Advanced Animation with DirectX by Jim Adams

Author:Jim Adams [Adams, Jim]
Language: eng
Format: epub, pdf
Published: 2003-11-24T23:00:53+00:00

Setting the Forces

}

if(vecSize−>y < MINIMUM_BONE_SIZE) {

vecSize−>y = MINIMUM_BONE_SIZE;

vecMax.y = MINIMUM_BONE_SIZE*0.5f;

}

if(vecSize−>z < MINIMUM_BONE_SIZE) {

vecSize−>z = MINIMUM_BONE_SIZE;

vecMax.z = MINIMUM_BONE_SIZE*0.5f;

}

// Set the bone's offset to center based on half the size

// of the bounding box and the max position

(*vecJointOffset) = ((*vecSize) * 0.5f) − vecMax;

}

At the very end of the function, you finally encounter the vecJointOffset vector object that I mentioned when you started creating the GetBoundingBoxSize function. Because a rigid body bone can be any size, and you track the bone by its center coordinates, you need to create an extra point that represents the point in the bounding box where the bone connects to its parent. This is the joint offset vector. You'll read more about the joint offset vector when you enforce the bone−to−bone connections.

Now that you've computed the bounding−box size and set the various bones' data, you can set the various forces and resolve the motion of your bones.

Setting the Forces

For any applied forces you want to use (which I'll leave up to you), you must handle gravity and damping. In the cRagdoll class, I defined a function that clears out a single bone's force and torque vectors and then applies gravity and damping forces.

void cRagdoll::SetForces(DWORD BoneNum,

D3DXVECTOR3 *vecGravity,

float LinearDamping,

float AngularDamping)

{

// Get a pointer to the bone for easier handling

cRagdollBone *Bone = &m_Bones[BoneNum];

// Get pointer to the current state for easier handling

cRagdollBoneState *BCState = &Bone−>m_State;

// Set gravity and clear torque

Bone−>m_vecForce = ((*vecGravity) * Bone−>m_Mass);

Bone−>m_vecTorque = D3DXVECTOR3(0.0f, 0.0f, 0.0f);

// Apply damping on force and torque

Bone−>m_vecForce += (BCState−>m_vecLinearVelocity * \

LinearDamping);

Bone−>m_vecTorque += (BCState−>m_vecAngularVelocity * \

AngularDamping);

}

You read about gravity and damping forces earlier in this chapter, so I shouldn't need to explain anything here. You'll notice that I'm scaling the gravity vector by the mass of the bone. Remember that this is necessary so that gravity will pull all objects with the same force when you later scale the forces due to mass.

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