private static EPAxis ComputePolygonSeparation(ref TempPolygon polygonB, Vector2 v1, Vector2 v2)
{
EPAxis axis;
axis.Type = EPAxisType.Unknown;
axis.Index = -1;
axis.Separation = -MathConstants.MaxFloat;
axis.Normal = Vector2.Zero;
for (int i = 0; i < polygonB.Count; ++i)
{
Vector2 n = -polygonB.Normals[i];
float s1 = MathUtils.Dot(n, polygonB.Vertices[i] - v1);
float s2 = MathUtils.Dot(n, polygonB.Vertices[i] - v2);
float s = MathUtils.Min(s1, s2);
if (s > axis.Separation)
{
axis.Type = EPAxisType.EdgeB;
axis.Index = i;
axis.Separation = s;
axis.Normal = n;
}
}
return(axis);
}
private static EPAxis ComputeEdgeSeparation(ref TempPolygon polygonB, Vector2 v1, Vector2 normal1)
{
EPAxis axis;
axis.Type = EPAxisType.EdgeA;
axis.Index = -1;
axis.Separation = -MathConstants.MaxFloat;
axis.Normal = Vector2.Zero;
Vector2[] axes = { normal1, -normal1 };
// Find axis with least overlap (min-max problem)
for (int j = 0; j < 2; ++j)
{
float sj = MathConstants.MaxFloat;
// Find deepest polygon vertex along axis j
for (int i = 0; i < polygonB.Count; ++i)
{
float si = MathUtils.Dot(axes[j], polygonB.Vertices[i] - v1);
if (si < sj)
{
sj = si;
}
}
if (sj > axis.Separation)
{
axis.Index = j;
axis.Separation = sj;
axis.Normal = axes[j];
}
}
return(axis);
}
public static void CollideEdgeAndPolygon(ref Manifold manifold, EdgeShape edgeA, ref Transform xfA, PolygonShape polygonB, ref Transform xfB)
{
manifold.PointCount = 0;
Transform xf = MathUtils.MulT(xfA, xfB);
Vector2 centroidB = MathUtils.Mul(ref xf, polygonB._massData._centroid);
Vector2 v1 = edgeA._vertex1;
Vector2 v2 = edgeA._vertex2;
Vector2 edge1 = v2 - v1;
edge1.Normalize();
// Normal points to the right for a CCW winding
Vector2 normal1 = new Vector2(edge1.Y, -edge1.X);
float offset1 = MathUtils.Dot(normal1, centroidB - v1);
bool oneSided = edgeA._oneSided;
if (oneSided && offset1 < 0.0f)
{
return;
}
// Get polygonB in frameA
TempPolygon tempPolygonB = new TempPolygon(polygonB._vertices.Count);
for (int i = 0; i < polygonB._vertices.Count; ++i)
{
tempPolygonB.Vertices[i] = MathUtils.Mul(ref xf, polygonB._vertices[i]);
tempPolygonB.Normals[i] = MathUtils.Mul(xf.q, polygonB._normals[i]);
}
float radius = polygonB._radius + edgeA._radius;
EPAxis edgeAxis = ComputeEdgeSeparation(ref tempPolygonB, v1, normal1);
if (edgeAxis.Separation > radius)
{
return;
}
EPAxis polygonAxis = ComputePolygonSeparation(ref tempPolygonB, v1, v2);
if (polygonAxis.Separation > radius)
{
return;
}
// Use hysteresis for jitter reduction.
const float k_relativeTol = 0.98f;
const float k_absoluteTol = 0.001f;
EPAxis primaryAxis;
if (polygonAxis.Separation - radius > k_relativeTol * (edgeAxis.Separation - radius) + k_absoluteTol)
{
primaryAxis = polygonAxis;
}
else
{
primaryAxis = edgeAxis;
}
if (oneSided)
{
// Smooth collision
// See https://box2d.org/posts/2020/06/ghost-collisions/
Vector2 edge0 = v1 - edgeA._vertex0;
edge0.Normalize();
Vector2 normal0 = new Vector2(edge0.Y, -edge0.X);
bool convex1 = MathUtils.Cross(edge0, edge1) >= 0.0f;
Vector2 edge2 = edgeA._vertex3 - v2;
edge2.Normalize();
Vector2 normal2 = new Vector2(edge2.Y, -edge2.X);
bool convex2 = MathUtils.Cross(edge1, edge2) >= 0.0f;
const float sinTol = 0.1f;
bool side1 = MathUtils.Dot(primaryAxis.Normal, edge1) <= 0.0f;
// Check Gauss Map
if (side1)
{
if (convex1)
{
if (MathUtils.Cross(primaryAxis.Normal, normal0) > sinTol)
{
// Skip region
return;
}
// Admit region
}
else
{
// Snap region
primaryAxis = edgeAxis;
}
}
else
{
if (convex2)
{
if (MathUtils.Cross(normal2, primaryAxis.Normal) > sinTol)
{
// Skip region
return;
}
// Admit region
}
else
{
// Snap region
primaryAxis = edgeAxis;
}
}
}
FixedArray2 <ClipVertex> clipPoints = new FixedArray2 <ClipVertex>();
ReferenceFace ref1;
if (primaryAxis.Type == EPAxisType.EdgeA)
{
manifold.Type = ManifoldType.FaceA;
// Search for the polygon normal that is most anti-parallel to the edge normal.
