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/*
Box2DX Copyright (c) 2009 Ihar Kalasouski http://code.google.com/p/box2dx
Box2D original C++ version Copyright (c) 2006-2009 Erin Catto http://www.gphysics.com
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.
*/
using Box2DX.Common;
namespace Box2DX.Collision
{
public partial class Collision
{
public static void CollideCircles(ref Manifold manifold,
CircleShape circle1, XForm xf1, CircleShape circle2, XForm xf2)
{
manifold.PointCount = 0;
Vec2 p1 = Common.Math.Mul(xf1, circle1._position);
Vec2 p2 = Common.Math.Mul(xf2, circle2._position);
Vec2 d = p2 - p1;
float distSqr = Vec2.Dot(d, d);
float radius = circle1._radius + circle2._radius;
if (distSqr > radius * radius)
{
return;
}
manifold.Type = ManifoldType.Circles;
manifold.LocalPoint = circle1._position;
manifold.LocalPlaneNormal.SetZero();
manifold.PointCount = 1;
manifold.Points[0].LocalPoint = circle2._position;
manifold.Points[0].ID.Key = 0;
}
public static void CollidePolygonAndCircle(ref Manifold manifold,
PolygonShape polygon, XForm xf1, CircleShape circle, XForm xf2)
{
manifold.PointCount = 0;
// Compute circle position in the frame of the polygon.
Vec2 c = Common.Math.Mul(xf2, circle._position);
Vec2 cLocal = Common.Math.MulT(xf1, c);
// Find the min separating edge.
int normalIndex = 0;
float separation = -Settings.FLT_MAX;
float radius = polygon._radius + circle._radius;
int vertexCount = polygon._vertexCount;
Vec2[] vertices = polygon._vertices;
Vec2[] normals = polygon._normals;
for (int i = 0; i < vertexCount; ++i)
{
float s = Vec2.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;
Vec2 v1 = vertices[vertIndex1];
Vec2 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 = Vec2.Dot(cLocal - v1, v2 - v1);
float u2 = Vec2.Dot(cLocal - v2, v1 - v2);
if (u1 <= 0.0f)
{
if (Vec2.DistanceSquared(cLocal, v1) > 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 (Vec2.DistanceSquared(cLocal, v2) > 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
{
Vec2 faceCenter = 0.5f * (v1 + v2);
float separation_ = Vec2.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;
}
}
}
}
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