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[3.2] Fixes division by zero when 3d body does not have valid shape #46809

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Mar 9, 2021
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[3.2] Fixes division by zero when 3d body does not have valid shape #46809

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20 changes: 14 additions & 6 deletions servers/physics/body_sw.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -53,44 +53,47 @@ void BodySW::_update_transform_dependant() {

void BodySW::update_inertias() {

//update shapes and motions
// Update shapes and motions.

switch (mode) {

case PhysicsServer::BODY_MODE_RIGID: {

//update tensor for all shapes, not the best way but should be somehow OK. (inspired from bullet)
// Update tensor for all shapes, not the best way but should be somehow OK. (inspired from bullet)
real_t total_area = 0;

for (int i = 0; i < get_shape_count(); i++) {

total_area += get_shape_area(i);
}

// We have to recompute the center of mass
// We have to recompute the center of mass.
center_of_mass_local.zero();

for (int i = 0; i < get_shape_count(); i++) {
real_t area = get_shape_area(i);

real_t mass = area * this->mass / total_area;

// NOTE: we assume that the shape origin is also its center of mass
// NOTE: we assume that the shape origin is also its center of mass.
center_of_mass_local += mass * get_shape_transform(i).origin;
}

center_of_mass_local /= mass;

// Recompute the inertia tensor
// Recompute the inertia tensor.
Basis inertia_tensor;
inertia_tensor.set_zero();
bool inertia_set = false;

for (int i = 0; i < get_shape_count(); i++) {

if (is_shape_disabled(i)) {
continue;
}

inertia_set = true;

const ShapeSW *shape = get_shape(i);

real_t area = get_shape_area(i);
Expand All @@ -108,7 +111,12 @@ void BodySW::update_inertias() {
inertia_tensor += shape_inertia_tensor + (Basis() * shape_origin.dot(shape_origin) - shape_origin.outer(shape_origin)) * mass;
}

// Compute the principal axes of inertia
// Set the inertia to a valid value when there are no valid shapes.
if (!inertia_set) {
inertia_tensor.set_diagonal(Vector3(1.0, 1.0, 1.0));
}

// Compute the principal axes of inertia.
principal_inertia_axes_local = inertia_tensor.diagonalize().transposed();
_inv_inertia = inertia_tensor.get_main_diagonal().inverse();

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