path: root/eel/eel-canvas-util.c

/*
 * Copyright (C) 1997, 1998, 1999, 2000 Free Software Foundation
 * All rights reserved.
 *
 * This file is part of the Mate Library.
 *
 * The Mate Library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * The Mate Library 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
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with the Mate Library; see the file COPYING.LIB.  If not,
 * write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */
/*
  @NOTATION@
 */
/* Miscellaneous utility functions for the EelCanvas widget
 *
 * EelCanvas is basically a port of the Tk toolkit's most excellent canvas widget.  Tk is
 * copyrighted by the Regents of the University of California, Sun Microsystems, and other parties.
 *
 *
 * Author: Federico Mena <federico@nuclecu.unam.mx>
 */

#include <config.h>

#include <sys/types.h>
#include <glib.h>
#include <math.h>

#include "eel-canvas.h"
#include "eel-canvas-util.h"

/*
 * Ok, so some systems require magic incantations for M_PI to be defined.
 * It's not important enough to worry about.
 */
#ifndef M_PI
#define M_PI 3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117
#endif

/**
 * eel_canvas_points_new:
 * @num_points: The number of points to allocate space for in the array.
 *
 * Creates a structure that should be used to pass an array of points to
 * items.
 *
 * Return value: A newly-created array of points.  It should be filled in
 * by the user.
 **/
EelCanvasPoints *
eel_canvas_points_new (int num_points)
{
    EelCanvasPoints *points;

    g_return_val_if_fail (num_points > 1, NULL);

    points = g_new (EelCanvasPoints, 1);
    points->num_points = num_points;
    points->coords = g_new (double, 2 * num_points);
    points->ref_count = 1;

    return points;
}

/**
 * eel_canvas_points_ref:
 * @points: A canvas points structure.
 *
 * Increases the reference count of the specified points structure.
 *
 * Return value: The canvas points structure itself.
 **/
EelCanvasPoints *
eel_canvas_points_ref (EelCanvasPoints *points)
{
    g_return_val_if_fail (points != NULL, NULL);

    points->ref_count += 1;
    return points;
}

/**
 * eel_canvas_points_free:
 * @points: A canvas points structure.
 *
 * Decreases the reference count of the specified points structure.  If it
 * reaches zero, then the structure is freed.
 **/
void
eel_canvas_points_free (EelCanvasPoints *points)
{
    g_return_if_fail (points != NULL);

    points->ref_count -= 1;
    if (points->ref_count == 0)
    {
        g_free (points->coords);
        g_free (points);
    }
}

/**
 * eel_canvas_get_miter_points:
 * @x1: X coordinate of the first point
 * @y1: Y coordinate of the first point
 * @x2: X coordinate of the second (angle) point
 * @y2: Y coordinate of the second (angle) point
 * @x3: X coordinate of the third point
 * @y3: Y coordinate of the third point
 * @width: Width of the line
 * @mx1: The X coordinate of the first miter point is returned here.
 * @my1: The Y coordinate of the first miter point is returned here.
 * @mx2: The X coordinate of the second miter point is returned here.
 * @my2: The Y coordinate of the second miter point is returned here.
 *
 * Given three points forming an angle, computes the coordinates of the inside
 * and outside points of the mitered corner formed by a line of a given width at
 * that angle.
 *
 * Return value: FALSE if the angle is less than 11 degrees (this is the same
 * threshold as X uses.  If this occurs, the return points are not modified.
 * Otherwise, returns TRUE.
 **/
int
eel_canvas_get_miter_points (double x1, double y1, double x2, double y2, double x3, double y3,
                             double width,
                             double *mx1, double *my1, double *mx2, double *my2)
{
    double theta1;		/* angle of segment p2-p1 */
    double theta2;		/* angle of segment p2-p3 */
    double theta;		/* angle between line segments */
    double theta3;		/* angle that bisects theta1 and theta2 and points to p1 */
    double dist;		/* distance of miter points from p2 */
    double dx, dy;		/* x and y offsets corresponding to dist */

    double ELEVEN_DEGREES = 11.0 * M_PI / 180.0;

    /* Degenerate cases.  */
    if ((x1 == x2 && y1 == y2) || (x2 == x3 && y2 == y3))
        return FALSE;

    theta1 = atan2 (y1 - y2, x1 - x2);
    theta2 = atan2 (y3 - y2, x3 - x2);
    theta = theta1 - theta2;

    /* Normalize to (-pi; pi].  */
    if (theta > M_PI)
        theta -= 2.0 * M_PI;
    else if (theta <= -M_PI)
        theta += 2.0 * M_PI;

    if (fabs (theta) < ELEVEN_DEGREES)
        return FALSE;

    dist = fabs (0.5 * width / sin (0.5 * theta));

    theta3 = (theta1 + theta2) / 2.0;
    if (sin (theta3 - theta1) > 0.0)
        theta3 += M_PI;

    dx = dist * cos (theta3);
    dy = dist * sin (theta3);

