best_trap = t;
	}
	if (t == t1)
	    break;
    }
    w = t->xrtop - t->xltop;
    wd = any_abs(w - ave_width);
    if (w > 0 && wd < best_width_diff) {
	best_width_diff = wd;
	best_trap = t;
	at_top = true;
    }
    if (best_trap != NULL) {
	/* Make a stem section hint at_top of best_trap : */
	sect.yl = at_top ? best_trap->ytop : best_trap->ybot; 
	sect.yr = sect.yl;
	sect.xl = at_top ? best_trap->xltop : best_trap->xlbot; 
	sect.xr = at_top ? best_trap->xrtop : best_trap->xrbot;
	sect.l = best_trap->l; 
	sect.r = best_trap->r;
	vd_bar(sect.xl, sect.yl, sect.xr, sect.yr, 0, VD_HINT_COLOR);
	code = handler(client_data, &sect);
	if (code < 0)
	    return code;
    }
    return 0;
}

static inline void
choose_by_vector(fixed x0, fixed y0, fixed x1, fixed y1, const segment *s, 
	double *slope, double *len, const segment **store_segm, fixed *store_x, fixed *store_y)
{
    if (y0 != y1) {
	double t = (double)any_abs(x1 - x0) / any_abs(y1 - y0);
	double l = any_abs(y1 - y0); /* Don't want 'hypot'. */

	if (*slope > t || (*slope == t && l > *len)) {
	    *slope = t;
	    *len = l;
	    *store_segm = s;
	    *store_x = x1;
	    *store_y = y1;
	}
    }
}

static inline void
choose_by_tangent(const segment *p, const segment *s, 
	double *slope, double *len, const segment **store_segm, fixed *store_x, fixed *store_y,
	fixed ybot, fixed ytop)
{
    if (s->type == s_curve) {
	const curve_segment *c = (const curve_segment *)s;
	vd_curve(p->pt.x, p->pt.y, c->p1.x, c->p1.y, c->p2.x, c->p2.y, 
		 s->pt.x, s->pt.y, 0, VD_HINT_COLOR);
	if (ybot <= p->pt.y && p->pt.y <= ytop)
	    choose_by_vector(c->p1.x, c->p1.y, p->pt.x, p->pt.y, s, slope, len, store_segm, store_x, store_y);
	if (ybot <= s->pt.y && s->pt.y <= ytop)
	    choose_by_vector(c->p2.x, c->p2.y, s->pt.x, s->pt.y, s, slope, len, store_segm, store_x, store_y);
    } else {
	vd_bar(p->pt.x, p->pt.y, s->pt.x, s->pt.y, 0, VD_HINT_COLOR);
	choose_by_vector(s->pt.x, s->pt.y, p->pt.x, p->pt.y, s, slope, len, store_segm, store_x, store_y);
    }
}

static gx_san_trap * 
upper_neighbour(gx_san_trap *t0, int left_right)
{
    gx_san_trap_contact *cont = t0->upper, *c0 = cont, *c;
    fixed x = (!left_right ? cont->upper->xlbot : cont->upper->xrbot);

    for (c = c0->next; c != c0; c = c->next) {
	fixed xx = (!left_right ? c->upper->xlbot : c->upper->xrbot);

	if ((xx - x) * (left_right * 2 - 1) > 0) {
    	    cont = c;
	    x = xx;
	}
    }
    return cont->upper;
}

static int
hint_by_tangent(gx_device_spot_analyzer *padev, int side_mask,
    void *client_data, gx_san_trap *t0, gx_san_trap *t1, double ave_width,
    int (*handler)(void *client_data, gx_san_sect *ss))
{   gx_san_trap *t;
    gx_san_sect sect;
    double slope0 = 0.2, slope1 = slope0, len0 = 0, len1 = 0;
    const segment *s, *p;
    int left_right = (side_mask & 1 ? 0 : 1);
    int code;
    
    sect.l = sect.r = NULL;
    sect.xl = t0->xltop; /* only for vdtrace. */
    sect.xr = t0->xrtop; /* only for vdtrace. */
    sect.yl = sect.yr = t0->ytop; /* only for vdtrace. */
    sect.side_mask = side_mask;
    for (t = t0; ; t = upper_neighbour(t, left_right)) {
	if (side_mask & 1) {
	    s = t->l;
	    if (t->dir_l < 0)
		s = (s->type == s_line_close ? ((const line_close_segment *)s)->sub->next : s->next);
	    p = (s->type == s_start ? ((const subpath *)s)->last->prev : s->prev);
	    choose_by_tangent(p, s, &slope0, &len0, &sect.l, &sect.xl, &sect.yl, t->ybot, t->ytop);
	}
	if (side_mask & 2) {
	    s = t->r;
	    if (t->dir_r < 0)
		s = (s->type == s_line_close ? ((const line_close_segment *)s)->sub->next : s->next);
	    p = (s->type == s_start ? ((const subpath *)s)->last->prev : s->prev);
	    choose_by_tangent(p, s, &slope1, &len1, &sect.r, &sect.xr, &sect.yr, t->ybot, t->ytop);
	}
	if (t == t1)
	    break;
    }
    if ((sect.l != NULL  || !(side_mask & 1)) && 
	(sect.r != NULL  || !(side_mask & 2))) {
	const int w = 3;

	if (!(side_mask & 1)) {
	    if (sect.xr < (padev->xmin * w + padev->xmax) / (w + 1))
		return 0;
	    sect.xl = padev->xmin - 1000; /* ignore side */
	}
	if (!(side_mask & 2)) {
	    if (sect.xl > (padev->xmax * w + padev->xmin) / (w + 1))
		return 0;
	    sect.xr = padev->xmax + 1000; /* ignore side */
	}
	vd_bar(sect.xl, sect.yl, sect.xr, sect.yr, 0, VD_HINT_COLOR);
	code = handler(client_data, &sect);
	if (code < 0)
	    return code;
    }
    return 0;
}

