Add SoftBody3D::apply_impulse() and SoftBody3D::apply_force()

[PiCode9560]

Closes godotengine/godot-proposals#1013

The goal of this PR is to add apply_impulse and apply_force to the Softbody node

Adding them to the GodotPhysics and JoltPhysics.

Added functions

Softbody3D:
void apply_central_force(force: Vector3)
void apply_force(force: Vector3, point_index: int)
void apply_central_impulse(impulse: Vector3)
void apply_impulse(impulse: Vector3, point_index: int)

PhysicsServer3D:
void soft_body_apply_central_force(body: RID, force: Vector3)
void soft_body_apply_central_impulse(body: RID, impulse: Vector3)
void soft_body_apply_point_force(body: RID, force: Vector3, point_index: int)
void soft_body_apply_point_impulse(body: RID, impulse: Vector3, point_index: int)

Built-in documentation

Show documentation

PhysicsServer3D

● void soft_body_apply_central_force(body: RID, force: Vector3)

Distributes and applies an force to all vertices. A force is time dependent and meant to be applied every physics update.

● void soft_body_apply_central_impulse(body: RID, impulse: Vector3)

Distributes and applies an impulse to all vertices.

An impulse is time-independent! Applying an impulse every frame would result in a framerate-dependent force. For this reason, it should only be used when simulating one-time impacts (use the "_force" functions otherwise).

● void soft_body_apply_point_force(body: RID, force: Vector3, point_index: int)

Applies a force to a vertex. A force is time dependent and meant to be applied every physics update.

● void soft_body_apply_point_impulse(body: RID, impulse: Vector3, point_index: int)

Applies an impulse to a vertex.

An impulse is time-independent! Applying an impulse every frame would result in a framerate-dependent force. For this reason, it should only be used when simulating one-time impacts (use the "_force" functions otherwise).

SoftBody3D

● void apply_central_force(force: Vector3)

Distributes and applies an force to all vertices. A force is time dependent and meant to be applied every physics update.

● void apply_central_impulse(impulse: Vector3)

Distributes and applies an impulse to all vertices.

An impulse is time-independent! Applying an impulse every frame would result in a framerate-dependent force. For this reason, it should only be used when simulating one-time impacts (use the "_force" functions otherwise).

● void apply_force(force: Vector3, point_index: int)

Applies a force to a vertex. A force is time dependent and meant to be applied every physics update.

● void apply_impulse(impulse: Vector3, point_index: int)

Applies an impulse to a vertex.

An impulse is time-independent! Applying an impulse every frame would result in a framerate-dependent force. For this reason, it should only be used when simulating one-time impacts (use the "_force" functions otherwise).

Demo

These are how the functions compared to rigidbody.

The impulses have a strength of 0.2.
The forces have a strength of 15.

Jolt physics:

Jolt.SoftBody.mp4

Godot physics:

Godot.SoftBody.mp4

Implementation Details

Godot apply_impulse

GodotSoftbody3D already have apply_node_impulse method which apply impulse to a vertex. So I just use that for the softbody.apply_impulse.

Godot apply_force

GodotSoftbody3D have vertex.f which stores the applied forces, and it will handle it somewhere. Therefore, I only need to add a method that add the forces to it.

Jolt apply_impulse

JoltSoftbody3D didn't have a method to apply impulse. So I added JoltSoftBody3D::apply_node_impulse. It works like the GodotSoftBody3D::apply_node_impulse which just add impulse * vertex.inverse_mass to the vertex velocity.

Jolt apply_force

[Outdated]
I notice that the core JoltPhysics didn't have a way to apply force to softbody vertex. Hence, I have to add that functionality into the core of the JoltPhysics engine.

I added vertex.mForce, which store the forces that are going to be applied. Then applies it in the SoftBodyMotionProperties::IntegratePositions and reset the force on SoftBodyMotionProperties::UpdateSoftBodyState.

apply_central_impulse/force

For SoftBody.apply_central_impulse and SoftBody.apply_central_force I added apply_central_impulse and apply_central_force methods to jolt and godot. It works like the apply_node_impulse/force but the impulse/force is divided by the vertex count and applies it to all vertices.

[PiCode9560]

It's fine, right? If I add it to jolt and godotphysics in the same PR.

Edit: I'm just going to do it, I think it's fine.

[PiCode9560]

apply_force added.

The Softbody class didn't have apply_force method, so I have to make it myself. I don't really know how force works. So I just tried stealing it from the GodotBody3D. Also, assuming that the GodotSoftBody3D's node.f handle the forces, this is how the force is done: node.f += p_force;
After testing it, the force looks kind of correct. So... good enough for now!

[PiCode9560]

apply_impulse added to jolt.

Most of the code from the apply_node_impulse is just copied from other methods, So I'm not 100% sure if all the error checking is necessary.

[PiCode9560]

What I made with it so far:

softbody.controller.mp4

[PiCode9560]

Next, I'm working on adding apply_force() to jolt, but I can't figure out how to do that. If there's smart people out there want to give suggestions, you are welcome to.

Edit: Or just, @mihe HELP!

[PiCode9560]

I think I figure it out, from comparing jolt with godot physics' GodotSoftBody3D and GodotBody3D.

What I understand is, Jolt softbody don't have the functionality to apply force. So I think I have to add the functionality to the SoftBodyMotionProperties class.

[PiCode9560]

Added apply_force to jolt, but not sure if it behaves properly.

Also, I just found out that sometimes when running the scene, the softbody just disappear. IDK how that happened.

[PiCode9560]

Added apply_central_force and apply_central_impulse to jolt and godot.

The way it works is just applying the force/impulse to all vertices, but the force/impulse is divided by the vertices count.

[PiCode9560]

These are how the functions compared to rigidbody.

The impulses have a strength of 0.2.
The forces have a strength of 15.

Jolt physics:

softbody.jolt.mp4

Godot physics:

softbody.godot.mp4

[PiCode9560]

It's ready to review!

[jrouwe]

Looks good to me!

One nitpick would be to update all of Jolt to 248253f88a5945c2032ffb397101afb9f88aeca5 or higher. I didn't initially suggest this because I knew there was another PR in progress that was touching the same files. But a full integrate can happen another time too.

[PiCode9560]

I've never done full integration before, because of that, I don't know how to do it. So let's just do full integration another time. :D

[PiCode9560]

Now, can someone else review it, merge it, or whatever to do next.