b2CollideCircle.cpp
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上传日期:2022-01-07
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- /*
- * Copyright (c) 2007-2009 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.
- */
- #include <Box2D/Collision/b2Collision.h>
- #include <Box2D/Collision/Shapes/b2CircleShape.h>
- #include <Box2D/Collision/Shapes/b2PolygonShape.h>
- void b2CollideCircles(
- b2Manifold* manifold,
- const b2CircleShape* circleA, const b2Transform& xfA,
- const b2CircleShape* circleB, const b2Transform& xfB)
- {
- manifold->pointCount = 0;
- b2Vec2 pA = b2Mul(xfA, circleA->m_p);
- b2Vec2 pB = b2Mul(xfB, circleB->m_p);
- b2Vec2 d = pB - pA;
- float32 distSqr = b2Dot(d, d);
- float32 rA = circleA->m_radius, rB = circleB->m_radius;
- float32 radius = rA + rB;
- if (distSqr > radius * radius)
- {
- return;
- }
- manifold->type = b2Manifold::e_circles;
- manifold->localPoint = circleA->m_p;
- manifold->localNormal.SetZero();
- manifold->pointCount = 1;
- manifold->points[0].localPoint = circleB->m_p;
- manifold->points[0].id.key = 0;
- }
- void b2CollidePolygonAndCircle(
- b2Manifold* manifold,
- const b2PolygonShape* polygonA, const b2Transform& xfA,
- const b2CircleShape* circleB, const b2Transform& xfB)
- {
- manifold->pointCount = 0;
- // Compute circle position in the frame of the polygon.
- b2Vec2 c = b2Mul(xfB, circleB->m_p);
- b2Vec2 cLocal = b2MulT(xfA, c);
- // Find the min separating edge.
- int32 normalIndex = 0;
- float32 separation = -b2_maxFloat;
- float32 radius = polygonA->m_radius + circleB->m_radius;
- int32 vertexCount = polygonA->m_vertexCount;
- const b2Vec2* vertices = polygonA->m_vertices;
- const b2Vec2* normals = polygonA->m_normals;
- for (int32 i = 0; i < vertexCount; ++i)
- {
- float32 s = b2Dot(normals[i], cLocal - vertices[i]);
- if (s > radius)
- {
- // Early out.
- return;
- }
- if (s > separation)
- {
- separation = s;
- normalIndex = i;
- }
- }
- // Vertices that subtend the incident face.
- int32 vertIndex1 = normalIndex;
- int32 vertIndex2 = vertIndex1 + 1 < vertexCount ? vertIndex1 + 1 : 0;
- b2Vec2 v1 = vertices[vertIndex1];
- b2Vec2 v2 = vertices[vertIndex2];
- // If the center is inside the polygon ...
- if (separation < b2_epsilon)
- {
- manifold->pointCount = 1;
- manifold->type = b2Manifold::e_faceA;
- manifold->localNormal = normals[normalIndex];
- manifold->localPoint = 0.5f * (v1 + v2);
- manifold->points[0].localPoint = circleB->m_p;
- manifold->points[0].id.key = 0;
- return;
- }
- // Compute barycentric coordinates
- float32 u1 = b2Dot(cLocal - v1, v2 - v1);
- float32 u2 = b2Dot(cLocal - v2, v1 - v2);
- if (u1 <= 0.0f)
- {
- if (b2DistanceSquared(cLocal, v1) > radius * radius)
- {
- return;
- }
- manifold->pointCount = 1;
- manifold->type = b2Manifold::e_faceA;
- manifold->localNormal = cLocal - v1;
- manifold->localNormal.Normalize();
- manifold->localPoint = v1;
- manifold->points[0].localPoint = circleB->m_p;
- manifold->points[0].id.key = 0;
- }
- else if (u2 <= 0.0f)
- {
- if (b2DistanceSquared(cLocal, v2) > radius * radius)
- {
- return;
- }
- manifold->pointCount = 1;
- manifold->type = b2Manifold::e_faceA;
- manifold->localNormal = cLocal - v2;
- manifold->localNormal.Normalize();
- manifold->localPoint = v2;
- manifold->points[0].localPoint = circleB->m_p;
- manifold->points[0].id.key = 0;
- }
- else
- {
- b2Vec2 faceCenter = 0.5f * (v1 + v2);
- float32 separation = b2Dot(cLocal - faceCenter, normals[vertIndex1]);
- if (separation > radius)
- {
- return;
- }
- manifold->pointCount = 1;
- manifold->type = b2Manifold::e_faceA;
- manifold->localNormal = normals[vertIndex1];
- manifold->localPoint = faceCenter;
- manifold->points[0].localPoint = circleB->m_p;
- manifold->points[0].id.key = 0;
- }
- }