b2_edge_shape.cpp

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// MIT License

// Copyright (c) 2019 Erin Catto

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

#include "box2d/b2_edge_shape.h"
#include "box2d/b2_block_allocator.h"
#include <new>

void b2EdgeShape::SetOneSided(const b2Vec2& v0, const b2Vec2& v1, const b2Vec2& v2, const b2Vec2& v3)
{
        m_vertex0 = v0;
        m_vertex1 = v1;
        m_vertex2 = v2;
        m_vertex3 = v3;
        m_oneSided = true;
}

void b2EdgeShape::SetTwoSided(const b2Vec2& v1, const b2Vec2& v2)
{
        m_vertex1 = v1;
        m_vertex2 = v2;
        m_oneSided = false;
}

b2Shape* b2EdgeShape::Clone(b2BlockAllocator* allocator) const
{
        void* mem = allocator->Allocate(sizeof(b2EdgeShape));
        b2EdgeShape* clone = new (mem) b2EdgeShape;
        *clone = *this;
        return clone;
}

int32 b2EdgeShape::GetChildCount() const
{
        return 1;
}

bool b2EdgeShape::TestPoint(const b2Transform& xf, const b2Vec2& p) const
{
        B2_NOT_USED(xf);
        B2_NOT_USED(p);
        return false;
}

// p = p1 + t * d
// v = v1 + s * e
// p1 + t * d = v1 + s * e
// s * e - t * d = p1 - v1
bool b2EdgeShape::RayCast(b2RayCastOutput* output, const b2RayCastInput& input,
                                                        const b2Transform& xf, int32 childIndex) const
{
        B2_NOT_USED(childIndex);

        // Put the ray into the edge's frame of reference.
        b2Vec2 p1 = b2MulT(xf.q, input.p1 - xf.p);
        b2Vec2 p2 = b2MulT(xf.q, input.p2 - xf.p);
        b2Vec2 d = p2 - p1;

        b2Vec2 v1 = m_vertex1;
        b2Vec2 v2 = m_vertex2;
        b2Vec2 e = v2 - v1;

        // Normal points to the right, looking from v1 at v2
        b2Vec2 normal(e.y, -e.x);
        normal.Normalize();

        // q = p1 + t * d
        // dot(normal, q - v1) = 0
        // dot(normal, p1 - v1) + t * dot(normal, d) = 0
        float numerator = b2Dot(normal, v1 - p1);
        if (m_oneSided && numerator > 0.0f)
        {
                return false;
        }

        float denominator = b2Dot(normal, d);

        if (denominator == 0.0f)
        {
                return false;
        }

        float t = numerator / denominator;
        if (t < 0.0f || input.maxFraction < t)
        {
                return false;
        }

        b2Vec2 q = p1 + t * d;

        // q = v1 + s * r
        // s = dot(q - v1, r) / dot(r, r)
        b2Vec2 r = v2 - v1;
        float rr = b2Dot(r, r);
        if (rr == 0.0f)
        {
                return false;
        }

        float s = b2Dot(q - v1, r) / rr;
        if (s < 0.0f || 1.0f < s)
        {
                return false;
        }

        output->fraction = t;
        if (numerator > 0.0f)
        {
                output->normal = -b2Mul(xf.q, normal);
        }
        else
        {
                output->normal = b2Mul(xf.q, normal);
        }
        return true;
}

void b2EdgeShape::ComputeAABB(b2AABB* aabb, const b2Transform& xf, int32 childIndex) const
{
        B2_NOT_USED(childIndex);

        b2Vec2 v1 = b2Mul(xf, m_vertex1);
        b2Vec2 v2 = b2Mul(xf, m_vertex2);

        b2Vec2 lower = b2Min(v1, v2);
        b2Vec2 upper = b2Max(v1, v2);

        b2Vec2 r(m_radius, m_radius);
        aabb->lowerBound = lower - r;
        aabb->upperBound = upper + r;
}

void b2EdgeShape::ComputeMass(b2MassData* massData, float density) const
{
        B2_NOT_USED(density);

        massData->mass = 0.0f;
        massData->center = 0.5f * (m_vertex1 + m_vertex2);
        massData->I = 0.0f;
}