/* Generate stems. */
static int 
gx_san_generate_stems_aux(gx_device_spot_analyzer *padev, 
		bool overall_hints, void *client_data,
		int (*handler)(void *client_data, gx_san_sect *ss))
{
    gx_san_trap *t0;
    const bool by_trap = false;
    int k;

    /* Overall hints : */
    /* An overall hint designates an outer side of a glyph,
       being nearly parallel to a coordinate axis. 
       It aligns a stem end rather than stem sides.
       See t1_hinter__overall_hstem.
     */
    for (k = 0; overall_hints && k < 2; k++) { /* left, right. */
	for (t0 = padev->trap_buffer; t0 != padev->trap_free; t0 = t0->link) {
	    if (!t0->visited && (!k ? t0->leftmost : t0->rightmost)) {
		if (is_stem_boundaries(t0, 1 << k)) {
		    gx_san_trap *t1 = t0, *tt = t0, *t = t0;
		    int code;

		    while (t->upper != NULL) {
			t = upper_neighbour(tt, k);
			if (!k ? !t->leftmost : !t->rightmost) {
			    break;
			}
			if (!is_stem_boundaries(t, 1 << k)) {
			    t->visited = true;
			    break;
			}
			if ((!k ? tt->xltop : tt->xrtop) != (!k ? t->xlbot : t->xrbot))
			    break; /* Not a contigouos boundary. */
    			t->visited = true;
			tt = t;
		    }
		    if (!k ? !t->leftmost : !t->rightmost)
			continue;
		    t1 = t;
		    /* leftmost/rightmost boundary from t0 to t1. */
		    code = hint_by_tangent(padev, 1 << k, client_data, t0, t1, 0, handler);
		    if (code < 0)
			return code;
		}
	    }
	}
	for (t0 = padev->trap_buffer; t0 != padev->trap_free; t0 = t0->link)
	    t0->visited = false;
    }
    /* Stem hints : */
    for (t0 = padev->trap_buffer; t0 != padev->trap_free; t0 = t0->link) {
	if (!t0->visited) {
	    if (is_stem_boundaries(t0, 3)) {
		gx_san_trap_contact *cont = t0->upper;
		gx_san_trap *t1 = t0, *t;
		double area = 0, length = 0, ave_width;
		
		while(cont != NULL && cont->next == cont /* <= 1 descendent. */) {
		    gx_san_trap *t = cont->upper;

		    if (!is_stem_boundaries(t, 3)) {
			t->visited = true;
			break;
		    }
		    if (t->fork > 1)
			break; /* > 1 accendents.  */
		    if (t1->xltop != t->xlbot || t1->xrtop != t->xrbot)
			break; /* Not a contigouos boundary. */
		    t1 = t;
		    cont = t1->upper;
		    t1->visited = true;
		}
		/* We've got a stem suspection from t0 to t1. */
		vd_quad(t0->xlbot, t0->ybot, t0->xrbot, t0->ybot, 
			t1->xrtop, t1->ytop, t1->xltop, t1->ytop, 1, VD_STEM_COLOR);
		for (t = t0; ; t = t->upper->upper) {
		    length += trap_axis_length(t);
		    area += trap_area(t);
		    if (t == t1)
			break;
		}
		ave_width = area / length;
		if (length > ave_width / ( 2.0 /* arbitrary */)) {
		    /* We've got a stem from t0 to t1. */
		    int code = (by_trap ? hint_by_trap : hint_by_tangent)(padev, 
			3, client_data, t0, t1, ave_width, handler);

		    if (code < 0)
			return code;
		}
	    }
	}
	t0->visited = true;
    }
    return 0;
}

int 
gx_san_generate_stems(gx_device_spot_analyzer *padev, 
		bool overall_hints, void *client_data,
		int (*handler)(void *client_data, gx_san_sect *ss))
{
    int code;
    bool got_dc = false;
    vd_save;

    if (vd_allowed('F') || vd_allowed('f')) {
	if (!vd_enabled) {
	    vd_get_dc('f');
	    got_dc = vd_enabled;
	}
	if (vd_enabled) {
	    vd_set_shift(0, 0);
	    vd_set_scale(VD_SCALE);
	    vd_set_origin(0, 0);
	}
    } else
	vd_disable;
    code = gx_san_generate_stems_aux(padev, overall_hints, client_data, handler);
    if (got_dc)
	vd_release_dc;
    vd_restore;
    return code;
}