int bestIndex = 0;
float bestValue = MathUtils.Dot(primaryAxis.Normal, tempPolygonB.Normals[0]);
for (int i = 1; i < tempPolygonB.Count; ++i)
{
float value = MathUtils.Dot(primaryAxis.Normal, tempPolygonB.Normals[i]);
if (value < bestValue)
{
bestValue = value;
bestIndex = i;
}
}
int i1 = bestIndex;
int i2 = i1 + 1 < tempPolygonB.Count ? i1 + 1 : 0;
clipPoints.Value0.V = tempPolygonB.Vertices[i1];
clipPoints.Value0.Id.ContactFeature.IndexA = 0;
clipPoints.Value0.Id.ContactFeature.IndexB = (byte)i1;
clipPoints.Value0.Id.ContactFeature.TypeA = ContactFeatureType.Face;
clipPoints.Value0.Id.ContactFeature.TypeB = ContactFeatureType.Vertex;
clipPoints.Value1.V = tempPolygonB.Vertices[i2];
clipPoints.Value1.Id.ContactFeature.IndexA = 0;
clipPoints.Value1.Id.ContactFeature.IndexB = (byte)i2;
clipPoints.Value1.Id.ContactFeature.TypeA = ContactFeatureType.Face;
clipPoints.Value1.Id.ContactFeature.TypeB = ContactFeatureType.Vertex;
ref1.i1 = 0;
ref1.i2 = 1;
ref1.v1 = v1;
ref1.v2 = v2;
ref1.Normal = primaryAxis.Normal;
ref1.SideNormal1 = -edge1;
ref1.SideNormal2 = edge1;
}
else
{
manifold.Type = ManifoldType.FaceB;
clipPoints.Value0.V = v2;
clipPoints.Value0.Id.ContactFeature.IndexA = 1;
clipPoints.Value0.Id.ContactFeature.IndexB = (byte)primaryAxis.Index;
clipPoints.Value0.Id.ContactFeature.TypeA = ContactFeatureType.Vertex;
clipPoints.Value0.Id.ContactFeature.TypeB = ContactFeatureType.Face;
clipPoints.Value1.V = v1;
clipPoints.Value1.Id.ContactFeature.IndexA = 0;
clipPoints.Value1.Id.ContactFeature.IndexB = (byte)primaryAxis.Index;
clipPoints.Value1.Id.ContactFeature.TypeA = ContactFeatureType.Vertex;
clipPoints.Value1.Id.ContactFeature.TypeB = ContactFeatureType.Face;
ref1.i1 = primaryAxis.Index;
ref1.i2 = ref1.i1 + 1 < tempPolygonB.Count ? ref1.i1 + 1 : 0;
ref1.v1 = tempPolygonB.Vertices[ref1.i1];
ref1.v2 = tempPolygonB.Vertices[ref1.i2];
ref1.Normal = tempPolygonB.Normals[ref1.i1];
// CCW winding
ref1.SideNormal1 = new Vector2(ref1.Normal.Y, -ref1.Normal.X);
ref1.SideNormal2 = -ref1.SideNormal1;
}
ref1.SideOffset1 = MathUtils.Dot(ref1.SideNormal1, ref1.v1);
ref1.SideOffset2 = MathUtils.Dot(ref1.SideNormal2, ref1.v2);
// Clip incident edge against reference face side planes
FixedArray2 <ClipVertex> clipPoints1;
FixedArray2 <ClipVertex> clipPoints2;
int np;
// Clip to side 1
np = Collision.ClipSegmentToLine(out clipPoints1, ref clipPoints, ref1.SideNormal1, ref1.SideOffset1, ref1.i1);
if (np < Settings.MaxManifoldPoints)
{
return;
}
// Clip to side 2
np = Collision.ClipSegmentToLine(out clipPoints2, ref clipPoints1, ref1.SideNormal2, ref1.SideOffset2, ref1.i2);
if (np < Settings.MaxManifoldPoints)
{
return;
}
// Now clipPoints2 contains the clipped points.
if (primaryAxis.Type == EPAxisType.EdgeA)
{
manifold.LocalNormal = ref1.Normal;
manifold.LocalPoint = ref1.v1;
}
else
{
manifold.LocalNormal = polygonB._normals[ref1.i1];
manifold.LocalPoint = polygonB._vertices[ref1.i1];
}
int pointCount = 0;
for (int i = 0; i < Settings.MaxManifoldPoints; ++i)
{
float separation = MathUtils.Dot(ref1.Normal, clipPoints2[i].V - ref1.v1);
if (separation <= radius)
{
ManifoldPoint cp = manifold.Points[pointCount];
if (primaryAxis.Type == EPAxisType.EdgeA)
{
cp.LocalPoint = MathUtils.MulT(xf, clipPoints2[i].V);
cp.Id = clipPoints2[i].Id;
}
else
{
cp.LocalPoint = clipPoints2[i].V;
cp.Id.ContactFeature.TypeA = clipPoints2[i].Id.ContactFeature.TypeB;
cp.Id.ContactFeature.TypeB = clipPoints2[i].Id.ContactFeature.TypeA;
cp.Id.ContactFeature.IndexA = clipPoints2[i].Id.ContactFeature.IndexB;
cp.Id.ContactFeature.IndexB = clipPoints2[i].Id.ContactFeature.IndexA;
}
manifold.Points[pointCount] = cp;
++pointCount;
}
}
manifold.PointCount = pointCount;
}
