Bouyancy?

[Leadwerks]

I am trying to add water physics.

Here I call the NewtonBodyAddBuoyancyForce function in the add body force & torque callback:

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NewtonBodyAddBuoyancyForce( newtonBody,0.1,0.1,0.1,[TWorld.current.gravity.x,TWorld.current.gravity.y,TWorld.current.gravity.z],NewtonGetBuoyancyPlane,Null)

And here is my NewtonGetBuoyancyPlane callback:

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   Function NewtonGetBuoyancyPlane:Int(collisionID:Byte Ptr,context:Byte Ptr,globalSpaceMatrix:Float Ptr,globalSpacePlane:Float Ptr) "c"
      globalSpacePlane[0]=0.0
      globalSpacePlane[1]=1.0
      globalSpacePlane[2]=0.0
      globalSpacePlane[3]=-15.6
      Return 1
   EndFunction

This only slows down bodies when they roll down a beach into the ocean. They are harder to roll, but they won't float. How can I increase the force so they float?

[Leadwerks]

Ah, fluid density, it's all coming back now.

[Leadwerks]

So there is this callback:

NewtonGetBuoyancyPlane:Int(collisionID:Byte Ptr,context:Byte Ptr,globalSpaceMatrix:Float Ptr,globalSpacePlane:Float Ptr)

But my body matrix is not the same as the body's center of mass. What are the collisionID and context parameters? How should I get pass the body to the callback function so I can find the wave height at the body's center?

I am doing 3D waves, so the body center is important for finding the height:
http://www.youtube.com/watch?v=HrUEnT277WQ

[Julio Jerez]

for teh buoyancy demo, you can see that teh funtion pass a trigger volume as a paramete in teh cal lback

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static int ApplyBuoyancyAABBLevel (const NewtonMaterial* material, const NewtonBody* body0, const NewtonBody* body1, int threadIndex)
{
   const NewtonBody* body;
   const NewtonBody* trigger;
   RenderPrimitive* primitive;

   _ASSERTE (NewtonBodyGetUserData(body0));
   _ASSERTE (NewtonBodyGetUserData(body1));

   // get the body with the trigger volume
   if (NewtonCollisionIsTriggerVolume (NewtonBodyGetCollision(body0))) {
      body = body1;
      trigger = body0;
   } else {
      body = body0;
      trigger = body1;
   }

   _ASSERTE (NewtonCollisionIsTriggerVolume (NewtonBodyGetCollision(trigger)));
   _ASSERTE (!NewtonCollisionIsTriggerVolume (NewtonBodyGetCollision(body)));

   dVector gravity (0.0f, -10.0f, 0.0f, 0.0f);

   primitive = (RenderPrimitive*) NewtonBodyGetUserData(body);

//   dFloat density;
//   dFloat mass;
//   dFloat dommy;
//   dFloat volume;
//   NewtonBodyGetMassMatrix(body, &mass, &dommy, &dommy, &dommy);
//   volume = NewtonConvexCollisionCalculateVolume(NewtonBodyGetCollision(body));
//   density = 1.5f * mass / volume;

// leadwerek check here
 // check here trigger is a trigger volume
   NewtonBodyAddBuoyancyForce (body, primitive->m_density, 0.8f, 0.8f, &gravity[0], PhysicsBouyancyPlane, (void*) trigger);
   return 1;
}

then in the callback I use a ray cast a vertical on the trigger volume using the center o fteh object which is opass to teh call back in the matrix parameter

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static int PhysicsBouyancyPlane (const int collisionID, void *context, const dFloat* matrix, dFloat* globalSpacePlane)
{
   const NewtonBody* trigger;
   const dMatrix& globalSpaceMatrix =  *(dMatrix*)matrix;

   trigger = (const NewtonBody*) context;

   // find the fluid surface by casting a ray on the trigger volume in the direction of teh gravity

   dVector p0 (globalSpaceMatrix.m_posit);
   dVector p1 (globalSpaceMatrix.m_posit);

   p0.m_y += 100.0f;
   p1.m_y -= 100.0f;

   // get the matrix of the trigger volume
   dMatrix volumeMatrix;
   NewtonBodyGetMatrix(trigger, &volumeMatrix[0][0]);

   // transform the ray to the local space of the trigger volume
   dVector q0 (volumeMatrix.UntransformVector(p0));
   dVector q1 (volumeMatrix.UntransformVector(p1));

   // cast the ray of the collision shape of the trigger volume
   int attribute;
   dFloat param;
   dVector normal;
   param = NewtonCollisionRayCast (NewtonBodyGetCollision(trigger), &q0[0], &q1[0], &normal[0], &attribute);

   _ASSERTE (param >= 0.0f);
   _ASSERTE (param <= 1.0f);

   // now rotate the ray normal  and the intersection point to global space
   normal = volumeMatrix.RotateVector(normal);
   dVector point (p0 + (p1 - p0).Scale(param));

   // return the plane equation
   globalSpacePlane[0] = normal.m_x;
   globalSpacePlane[1] = normal.m_y;
   globalSpacePlane[2] = normal.m_z;
   globalSpacePlane[3] = -(normal % point);
   return 1;   
}

what I wou do in your case in to pass teh pointer to teh water object ih nth conxtext, the shot the ray oin teh water surface.
to alliviate the problem of hitter vecaus you ciode will use a chngae susrafe to calcula teh plane, you can use a trick of sampel a few point aroun the surace of the water and average them
for example you can use the ray at the center at 100% plus a ray in te front, back, left an dright at 25% each then avarage themn together to get the surface normal.

