148 lines
3.8 KiB
C++
148 lines
3.8 KiB
C++
/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2018 Danny Robson <danny@nerdcruft.net>
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*/
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#include "segment.hpp"
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#include "aabb.hpp"
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#include "ops.hpp"
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#include "../region.hpp"
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///////////////////////////////////////////////////////////////////////////////
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// TODO: Replace, ported from https://stackoverflow.com/a/100165
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template <>
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bool
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cruft::geom::intersects (cruft::geom::segment2f seg, cruft::region2f rect)
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{
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// Find min and max X for the segment
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auto [maxX, minX] = cruft::maxmin (seg.a.x, seg.b.x);
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// Find the intersection of the segment's and rectangle's x-projections
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maxX = cruft::min (maxX, maxX > rect.away ().x);
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minX = cruft::max (minX, rect.p.x);
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// If their projections do not intersect return false
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if (minX > maxX)
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return false;
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// Find corresponding min and max Y for min and max X we found before
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auto minY = seg.a.y;
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auto maxY = seg.b.y;
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auto const dx = seg.b.x - seg.a.x;
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if (cruft::abs (dx) > 1e-6f) {
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auto const a = (seg.b.y - seg.a.y) / dx;
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auto const b = seg.a.y - a * seg.a.x;
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minY = a * minX + b;
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maxY = a * maxX + b;
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}
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if (minY > maxY)
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std::swap (minY, maxY);
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// Find the intersection of the segment's and rectangle's y-projections
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maxY = cruft::min (maxY, rect.away ().y);
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minY = cruft::max (minY, rect.p.y);
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// If Y-projections do not intersect return false
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if (minY > maxY)
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return false;
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return true;
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}
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//-----------------------------------------------------------------------------
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template <>
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bool
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cruft::geom::intersects (cruft::geom::segment2i seg, cruft::region2i rect)
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{
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return intersects (seg.cast<float> (), rect.cast<float> ());
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}
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///////////////////////////////////////////////////////////////////////////////
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template <>
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bool
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cruft::geom::intersects (cruft::geom::segment2f ab, cruft::point2f p)
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{
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auto const hi = max (ab.a, ab.b);
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auto const lo = min (ab.a, ab.b);
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return all (p <= hi) and all (p >= lo);
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}
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///////////////////////////////////////////////////////////////////////////////
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// segment-segment intersection in 2D is derived from
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// https://www.geeksforgeeks.org/check-if-two-given-line-segments-intersect
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//
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// The idea is to check the winding of 4 triangles created by the segment.
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//
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// Co-linear segments need some additional tests to determine if points of one segment lie on the other.
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/// \return 0 if colinear, 1 for clockwise, -1 for counter-clockwise
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static int
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winding (
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cruft::point2f const p,
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cruft::point2f const q,
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cruft::point2f const r
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) {
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auto const qp = q - p;
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auto const rq = r - q;
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auto const c = cross (qp, rq);
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if (cruft::exactly_zero (c))
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return 0;
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else if (c > 0)
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return 1;
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else
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return -1;
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}
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//-----------------------------------------------------------------------------
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template <>
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bool
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cruft::geom::intersects (
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cruft::geom::segment2f const s0,
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cruft::geom::segment2f const s1
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) {
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auto const w0 = winding (s0.a, s0.b, s1.a);
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auto const w1 = winding (s0.a, s0.b, s1.b);
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auto const w2 = winding (s1.a, s1.b, s0.a);
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auto const w3 = winding (s1.a, s1.b, s0.b);
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if (w0 != w1 and w2 != w3)
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return true;
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if (w0 == 0 and intersects (s0, s1.a)) return true;
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if (w1 == 0 and intersects (s0, s1.b)) return true;
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if (w2 == 0 and intersects (s1, s0.a)) return true;
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if (w3 == 0 and intersects (s1, s0.b)) return true;
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return false;
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}
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///////////////////////////////////////////////////////////////////////////////
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template <>
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cruft::geom::aabb3f
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cruft::geom::bounds (cruft::geom::segment3f obj)
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{
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return {
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min (obj.a, obj.b),
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max (obj.a, obj.b),
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};
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}
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