318 lines
8.8 KiB
C++
318 lines
8.8 KiB
C++
/*
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* Copyright (c) 2006-2009 Erin Catto http://www.box2d.org
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* 2. Altered source versions must be plainly marked as such, and must not be
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* misrepresented as being the original software.
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* 3. This notice may not be removed or altered from any source distribution.
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*/
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#include "b2Collision.h"
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#include "Shapes/b2PolygonShape.h"
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// Find the separation between poly1 and poly2 for a give edge normal on poly1.
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static float32 b2EdgeSeparation(const b2PolygonShape* poly1, const b2Transform& xf1, int32 edge1,
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const b2PolygonShape* poly2, const b2Transform& xf2)
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{
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const b2Vec2* vertices1 = poly1->m_vertices;
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const b2Vec2* normals1 = poly1->m_normals;
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int32 count2 = poly2->m_vertexCount;
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const b2Vec2* vertices2 = poly2->m_vertices;
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b2Assert(0 <= edge1 && edge1 < poly1->m_vertexCount);
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// Convert normal from poly1's frame into poly2's frame.
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b2Vec2 normal1World = b2Mul(xf1.q, normals1[edge1]);
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b2Vec2 normal1 = b2MulT(xf2.q, normal1World);
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// Find support vertex on poly2 for -normal.
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int32 index = 0;
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float32 minDot = b2_maxFloat;
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for (int32 i = 0; i < count2; ++i)
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{
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float32 dot = b2Dot(vertices2[i], normal1);
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if (dot < minDot)
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{
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minDot = dot;
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index = i;
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}
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}
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b2Vec2 v1 = b2Mul(xf1, vertices1[edge1]);
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b2Vec2 v2 = b2Mul(xf2, vertices2[index]);
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float32 separation = b2Dot(v2 - v1, normal1World);
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return separation;
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}
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// Find the max separation between poly1 and poly2 using edge normals from poly1.
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static float32 b2FindMaxSeparation(int32* edgeIndex,
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const b2PolygonShape* poly1, const b2Transform& xf1,
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const b2PolygonShape* poly2, const b2Transform& xf2)
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{
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int32 count1 = poly1->m_vertexCount;
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const b2Vec2* normals1 = poly1->m_normals;
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// Vector pointing from the centroid of poly1 to the centroid of poly2.
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b2Vec2 d = b2Mul(xf2, poly2->m_centroid) - b2Mul(xf1, poly1->m_centroid);
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b2Vec2 dLocal1 = b2MulT(xf1.q, d);
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// Find edge normal on poly1 that has the largest projection onto d.
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int32 edge = 0;
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float32 maxDot = -b2_maxFloat;
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for (int32 i = 0; i < count1; ++i)
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{
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float32 dot = b2Dot(normals1[i], dLocal1);
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if (dot > maxDot)
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{
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maxDot = dot;
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edge = i;
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}
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}
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// Get the separation for the edge normal.
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float32 s = b2EdgeSeparation(poly1, xf1, edge, poly2, xf2);
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// Check the separation for the previous edge normal.
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int32 prevEdge = edge - 1 >= 0 ? edge - 1 : count1 - 1;
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float32 sPrev = b2EdgeSeparation(poly1, xf1, prevEdge, poly2, xf2);
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// Check the separation for the next edge normal.
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int32 nextEdge = edge + 1 < count1 ? edge + 1 : 0;
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float32 sNext = b2EdgeSeparation(poly1, xf1, nextEdge, poly2, xf2);
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// Find the best edge and the search direction.
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int32 bestEdge;
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float32 bestSeparation;
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int32 increment;
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if (sPrev > s && sPrev > sNext)
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{
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increment = -1;
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bestEdge = prevEdge;
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bestSeparation = sPrev;
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}
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else if (sNext > s)
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{
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increment = 1;
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bestEdge = nextEdge;
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bestSeparation = sNext;
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}
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else
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{
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*edgeIndex = edge;
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return s;
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}
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// Perform a local search for the best edge normal.
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for ( ; ; )
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{
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if (increment == -1)
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edge = bestEdge - 1 >= 0 ? bestEdge - 1 : count1 - 1;
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else
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edge = bestEdge + 1 < count1 ? bestEdge + 1 : 0;
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s = b2EdgeSeparation(poly1, xf1, edge, poly2, xf2);
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if (s > bestSeparation)
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{
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bestEdge = edge;
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bestSeparation = s;
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}
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else
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{
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break;
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}
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}
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*edgeIndex = bestEdge;
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return bestSeparation;
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}
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static void b2FindIncidentEdge(b2ClipVertex c[2],
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const b2PolygonShape* poly1, const b2Transform& xf1, int32 edge1,
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const b2PolygonShape* poly2, const b2Transform& xf2)
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{
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const b2Vec2* normals1 = poly1->m_normals;
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int32 count2 = poly2->m_vertexCount;
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const b2Vec2* vertices2 = poly2->m_vertices;
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const b2Vec2* normals2 = poly2->m_normals;
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b2Assert(0 <= edge1 && edge1 < poly1->m_vertexCount);
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// Get the normal of the reference edge in poly2's frame.
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b2Vec2 normal1 = b2MulT(xf2.q, b2Mul(xf1.q, normals1[edge1]));
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// Find the incident edge on poly2.
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int32 index = 0;
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float32 minDot = b2_maxFloat;
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for (int32 i = 0; i < count2; ++i)
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{
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float32 dot = b2Dot(normal1, normals2[i]);
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if (dot < minDot)
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{
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minDot = dot;
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index = i;
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}
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}
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// Build the clip vertices for the incident edge.
