Check for motion in cast_motion() before doing Bullet convexSweepTest().

[madmiraal]

Addresses: #34210 (comment)

Also ensures that default closest_safe and closest_unsafe values are
defined both in cast_motion() and before cast_motion() is called in camera.cpp and physics_server.cpp.

Note: The other use of cast_motion() (in spring_arm.cpp) defines default values for the variables used for closest_safe and closest_unsafe:

godot/scene/3d/spring_arm.cpp

Lines 141 to 142 in 2ebc783

	real_t motion_delta(1);
	real_t motion_delta_unsafe(1);

before calling cast_motion():

godot/scene/3d/spring_arm.cpp

Line 158 in 2ebc783

get_world()->get_direct_space_state()->cast_motion(shape->get_rid(), get_global_transform(), motion, 0, motion_delta, motion_delta_unsafe, excluded_objects, mask);

[akien-mga]

Ping @AndreaCatania

[akien-mga]

Does cast_motion in servers/physics/space_sw.cpp also need changes? (Beyond fixing its wrongly prefixed p_closest_safe and p_closest_unsafe which should start with r_ instead.)

[madmiraal]

Does cast_motion in servers/physics/space_sw.cpp also need changes?

The short answer is yes, and it should be the same as whatever we decided here.

The long answer is that the problem lies with the gjk_epa_calculate_distance() function, which discards the sResults::Penetrating status set by the GjkEpa2::Distance() function, when it returns false:

godot/servers/physics/gjk_epa.cpp

Lines 843 to 846 in 1c6d1fc

	results.status = gjk_status==GJK::eStatus::Inside?
	sResults::Penetrating :
	sResults::GJK_Failed ;
	return(false);

godot/servers/physics/gjk_epa.cpp

Lines 917 to 929 in 1c6d1fc

	bool gjk_epa_calculate_distance(const ShapeSW *p_shape_A, const Transform &p_transform_A, const ShapeSW *p_shape_B, const Transform &p_transform_B, Vector3 &r_result_A, Vector3 &r_result_B) {
	GjkEpa2::sResults res;
	if (GjkEpa2::Distance(p_shape_A, p_transform_A, p_shape_B, p_transform_B, p_transform_B.origin - p_transform_A.origin, res)) {
	r_result_A = res.witnesses[0];
	r_result_B = res.witnesses[1];
	return true;
	}
	return false;
	}

Therefore, instead of returning a negative distance or even zero, it sends a signal that it is unable to calculate the distance.

This false cascades back to PhysicsDirectSpaceStateSW::cast_motion(), which in turn returns false without setting values for p_closest_safe and p_closest_unsafe:

godot/servers/physics/space_sw.cpp

Lines 271 to 273 in 1c6d1fc

	if (!CollisionSolverSW::solve_distance(shape, p_xform, col_obj->get_shape(shape_idx), col_obj_xform, point_A, point_B, aabb, &sep_axis)) {
	return false;
	}

[madmiraal]

Rebased following multiple changes to master. Since this is no longer cherry-pickable. I'll create a separate pull request with the original changes against the 3.2 branch.

[AndreaCatania]

Seems ok to be merged, Thanks!!

[akien-mga]

Thanks!