In this article, we will analyze the causes of physics inconsistencies in Godot, explore debugging techniques, and provide best practices to ensure frame-rate-independent physics behavior.

Understanding Frame-Rate-Dependent Physics in Godot

Godot’s physics engine updates at a fixed time step, but certain factors can still cause frame-dependent behavior. Common causes include:

• Updating physics logic inside _process() instead of _physics_process().
• Relying on frame time (delta) for physics calculations.
• Incorrect collision detection settings for fast-moving objects.
• Variability in Engine.iterations_per_second affecting simulation accuracy.

Common Symptoms

• Objects moving faster on high frame rates and slower on low frame rates.
• Collisions not registering correctly at different frame rates.
• Jittery movement, especially when changing frame rates dynamically.
• Physics behavior differing between fast and slow devices.

Diagnosing Physics Frame-Rate Issues

1. Checking Frame Rate Stability

Monitor FPS fluctuations using:

print("FPS:", Engine.get_frames_per_second())

2. Verifying Physics Process Execution

Ensure physics logic runs in _physics_process():

func _physics_process(delta):
    velocity.y += gravity * delta
    move_and_slide()

3. Inspecting Engine Physics Iterations

Check physics accuracy settings:

print("Physics FPS:", Engine.iterations_per_second)

4. Debugging Fast-Moving Object Collisions

Ensure continuous collision detection (CCD) is enabled:

$RigidBody2D.contact_monitor = true
$RigidBody2D.max_contacts_reported = 5

5. Testing Physics Consistency Across Devices

Run the game at different frame rates to compare behavior:

Engine.target_fps = 30  # Lower the FPS and observe

Fixing Physics Inconsistencies in Godot

Solution 1: Using _physics_process() for Physics Updates

Ensure all physics calculations are handled in _physics_process() instead of _process():

func _physics_process(delta):
    velocity += gravity * delta
    move_and_slide()

Solution 2: Avoiding Direct Frame-Dependent Calculations

Do not multiply by delta when working with physics forces:

apply_impulse(Vector2(0, -500))

Solution 3: Enabling Continuous Collision Detection

Prevent fast objects from tunneling through collisions:

$RigidBody2D.continuous_cd = true

Solution 4: Increasing Physics Iteration Rate

Improve simulation accuracy for smoother physics:

Engine.iterations_per_second = 120

Solution 5: Normalizing Movement Across Frame Rates

Use a fixed time step for manually controlled physics calculations:

var time_step = 1.0 / 60.0  # Fixed step size
velocity.y += gravity * time_step

Best Practices for Frame-Rate-Independent Physics

• Use _physics_process() instead of _process() for physics logic.
• Avoid multiplying forces by delta unless using custom time steps.
• Enable continuous collision detection for fast-moving objects.
• Increase Engine.iterations_per_second for improved accuracy.
• Test physics behavior at both high and low frame rates.

Conclusion

Frame-rate-dependent physics behavior in Godot can lead to inconsistent gameplay across different devices. By handling physics logic correctly, enabling continuous collision detection, and ensuring frame-rate independence, developers can create a stable and predictable physics simulation.

FAQ

1. Why does my object move faster at higher frame rates?

Physics calculations might be happening inside _process() instead of _physics_process(), making them frame-dependent.

2. How do I prevent physics jitter in Godot?

Increase Engine.iterations_per_second and enable continuous collision detection.

3. Can I use delta for physics calculations?

Only for manually controlled physics, but avoid it for forces applied to RigidBody2D objects.

4. How do I make physics consistent across devices?

Ensure physics runs inside _physics_process() and test with different frame rates.

5. What is the best way to debug physics issues in Godot?

Use the Physics Profiler, enable collision debugging, and check Engine.iterations_per_second for accuracy.