File indexing completed on 2024-05-19 14:56:21

 /*
  * Copyright (c) 2007-2009 Erin Catto http://www.box2d.org
  *
  * This software is provided 'as-is', without any express or implied
  * warranty.  In no event will the authors be held liable for any damages
  * arising from the use of this software.
  * Permission is granted to anyone to use this software for any purpose,
  * including commercial applications, and to alter it and redistribute it
  * freely, subject to the following restrictions:
  * 1. The origin of this software must not be misrepresented; you must not
  * claim that you wrote the original software. If you use this software
  * in a product, an acknowledgment in the product documentation would be
  * appreciated but is not required.
  * 2. Altered source versions must be plainly marked as such, and must not be
  * misrepresented as being the original software.
  * 3. This notice may not be removed or altered from any source distribution.
  */
 
 #include <Box2D/Collision/b2Collision.h>
 #include <Box2D/Collision/Shapes/b2CircleShape.h>
 #include <Box2D/Collision/Shapes/b2EdgeShape.h>
 #include <Box2D/Collision/Shapes/b2PolygonShape.h>
 
 
 // Compute contact points for edge versus circle.
 // This accounts for edge connectivity.
 void b2CollideEdgeAndCircle(b2Manifold* manifold,
                             const b2EdgeShape* edgeA, const b2Transform& xfA,
                             const b2CircleShape* circleB, const b2Transform& xfB)
 {
     manifold->pointCount = 0;
     
     // Compute circle in frame of edge
     b2Vec2 Q = b2MulT(xfA, b2Mul(xfB, circleB->m_p));
     
     b2Vec2 A = edgeA->m_vertex1, B = edgeA->m_vertex2;
     b2Vec2 e = B - A;
     
     // Barycentric coordinates
     float32 u = b2Dot(e, B - Q);
     float32 v = b2Dot(e, Q - A);
     
     float32 radius = edgeA->m_radius + circleB->m_radius;
     
     b2ContactFeature cf;
     cf.indexB = 0;
     cf.typeB = b2ContactFeature::e_vertex;
     
     // Region A
     if (v <= 0.0f)
     {
         b2Vec2 P = A;
         b2Vec2 d = Q - P;
         float32 dd = b2Dot(d, d);
         if (dd > radius * radius)
         {
             return;
         }
         
         // Is there an edge connected to A?
         if (edgeA->m_hasVertex0)
         {
             b2Vec2 A1 = edgeA->m_vertex0;
             b2Vec2 B1 = A;
             b2Vec2 e1 = B1 - A1;
             float32 u1 = b2Dot(e1, B1 - Q);
             
             // Is the circle in Region AB of the previous edge?
             if (u1 > 0.0f)
             {
                 return;
             }
         }
         
         cf.indexA = 0;
         cf.typeA = b2ContactFeature::e_vertex;
         manifold->pointCount = 1;
         manifold->type = b2Manifold::e_circles;
         manifold->localNormal.SetZero();
         manifold->localPoint = P;
         manifold->points[0].id.key = 0;
         manifold->points[0].id.cf = cf;
         manifold->points[0].localPoint = circleB->m_p;
         return;
     }
     
     // Region B
     if (u <= 0.0f)
     {
         b2Vec2 P = B;
         b2Vec2 d = Q - P;
         float32 dd = b2Dot(d, d);
         if (dd > radius * radius)
         {
             return;
         }
         
         // Is there an edge connected to B?
         if (edgeA->m_hasVertex3)
         {
             b2Vec2 B2 = edgeA->m_vertex3;
             b2Vec2 A2 = B;
             b2Vec2 e2 = B2 - A2;
             float32 v2 = b2Dot(e2, Q - A2);
             
             // Is the circle in Region AB of the next edge?
             if (v2 > 0.0f)
             {
                 return;
             }
         }
         
         cf.indexA = 1;
         cf.typeA = b2ContactFeature::e_vertex;
         manifold->pointCount = 1;
         manifold->type = b2Manifold::e_circles;
         manifold->localNormal.SetZero();
         manifold->localPoint = P;
         manifold->points[0].id.key = 0;
         manifold->points[0].id.cf = cf;
         manifold->points[0].localPoint = circleB->m_p;
         return;
     }
     
