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cirosantillicirosantilli
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Better collision info
1 parent a6836a5 commit 503a3b6

4 files changed

Lines changed: 49 additions & 37 deletions

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‎bullet/README.md‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -10,6 +10,6 @@ Tested on Bullet 2.83.
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1. [Users](users.md)
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1. Examples
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1. [Gravity](gravity.cpp)
13-
1. [Ground ball](ground ball.cpp)
13+
1. [Ground ball](ground_ball.cpp)
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1. [gnuplot-run](gnuplot-run)
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1. [TODO](TODO.md)

‎bullet/TODO.md‎

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@@ -1,10 +1,5 @@
11
# TODO
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3-
- detect when objects collide
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- http://www.bulletphysics.org/mediawiki-1.5.8/index.php?title=Collision_Callbacks_and_Triggers
5-
- http://stackoverflow.com/questions/9117932/detecting-collisions-with-bullet
6-
- http://gamedev.stackexchange.com/questions/22442/how-get-collision-callback-of-two-specific-objects-using-bullet-physics
7-
- http://www.bulletphysics.org/mediawiki-1.5.8/index.php?title=Collision_Callbacks_and_Triggers
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- get object rotation: 3 Euler angles. Attempt made at `gravity.cpp`
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- Stairs physics: http://gamedev.stackexchange.com/questions/74794/make-the-player-run-onto-stairs-smoothly
105
- Voronoi: https://www.youtube.com/watch?v=FIPu9_OGFgc

‎bullet/ground_ball.cpp‎

Lines changed: 46 additions & 30 deletions
Original file line numberDiff line numberDiff line change
@@ -1,9 +1,19 @@
11
/*
22
A sphere falling and hitting the ground.
3+
4+
It may bounce up a few times depending on the restitution coefficients.
5+
6+
Collisions are detected and printed to output. Releated threads:
7+
8+
- http://stackoverflow.com/questions/11175694/bullet-physics-simplest-collision-example
9+
- http://stackoverflow.com/questions/9117932/detecting-collisions-with-bullet
10+
- http://gamedev.stackexchange.com/questions/22442/how-get-collision-callback-of-two-specific-objects-using-bullet-physics
11+
- http://www.bulletphysics.org/mediawiki-1.5.8/index.php?title=Collision_Callbacks_and_Triggers
312
*/
413

514
#include <cstdio>
615
#include <cstdlib>
16+
#include <vector>
717

818
#include <btBulletDynamicsCommon.h>
919

@@ -18,35 +28,31 @@ constexpr float groundRestitution = 0.9f;
1828
constexpr float sphereRestitution = 0.9f;
1929
constexpr int maxNPoints = 500;
2030

21-
static void myTickCallback(btDynamicsWorld *world, btScalar timeStep) {
22-
bool hadCollision = false;
31+
std::vector<btVector3> collisions;
32+
void myTickCallback(btDynamicsWorld *dynamicsWorld, btScalar timeStep) {
33+
collisions.clear();
34+
int numManifolds = dynamicsWorld->getDispatcher()->getNumManifolds();
2335
for (int i = 0; i < numManifolds; i++) {
24-
btPersistentManifold* contactManifold = dynamicsWorld->getDispatcher()->getManifoldByIndexInternal(i);
25-
const btCollisionObject* obA = static_cast<const btCollisionObject*>(contactManifold->getBody0());
26-
const btCollisionObject* obB = static_cast<const btCollisionObject*>(contactManifold->getBody1());
36+
btPersistentManifold *contactManifold = dynamicsWorld->getDispatcher()->getManifoldByIndexInternal(i);
37+
// TODO those are unused. What can be done with them?
38+
// I think they are the same objects as those in the main loop
39+
// dynamicsWorld->getCollisionObjectArray() and we could compare
40+
// the pointers to see which object collided with which.
41+
{
42+
const btCollisionObject *objA = contactManifold->getBody0();
43+
const btCollisionObject *objB = contactManifold->getBody1();
44+
}
2745
int numContacts = contactManifold->getNumContacts();
2846
for (int j = 0; j < numContacts; j++) {
29-
if (!hadCollision)
30-
std::printf("1 ");
31-
hadCollision = true;
3247
btManifoldPoint& pt = contactManifold->getContactPoint(j);
33-
if (pt.getDistance() < 0.0f) {
34-
const btVector3& ptA = pt.getPositionWorldOnA();
35-
const btVector3& ptB = pt.getPositionWorldOnB();
36-
const btVector3& normalOnB = pt.m_normalWorldOnB;
37-
std::printf(
38-
PRINTF_FLOAT " " PRINTF_FLOAT " " PRINTF_FLOAT " "
39-
PRINTF_FLOAT " " PRINTF_FLOAT " " PRINTF_FLOAT " "
40-
PRINTF_FLOAT " " PRINTF_FLOAT " " PRINTF_FLOAT " ",
41-
ptA.getX(), ptA.getY(), ptA.getZ(),
42-
ptB.getX(), ptB.getY(), ptB.getZ(),
43-
normalOnB.getX(), normalOnB.getY(), normalOnB.getZ());
44-
}
48+
const btVector3& ptA = pt.getPositionWorldOnA();
49+
const btVector3& ptB = pt.getPositionWorldOnB();
50+
const btVector3& normalOnB = pt.m_normalWorldOnB;
51+
collisions.push_back(ptA);
52+
collisions.push_back(ptB);
53+
collisions.push_back(normalOnB);
4554
}
4655
}
47-
if (!hadCollision)
48-
std::printf("0 ");
49-
puts("");
5056
}
5157

