+/*
+* Copyright (c) 2006-2007 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 "b2Collision.h"
+#include "Shapes/b2PolygonShape.h"
+
+struct ClipVertex
+{
+ b2Vec2 v;
+ b2ContactID id;
+};
+
+static int32 ClipSegmentToLine(ClipVertex vOut[2], ClipVertex vIn[2],
+ const b2Vec2& normal, float32 offset)
+{
+ // Start with no output points
+ int32 numOut = 0;
+
+ // Calculate the distance of end points to the line
+ float32 distance0 = b2Dot(normal, vIn[0].v) - offset;
+ float32 distance1 = b2Dot(normal, vIn[1].v) - offset;
+
+ // If the points are behind the plane
+ if (distance0 <= 0.0f) vOut[numOut++] = vIn[0];
+ if (distance1 <= 0.0f) vOut[numOut++] = vIn[1];
+
+ // If the points are on different sides of the plane
+ if (distance0 * distance1 < 0.0f)
+ {
+ // Find intersection point of edge and plane
+ float32 interp = distance0 / (distance0 - distance1);
+ vOut[numOut].v = vIn[0].v + interp * (vIn[1].v - vIn[0].v);
+ if (distance0 > 0.0f)
+ {
+ vOut[numOut].id = vIn[0].id;
+ }
+ else
+ {
+ vOut[numOut].id = vIn[1].id;
+ }
+ ++numOut;
+ }
+
+ return numOut;
+}
+
+// Find the separation between poly1 and poly2 for a give edge normal on poly1.
+static float32 EdgeSeparation(const b2PolygonShape* poly1, const b2XForm& xf1, int32 edge1,
+ const b2PolygonShape* poly2, const b2XForm& xf2)
+{
+ int32 count1 = poly1->GetVertexCount();
+ const b2Vec2* vertices1 = poly1->GetVertices();
+ const b2Vec2* normals1 = poly1->GetNormals();
+
+ int32 count2 = poly2->GetVertexCount();
+ const b2Vec2* vertices2 = poly2->GetVertices();
+
+ b2Assert(0 <= edge1 && edge1 < count1);
+
+ // Convert normal from poly1's frame into poly2's frame.
+ b2Vec2 normal1World = b2Mul(xf1.R, normals1[edge1]);
+ b2Vec2 normal1 = b2MulT(xf2.R, normal1World);
+
+ // Find support vertex on poly2 for -normal.
+ int32 index = 0;
+ float32 minDot = B2_FLT_MAX;
+
+ for (int32 i = 0; i < count2; ++i)
+ {
+ float32 dot = b2Dot(vertices2[i], normal1);
+ if (dot < minDot)
+ {
+ minDot = dot;
+ index = i;
+ }
+ }
+
+ b2Vec2 v1 = b2Mul(xf1, vertices1[edge1]);
+ b2Vec2 v2 = b2Mul(xf2, vertices2[index]);
+ float32 separation = b2Dot(v2 - v1, normal1World);
+ return separation;
+}
+
+// Find the max separation between poly1 and poly2 using edge normals from poly1.
+static float32 FindMaxSeparation(int32* edgeIndex,
+ const b2PolygonShape* poly1, const b2XForm& xf1,
+ const b2PolygonShape* poly2, const b2XForm& xf2)
+{
+ int32 count1 = poly1->GetVertexCount();
+ const b2Vec2* normals1 = poly1->GetNormals();
+
+ // Vector pointing from the centroid of poly1 to the centroid of poly2.
+ b2Vec2 d = b2Mul(xf2, poly2->GetCentroid()) - b2Mul(xf1, poly1->GetCentroid());
+ b2Vec2 dLocal1 = b2MulT(xf1.R, d);
+
+ // Find edge normal on poly1 that has the largest projection onto d.
+ int32 edge = 0;
+ float32 maxDot = -B2_FLT_MAX;
+ for (int32 i = 0; i < count1; ++i)
+ {
+ float32 dot = b2Dot(normals1[i], dLocal1);
+ if (dot > maxDot)
+ {
+ maxDot = dot;
+ edge = i;
+ }
+ }
+
+ // Get the separation for the edge normal.