     // Region AB
     float32 den = b2Dot(e, e);
     b2Assert(den > 0.0f);
     b2Vec2 P = (1.0f / den) * (u * A + v * B);
     b2Vec2 d = Q - P;
     float32 dd = b2Dot(d, d);
     if (dd > radius * radius)
     {
         return;
     }
     
     b2Vec2 n(-e.y, e.x);
     if (b2Dot(n, Q - A) < 0.0f)
     {
         n.Set(-n.x, -n.y);
     }
     n.Normalize();
     
     cf.indexA = 0;
     cf.typeA = b2ContactFeature::e_face;
     manifold->pointCount = 1;
     manifold->type = b2Manifold::e_faceA;
     manifold->localNormal = n;
     manifold->localPoint = A;
     manifold->points[0].id.key = 0;
     manifold->points[0].id.cf = cf;
     manifold->points[0].localPoint = circleB->m_p;
 }
 
 // This structure is used to keep track of the best separating axis.
 struct b2EPAxis
 {
     enum Type
     {
         e_unknown,
         e_edgeA,
         e_edgeB
     };
     
     Type type;
     int32 index;
     float32 separation;
 };
 
 // This holds polygon B expressed in frame A.
 struct b2TempPolygon
 {
     b2Vec2 vertices[b2_maxPolygonVertices];
     b2Vec2 normals[b2_maxPolygonVertices];
     int32 count;
 };
 
 // Reference face used for clipping
 struct b2ReferenceFace
 {
     int32 i1, i2;
     
     b2Vec2 v1, v2;
     
     b2Vec2 normal;
     
     b2Vec2 sideNormal1;
     float32 sideOffset1;
     
     b2Vec2 sideNormal2;
     float32 sideOffset2;
 };
 
 // This class collides and edge and a polygon, taking into account edge adjacency.
 struct b2EPCollider
 {
     void Collide(b2Manifold* manifold, const b2EdgeShape* edgeA, const b2Transform& xfA,
                  const b2PolygonShape* polygonB, const b2Transform& xfB);
     b2EPAxis ComputeEdgeSeparation();
     b2EPAxis ComputePolygonSeparation();
     
     enum VertexType
     {
         e_isolated,
         e_concave,
         e_convex
     };
     
     b2TempPolygon m_polygonB;
     
     b2Transform m_xf;
     b2Vec2 m_centroidB;
     b2Vec2 m_v0, m_v1, m_v2, m_v3;
     b2Vec2 m_normal0, m_normal1, m_normal2;
     b2Vec2 m_normal;
     VertexType m_type1, m_type2;
     b2Vec2 m_lowerLimit, m_upperLimit;
     float32 m_radius;
     bool m_front;
 };
 
 // Algorithm:
 // 1. Classify v1 and v2
 // 2. Classify polygon centroid as front or back
 // 3. Flip normal if necessary
 // 4. Initialize normal range to [-pi, pi] about face normal
 // 5. Adjust normal range according to adjacent edges
 // 6. Visit each separating axes, only accept axes within the range
 // 7. Return if _any_ axis indicates separation
 // 8. Clip
 void b2EPCollider::Collide(b2Manifold* manifold, const b2EdgeShape* edgeA, const b2Transform& xfA,
                            const b2PolygonShape* polygonB, const b2Transform& xfB)
 {
     m_xf = b2MulT(xfA, xfB);
     
     m_centroidB = b2Mul(m_xf, polygonB->m_centroid);
     
     m_v0 = edgeA->m_vertex0;
     m_v1 = edgeA->m_vertex1;
     m_v2 = edgeA->m_vertex2;
     m_v3 = edgeA->m_vertex3;
     
     bool hasVertex0 = edgeA->m_hasVertex0;
     bool hasVertex3 = edgeA->m_hasVertex3;
     
     b2Vec2 edge1 = m_v2 - m_v1;
     edge1.Normalize();
     m_normal1.Set(edge1.y, -edge1.x);
     float32 offset1 = b2Dot(m_normal1, m_centroidB - m_v1);
     float32 offset0 = 0.0f, offset2 = 0.0f;
     bool convex1 = false, convex2 = false;
     
     // Is there a preceding edge?
     if (hasVertex0)
     {
         b2Vec2 edge0 = m_v1 - m_v0;
         edge0.Normalize();
         m_normal0.Set(edge0.y, -edge0.x);
         convex1 = b2Cross(edge0, edge1) >= 0.0f;
         offset0 = b2Dot(m_normal0, m_centroidB - m_v0);
     }
     
     // Is there a following edge?
     if (hasVertex3)
     {
         b2Vec2 edge2 = m_v3 - m_v2;
         edge2.Normalize();
         m_normal2.Set(edge2.y, -edge2.x);
         convex2 = b2Cross(edge1, edge2) > 0.0f;
         offset2 = b2Dot(m_normal2, m_centroidB - m_v2);
     }
     
