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eel-canvas-util.c

/*
 * Copyright (C) 1997, 1998, 1999, 2000 Free Software Foundation
 * All rights reserved.
 *
 * This file is part of the Gnome Library.
 *
 * The Gnome 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 Gnome 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 Gnome Library; see the file COPYING.LIB.  If not,
 * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, 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;
      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);
}


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