+ float32 s = EdgeSeparation(poly1, xf1, edge, poly2, xf2);
+ if (s > 0.0f)
+ {
+ return s;
+ }
+
+ // Check the separation for the previous edge normal.
+ int32 prevEdge = edge - 1 >= 0 ? edge - 1 : count1 - 1;
+ float32 sPrev = EdgeSeparation(poly1, xf1, prevEdge, poly2, xf2);
+ if (sPrev > 0.0f)
+ {
+ return sPrev;
+ }
+
+ // Check the separation for the next edge normal.
+ int32 nextEdge = edge + 1 < count1 ? edge + 1 : 0;
+ float32 sNext = EdgeSeparation(poly1, xf1, nextEdge, poly2, xf2);
+ if (sNext > 0.0f)
+ {
+ return sNext;
+ }
+
+ // Find the best edge and the search direction.
+ int32 bestEdge;
+ float32 bestSeparation;
+ int32 increment;
+ if (sPrev > s && sPrev > sNext)
+ {
+ increment = -1;
+ bestEdge = prevEdge;
+ bestSeparation = sPrev;
+ }
+ else if (sNext > s)
+ {
+ increment = 1;
+ bestEdge = nextEdge;
+ bestSeparation = sNext;
+ }
+ else
+ {
+ *edgeIndex = edge;
+ return s;
+ }
+
+ // Perform a local search for the best edge normal.
+ for ( ; ; )
+ {
+ if (increment == -1)
+ edge = bestEdge - 1 >= 0 ? bestEdge - 1 : count1 - 1;
+ else
+ edge = bestEdge + 1 < count1 ? bestEdge + 1 : 0;
+
+ s = EdgeSeparation(poly1, xf1, edge, poly2, xf2);
+ if (s > 0.0f)
+ {
+ return s;
+ }
+
+ if (s > bestSeparation)
+ {
+ bestEdge = edge;
+ bestSeparation = s;
+ }
+ else
+ {
+ break;
+ }
+ }
+
+ *edgeIndex = bestEdge;
+ return bestSeparation;
+}
+
+static void FindIncidentEdge(ClipVertex c[2],
+ const b2PolygonShape* poly1, const b2XForm& xf1, int32 edge1,
+ const b2PolygonShape* poly2, const b2XForm& xf2)
+{
+ int32 count1 = poly1->GetVertexCount();
+ const b2Vec2* normals1 = poly1->GetNormals();
+
+ int32 count2 = poly2->GetVertexCount();
+ const b2Vec2* vertices2 = poly2->GetVertices();
+ const b2Vec2* normals2 = poly2->GetNormals();
+
+ b2Assert(0 <= edge1 && edge1 < count1);
+
+ // Get the normal of the reference edge in poly2's frame.
+ b2Vec2 normal1 = b2MulT(xf2.R, b2Mul(xf1.R, normals1[edge1]));
+
+ // Find the incident edge on poly2.
+ int32 index = 0;
+ float32 minDot = B2_FLT_MAX;
+ for (int32 i = 0; i < count2; ++i)
+ {
+ float32 dot = b2Dot(normal1, normals2[i]);
+ if (dot < minDot)
+ {
+ minDot = dot;
+ index = i;
+ }
+ }
+
+ // Build the clip vertices for the incident edge.