     // Determine front or back collision. Determine collision normal limits.
     if (hasVertex0 && hasVertex3)
     {
         if (convex1 && convex2)
         {
             m_front = offset0 >= 0.0f || offset1 >= 0.0f || offset2 >= 0.0f;
             if (m_front)
             {
                 m_normal = m_normal1;
                 m_lowerLimit = m_normal0;
                 m_upperLimit = m_normal2;
             }
             else
             {
                 m_normal = -m_normal1;
                 m_lowerLimit = -m_normal1;
                 m_upperLimit = -m_normal1;
             }
         }
         else if (convex1)
         {
             m_front = offset0 >= 0.0f || (offset1 >= 0.0f && offset2 >= 0.0f);
             if (m_front)
             {
                 m_normal = m_normal1;
                 m_lowerLimit = m_normal0;
                 m_upperLimit = m_normal1;
             }
             else
             {
                 m_normal = -m_normal1;
                 m_lowerLimit = -m_normal2;
                 m_upperLimit = -m_normal1;
             }
         }
         else if (convex2)
         {
             m_front = offset2 >= 0.0f || (offset0 >= 0.0f && offset1 >= 0.0f);
             if (m_front)
             {
                 m_normal = m_normal1;
                 m_lowerLimit = m_normal1;
                 m_upperLimit = m_normal2;
             }
             else
             {
                 m_normal = -m_normal1;
                 m_lowerLimit = -m_normal1;
                 m_upperLimit = -m_normal0;
             }
         }
         else
         {
             m_front = offset0 >= 0.0f && offset1 >= 0.0f && offset2 >= 0.0f;
             if (m_front)
             {
                 m_normal = m_normal1;
                 m_lowerLimit = m_normal1;
                 m_upperLimit = m_normal1;
             }
             else
             {
                 m_normal = -m_normal1;
                 m_lowerLimit = -m_normal2;
                 m_upperLimit = -m_normal0;
             }
         }
     }
     else if (hasVertex0)
     {
         if (convex1)
         {
             m_front = offset0 >= 0.0f || offset1 >= 0.0f;
             if (m_front)
             {
                 m_normal = m_normal1;
                 m_lowerLimit = m_normal0;
                 m_upperLimit = -m_normal1;
             }
             else
             {
                 m_normal = -m_normal1;
                 m_lowerLimit = m_normal1;
                 m_upperLimit = -m_normal1;
             }
         }
         else
         {
             m_front = offset0 >= 0.0f && offset1 >= 0.0f;
             if (m_front)
             {
                 m_normal = m_normal1;
                 m_lowerLimit = m_normal1;
                 m_upperLimit = -m_normal1;
             }
             else
             {
                 m_normal = -m_normal1;
                 m_lowerLimit = m_normal1;
                 m_upperLimit = -m_normal0;
             }
         }
     }
     else if (hasVertex3)
     {
         if (convex2)
         {
             m_front = offset1 >= 0.0f || offset2 >= 0.0f;
             if (m_front)
             {
                 m_normal = m_normal1;
                 m_lowerLimit = -m_normal1;
                 m_upperLimit = m_normal2;
             }
             else
             {
                 m_normal = -m_normal1;
                 m_lowerLimit = -m_normal1;
                 m_upperLimit = m_normal1;
             }
         }
         else
         {
             m_front = offset1 >= 0.0f && offset2 >= 0.0f;
             if (m_front)
             {
                 m_normal = m_normal1;
                 m_lowerLimit = -m_normal1;
                 m_upperLimit = m_normal1;
             }
             else
             {
                 m_normal = -m_normal1;
                 m_lowerLimit = -m_normal2;
                 m_upperLimit = m_normal1;
             }
         }       
     }
     else
     {
         m_front = offset1 >= 0.0f;
         if (m_front)
         {
             m_normal = m_normal1;
             m_lowerLimit = -m_normal1;
             m_upperLimit = -m_normal1;
         }
         else
         {
             m_normal = -m_normal1;
             m_lowerLimit = m_normal1;
             m_upperLimit = m_normal1;
         }
     }
     
     // Get polygonB in frameA
     m_polygonB.count = polygonB->m_count;
     for (int32 i = 0; i < polygonB->m_count; ++i)
     {
         m_polygonB.vertices[i] = b2Mul(m_xf, polygonB->m_vertices[i]);
         m_polygonB.normals[i] = b2Mul(m_xf.q, polygonB->m_normals[i]);
     }
     
     m_radius = 2.0f * b2_polygonRadius;
     
     manifold->pointCount = 0;
     
     b2EPAxis edgeAxis = ComputeEdgeSeparation();
     