[Leadwerks]

So the context parameter is just an extra parameter for custom user data?

[Julio Jerez]

yes.
you can encude a pointe to you water object there.

[Leadwerks]

Thanks, it works.

[VeT]

okay... so i'm trying

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void onBuoforceandtorque(NewtonBody* body)
{
   float mass, ixx, iyy, izz;
   NewtonBodyGetMassMatrix(body, &mass, &ixx, &iyy, &izz);
   NewtonBodySetForce(body, vectorf(0, 0, -9.8 * mass));
   
   float grav[3];
   grav[0]=0.0;
   grav[1]=0.0;
   grav[2]=100.0;
   
   NewtonBodyAddBuoyancyForce (body, floatv(10), floatv(0.8), floatv(0.8), &grav[0], NULL, NULL);
}

action box_newt()
{
   wait(3);
   newton_addentity(me, 75, NEWTON_BOX, onBuoforceandtorque);
}


but seems to be that buoyancy force dont added

[VeT]

i tried that in entity's callback and in material's calback, no results... i missed something, but what?....

[VeT]

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int ApplyBuoyancyAABBLevel (NewtonMaterial* mat, NewtonBody* body0, NewtonBody* body1, int threadIndex)
{
   NewtonBody* body;
   NewtonBody* trigger;
   
   if (NewtonCollisionIsTriggerVolume (NewtonBodyGetCollision(body0))) {
      body = body1;
      trigger = body0;
   } else {
      body = body0;
      trigger = body1;
   }
   
   float grav[4]= {0,-10,0,0};
   
   NewtonBodyAddBuoyancyForce (body, 0.1, 0.8, 0.8, &grav[0], NULL, (void*) trigger); // PhysicsBouyancyPlane
   return 1;
}

action box_23_newt()
{
   wait(3);
   newton_addentity(me, 75, NEWTON_BOX, onforceandtorque);
}


action newt_water()
{
   wait(3);
   set(my,TRANSLUCENT);   
   
   static int waterID = NewtonMaterialCreateGroupID (nworld);   
            NewtonMaterialSetCollisionCallback(nworld, waterID, defaultID, NULL, ApplyBuoyancyAABBLevel, NULL );


   NewtonBody * temp_body = newton_addentity(me, 0, NEWTON_BOX, onBuoforceandtorque);
   NewtonBodySetMaterialGroupID(temp_body, waterID);
   
   NewtonCollision* collision = NewtonBodyGetCollision(temp_body);
   NewtonCollisionSetAsTriggerVolume(collision, 1);
}


Julio, what i do wrong? i wrap every string from your original code to lite-c, where problem could be?

[Julio Jerez]

have you checked the Bouyancy demo in the SDK?

[VeT]

of course, i wrap every string to lite-c, exept "PhysicsBouyancyPlane", but as said in wiki, if NULL, then

When the parameter buoyancyPlane is set to NULL, the body is considered to completely immersed in the fluid.

[Julio Jerez]

you can see i fteh Buoyancy force was added by calling GetForce after the call to apply bouyancy force.

[VeT]

good idea, i'd try

[coimbra79]

hi boiz!!
I'm using this discussion insteand create a new with same content
as u i'm adding performant NGD buoyancy into my 3dEngine (coiAxis*), but result = 0

what is bat into my vb6 code?
here are a semplification

__________________________________________________________________
dim collision as long
dim NewBody as long
'creating a new body
collision=NewtonCreateBox(newtonWorld, 1, 1, 1, 0)
NewBody=NewtonCreateBody(newtonWorld, collision)
NewtonReleaseCollision newtonWorld, collision
NewtonBodySetMassMatrix NewBody,Massa,Inerzia(0),Inerzia(1),Inerzia(2)
NewtonBodySetForceAndTorqueCallback NewBody, AddressOf ForceAndTorqueCallback

'gravity vector
Gravity4.(1) = 0
Gravity4.(1) = -10
Gravity4.(1) = 0
Gravity4.(1) = 0

'plave equation
PianoEQ4.(0) = 0
PianoEQ4.(1) = 1
PianoEQ4.(2) = 0
PianoEQ4.(3) = -2

NewtonBodyAddBuoyancyForce NewBody, 0.8, 0.8, 0.8, Gravity4(0), PianoEQ4(0), vbNull
__________________________________________________________________

it happen nothing!