public static void CollidePolygonAndCircle(ref Manifold manifold, PolygonShape polygon, Transform xf1, CircleShape circle, Transform xf2)
{
manifold.PointCount = 0;
// Compute circle position in the frame of the polygon.
Vector2 c = xf2.TransformPoint(circle._position);
Vector2 cLocal = xf1.InverseTransformPoint(c);
// Find the min separating edge.
int normalIndex = 0;
float separation = -Settings.FLT_MAX;
float radius = polygon._radius + circle._radius;
int vertexCount = polygon._vertexCount;
Vector2[] vertices = polygon._vertices;
Vector2[] normals = polygon._normals;
for (int i = 0; i < vertexCount; ++i)
{
float s = Vector2.Dot(normals[i], cLocal - vertices[i]);
if (s > radius)
{
// Early out.
return;
}
if (s > separation)
{
separation = s;
normalIndex = i;
}
}
// Vertices that subtend the incident face.
int vertIndex1 = normalIndex;
int vertIndex2 = vertIndex1 + 1 < vertexCount ? vertIndex1 + 1 : 0;
Vector2 v1 = vertices[vertIndex1];
Vector2 v2 = vertices[vertIndex2];
// If the center is inside the polygon ...
if (separation < Common.Settings.FLT_EPSILON)
{
manifold.PointCount = 1;
manifold.Type = ManifoldType.FaceA;
manifold.LocalPlaneNormal = normals[normalIndex];
manifold.LocalPoint = 0.5f * (v1 + v2);
manifold.Points[0].LocalPoint = circle._position;
manifold.Points[0].ID.Key = 0;
return;
}
// Compute barycentric coordinates
float u1 = Vector2.Dot(cLocal - v1, v2 - v1);
float u2 = Vector2.Dot(cLocal - v2, v1 - v2);
if (u1 <= 0.0f)
{
if ((cLocal - v1).LengthSquared() > radius * radius)
{
return;
}
manifold.PointCount = 1;
manifold.Type = ManifoldType.FaceA;
manifold.LocalPlaneNormal = cLocal - v1;
manifold.LocalPlaneNormal.Normalize();
manifold.LocalPoint = v1;
manifold.Points[0].LocalPoint = circle._position;
manifold.Points[0].ID.Key = 0;
}
else if (u2 <= 0.0f)
{
if ((cLocal - v2).LengthSquared() > radius * radius)
{
return;
}
manifold.PointCount = 1;
manifold.Type = ManifoldType.FaceA;
manifold.LocalPlaneNormal = cLocal - v2;
manifold.LocalPlaneNormal.Normalize();
manifold.LocalPoint = v2;
manifold.Points[0].LocalPoint = circle._position;
manifold.Points[0].ID.Key = 0;
}
else
{
Vector2 faceCenter = 0.5f * (v1 + v2);
float separation_ = Vector2.Dot(cLocal - faceCenter, normals[vertIndex1]);
if (separation_ > radius)
{
return;
}
manifold.PointCount = 1;
manifold.Type = ManifoldType.FaceA;
manifold.LocalPlaneNormal = normals[vertIndex1];
manifold.LocalPoint = faceCenter;
manifold.Points[0].LocalPoint = circle._position;
manifold.Points[0].ID.Key = 0;
}
}
/// <summary>
/// Gets a local point relative to the body's origin given a world point.
/// </summary>
/// <param name="worldPoint">A point in world coordinates.</param>
/// <returns>Return the corresponding local point relative to the body's origin.</returns>
public Vector2 GetLocalPoint(Vector2 worldPoint)
{
return(_xf.InverseTransformPoint(worldPoint));
}
