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/* cairo - a vector graphics library with display and print output

 *

 * Copyright © 2002 University of Southern California

 *

 * This library is free software; you can redistribute it and/or

 * modify it either under the terms of the GNU Lesser General Public

 * License version 2.1 as published by the Free Software Foundation

 * (the "LGPL") or, at your option, under the terms of the Mozilla

 * Public License Version 1.1 (the "MPL"). If you do not alter this

 * notice, a recipient may use your version of this file under either

 * the MPL or the LGPL.

 *

 * You should have received a copy of the LGPL along with this library

 * in the file COPYING-LGPL-2.1; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335, USA

 * You should have received a copy of the MPL along with this library

 * in the file COPYING-MPL-1.1

 *

 * The contents of this file are subject to the Mozilla Public License

 * Version 1.1 (the "License"); you may not use this file except in

 * compliance with the License. You may obtain a copy of the License at

 * http://www.mozilla.org/MPL/

 *

 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY

 * OF ANY KIND, either express or implied. See the LGPL or the MPL for

 * the specific language governing rights and limitations.

 *

 * The Original Code is the cairo graphics library.

 *

 * The Initial Developer of the Original Code is University of Southern

 * California.

 *

 * Contributor(s):

 *	Carl D. Worth 

 */

#include "cairoint.h"

#include "cairo-box-inline.h"

#include "cairo-slope-private.h"

cairo_bool_t

_cairo_spline_intersects (const cairo_point_t *a,

			  const cairo_point_t *b,

			  const cairo_point_t *c,

			  const cairo_point_t *d,

			  const cairo_box_t *box)

{

    cairo_box_t bounds;

    if (_cairo_box_contains_point (box, a) ||

	_cairo_box_contains_point (box, b) ||

	_cairo_box_contains_point (box, c) ||

	_cairo_box_contains_point (box, d))

    {

	return TRUE;

    }

    bounds.p2 = bounds.p1 = *a;

    _cairo_box_add_point (&bounds, b);

    _cairo_box_add_point (&bounds, c);

    _cairo_box_add_point (&bounds, d);

    if (bounds.p2.x <= box->p1.x || bounds.p1.x >= box->p2.x ||

	bounds.p2.y <= box->p1.y || bounds.p1.y >= box->p2.y)

    {

	return FALSE;

    }

#if 0 /* worth refining? */

    bounds.p2 = bounds.p1 = *a;

    _cairo_box_add_curve_to (&bounds, b, c, d);

    if (bounds.p2.x <= box->p1.x || bounds.p1.x >= box->p2.x ||

	bounds.p2.y <= box->p1.y || bounds.p1.y >= box->p2.y)

    {

	return FALSE;

    }

#endif

    return TRUE;

}

cairo_bool_t

_cairo_spline_init (cairo_spline_t *spline,

		    cairo_spline_add_point_func_t add_point_func,

		    void *closure,

		    const cairo_point_t *a, const cairo_point_t *b,

		    const cairo_point_t *c, const cairo_point_t *d)

{

    /* If both tangents are zero, this is just a straight line */

    if (a->x == b->x && a->y == b->y && c->x == d->x && c->y == d->y)

	return FALSE;

    spline->add_point_func = add_point_func;

    spline->closure = closure;

    spline->knots.a = *a;

    spline->knots.b = *b;

    spline->knots.c = *c;

    spline->knots.d = *d;

    if (a->x != b->x || a->y != b->y)

	_cairo_slope_init (&spline->initial_slope, &spline->knots.a, &spline->knots.b);

    else if (a->x != c->x || a->y != c->y)

	_cairo_slope_init (&spline->initial_slope, &spline->knots.a, &spline->knots.c);

    else if (a->x != d->x || a->y != d->y)

	_cairo_slope_init (&spline->initial_slope, &spline->knots.a, &spline->knots.d);

    else

	return FALSE;

    if (c->x != d->x || c->y != d->y)

	_cairo_slope_init (&spline->final_slope, &spline->knots.c, &spline->knots.d);

    else if (b->x != d->x || b->y != d->y)

	_cairo_slope_init (&spline->final_slope, &spline->knots.b, &spline->knots.d);

    else

	return FALSE; /* just treat this as a straight-line from a -> d */

    /* XXX if the initial, final and vector are all equal, this is just a line */

    return TRUE;

}

static cairo_status_t

_cairo_spline_add_point (cairo_spline_t *spline,

			 const cairo_point_t *point,

			 const cairo_point_t *knot)

{

    cairo_point_t *prev;

    cairo_slope_t slope;

    prev = &spline->last_point;

    if (prev->x == point->x && prev->y == point->y)

	return CAIRO_STATUS_SUCCESS;

    _cairo_slope_init (&slope, point, knot);

    spline->last_point = *point;

    return spline->add_point_func (spline->closure, point, &slope);

}

static void

_lerp_half (const cairo_point_t *a, const cairo_point_t *b, cairo_point_t *result)

