Godot Physics collisions and solver processed on threads

Use ThreadWorkPool to process physics step tasks in multiple threads. Collisions are all processed in parallel and solving impulses is
processed in parallel for rigid body islands.

Additional changes:
- Proper islands for soft bodies linked to active bodies
- All moving areas are on separate islands (can be parallelized)
- Fix inconsistencies with body islands (Kinematic bodies could link
bodies together or not depending on the processing order)
- Completely prevent static bodies to be active (it could cause islands
to be wrongly created and cause dangerous multi-threading operations as
well as inconsistencies in created islands)
- Apply impulses only on dynamic bodies to avoid unsafe multi-threaded
operations (static bodies can be on multiple islands)
- Removed inverted iterations when populating body islands, it's now
faster in regular order (maybe after fixing inconsistencies)

1 files changed, 10 insertions, 6 deletions

diff --git a/servers/physics_3d/area_pair_3d_sw.h b/servers/physics_3d/area_pair_3d_sw.h
index fbdaa25cbb..596d893082 100644
--- a/servers/physics_3d/area_pair_3d_sw.h
+++ b/servers/physics_3d/area_pair_3d_sw.h
@@ -40,11 +40,13 @@ class AreaPair3DSW : public Constraint3DSW {
 	Area3DSW *area;
 	int body_shape;
 	int area_shape;
-	bool colliding;
+	bool colliding = false;
+	bool process_collision = false;
 
 public:
-	bool setup(real_t p_step);
-	void solve(real_t p_step);
+	virtual bool setup(real_t p_step) override;
+	virtual bool pre_solve(real_t p_step) override;
+	virtual void solve(real_t p_step) override;
 
 	AreaPair3DSW(Body3DSW *p_body, int p_body_shape, Area3DSW *p_area, int p_area_shape);
 	~AreaPair3DSW();
@@ -55,11 +57,13 @@ class Area2Pair3DSW : public Constraint3DSW {
 	Area3DSW *area_b;
 	int shape_a;
 	int shape_b;
-	bool colliding;
+	bool colliding = false;
+	bool process_collision = false;
 
 public:
-	bool setup(real_t p_step);
-	void solve(real_t p_step);
+	virtual bool setup(real_t p_step) override;
+	virtual bool pre_solve(real_t p_step) override;
+	virtual void solve(real_t p_step) override;
 
 	Area2Pair3DSW(Area3DSW *p_area_a, int p_shape_a, Area3DSW *p_area_b, int p_shape_b);
 	~Area2Pair3DSW();