Godot: Add simulated bool flag for physic bodies

[Alexia-AT-Digitecnology]

Issue description:
I made a closed game in Godot, an asteroids clone. And I have problem with instancing asteroids (because they are rigidbodies) and it makes lot of comsumption because the 2d physics engine in Godot. For avoiding the lot of instancing time I made a SceneResourcePooler who gets resources by demaning, and it has a constant size of elements. This pooler at initialization creates the instance of the asteroid's scene (using .instance()) and adds to the parent node (using .add_child). This removes the initial loading time of the asteroids (_init(), ready(), etc). When an asteroid is needed we call a method of the pooler to get a unused asteroid. Remember, all asteroids are childs of the parent node in the scene, so if we made a pool of 30 asteroids, there will be 30 asteroids allocated in the scene. Those asteroids that will not be used has collisionshaped disabled ans sprites too. But I cannot "disable" the rigidbody. I saw in the Unity's documentation a property of RigidBody2d called "simulated" that enables/disables the rigidbody.

I think Godot needs this feature: https://docs.unity3d.com/ScriptReference/Rigidbody2D-simulated.html

Can be the feature made for Godot v3.0 or I need to fork the engine and add this property?

What do you think about this property?

[akien-mga]

Can't you just remove unused asteroids from the scene (remove_child) and add them back (add_child) when needed?

[Alexia-AT-Digitecnology]

@akien-mga, it generates overhead (0,2s per each asteroid), because they are complex entities. That's why I need this "simulated" parameter. The root of the asteroid tree is a RigidBody2D.

[nhydock]

Since rigidtbodies are a type of node, and they don't really have a renderable shape to them, is it possible to just ignore collision if the body's node is set to not visible in the tree?

[Alexia-AT-Digitecnology]

@nhydock, I change RigidBody mode to MODE_STATIC, but it is not ignored by the physics system, and I deactivate collision nodes too. It keeps lagging a lot because it's not ignored by the physics system.

[Alexia-AT-Digitecnology]

@AndreaCatania, @akien-mga, is simple to add this property? I saw that in body_2d_sw.h there is a method called set_active(bool) that adds to a list in space_2d_sw.h of "active" elements.

[AndreaCatania]

This property is not required since is easy avoid collisions.

These are tree possible soluzions (the second solution is the one that you should use)

1. Remove it from the scene (Could be fine)
2. Set Layer and Mask to 0 (Recommended way)
3. add collision exceptions (Don't to that)

[Alexia-AT-Digitecnology]

@AndreaCatania, I applied the second option, and stills lagging (the object is still used by the physics system). It will not collide because I disabled the collider and mask and layer is set to 0. If you need access to the source code I can give it to you by a private way to see and test it.

[AndreaCatania]

I don't know what do you mean with "It will not collide because I disabled the collider"; however (without going deeper) by setting Layer and Mask to 0 is like if you have completelly remove it from the physics scene.

I don't know exactly what's causing the problem, but probably it is elsewhere. Try to debug it in order to find the exact problem origin.

[Alexia-AT-Digitecnology]

@AndreaCatania, I see the profiler and it says the main problem is the physics system. The object set with mask and layer 0 is not completely removed from physics system, is still processing internally and generates lot of lag.

[Alexia-AT-Digitecnology]

If you generate for example 4000 rigid bodies and set the collision mask and layer to 0, it will keep processing into physics system, generating lot of lag.

[groud]

I honestly don't think the physics engine would lag with only 30 entities... Can you copy-paste the code you use in the physics_process (the new fixed_process) ?

[AndreaCatania]

@groud exactly.
@Alexia-AT-Digitecnology share a sample project would be useful for debug

[AndreaCatania]

If you generate for example 4000 rigid bodies and set the collision mask and layer to 0, it will keep processing into physics system, generating lot of lag.

Are these object moving? Another thing that you can do is set it as sleeping or static.

[Alexia-AT-Digitecnology]

I will free the code of the game. I think it's the only way to fix this.

Code: https://gitlab.com/Rockroids/RockroidsGame

Please, clone the project and see the lag. In Asteroid.gd line 178, change from MODE_STATIC to MODE_RIGID and you will see the master lag.

@AndreaCatania, @groud, @akien-mga : Please, test it.

[groud]

You're setting the position in the _process function ! Movement shouldn't be done there.
Also you'd better use kinematic body instead, if you don't need realistic physics.

[Zireael07]

@Alexia-AT-Digitecnology: hint hint, gitlab offers free private repos. So if you later on want the code to be closed, just switch it to private :)

[Alexia-AT-Digitecnology]

@Zireael07, It was private, I freed to public for your testing.

[AndreaCatania]

@Alexia-AT-Digitecnology I didn't test your code, but from @groud comment I think I understand what's going on.

So if you have some code inside the _process function of asteroids that is used to move it you MUST muve it inside the _integrate_forcesfunction.

This is because this function is called only when the RigidBody is not sleping. This means this code is not executed when you "hide" the asteroid.

In order to fully stoop the asteroid you should set layer and mask to 0 and set as sleeping.

I understand that this is not userfriendly so I will add the "active physics" parameter in order that I do these things in backend.

Side note: if you are using _process you have to use set_process(false) when your asteroid is "hidden" in order to avoid useless code.

[Alexia-AT-Digitecnology]

@AndreaCatania, the asteroid when it is not used is in sleeping mode, layer and mask 0, sprite disabled, and colliders disabled and set_process(false). Please, test the game.