{

    result->x = a->x + ((b->x - a->x) >> 1);

    result->y = a->y + ((b->y - a->y) >> 1);

}

static void

_de_casteljau (cairo_spline_knots_t *s1, cairo_spline_knots_t *s2)

{

    cairo_point_t ab, bc, cd;

    cairo_point_t abbc, bccd;

    cairo_point_t final;

    _lerp_half (&s1->a, &s1->b, &ab);

    _lerp_half (&s1->b, &s1->c, &bc);

    _lerp_half (&s1->c, &s1->d, &cd);

    _lerp_half (&ab, &bc, &abbc);

    _lerp_half (&bc, &cd, &bccd);

    _lerp_half (&abbc, &bccd, &final);

    s2->a = final;

    s2->b = bccd;

    s2->c = cd;

    s2->d = s1->d;

    s1->b = ab;

    s1->c = abbc;

    s1->d = final;

}

/* Return an upper bound on the error (squared) that could result from

 * approximating a spline as a line segment connecting the two endpoints. */

static double

_cairo_spline_error_squared (const cairo_spline_knots_t *knots)

{

    double bdx, bdy, berr;

    double cdx, cdy, cerr;

    /* We are going to compute the distance (squared) between each of the the b

     * and c control points and the segment a-b. The maximum of these two

     * distances will be our approximation error. */

    bdx = _cairo_fixed_to_double (knots->b.x - knots->a.x);

    bdy = _cairo_fixed_to_double (knots->b.y - knots->a.y);

    cdx = _cairo_fixed_to_double (knots->c.x - knots->a.x);

    cdy = _cairo_fixed_to_double (knots->c.y - knots->a.y);

    if (knots->a.x != knots->d.x || knots->a.y != knots->d.y) {

	/* Intersection point (px):

	 *     px = p1 + u(p2 - p1)

	 *     (p - px) ∙ (p2 - p1) = 0

	 * Thus:

	 *     u = ((p - p1) ∙ (p2 - p1)) / ∥p2 - p1∥²;

	 */

	double dx, dy, u, v;

	dx = _cairo_fixed_to_double (knots->d.x - knots->a.x);

	dy = _cairo_fixed_to_double (knots->d.y - knots->a.y);

	 v = dx * dx + dy * dy;

	u = bdx * dx + bdy * dy;

	if (u <= 0) {

	    /* bdx -= 0;

	     * bdy -= 0;

	     */

	} else if (u >= v) {

	    bdx -= dx;

	    bdy -= dy;

	} else {

	    bdx -= u/v * dx;

	    bdy -= u/v * dy;

	}

	u = cdx * dx + cdy * dy;

	if (u <= 0) {

	    /* cdx -= 0;

	     * cdy -= 0;

	     */

	} else if (u >= v) {

	    cdx -= dx;

	    cdy -= dy;

	} else {

	    cdx -= u/v * dx;

	    cdy -= u/v * dy;

	}

    }

    berr = bdx * bdx + bdy * bdy;

    cerr = cdx * cdx + cdy * cdy;

    if (berr > cerr)

	return berr;

    else

	return cerr;

}

static cairo_status_t

_cairo_spline_decompose_into (cairo_spline_knots_t *s1,

			      double tolerance_squared,

			      cairo_spline_t *result)

{

    cairo_spline_knots_t s2;

    cairo_status_t status;

    if (_cairo_spline_error_squared (s1) < tolerance_squared)

	return _cairo_spline_add_point (result, &s1->a, &s1->b);

    _de_casteljau (s1, &s2);

    status = _cairo_spline_decompose_into (s1, tolerance_squared, result);

    if (unlikely (status))

	return status;

    return _cairo_spline_decompose_into (&s2, tolerance_squared, result);

}

cairo_status_t

_cairo_spline_decompose (cairo_spline_t *spline, double tolerance)

{

    cairo_spline_knots_t s1;

    cairo_status_t status;

    s1 = spline->knots;

    spline->last_point = s1.a;

    status = _cairo_spline_decompose_into (&s1, tolerance * tolerance, spline);

    if (unlikely (status))

	return status;

    return spline->add_point_func (spline->closure,

				   &spline->knots.d, &spline->final_slope);

}

/* Note: this function is only good for computing bounds in device space. */

cairo_status_t

_cairo_spline_bound (cairo_spline_add_point_func_t add_point_func,

		     void *closure,

		     const cairo_point_t *p0, const cairo_point_t *p1,

		     const cairo_point_t *p2, const cairo_point_t *p3)

{

    double x0, x1, x2, x3;

    double y0, y1, y2, y3;

    double a, b, c;

    double t[4];

    int t_num = 0, i;

    cairo_status_t status;

    x0 = _cairo_fixed_to_double (p0->x);

    y0 = _cairo_fixed_to_double (p0->y);

    x1 = _cairo_fixed_to_double (p1->x);

    y1 = _cairo_fixed_to_double (p1->y);

    x2 = _cairo_fixed_to_double (p2->x);

    y2 = _cairo_fixed_to_double (p2->y);

    x3 = _cairo_fixed_to_double (p3->x);

    y3 = _cairo_fixed_to_double (p3->y);

    /* The spline can be written as a polynomial of the four points:

     *

     *   (1-t)³p0 + 3t(1-t)²p1 + 3t²(1-t)p2 + t³p3

     *

     * for 0≤t≤1.  Now, the X and Y components of the spline follow the

     * same polynomial but with x and y replaced for p.  To find the

     * bounds of the spline, we just need to find the X and Y bounds.

