Box3D how do UserFunction callback after collision ?

[Ronniko]

I created two Hull boxes. Like as in [docs
/hello.md](https://github.com/erincatto/box3d/blob/main/docs/hello.md)
Static ground hull box as World ground size (8000,2,8000)
And dynamic hull box size(2,2,2) this box fall down to groundBox.

I run test and see two boxes collided.
But how set my function callback for collided ?
CallBack set in b3WorldDef or in b3BodyDef ?

Two situations for CallBack ,when dynamic hull box collided with groundBox, and when dynamic hull box stop moving.

b3BodyDef or b3ShapeDef did have bool flags ? When stopping or set static, or hit any body ?

[Ronniko]

I try this but allways get sensorEvents.beginCount = 0

Sensor events are available after every call to b3World_Step(). Sensor events are the best way to get information about sensor overlaps. There are events for when a shape begins to overlap with a sensor.

b3SensorEvents sensorEvents = b3World_GetSensorEvents(myWorldId);
for (int i = 0; i < sensorEvents.beginCount; ++i)
{
b3SensorBeginTouchEvent* beginTouch = sensorEvents.beginEvents + i;
void* myUserData = b3Shape_GetUserData(beginTouch->visitorShapeId);
// process begin event
}

I try b3ContactEvents ContEvnt = b3World_GetContactEvents(myWorldId);
But i get always the same data, even two boxes touched.

I get always ContEvnt.beginCount = 0;
I get always ContEvnt.hitCount = 0;

[Ronniko]

I try this and get events.moveCount = 1 and when boxes touched i get events.moveCount = 0

b3BodyEvents events = b3World_GetBodyEvents(myWorldId);
for (int i = 0; i < events.moveCount; ++i)
{
const b3BodyMoveEvent* event = events.moveEvents + i;
MyGameObject* gameObject = event->userData;
MoveGameObject(gameObject, event->transform);
if (event->fellAsleep)
{
SleepGameObject(gameObject);
}
}

I try method b3World_OverlapShape and get callback myFunction.
I clearly not understood how work OverlapShape.
How i understood if sphere collided any object in world, run UserCallBack.
But I did not understand that the overlapShape. Does the overlapShape move or stay in one place as a static body?

[Ronniko]

I try this but my callback function not calling.

Friction and Restitution Callbacks
Advanced users can override friction and restitution mixing using b3FrictionCallback and b3RestitutionCallback. These should be very lightweight functions because they are called frequently. The callbacks receive the two friction (or restitution) values and the user material ids from each shape's surface material.

float MyFrictionCallback(float frictionA, uint64_t userMaterialIdA,
float frictionB, uint64_t userMaterialIdB)
{
if (userMaterialIdA > userMaterialIdB)
{
return frictionA;
}

return frictionB;

}

b3WorldDef worldDef = b3DefaultWorldDef();
worldDef.frictionCallback = MyFrictionCallback;
worldDef.restitutionCallback = MyFrictionCallback;

[Ronniko]

Not clear understood this.

b3Vec3 queryPoint = {0.0f, 8.0f, 1.0f};
b3ShapeProxy proxy;
proxy.points = &queryPoint;
proxy.count = 1;
proxy.radius = 1.0f;

b3Transform shapeTransform = b3Transform_identity;
bool hit = b3OverlapHull(&myHull, shapeTransform, &proxy);

I try this code for dynamic boxhull. But not get true from b3OverlapHull
My boxhull start from 0,20,0 and fall down to ground.

Proxy point what is this ? Proxy point move or not ?
if i set proxy.radius = 6.1f; i always get hit from b3OverlapHull.

This all very strange.

And i not see in samples example b3OverlapHull.

How i understood b3OverlapHull for b3CreateHull(points, 16, 16);
But not work b3OverlapHull for b3CreateHullShape.

[erincatto]

There are many samples that show how to use events in sample_events.cpp. Look at the PersistentContact sample.

[Ronniko]

Thanks.