     // If no valid normal can be found than this edge should not collide.
     if (edgeAxis.type == b2EPAxis::e_unknown)
     {
         return;
     }
     
     if (edgeAxis.separation > m_radius)
     {
         return;
     }
     
     b2EPAxis polygonAxis = ComputePolygonSeparation();
     if (polygonAxis.type != b2EPAxis::e_unknown && polygonAxis.separation > m_radius)
     {
         return;
     }
     
     // Use hysteresis for jitter reduction.
     const float32 k_relativeTol = 0.98f;
     const float32 k_absoluteTol = 0.001f;
     
     b2EPAxis primaryAxis;
     if (polygonAxis.type == b2EPAxis::e_unknown)
     {
         primaryAxis = edgeAxis;
     }
     else if (polygonAxis.separation > k_relativeTol * edgeAxis.separation + k_absoluteTol)
     {
         primaryAxis = polygonAxis;
     }
     else
     {
         primaryAxis = edgeAxis;
     }
     
     b2ClipVertex ie[2];
     b2ReferenceFace rf;
     if (primaryAxis.type == b2EPAxis::e_edgeA)
     {
         manifold->type = b2Manifold::e_faceA;
         
         // Search for the polygon normal that is most anti-parallel to the edge normal.
         int32 bestIndex = 0;
         float32 bestValue = b2Dot(m_normal, m_polygonB.normals[0]);
         for (int32 i = 1; i < m_polygonB.count; ++i)
         {
             float32 value = b2Dot(m_normal, m_polygonB.normals[i]);
             if (value < bestValue)
             {
                 bestValue = value;
                 bestIndex = i;
             }
         }
         
         int32 i1 = bestIndex;
         int32 i2 = i1 + 1 < m_polygonB.count ? i1 + 1 : 0;
         
         ie[0].v = m_polygonB.vertices[i1];
         ie[0].id.cf.indexA = 0;
         ie[0].id.cf.indexB = static_cast<uint8>(i1);
         ie[0].id.cf.typeA = b2ContactFeature::e_face;
         ie[0].id.cf.typeB = b2ContactFeature::e_vertex;
         
         ie[1].v = m_polygonB.vertices[i2];
         ie[1].id.cf.indexA = 0;
         ie[1].id.cf.indexB = static_cast<uint8>(i2);
         ie[1].id.cf.typeA = b2ContactFeature::e_face;
         ie[1].id.cf.typeB = b2ContactFeature::e_vertex;
         
         if (m_front)
         {
             rf.i1 = 0;
             rf.i2 = 1;
             rf.v1 = m_v1;
             rf.v2 = m_v2;
             rf.normal = m_normal1;
         }
         else
         {
             rf.i1 = 1;
             rf.i2 = 0;
             rf.v1 = m_v2;
             rf.v2 = m_v1;
             rf.normal = -m_normal1;
         }       
     }
     else
     {
         manifold->type = b2Manifold::e_faceB;
         
         ie[0].v = m_v1;
         ie[0].id.cf.indexA = 0;
         ie[0].id.cf.indexB = static_cast<uint8>(primaryAxis.index);
         ie[0].id.cf.typeA = b2ContactFeature::e_vertex;
         ie[0].id.cf.typeB = b2ContactFeature::e_face;
         
         ie[1].v = m_v2;
         ie[1].id.cf.indexA = 0;
         ie[1].id.cf.indexB = static_cast<uint8>(primaryAxis.index);     
         ie[1].id.cf.typeA = b2ContactFeature::e_vertex;
         ie[1].id.cf.typeB = b2ContactFeature::e_face;
         
         rf.i1 = primaryAxis.index;
         rf.i2 = rf.i1 + 1 < m_polygonB.count ? rf.i1 + 1 : 0;
         rf.v1 = m_polygonB.vertices[rf.i1];
         rf.v2 = m_polygonB.vertices[rf.i2];
         rf.normal = m_polygonB.normals[rf.i1];
     }
     
     rf.sideNormal1.Set(rf.normal.y, -rf.normal.x);
     rf.sideNormal2 = -rf.sideNormal1;
     rf.sideOffset1 = b2Dot(rf.sideNormal1, rf.v1);
     rf.sideOffset2 = b2Dot(rf.sideNormal2, rf.v2);
     
