Fix StaticBody2D not triggering collisions when waking up

[xuhuisheng]

• Fixes: Toggling body collision layer/mask will not update overlapping areas #111823

Issue Description

Because StaticBody2D cannot be set active and cannot be add to active_list. So the StaticBody2D wont trigger actively collision itself.

godot/modules/godot_physics_2d/godot_body_2d.h

Lines 287 to 292 in f50d7fa

	_FORCE_INLINE_ void wakeup() {
	if ((!get_space()) || mode == PhysicsServer2D::BODY_MODE_STATIC || mode == PhysicsServer2D::BODY_MODE_KINEMATIC) {
	return;
	}
	set_active(true);
	}

godot/modules/godot_physics_2d/godot_body_2d.cpp

Lines 140 to 146 in f50d7fa

	if (active) {
	if (mode == PhysicsServer2D::BODY_MODE_STATIC) {
	// Static bodies can't be active.
	active = false;
	} else if (get_space()) {
	get_space()->body_add_to_active_list(&active_list);
	}

Please notice this PR is just a demo to fix relevant issue. I am not sure it is the correct solution. Maybe current behavior is expected.

Explaination

In PhysicsServer2D, it decides which body need be detected collision depends on get_active_body_list() and get_moved_area_list().

godot/modules/godot_physics_2d/godot_step_2d.cpp

Line 139 in 9cd297b

const SelfList<GodotBody2D>::List *body_list = &p_space->get_active_body_list();

godot/modules/godot_physics_2d/godot_step_2d.cpp

Line 170 in 9cd297b

const SelfList<GodotArea2D>::List &aml = p_space->get_moved_area_list();

If there is no active_list or moved_area, the collision detection wont execute.

When we changed layer or mask, it invoke parent class GodotCollisionBody2D. It is the parent class of GodotBody2D and GodotArea2D. Then GodotArea2D added itself to moved_area_list, so next iteration will detect collision. But GodotBody2D wont add static body to active_list, so it can only wait other body to trigger collision detection.

It looks like StaticBody2D wont participate with integrate_force or integrate_velocity, maybe only add it to active_list is safe. But still need test for confirming.

[AThousandShips]

Does this actually fix the case when changing the layers only? This seems to fix just waking up the body

[xuhuisheng]

@AThousandShips

As in description, current physics engine does not support active StaticBody2D. So we cannot add StaticBody2D to active_body_list, so only update StaticBody2D layer or mask won't trigger collision. That is the reason.

The straight way to fix this issue is allow StaticBody2D to be set active and added to active_body_list, then it can trigger collision by itself.

If we dont want fixing issue this way, maybe we need add additional logic for StaticBody2D.

[AThousandShips]

No what I'm asking is:
Does this fix the problem where changing the collision layers and mask doesn't trigger these signals, does changing the layers wake bodies up regardless if they are sleeping or not? The bug report has nothing to do with changing active

[xuhuisheng]

@AThousandShips

I can get your point, I will test for only triggering adding active_list without set active.

[AThousandShips]

The test project from the issue should confirm if this solves it!

[xuhuisheng]

@AThousandShips

I tested only add StaticBody2D toactive_list, without active = true. It can still solve the issue. I think it is better.

wakeup.webm