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int32 i1 = index;
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int32 i2 = i1 + 1 < count2 ? i1 + 1 : 0;
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c[0].v = b2Mul(xf2, vertices2[i1]);
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c[0].id.cf.indexA = (uint8)edge1;
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c[0].id.cf.indexB = (uint8)i1;
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c[0].id.cf.typeA = b2ContactFeature::e_face;
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c[0].id.cf.typeB = b2ContactFeature::e_vertex;
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c[1].v = b2Mul(xf2, vertices2[i2]);
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c[1].id.cf.indexA = (uint8)edge1;
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c[1].id.cf.indexB = (uint8)i2;
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c[1].id.cf.typeA = b2ContactFeature::e_face;
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c[1].id.cf.typeB = b2ContactFeature::e_vertex;
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}
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// Find edge normal of max separation on A - return if separating axis is found
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// Find edge normal of max separation on B - return if separation axis is found
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// Choose reference edge as min(minA, minB)
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// Find incident edge
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// Clip
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// The normal points from 1 to 2
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void b2CollidePolygons(b2Manifold* manifold,
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const b2PolygonShape* polyA, const b2Transform& xfA,
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const b2PolygonShape* polyB, const b2Transform& xfB)
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{
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manifold->pointCount = 0;
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float32 totalRadius = polyA->m_radius + polyB->m_radius;
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int32 edgeA = 0;
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float32 separationA = b2FindMaxSeparation(&edgeA, polyA, xfA, polyB, xfB);
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if (separationA > totalRadius)
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return;
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int32 edgeB = 0;
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float32 separationB = b2FindMaxSeparation(&edgeB, polyB, xfB, polyA, xfA);
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if (separationB > totalRadius)
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return;
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const b2PolygonShape* poly1; // reference polygon
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const b2PolygonShape* poly2; // incident polygon
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b2Transform xf1, xf2;
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int32 edge1; // reference edge
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uint8 flip;
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const float32 k_relativeTol = 0.98f;
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const float32 k_absoluteTol = 0.001f;
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if (separationB > k_relativeTol * separationA + k_absoluteTol)
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{
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poly1 = polyB;
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poly2 = polyA;
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xf1 = xfB;
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xf2 = xfA;
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edge1 = edgeB;
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manifold->type = b2Manifold::e_faceB;
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flip = 1;
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}
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else
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{
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poly1 = polyA;
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poly2 = polyB;
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xf1 = xfA;
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xf2 = xfB;
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edge1 = edgeA;
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manifold->type = b2Manifold::e_faceA;
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flip = 0;
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}
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b2ClipVertex incidentEdge[2];
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b2FindIncidentEdge(incidentEdge, poly1, xf1, edge1, poly2, xf2);
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int32 count1 = poly1->m_vertexCount;
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const b2Vec2* vertices1 = poly1->m_vertices;
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int32 iv1 = edge1;
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int32 iv2 = edge1 + 1 < count1 ? edge1 + 1 : 0;
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b2Vec2 v11 = vertices1[iv1];
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b2Vec2 v12 = vertices1[iv2];
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b2Vec2 localTangent = v12 - v11;
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localTangent.Normalize();
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b2Vec2 localNormal = b2Cross(localTangent, 1.0f);
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b2Vec2 planePoint = 0.5f * (v11 + v12);
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b2Vec2 tangent = b2Mul(xf1.q, localTangent);
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b2Vec2 normal = b2Cross(tangent, 1.0f);
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v11 = b2Mul(xf1, v11);
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v12 = b2Mul(xf1, v12);
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// Face offset.
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float32 frontOffset = b2Dot(normal, v11);
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// Side offsets, extended by polytope skin thickness.
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float32 sideOffset1 = -b2Dot(tangent, v11) + totalRadius;
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float32 sideOffset2 = b2Dot(tangent, v12) + totalRadius;
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// Clip incident edge against extruded edge1 side edges.
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b2ClipVertex clipPoints1[2];
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b2ClipVertex clipPoints2[2];
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int np;
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// Clip to box side 1
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np = b2ClipSegmentToLine(clipPoints1, incidentEdge, -tangent, sideOffset1, iv1);
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if (np < 2)
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return;
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// Clip to negative box side 1
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np = b2ClipSegmentToLine(clipPoints2, clipPoints1, tangent, sideOffset2, iv2);
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if (np < 2)
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{
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return;
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}
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// Now clipPoints2 contains the clipped points.
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manifold->localNormal = localNormal;
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manifold->localPoint = planePoint;
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int32 pointCount = 0;
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for (int32 i = 0; i < b2_maxManifoldPoints; ++i)
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{
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float32 separation = b2Dot(normal, clipPoints2[i].v) - frontOffset;
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if (separation <= totalRadius)
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{
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b2ManifoldPoint* cp = manifold->points + pointCount;
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cp->localPoint = b2MulT(xf2, clipPoints2[i].v);
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cp->id = clipPoints2[i].id;
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if (flip)
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{
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// Swap features
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b2ContactFeature cf = cp->id.cf;
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cp->id.cf.indexA = cf.indexB;
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cp->id.cf.indexB = cf.indexA;
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cp->id.cf.typeA = cf.typeB;
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cp->id.cf.typeB = cf.typeA;
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}
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++pointCount;
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}
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}
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manifold->pointCount = pointCount;
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}
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