Stair-Stepping Character Example for Godot in C#

StairsCharacter.cs

using Godot;

// Use this class as a base for a character controller in Godot to enable stair-stepping
// 
// In your character code, simply call StairStepUp() just before MoveAndSlide(),
// and then StairStepDown() afterward.
//
// Make sure your character collider margins are set as low as possible.
// Inspired by and partially based on https://github.com/JheKWall/Godot-Stair-Step-Demo
public partial class StairsCharacter : CharacterBody3D
{
	[ExportCategory("Stair Stepping")]
	[Export] private float _stepHeight = 0.33f;

	private float _colliderMargin;
	private RayCast3D _collisionRay;

	public bool Grounded;
	private readonly Vector3 _horizontal = new Vector3(1, 0, 1);

	protected Vector3 DesiredVelocity = Vector3.Zero;
	
	public override void _Ready()
	{
		base._Ready();
		// Only requirement for your Player scene is that your collider is named Collider
		// (or replace this with an [Export]'ed Node3D and just grab it from there)
		// Your margin should be set real low or it starts snagging on everything - 0.001 works for me.
		_colliderMargin = GetNode<CollisionShape3D>("Collider").Shape.Margin;
	}

	public override void _PhysicsProcess(double delta)
	{
		// Use Grounded instead of IsOnFloor() in actual character controller because we reset this if we step down
		Grounded = IsOnFloor();
		
		// !!IMPORTANT!!
		// DesiredVelocity should be set in your character controller just so we know where we _want_ to go
		// In my character code it's just the direction of the controller input rotated with the camera
		// The magnitude doesn't matter much, it just needs a direction. Y component should be zero.
		DesiredVelocity = Vector3.Zero;
	}

	protected void StairStepDown()
	{
		// Not on the ground last stair step, or currently jumping? Don't snap to the ground
		// Prevents from suddenly snapping when you're falling
		if (Grounded == false || Velocity.Y >= 0) return;

		// MoveAndSlide() kept us on the floor so no need to do anything
		if (IsOnFloor()) return;
		
		var result = new PhysicsTestMotionResult3D();
		var parameters = new PhysicsTestMotionParameters3D();

		parameters.From = GlobalTransform;
		parameters.Motion = Vector3.Down * _stepHeight;
		parameters.Margin = _colliderMargin;

		if (!PhysicsServer3D.BodyTestMotion(GetRid(), parameters, result)) return;
		
		GlobalTransform = GlobalTransform.Translated(result.GetTravel());
		ApplyFloorSnap();
	}

	protected void StairStepUp()
	{
		if (!Grounded) return; //Let's not bother if we're in the air
		
		var horizontalVelocity = Velocity * _horizontal;
		var testingVelocity = horizontalVelocity;

		if (horizontalVelocity == Vector3.Zero) 
			testingVelocity = DesiredVelocity;
			
		// Not moving or attempting to move, let's not bother	
		if (testingVelocity == Vector3.Zero) return;

		var result = new PhysicsTestMotionResult3D();
		var parameters = new PhysicsTestMotionParameters3D();

		var transform = GlobalTransform;
		
		// Game is my autoload because I don't like passing 'delta' around everywhere
		// Replace with 'delta' parameter if in your own game
		var distance = testingVelocity * Game.PhysicsDeltaTime;
		parameters.From = transform;
		parameters.Motion = distance;
		parameters.Margin = _colliderMargin;

		if (PhysicsServer3D.BodyTestMotion(GetRid(), parameters, result) == false)
			return; // No stair step to bother with because we're not hitting anything

		//Move to collision
		var remainder = result.GetRemainder();
		transform = transform.Translated(result.GetTravel());
		var horizontalCollision = transform.Origin * _horizontal;

		// Raise up to ceiling - can't walk on steps if the corridor is too low for example
		var stepUp = _stepHeight * Vector3.Up;
		parameters.From = transform;
		parameters.Motion = stepUp;
		PhysicsServer3D.BodyTestMotion(GetRid(), parameters, result);
		transform = transform.Translated(result.GetTravel()); // GetTravel will be full length if we didn't hit anything
		var stepUpDistance = result.GetTravel().Length();

		// Move forward remaining distance
		parameters.From = transform;
		parameters.Motion = remainder;
		PhysicsServer3D.BodyTestMotion(GetRid(), parameters, result);
		transform = transform.Translated(result.GetTravel());
		
		// And set the collider back down again
		parameters.From = transform;
		// But no further than how far we stepped up
		parameters.Motion = Vector3.Down * stepUpDistance;
		
		// Don't bother with the rest if we're not actually gonna land back down on something
		if (PhysicsServer3D.BodyTestMotion(GetRid(), parameters, result) == false)
			return;
		
		transform = transform.Translated(result.GetTravel());
		
		var surfaceNormal = result.GetCollisionNormal();
		if (surfaceNormal.AngleTo(Vector3.Up) > FloorMaxAngle) return; //Can't stand on the thing we're trying to step on anyway
		
		var gp = GlobalPosition;
		gp.Y = transform.Origin.Y;
		GlobalPosition = gp;
	}
}