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Fix computation of interaction transform used in PositionProp #141

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Fix computation of interaction transform used in PositionProp #141

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26 changes: 24 additions & 2 deletions VirtualReality/MRML/vtkVirtualRealityViewInteractorStyle.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -281,36 +281,58 @@ void vtkVirtualRealityViewInteractorStyle::PositionProp(vtkEventData* ed, double
return;
}

// Get positions and orientations
vtkRenderWindowInteractor3D* rwi = static_cast<vtkRenderWindowInteractor3D*>(this->Interactor);

// Retrieve the last and current event positions in world coordinates
double worldPos[3] = {0.0};
edd->GetWorldPosition(worldPos);
double* lastWorldPos = rwi->GetLastWorldEventPosition(rwi->GetPointerIndex());

// Retrieve the last and current event orientations as angle-axis representation
double* worldOrientation = rwi->GetWorldEventOrientation(rwi->GetPointerIndex());
double* lastWorldOrientation = rwi->GetLastWorldEventOrientation(rwi->GetPointerIndex());

// Calculate transform
// Calculate the interaction transform
vtkNew<vtkTransform> interactionTransform;
interactionTransform->PreMultiply();

// Calculate the translation vector
double translation[3] = {0.0};
for (int i = 0; i < 3; i++)
{
translation[i] = worldPos[i] - lastWorldPos[i];
}

// Convert from angle-axis to quaternion for the last and current orientations
vtkQuaternion<double> q1;
q1.SetRotationAngleAndAxis(vtkMath::RadiansFromDegrees(
lastWorldOrientation[0]), lastWorldOrientation[1], lastWorldOrientation[2], lastWorldOrientation[3]);
vtkQuaternion<double> q2;
q2.SetRotationAngleAndAxis(vtkMath::RadiansFromDegrees(
worldOrientation[0]), worldOrientation[1], worldOrientation[2], worldOrientation[3]);

// Calculate the relative quaternion rotation between the last and
// current orientations (q2 * q1')
q1.Conjugate();
q2 = q2*q1;

// Convert from quaternion to angle-axis representation
double axis[4] = {0.0};
axis[0] = vtkMath::DegreesFromRadians(q2.GetRotationAngleAndAxis(axis+1));

// Apply the calculated relative orientation and translation vector to the
// interaction transform

// Step 1: Translate to the current world position
interactionTransform->Translate(worldPos[0], worldPos[1], worldPos[2]);

// Step 2: Apply relative rotation
interactionTransform->RotateWXYZ(axis[0], axis[1], axis[2], axis[3]);

// Step 3: Translate back to the origin
interactionTransform->Translate(-worldPos[0], -worldPos[1], -worldPos[2]);

// Step 4: Final translation based on the computed translation vector
interactionTransform->Translate(translation[0], translation[1], translation[2]);

// Make sure that the topmost parent transform is the VR interaction transform
Expand Down