5258
int main() {
@@ -66,20 +72,17 @@ int main() {
6672
// Ground.
6773
{
6874
btTransform groundTransform;
69-
7075
groundTransform.setIdentity();
7176
groundTransform.setOrigin(btVector3(0, 0, 0));
72-
7377
btCollisionShape* groundShape;
7478
#if 1
75-
// x / z plane.
76-
// TODO: what is the planeConstant (second argument)?
77-
// Looks like the displacement from the origin.
79+
// x / z plane at y = -1.
7880
groundShape = new btStaticPlaneShape(btVector3(0, 1, 0), -1);
7981
#else
8082
// A cube of width 10 at y = -6.
8183
// Does not fall because we won't call:
8284
// colShape->calculateLocalInertia
85+
// TODO: remove this from this example into a collision shape example.
8386
groundTransform.setOrigin(btVector3(0, -6, 0));
8487
groundShape = new btBoxShape(
8588
btVector3(btScalar(5.0), btScalar(5.0), btScalar(5.0)));
@@ -113,7 +116,7 @@ int main() {
113116
// Main loop.
114117
std::printf("step body x y z collision a b normal\n");
115118
for (i = 0; i < maxNPoints; ++i) {
116-
dynamicsWorld->stepSimulation(timeStep, 10);
119+
dynamicsWorld->stepSimulation(timeStep);
117120
for (j = dynamicsWorld->getNumCollisionObjects() - 1; j >= 0; --j) {
118121
btCollisionObject *obj = dynamicsWorld->getCollisionObjectArray()[j];
119122
btRigidBody *body = btRigidBody::upcast(obj);
@@ -130,7 +133,20 @@ int main() {
130133
float(origin.getX()),
131134
float(origin.getY()),
132135
float(origin.getZ()));
133-
int numManifolds = dynamicsWorld->getDispatcher()->getNumManifolds();
136+
if (collisions.empty()) {
137+
std::printf("0 ");
138+
} else {
139+
std::printf("1 ");
140+
// Yes, this is getting reprinted for all bodies when collisions happen.
141+
// It's just a quick and dirty way to visualize it, should be outside
142+
// of this loop normally.
143+
for (auto& v : collisions) {
144+
std::printf(
145+
PRINTF_FLOAT " " PRINTF_FLOAT " " PRINTF_FLOAT " ",
146+
v.getX(), v.getY(), v.getZ());
147+
}
148+
}
149+
puts("");
134150
}
135151
}
136152

‎cpp/vector.cpp‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -430,10 +430,11 @@ int main() {
430430
}
431431

432432
// # clear
433+
// Make the vector empty.
433434
{
434435
std::vector<int> v{0, 1, 2};
435436
v.clear();
436-
assert(v.size() == 0);
437+
assert(v.empty());
437438
}
438439

439440
/*

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