1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
|
// MIT License
// Copyright (c) 2019 Erin Catto
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
#include "box2d/b2_collision.h"
#include "box2d/b2_polygon_shape.h"
// Find the max separation between poly1 and poly2 using edge normals from poly1.
static float b2FindMaxSeparation(int32* edgeIndex,
const b2PolygonShape* poly1, const b2Transform& xf1,
const b2PolygonShape* poly2, const b2Transform& xf2)
{
int32 count1 = poly1->m_count;
int32 count2 = poly2->m_count;
const b2Vec2* n1s = poly1->m_normals;
const b2Vec2* v1s = poly1->m_vertices;
const b2Vec2* v2s = poly2->m_vertices;
b2Transform xf = b2MulT(xf2, xf1);
int32 bestIndex = 0;
float maxSeparation = -b2_maxFloat;
for (int32 i = 0; i < count1; ++i)
{
// Get poly1 normal in frame2.
b2Vec2 n = b2Mul(xf.q, n1s[i]);
b2Vec2 v1 = b2Mul(xf, v1s[i]);
// Find deepest point for normal i.
float si = b2_maxFloat;
for (int32 j = 0; j < count2; ++j)
{
float sij = b2Dot(n, v2s[j] - v1);
if (sij < si)
{
si = sij;
}
}
if (si > maxSeparation)
{
maxSeparation = si;
bestIndex = i;
}
}
*edgeIndex = bestIndex;
return maxSeparation;
}
static void b2FindIncidentEdge(b2ClipVertex c[2],
const b2PolygonShape* poly1, const b2Transform& xf1, int32 edge1,
const b2PolygonShape* poly2, const b2Transform& xf2)
{
const b2Vec2* normals1 = poly1->m_normals;
int32 count2 = poly2->m_count;
const b2Vec2* vertices2 = poly2->m_vertices;
const b2Vec2* normals2 = poly2->m_normals;
b2Assert(0 <= edge1 && edge1 < poly1->m_count);
// Get the normal of the reference edge in poly2's frame.
b2Vec2 normal1 = b2MulT(xf2.q, b2Mul(xf1.q, normals1[edge1]));
// Find the incident edge on poly2.
int32 index = 0;
float minDot = b2_maxFloat;
for (int32 i = 0; i < count2; ++i)
{
float 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.cf.indexA = (uint8)edge1;
c[0].id.cf.indexB = (uint8)i1;
c[0].id.cf.typeA = b2ContactFeature::e_face;
c[0].id.cf.typeB = b2ContactFeature::e_vertex;
c[1].v = b2Mul(xf2, vertices2[i2]);
c[1].id.cf.indexA = (uint8)edge1;
c[1].id.cf.indexB = (uint8)i2;
c[1].id.cf.typeA = b2ContactFeature::e_face;
c[1].id.cf.typeB = b2ContactFeature::e_vertex;
}
// 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 b2Transform& xfA,
const b2PolygonShape* polyB, const b2Transform& xfB)
{
manifold->pointCount = 0;
float totalRadius = polyA->m_radius + polyB->m_radius;
int32 edgeA = 0;
float separationA = b2FindMaxSeparation(&edgeA, polyA, xfA, polyB, xfB);
if (separationA > totalRadius)
return;
int32 edgeB = 0;
float separationB = b2FindMaxSeparation(&edgeB, polyB, xfB, polyA, xfA);
if (separationB > totalRadius)
return;
const b2PolygonShape* poly1; // reference polygon
const b2PolygonShape* poly2; // incident polygon
b2Transform xf1, xf2;
int32 edge1; // reference edge
uint8 flip;
const float k_tol = 0.1f * b2_linearSlop;
if (separationB > separationA + k_tol)
{
poly1 = polyB;
poly2 = polyA;
xf1 = xfB;
xf2 = xfA;
edge1 = edgeB;
manifold->type = b2Manifold::e_faceB;
flip = 1;
}
else
{
poly1 = polyA;
poly2 = polyB;
xf1 = xfA;
xf2 = xfB;
edge1 = edgeA;
manifold->type = b2Manifold::e_faceA;
flip = 0;
}
b2ClipVertex incidentEdge[2];
b2FindIncidentEdge(incidentEdge, poly1, xf1, edge1, poly2, xf2);
int32 count1 = poly1->m_count;
const b2Vec2* vertices1 = poly1->m_vertices;
int32 iv1 = edge1;
int32 iv2 = edge1 + 1 < count1 ? edge1 + 1 : 0;
b2Vec2 v11 = vertices1[iv1];
b2Vec2 v12 = vertices1[iv2];
b2Vec2 localTangent = v12 - v11;
localTangent.Normalize();
b2Vec2 localNormal = b2Cross(localTangent, 1.0f);
b2Vec2 planePoint = 0.5f * (v11 + v12);
b2Vec2 tangent = b2Mul(xf1.q, localTangent);
b2Vec2 normal = b2Cross(tangent, 1.0f);
v11 = b2Mul(xf1, v11);
v12 = b2Mul(xf1, v12);
// Face offset.
float frontOffset = b2Dot(normal, v11);
// Side offsets, extended by polytope skin thickness.
float sideOffset1 = -b2Dot(tangent, v11) + totalRadius;
float sideOffset2 = b2Dot(tangent, v12) + totalRadius;
// Clip incident edge against extruded edge1 side edges.
b2ClipVertex clipPoints1[2];
b2ClipVertex clipPoints2[2];
int np;
// Clip to box side 1
np = b2ClipSegmentToLine(clipPoints1, incidentEdge, -tangent, sideOffset1, iv1);
if (np < 2)
return;
// Clip to negative box side 1
np = b2ClipSegmentToLine(clipPoints2, clipPoints1, tangent, sideOffset2, iv2);
if (np < 2)
{
return;
}
// Now clipPoints2 contains the clipped points.
manifold->localNormal = localNormal;
manifold->localPoint = planePoint;
int32 pointCount = 0;
for (int32 i = 0; i < b2_maxManifoldPoints; ++i)
{
float separation = b2Dot(normal, clipPoints2[i].v) - frontOffset;
if (separation <= totalRadius)
{
b2ManifoldPoint* cp = manifold->points + pointCount;
cp->localPoint = b2MulT(xf2, clipPoints2[i].v);
cp->id = clipPoints2[i].id;
if (flip)
{
// Swap features
b2ContactFeature cf = cp->id.cf;
cp->id.cf.indexA = cf.indexB;
cp->id.cf.indexB = cf.indexA;
cp->id.cf.typeA = cf.typeB;
cp->id.cf.typeB = cf.typeA;
}
++pointCount;
}
}
manifold->pointCount = pointCount;
}
|
