math_line_segment2.cpp

[詳解]

 
 
// Copyright(c) 2023-2025 Design Engineering Laboratory, Saitama University
// Released under the MIT license
// https://opensource.org/licenses/mit-license.php
 
#include "math_line_segment2.h"
 
#include "cassert_define.h"
#include "math_util.h"
 
 
namespace designlab
{
 
Vector2 LineSegment2::GetIntersection(const LineSegment2& other) const
{
    if (IsParallel(other))
    {
        return Vector2{ 0, 0 };  // 平行ならば交点は存在しない．
    }
 
    const Vector2 v1 = end - start;
    const Vector2 v2 = other.end - other.start;
    const Vector2 v3 = other.start - start;
    const float d = v1.Cross(v2);
 
    const float t1 = v3.Cross(v2) / d;
    const float t2 = v3.Cross(v1) / d;
 
    // t1, t2が0~1の範囲内にあるかならば，交点は線分上に存在する．
 
    if (t1 < 0.0f - MathConst<float>::kAllowableError ||
        t1 > 1.0f + MathConst<float>::kAllowableError ||
        t2 < 0.0f - MathConst<float>::kAllowableError ||
        t2 > 1.0f + MathConst<float>::kAllowableError)
    {
        return Vector2{ 0, 0 };  // 交点は線分の外．
    }
 
    return start + v1 * t1;
}
 
bool LineSegment2::HasIntersection(const LineSegment2& other) const
{
    if (IsParallel(other))
    {
        return false;  // 平行ならば交点は存在しない．
    }
 
    const Vector2 v1 = end - start;
    const Vector2 v2 = other.end - other.start;
    const Vector2 v3 = other.start - start;
    const float d = v1.Cross(v2);
 
    const float t1 = v3.Cross(v2) / d;
    const float t2 = v3.Cross(v1) / d;
 
    // t1, t2が0~1の範囲内にあるかならば，交点は線分上に存在する．
 
    if (t1 < 0.0f - MathConst<float>::kAllowableError ||
        t1 > 1.0f + MathConst<float>::kAllowableError ||
        t2 < 0.0f - MathConst<float>::kAllowableError ||
        t2 > 1.0f + MathConst<float>::kAllowableError)
    {
        return false;  // 交点は線分の外．
    }
 
    return true;
}
 
bool LineSegment2::CheckAndGetIntersection(const LineSegment2& other, Vector2* intersection) const
{
    // 交点を代入するポインタは nullptr であってはならない．
    assert(intersection != nullptr);
 
    // 端点一致の場合，その点を返す
    if ((start == other.start && end != other.end) ||
        (start == other.end && end != other.start))
    {
        (*intersection) = start;
        return true;
    }
    else if ((end == other.start && start != other.end) ||
             (end == other.end && start != other.start))
    {
        (*intersection) = end;
        return true;
    }
 
    if (IsParallel(other))
    {
        return false;  // 平行ならば交点は存在しない．
    }
 
    const Vector2 v1 = end - start;
    const Vector2 v2 = other.end - other.start;
    const Vector2 v3 = other.start - start;
    const float d = v1.Cross(v2);
 
    const float t1 = v3.Cross(v2) / d;
    const float t2 = v3.Cross(v1) / d;
 
    // t1, t2が0~1の範囲内にあるかならば，交点は線分上に存在する．
 
    if (t1 < 0.0f - MathConst<float>::kAllowableError ||
        t1 > 1.0f + MathConst<float>::kAllowableError ||
        t2 < 0.0f - MathConst<float>::kAllowableError ||
        t2 > 1.0f + MathConst<float>::kAllowableError)
    {
        return false;  // 交点は線分の外．
    }
 
    *intersection = start + v1 * t1;
    return true;
}
 
}  // namespace designlab