     * To find the bound, we take the derivative and equal it to zero,

     * and solve to find the t's that give the extreme points.

     *

     * Here is the derivative of the curve, sorted on t:

     *

     *   3t²(-p0+3p1-3p2+p3) + 2t(3p0-6p1+3p2) -3p0+3p1

     *

     * Let:

     *

     *   a = -p0+3p1-3p2+p3

     *   b =  p0-2p1+p2

     *   c = -p0+p1

     *

     * Gives:

     *

     *   a.t² + 2b.t + c = 0

     *

     * With:

     *

     *   delta = b*b - a*c

     *

     * the extreme points are at -c/2b if a is zero, at (-b±√delta)/a if

     * delta is positive, and at -b/a if delta is zero.

     */

#define ADD(t0) \

    { \

	double _t0 = (t0); \

	if (0 < _t0 && _t0 < 1) \

	    t[t_num++] = _t0; \

    }

#define FIND_EXTREMES(a,b,c) \

    { \

	if (a == 0) { \

	    if (b != 0) \

		ADD (-c / (2*b)); \

	} else { \

	    double b2 = b * b; \

	    double delta = b2 - a * c; \

	    if (delta > 0) { \

		cairo_bool_t feasible; \

		double _2ab = 2 * a * b; \

		/* We are only interested in solutions t that satisfy 0

		 * here.  We do some checks to avoid sqrt if the solutions \

		 * are not in that range.  The checks can be derived from: \

		 * \

		 *   0 < (-b±√delta)/a < 1 \

		 */ \

		if (_2ab >= 0) \

		    feasible = delta > b2 && delta < a*a + b2 + _2ab; \

		else if (-b / a >= 1) \

		    feasible = delta < b2 && delta > a*a + b2 + _2ab; \

		else \

		    feasible = delta < b2 || delta < a*a + b2 + _2ab; \

	        \

		if (unlikely (feasible)) { \

		    double sqrt_delta = sqrt (delta); \

		    ADD ((-b - sqrt_delta) / a); \

		    ADD ((-b + sqrt_delta) / a); \

		} \

	    } else if (delta == 0) { \

		ADD (-b / a); \

	    } \

	} \

    }

    /* Find X extremes */

    a = -x0 + 3*x1 - 3*x2 + x3;

    b =  x0 - 2*x1 + x2;

    c = -x0 + x1;

    FIND_EXTREMES (a, b, c);

    /* Find Y extremes */

    a = -y0 + 3*y1 - 3*y2 + y3;

    b =  y0 - 2*y1 + y2;

    c = -y0 + y1;

    FIND_EXTREMES (a, b, c);

    status = add_point_func (closure, p0, NULL);

    if (unlikely (status))

	return status;

    for (i = 0; i < t_num; i++) {

	cairo_point_t p;

	double x, y;

        double t_1_0, t_0_1;

        double t_2_0, t_0_2;

        double t_3_0, t_2_1_3, t_1_2_3, t_0_3;

        t_1_0 = t[i];          /*      t  */

        t_0_1 = 1 - t_1_0;     /* (1 - t) */

        t_2_0 = t_1_0 * t_1_0; /*      t  *      t  */

        t_0_2 = t_0_1 * t_0_1; /* (1 - t) * (1 - t) */

        t_3_0   = t_2_0 * t_1_0;     /*      t  *      t  *      t      */

        t_2_1_3 = t_2_0 * t_0_1 * 3; /*      t  *      t  * (1 - t) * 3 */

        t_1_2_3 = t_1_0 * t_0_2 * 3; /*      t  * (1 - t) * (1 - t) * 3 */

        t_0_3   = t_0_1 * t_0_2;     /* (1 - t) * (1 - t) * (1 - t)     */

        /* Bezier polynomial */

        x = x0 * t_0_3

          + x1 * t_1_2_3

          + x2 * t_2_1_3

          + x3 * t_3_0;

        y = y0 * t_0_3

          + y1 * t_1_2_3

          + y2 * t_2_1_3

          + y3 * t_3_0;

	p.x = _cairo_fixed_from_double (x);

	p.y = _cairo_fixed_from_double (y);

	status = add_point_func (closure, &p, NULL);

	if (unlikely (status))

	    return status;

    }

    return add_point_func (closure, p3, NULL);

}