public b2EPAxis ComputePolygonSeparation()
{
b2EPAxis axis = new b2EPAxis();
axis.type = b2EPAxis.Type.e_unknown;
axis.index = -1;
axis.separation = -float.MaxValue;
b2Vec2 perp = new b2Vec2(-m_normal.y, m_normal.x);
for (int i = 0; i < m_polygonB.count; ++i)
{
b2Vec2 n = -m_polygonB.normals[i];
float s1 = Utils.b2Dot(n, m_polygonB.vertices[i] - m_v1);
float s2 = Utils.b2Dot(n, m_polygonB.vertices[i] - m_v2);
float s = Utils.b2Min(s1, s2);
if (s > m_radius)
{
// No collision
axis.type = b2EPAxis.Type.e_edgeB;
axis.index = i;
axis.separation = s;
return(axis);
}
// Adjacency
if (Utils.b2Dot(n, perp) >= 0.0f)
{
if (Utils.b2Dot(n - m_upperLimit, m_normal) < -Settings.b2_angularSlop)
{
continue;
}
}
else
{
if (Utils.b2Dot(n - m_lowerLimit, m_normal) < -Settings.b2_angularSlop)
{
continue;
}
}
if (s > axis.separation)
{
axis.type = b2EPAxis.Type.e_edgeB;
axis.index = i;
axis.separation = s;
}
}
return(axis);
}
public b2EPAxis ComputeEdgeSeparation()
{
b2EPAxis axis = new b2EPAxis();
axis.type = b2EPAxis.Type.e_edgeA;
axis.index = m_front ? 0 : 1;
axis.separation = float.MaxValue;
for (int i = 0; i < m_polygonB.count; ++i)
{
float s = Utils.b2Dot(m_normal, m_polygonB.vertices[i] - m_v1);
if (s < axis.separation)
{
axis.separation = s;
}
}
return(axis);
}
// 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
public void Collide(b2Manifold manifold, b2EdgeShape edgeA, b2Transform xfA, b2PolygonShape polygonB, b2Transform xfB)
{
m_xf = Utils.b2MulT(xfA, xfB);
m_centroidB = Utils.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);
float offset1 = Utils.b2Dot(m_normal1, m_centroidB - m_v1);
float offset0 = 0.0f;
float offset2 = 0.0f;
bool convex1 = false;
bool 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 = Utils.b2Cross(edge0, edge1) >= 0.0f;
offset0 = Utils.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 = Utils.b2Cross(edge1, edge2) > 0.0f;
offset2 = Utils.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 (int i = 0; i < polygonB.m_count; ++i)
{
m_polygonB.vertices[i] = Utils.b2Mul(m_xf, polygonB.m_vertices[i]);
m_polygonB.normals[i] = Utils.b2Mul(m_xf.q, polygonB.m_normals[i]);
}
m_radius = polygonB.m_radius + edgeA.m_radius;
manifold.pointCount = 0;
b2EPAxis edgeAxis = ComputeEdgeSeparation();
// If no valid normal can be found than this edge should not collide.
if (edgeAxis.type == b2EPAxis.Type.e_unknown)
{
return;
}
if (edgeAxis.separation > m_radius)
{
return;
}
b2EPAxis polygonAxis = ComputePolygonSeparation();
if (polygonAxis.type != b2EPAxis.Type.e_unknown && polygonAxis.separation > m_radius)
{
return;
}
// Use hysteresis for jitter reduction.
const float k_relativeTol = 0.98f;
const float k_absoluteTol = 0.001f;
b2EPAxis primaryAxis = new b2EPAxis();
if (polygonAxis.type == b2EPAxis.Type.e_unknown)
{
primaryAxis = edgeAxis;
}
else if (polygonAxis.separation > k_relativeTol * edgeAxis.separation + k_absoluteTol)
{
primaryAxis = polygonAxis;
}
else
{
primaryAxis = edgeAxis;
}
b2ClipVertex[] ie = Arrays.InitializeWithDefaultInstances <b2ClipVertex>(2);
b2ReferenceFace rf = new b2ReferenceFace();
if (primaryAxis.type == b2EPAxis.Type.e_edgeA)
{
manifold.type = b2Manifold.Type.e_faceA;
// Search for the polygon normal that is most anti-parallel to the edge normal.
int bestIndex = 0;
float bestValue = Utils.b2Dot(m_normal, m_polygonB.normals[0]);
for (int i = 1; i < m_polygonB.count; ++i)
{
float value = Utils.b2Dot(m_normal, m_polygonB.normals[i]);
if (value < bestValue)
{
bestValue = value;
bestIndex = i;
}
}
int i1 = bestIndex;
int 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 = (byte)i1;
ie[0].id.cf.typeA = (int)b2ContactFeature.Type.e_face;
ie[0].id.cf.typeB = (int)b2ContactFeature.Type.e_vertex;
ie[1].v = m_polygonB.vertices[i2];
ie[1].id.cf.indexA = 0;
ie[1].id.cf.indexB = (byte)i2;
ie[1].id.cf.typeA = (int)b2ContactFeature.Type.e_face;
ie[1].id.cf.typeB = (int)b2ContactFeature.Type.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.Type.e_faceB;
ie[0].v = m_v1;
ie[0].id.cf.indexA = 0;
ie[0].id.cf.indexB = (byte)primaryAxis.index;
ie[0].id.cf.typeA = (int)b2ContactFeature.Type.e_vertex;
ie[0].id.cf.typeB = (int)b2ContactFeature.Type.e_face;
ie[1].v = m_v2;
ie[1].id.cf.indexA = 0;
ie[1].id.cf.indexB = (byte)primaryAxis.index;
ie[1].id.cf.typeA = (int)b2ContactFeature.Type.e_vertex;
ie[1].id.cf.typeB = (int)b2ContactFeature.Type.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 = Utils.b2Dot(rf.sideNormal1, rf.v1);
rf.sideOffset2 = Utils.b2Dot(rf.sideNormal2, rf.v2);
// Clip incident edge against extruded edge1 side edges.
b2ClipVertex[] clipPoints1 = Arrays.InitializeWithDefaultInstances <b2ClipVertex>(2);
b2ClipVertex[] clipPoints2 = Arrays.InitializeWithDefaultInstances <b2ClipVertex>(2);
int np;
// Clip to box side 1
np = Utils.b2ClipSegmentToLine(clipPoints1, ie, rf.sideNormal1, rf.sideOffset1, rf.i1);
if (np < Settings.b2_maxManifoldPoints)
{
return;
}
// Clip to negative box side 1
np = Utils.b2ClipSegmentToLine(clipPoints2, clipPoints1, rf.sideNormal2, rf.sideOffset2, rf.i2);
if (np < Settings.b2_maxManifoldPoints)
{
return;
}
// Now clipPoints2 contains the clipped points.
if (primaryAxis.type == b2EPAxis.Type.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];
}
int pointCount = 0;
for (int i = 0; i < Settings.b2_maxManifoldPoints; ++i)
{
float separation;
separation = Utils.b2Dot(rf.normal, clipPoints2[i].v - rf.v1);
if (separation <= m_radius)
{
b2ManifoldPoint cp = manifold.points[pointCount];
if (primaryAxis.type == b2EPAxis.Type.e_edgeA)
{
cp.localPoint = Utils.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;
}