[DmitriySalnikov]

@Alexia-AT-Digitecnology a lot of errors when colliding bullets and asteroids

but delays happen at other times

[Alexia-AT-Digitecnology]

@DmitriySalnikov, solved this error log, commited to master.

[DmitriySalnikov]

maybe there's another way?
for example load only one shape is needed at startup?

[Alexia-AT-Digitecnology]

@DmitriySalnikov, this is needed because there are types and subtypes of asteroids, each sprite inside animatedsprite has it's own collision.

[Alexia-AT-Digitecnology]

I made a project for testing Rigid Bodies: https://gitlab.com/Rockroids/Tests/RigidBenchmarkOMatic

The fps are lowered when the objects are not being used too. Just move the "Player" with the arrow keys.

You can configure STEP and MAX_ELEMENTS in Main.gd to test more/less asteroids on screen.

[Alexia-AT-Digitecnology]

@DmitriySalnikov, about the Asteroid collisions, I added the same number in the RigidBenchmarkOMatic app and frames dropped to 1 fps when I add asteroids. So this is one of the problems.

[Alexia-AT-Digitecnology]

Another thing that significantly reduces frames are the Particles2d nodes. I added in the benchmark app and the fps drops from 800 to 50 when 0 asteroids are used.

[Alexia-AT-Digitecnology]

I uploaded to master of RigidBenchmarkOMatic, a complex asteroid type, with multiple collisions (only one enabled) and Particles2D, and when you create the pool of asteroids it freezes some seconds, and drops the fps from 500 to 50. If you create 10 asteroids drops to 1-5 fps and the game crashes.

@AndreaCatania, does Godot uses all the colliders children of a RidigBody2d even though they are deactivated?

[AndreaCatania]

I tested this:

I made a project for testing Rigid Bodies: https://gitlab.com/Rockroids/Tests/RigidBenchmarkOMatic

And I found some problems.

I changed the pool size from 100 to 1000 and when I start it, the game starts lagging.

So I moved all code from _process to _integrate_forces and also I changed this set_mode(RigidBody2D.MODE_RIGID) to set_mode(RigidBody2D.MODE_STATIC).

For some reason with MODE_RIGID and sleep = true the physics is still running, but by using MODE_STATIC I'm able to stop body physics process.

In my test I was able to execute 400 asteroids with a pool of 1000 at 50FPS (more or less).

Also the pool is a good idea, but the iddle elements should be out of world.

However you have to optimize your code in order to fix this problem.

RigidBenchmark.zip

[AndreaCatania]

@AndreaCatania, does Godot uses all the colliders children of a RidigBody2d even though they are deactivated?

They are deactivated, so I don't think so.

[Alexia-AT-Digitecnology]

@AndreaCatania, I have added your changes into Benchmark App, please clone again to keep it updated. The main problem is if I create an asteroid with aprox. 9 CollisionPolygon2d (8 disabled 1 enabled) the physics engine keeps traking all (the disabled too) and there is lot of lag. Please, look at the new model of Asteroid I made (Scene Asteroid.tscn) and see the changes. I added in the pooler the ability to add to tree only the needed resources (Asteroids), so try and see the notorious change of frames using it or not. If you add only 10 asteroid the app crashes!!! (OMG)

With RIGID_MODE_STATIC, and sleep true, the physics system keeps tracking the RigidBody too (look at Rockroids game, and shoot with the ship at position (0,0) of the screen, you will see a serious lag. Please clone again to keep it updated. I'm working continuosly on it and working harder.

[Alexia-AT-Digitecnology]

@AndreaCatania, have you tested the new Benchmark app? @akien-mga, please test it too, I think there is a bug managing multiple collision shapes on a body.

[AndreaCatania]

As I said I tested it with 400 asteroid and a pool of 1000 and it was running at 50FPS after my modifications.

However the physics 2D engine doesn't put body in sleeping when you set it throught API and this is a bug.

[AndreaCatania]

To prove this:

I think there is a bug managing multiple collision shapes on a body.

You should create a sample project with a lot of Rigid body with multiple shapes and check how many bodies can Godot handle in your PC.

In this case if the number of bodies in the world is not acceptable we can investigate on how to improve it.

But debug your project in order to understand if it is an engine problem or if it's your game problem is not possible

[Alexia-AT-Digitecnology]

@AndreaCatania, the last version of Benchmark app does have complex asteroids with multiple shapes (all inactive minus one). And it crashes. Please, test it. It's an engine problem. The shapes inactive are still being processed by the physics system.

RigidBenchmarkOMatic.zip

[Alexia-AT-Digitecnology]

@AndreaCatania, @akien-mga. I'm going to create 2 issues found in this thread.

[akien-mga]

We have now entered release freeze for Godot 3.0 and want to focus only on release critical issues for that milestone. Therefore, we're moving this issue to the 3.1 milestone, though a fix may be made available for a 3.0.x maintenance release after it has been tested in the master branch during 3.1 development. If you consider that this issue is critical enough to warrant blocking the 3.0 release until fixed, please comment so that we can assess it more in-depth.

[akien-mga]

What's the status on this issue? There was a lot of discussion and the initial proposal has been dismissed, so maybe it should be closed, and if some of the points raised are still valid, they should be forked into a new thread?

[akien-mga]

No answer, so I'll assume it can be closed. If the later findings should lead to open new, more focused issues, please do so :)