+ int32 i1 = index;
+ int32 i2 = i1 + 1 < count2 ? i1 + 1 : 0;
+
+ c[0].v = b2Mul(xf2, vertices2[i1]);
+ c[0].id.features.referenceEdge = (uint8)edge1;
+ c[0].id.features.incidentEdge = (uint8)i1;
+ c[0].id.features.incidentVertex = 0;
+
+ c[1].v = b2Mul(xf2, vertices2[i2]);
+ c[1].id.features.referenceEdge = (uint8)edge1;
+ c[1].id.features.incidentEdge = (uint8)i2;
+ c[1].id.features.incidentVertex = 1;
+}
+
+// Find edge normal of max separation on A - return if separating axis is found
+// Find edge normal of max separation on B - return if separation axis is found
+// Choose reference edge as min(minA, minB)
+// Find incident edge
+// Clip
+
+// The normal points from 1 to 2
+void b2CollidePolygons(b2Manifold* manifold,
+ const b2PolygonShape* polyA, const b2XForm& xfA,
+ const b2PolygonShape* polyB, const b2XForm& xfB)
+{
+ manifold->pointCount = 0;
+
+ int32 edgeA = 0;
+ float32 separationA = FindMaxSeparation(&edgeA, polyA, xfA, polyB, xfB);
+ if (separationA > 0.0f)
+ return;
+
+ int32 edgeB = 0;
+ float32 separationB = FindMaxSeparation(&edgeB, polyB, xfB, polyA, xfA);
+ if (separationB > 0.0f)
+ return;
+
+ const b2PolygonShape* poly1; // reference poly
+ const b2PolygonShape* poly2; // incident poly
+ b2XForm xf1, xf2;
+ int32 edge1; // reference edge
+ uint8 flip;
+ const float32 k_relativeTol = 0.98f;
+ const float32 k_absoluteTol = 0.001f;
+
+ // TODO_ERIN use "radius" of poly for absolute tolerance.
+ if (separationB > k_relativeTol * separationA + k_absoluteTol)
+ {
+ poly1 = polyB;
+ poly2 = polyA;
+ xf1 = xfB;
+ xf2 = xfA;
+ edge1 = edgeB;
+ flip = 1;
+ }
+ else
+ {
+ poly1 = polyA;
+ poly2 = polyB;
+ xf1 = xfA;
+ xf2 = xfB;
+ edge1 = edgeA;
+ flip = 0;
+ }
+
+ ClipVertex incidentEdge[2];
+ FindIncidentEdge(incidentEdge, poly1, xf1, edge1, poly2, xf2);
+
+ int32 count1 = poly1->GetVertexCount();
+ const b2Vec2* vertices1 = poly1->GetVertices();
+
+ b2Vec2 v11 = vertices1[edge1];
+ b2Vec2 v12 = edge1 + 1 < count1 ? vertices1[edge1+1] : vertices1[0];
+
+ b2Vec2 dv = v12 - v11;
+ b2Vec2 sideNormal = b2Mul(xf1.R, v12 - v11);
+ sideNormal.Normalize();
+ b2Vec2 frontNormal = b2Cross(sideNormal, 1.0f);
+
+ v11 = b2Mul(xf1, v11);
+ v12 = b2Mul(xf1, v12);
+
+ float32 frontOffset = b2Dot(frontNormal, v11);
+ float32 sideOffset1 = -b2Dot(sideNormal, v11);
+ float32 sideOffset2 = b2Dot(sideNormal, v12);
+
+ // Clip incident edge against extruded edge1 side edges.
+ ClipVertex clipPoints1[2];
+ ClipVertex clipPoints2[2];
+ int np;
+
+ // Clip to box side 1
+ np = ClipSegmentToLine(clipPoints1, incidentEdge, -sideNormal, sideOffset1);
+
+ if (np < 2)
+ return;
+
+ // Clip to negative box side 1
+ np = ClipSegmentToLine(clipPoints2, clipPoints1, sideNormal, sideOffset2);
+
+ if (np < 2)
+ return;
+
+ // Now clipPoints2 contains the clipped points.
+ manifold->normal = flip ? -frontNormal : frontNormal;
+
+ int32 pointCount = 0;
+ for (int32 i = 0; i < b2_maxManifoldPoints; ++i)
+ {
+ float32 separation = b2Dot(frontNormal, clipPoints2[i].v) - frontOffset;
+
+ if (separation <= 0.0f)
+ {
+ b2ManifoldPoint* cp = manifold->points + pointCount;
+ cp->separation = separation;
+ cp->localPoint1 = b2MulT(xfA, clipPoints2[i].v);
+ cp->localPoint2 = b2MulT(xfB, clipPoints2[i].v);
+ cp->id = clipPoints2[i].id;
+ cp->id.features.flip = flip;
+ ++pointCount;
+ }
+ }
+
+ manifold->pointCount = pointCount;
+}
projects / blok / blobdiff