     // Clip incident edge against extruded edge1 side edges.
     b2ClipVertex clipPoints1[2];
     b2ClipVertex clipPoints2[2];
     int32 np;
     
     // Clip to box side 1
     np = b2ClipSegmentToLine(clipPoints1, ie, rf.sideNormal1, rf.sideOffset1, rf.i1);
     
     if (np < b2_maxManifoldPoints)
     {
         return;
     }
     
     // Clip to negative box side 1
     np = b2ClipSegmentToLine(clipPoints2, clipPoints1, rf.sideNormal2, rf.sideOffset2, rf.i2);
     
     if (np < b2_maxManifoldPoints)
     {
         return;
     }
     
     // Now clipPoints2 contains the clipped points.
     if (primaryAxis.type == b2EPAxis::e_edgeA)
     {
         manifold->localNormal = rf.normal;
         manifold->localPoint = rf.v1;
     }
     else
     {
         manifold->localNormal = polygonB->m_normals[rf.i1];
         manifold->localPoint = polygonB->m_vertices[rf.i1];
     }
     
     int32 pointCount = 0;
     for (int32 i = 0; i < b2_maxManifoldPoints; ++i)
     {
         float32 separation;
         
         separation = b2Dot(rf.normal, clipPoints2[i].v - rf.v1);
         
         if (separation <= m_radius)
         {
             b2ManifoldPoint* cp = manifold->points + pointCount;
             
             if (primaryAxis.type == b2EPAxis::e_edgeA)
             {
                 cp->localPoint = b2MulT(m_xf, clipPoints2[i].v);
                 cp->id = clipPoints2[i].id;
             }
             else
             {
                 cp->localPoint = clipPoints2[i].v;
                 cp->id.cf.typeA = clipPoints2[i].id.cf.typeB;
                 cp->id.cf.typeB = clipPoints2[i].id.cf.typeA;
                 cp->id.cf.indexA = clipPoints2[i].id.cf.indexB;
                 cp->id.cf.indexB = clipPoints2[i].id.cf.indexA;
             }
             
             ++pointCount;
         }
     }
     
     manifold->pointCount = pointCount;
 }
 
 b2EPAxis b2EPCollider::ComputeEdgeSeparation()
 {
     b2EPAxis axis;
     axis.type = b2EPAxis::e_edgeA;
     axis.index = m_front ? 0 : 1;
     axis.separation = FLT_MAX;
     
     for (int32 i = 0; i < m_polygonB.count; ++i)
     {
         float32 s = b2Dot(m_normal, m_polygonB.vertices[i] - m_v1);
         if (s < axis.separation)
         {
             axis.separation = s;
         }
     }
     
     return axis;
 }
 
 b2EPAxis b2EPCollider::ComputePolygonSeparation()
 {
     b2EPAxis axis;
     axis.type = b2EPAxis::e_unknown;
     axis.index = -1;
     axis.separation = -FLT_MAX;
 
     b2Vec2 perp(-m_normal.y, m_normal.x);
 
     for (int32 i = 0; i < m_polygonB.count; ++i)
     {
         b2Vec2 n = -m_polygonB.normals[i];
         
         float32 s1 = b2Dot(n, m_polygonB.vertices[i] - m_v1);
         float32 s2 = b2Dot(n, m_polygonB.vertices[i] - m_v2);
         float32 s = b2Min(s1, s2);
         
         if (s > m_radius)
         {
             // No collision
             axis.type = b2EPAxis::e_edgeB;
             axis.index = i;
             axis.separation = s;
             return axis;
         }
         
         // Adjacency
         if (b2Dot(n, perp) >= 0.0f)
         {
             if (b2Dot(n - m_upperLimit, m_normal) < -b2_angularSlop)
             {
                 continue;
             }
         }
         else
         {
             if (b2Dot(n - m_lowerLimit, m_normal) < -b2_angularSlop)
             {
                 continue;
             }
         }
         
         if (s > axis.separation)
         {
             axis.type = b2EPAxis::e_edgeB;
             axis.index = i;
             axis.separation = s;
         }
     }
     
     return axis;
 }
 
 void b2CollideEdgeAndPolygon(   b2Manifold* manifold,
                              const b2EdgeShape* edgeA, const b2Transform& xfA,
                              const b2PolygonShape* polygonB, const b2Transform& xfB)
 {
     b2EPCollider collider;
     collider.Collide(manifold, edgeA, xfA, polygonB, xfB);
 }