Table of Contents

1. Introduction
2. Features
3. Performance
4. Conclusion

1. Introduction

This post will focus on comparing each physics engine as a Physics Server in Godot, so they both have to implement the same API. When refering if a physics engine has a feature or not, I will refer to the Godot Asset that implements that physics engine (eg. Godot Box2D and Godot Rapier2D).

1.1 Godot Physics 2D (4.2)

The Godot Engine is a free, all-in-one, cross-platform game engine that makes it easy for you to create 2D and 3D games. So it’s no surprise it also has a physics engine that works great for most use cases.

1.2 Box2D (2.4.1)

Box2D is a free 2D open source physics engine for games and published under MIT license. It is written by Erin Catto and is one of the oldest (more than 15 years) and most stable 2d physics library out there.

1.3 Rapier2D (0.17.2)

Rapier is set of 2D and 3D physics engines focused on performance. They are written with the Rust programming language, by the Dimforge organization. It is forever free and open-source! It is a relatively new contender, with only about 3 years since it was created.

2. Features

As it’s expected, Godot Physics 2D has most of the node features, as it is the one defining the API for the other two.

Godot Feature	Dynamics features	Godot Physics 2D	Box2D	Rapier2D
DampedSpringJoint2D	A spring joint	✅	✅	❌
SIMD	Single instruction, multiple data	❌	❌	✅
Cross-platform determinism	The simulation would run the same on any platform	❌	❌	✅
64-bits physics	Large game worlds support	✅	❌	✅
Parallelization Support	Enables parallelism of the physics pipeline	✅	❌	✅

✅ - Implemented ❌ - Missing

1st	2nd	3rd
Rapier2D	Godot Physics 2D	Box2D

3. Performance

The project used is the appsinacup/benchmark. The steps for changing the physics backend is done by using the options menu from Godot. The default values from plugins are used.

3.1 Falling Circles

In this benchmark, we keep adding falling circles until the fps drops or stability is affected.

1st	2nd	3rd
Rapier2D	Godot Physics 2D	Box2D

3.2 Falling Boxes

In this benchmark, we keep adding falling boxes until the fps drops or stability is affected.

1st	2nd	3rd
Rapier2D	Godot Physics 2D	Box2D

3.3 Pyramid of Boxes

In this benchmark, we keep increasing the height of the pyramid until it is unstable.

Parameter	Godot Physics 2D	Box2D	Rapier2D
Max Height	10	40	20
Number of Rectangles	110	1640	420

1st	2nd	3rd
Box2D	Rapier2D	Godot Physics 2D

3.4 Fabric of Pin Joints

In this benchmark, we keep increasing the width and size of the fabric until we get instability.

Parameter	Godot Physics 2D	Box2D	Rapier2D
Max Size	10	60	30
Number of Rectangles	100	3600	900
Number of Pin Joints	172	7022	1722

1st	2nd	3rd
Box2D	Rapier2D	Godot Physics 2D

3.5 Fabric of Spring Joints

In this benchmark, we keep increasing the width and size of the fabric until we get instability.

Parameter	Godot Physics 2D	Box2D	Rapier2D
Max Size	10	30	-
Number of Rectangles	100	90	-
Number of Pin Joints	172	1712	-

1st	2nd	3rd
Box2D	Godot Physics 2D	Rapier2D

3.6 Stack of Boxes

In this benchmark, we keep increasing the height of the pyramid until it is unstable.

Parameter	Godot Physics 2D	Box2D	Rapier2D
Max Height	10	25	10

1st	2nd	2nd
Box2D	Rapier2D	Godot Physics 2D

4. Conclusion

4.1 Godot Physics 2D (4.2)

Performance	SIMD	Cross Platform Determinism	Stackability	Joint Stability
Performs ok for small amount of objects.	No	No	Last Place	Last Place

Notes:

• in reality after a certain amount of objects, it starts to jitter a lot, making it completely unusable (eg. objects pass through things and other bad things).

4.2 Box2D (2.4.1)

Performance	SIMD	Cross Platform Determinism	Stackability	Joint Stability
A little slower than godot.	No	No	Best	Best

4.3 Rapier (0.17.2)

Performance	SIMD	Cross Platform Determinism	Stackability	Joint Stability
Best, about 2x,3x faster than competition	Yes	Yes	Better than Godot, but not best	Better than Godot, but not best

Note:

• Missing spring joint.
• The stackability might be improved when warmstarter is implemented.

---

This article was inspired from the Announcing the Rapier physics engine post.