    *mx1 = x2 + dx;
    *mx2 = x2 - dx;
    *my1 = y2 + dy;
    *my2 = y2 - dy;

    return TRUE;
}

/**
 * eel_canvas_get_butt_points:
 * @x1: X coordinate of first point in the line
 * @y1: Y cooordinate of first point in the line
 * @x2: X coordinate of second point (endpoint) of the line
 * @y2: Y coordinate of second point (endpoint) of the line
 * @width: Width of the line
 * @project: Whether the butt points should project out by width/2 distance
 * @bx1: X coordinate of first butt point is returned here
 * @by1: Y coordinate of first butt point is returned here
 * @bx2: X coordinate of second butt point is returned here
 * @by2: Y coordinate of second butt point is returned here
 *
 * Computes the butt points of a line segment.
 **/
void
eel_canvas_get_butt_points (double x1, double y1, double x2, double y2,
                            double width, int project,
                            double *bx1, double *by1, double *bx2, double *by2)
{
    double length;
    double dx, dy;

    width *= 0.5;
    dx = x2 - x1;
    dy = y2 - y1;
    length = sqrt (dx * dx + dy * dy);

    if (length < EEL_CANVAS_EPSILON)
    {
        *bx1 = *bx2 = x2;
        *by1 = *by2 = y2;
    }
    else
    {
        dx = -width * (y2 - y1) / length;
        dy = width * (x2 - x1) / length;

        *bx1 = x2 + dx;
        *bx2 = x2 - dx;
        *by1 = y2 + dy;
        *by2 = y2 - dy;

        if (project)
        {
            *bx1 += dy;
            *bx2 += dy;
            *by1 -= dx;
            *by2 -= dx;
        }
    }
}

/**
 * eel_canvas_polygon_to_point:
 * @poly: Vertices of the polygon.  X coordinates are in the even indices, and Y
 * coordinates are in the odd indices
 * @num_points: Number of points in the polygon
 * @x: X coordinate of the point
 * @y: Y coordinate of the point
 *
 * Computes the distance between a point and a polygon.
 *
 * Return value: The distance from the point to the polygon, or zero if the
 * point is inside the polygon.
 **/
double
eel_canvas_polygon_to_point (double *poly, int num_points, double x, double y)
{
    double best;
    int intersections;
    int i;
    double *p;
    double dx, dy;

    /* Iterate through all the edges in the polygon, updating best and intersections.
     *
     * When computing intersections, include left X coordinate of line within its range, but not
     * Y coordinate.  Otherwise if the point lies exactly below a vertex we'll count it as two
     * intersections.
     */

    best = 1.0e36;
    if (poly == NULL)
        return best;

    intersections = 0;

    for (i = num_points, p = poly; i > 1; i--, p += 2)
    {
        double px, py, dist;

        /* Compute the point on the current edge closest to the point and update the
         * intersection count.  This must be done separately for vertical edges, horizontal
         * edges, and others.
         */

        if (p[2] == p[0])
        {
            /* Vertical edge */

            px = p[0];

            if (p[1] >= p[3])
            {
                py = MIN (p[1], y);
                py = MAX (py, p[3]);
            }
            else
            {
                py = MIN (p[3], y);
                py = MAX (py, p[1]);
            }
        }
        else if (p[3] == p[1])
        {
            /* Horizontal edge */

            py = p[1];

            if (p[0] >= p[2])
            {
                px = MIN (p[0], x);
                px = MAX (px, p[2]);

                if ((y < py) && (x < p[0]) && (x >= p[2]))
                    intersections++;
            }
            else
            {
                px = MIN (p[2], x);
                px = MAX (px, p[0]);

                if ((y < py) && (x < p[2]) && (x >= p[0]))
                    intersections++;
            }
        }
        else
        {
            double m1, b1, m2, b2;
            int lower;

            /* Diagonal edge.  Convert the edge to a line equation (y = m1*x + b1), then
             * compute a line perpendicular to this edge but passing through the point,
             * (y = m2*x + b2).
             */

            m1 = (p[3] - p[1]) / (p[2] - p[0]);
            b1 = p[1] - m1 * p[0];

            m2 = -1.0 / m1;
            b2 = y - m2 * x;

            px = (b2 - b1) / (m1 - m2);
            py = m1 * px + b1;

            if (p[0] > p[2])
            {
                if (px > p[0])
                {
                    px = p[0];
                    py = p[1];
                }
                else if (px < p[2])
                {
                    px = p[2];
                    py = p[3];
                }
            }
            else
            {
                if (px > p[2])
                {
                    px = p[2];
                    py = p[3];
                }
                else if (px < p[0])
                {
                    px = p[0];
                    py = p[1];
                }
            }

            lower = (m1 * x + b1) > y;

            if (lower && (x >= MIN (p[0], p[2])) && (x < MAX (p[0], p[2])))
                intersections++;
        }

        /* Compute the distance to the closest point, and see if that is the best so far */

        dx = x - px;
        dy = y - py;
        dist = sqrt (dx * dx + dy * dy);
        if (dist < best)
            best = dist;
    }

    /* We've processed all the points.  If the number of intersections is odd, the point is
     * inside the polygon.
     */

    if (intersections & 0x1)
        return 0.0;
    else
        return best;
}

/**
 * eel_canvas_item_reset_bounds:
 * @item: A canvas item
 *
 * Resets the bounding box of a canvas item to an empty rectangle.
 **/
void
eel_canvas_item_reset_bounds (EelCanvasItem *item)
{
    item->x1 = 0.0;
    item->y1 = 0.0;
    item->x2 = 0.0;
    item->y2 = 0.0;
}

/**
 * eel_canvas_update_bbox:
 * @canvas: the canvas needing update
 * @x1: Left coordinate of the new bounding box
 * @y1: Top coordinate of the new bounding box
 * @x2: Right coordinate of the new bounding box
 * @y2: Bottom coordinate of the new bounding box
 *
 * Sets the bbox to the new value, requesting full repaint.
 **/
void
eel_canvas_update_bbox (EelCanvasItem *item, int x1, int y1, int x2, int y2)
{
    eel_canvas_item_request_redraw (item);
    item->x1 = x1;
    item->y1 = y1;
    item->x2 = x2;
    item->y2 = y2;
    eel_canvas_item_request_redraw (item);
}