Add ability to apply forces and impulses to SoftBody3D

[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

Edit: I think these are a bit outdated

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

Demo project: godot-softbody-apply-force-and-impulse-test.zip

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

Player Controller (Jolt physics):

softbody.controller.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.

[jrouwe]

Latest changes look good to me.

[Calinou]

Tested locally (rebased on top of master c3ae6aa), it works as expected when using GodotPhysics3D. However, when using Jolt Physics, nothing happens when trying to set an impulse (on a single point or all points).

Testing project: test_pr_100463.zip
Press R to apply an upwards impulse on a single point (and all points) at the same time.

[PiCode9560]

when using Jolt Physics, nothing happens when trying to set an impulse (on a single point or all points).

I tested it. It does work, but need a very large force for it to work. Apparently, in jolt physics, the more vertices added, the greater the force needed (for apply impulse and force).

@jrouwe do you think this is an intentional behaviour? The code looks like it work the same as godot physics, but on godot physics the force seems consistent no mater how many vertices there are.

Edit:
@Calinou
Actually, I figured it out, the soft body mass is set to 0 on jolt by default, if you set it to 1 it will work just like godot physics.

[mihe]

Found some very minor cosmetic issues, but looks good to me otherwise.

[Repiteo]

Thanks! Congratulations on your first merged contribution! 🎉