96 lines
4.0 KiB
C++
96 lines
4.0 KiB
C++
/*
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* Copyright (C) 2012 Carl Hetherington <carl@carlh.net>
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* Copyright (C) 2013-2015 Paul Davis <paul@linuxaudiosystems.com>
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* Copyright (C) 2015-2017 Robin Gareus <robin@gareus.org>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#include <algorithm>
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#include <cmath>
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#include <stdint.h>
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#include <cairomm/context.h>
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#include "canvas/utils.h"
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using namespace std;
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using namespace ArdourCanvas;
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ArdourCanvas::Distance
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ArdourCanvas::distance_to_segment_squared (Duple const & p, Duple const & p1, Duple const & p2, double& t, Duple& at)
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{
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static const double kMinSegmentLenSquared = 0.00000001; // adjust to suit. If you use float, you'll probably want something like 0.000001f
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static const double kEpsilon = 1.0E-14; // adjust to suit. If you use floats, you'll probably want something like 1E-7f
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double dx = p2.x - p1.x;
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double dy = p2.y - p1.y;
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double dp1x = p.x - p1.x;
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double dp1y = p.y - p1.y;
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const double segLenSquared = (dx * dx) + (dy * dy);
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if (segLenSquared >= -kMinSegmentLenSquared && segLenSquared <= kMinSegmentLenSquared) {
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// segment is a point.
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at = p1;
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t = 0.0;
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return ((dp1x * dp1x) + (dp1y * dp1y));
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}
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// Project a line from p to the segment [p1,p2]. By considering the line
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// extending the segment, parameterized as p1 + (t * (p2 - p1)),
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// we find projection of point p onto the line.
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// It falls where t = [(p - p1) . (p2 - p1)] / |p2 - p1|^2
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t = ((dp1x * dx) + (dp1y * dy)) / segLenSquared;
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if (t < kEpsilon) {
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// intersects at or to the "left" of first segment vertex (p1.x, p1.y). If t is approximately 0.0, then
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// intersection is at p1. If t is less than that, then there is no intersection (i.e. p is not within
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// the 'bounds' of the segment)
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if (t > -kEpsilon) {
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// intersects at 1st segment vertex
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t = 0.0;
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}
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// set our 'intersection' point to p1.
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at = p1;
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// Note: If you wanted the ACTUAL intersection point of where the projected lines would intersect if
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// we were doing PointLineDistanceSquared, then qx would be (p1.x + (t * dx)) and qy would be (p1.y + (t * dy)).
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} else if (t > (1.0 - kEpsilon)) {
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// intersects at or to the "right" of second segment vertex (p2.x, p2.y). If t is approximately 1.0, then
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// intersection is at p2. If t is greater than that, then there is no intersection (i.e. p is not within
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// the 'bounds' of the segment)
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if (t < (1.0 + kEpsilon)) {
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// intersects at 2nd segment vertex
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t = 1.0;
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}
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// set our 'intersection' point to p2.
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at = p2;
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// Note: If you wanted the ACTUAL intersection point of where the projected lines would intersect if
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// we were doing PointLineDistanceSquared, then qx would be (p1.x + (t * dx)) and qy would be (p1.y + (t * dy)).
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} else {
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// The projection of the point to the point on the segment that is perpendicular succeeded and the point
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// is 'within' the bounds of the segment. Set the intersection point as that projected point.
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at = Duple (p1.x + (t * dx), p1.y + (t * dy));
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}
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// return the squared distance from p to the intersection point. Note that we return the squared distance
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// as an optimization because many times you just need to compare relative distances and the squared values
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// works fine for that. If you want the ACTUAL distance, just take the square root of this value.
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double dpqx = p.x - at.x;
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double dpqy = p.y - at.y;
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return ((dpqx * dpqx) + (dpqy * dpqy));
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}
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