cirnogodot/Scripts/Components/Actors/ShadowProvider.cs

using Godot;
using Godot.Collections;

namespace Cirno.Scripts.Components.Actors;

public partial class ShadowProvider : Node3D
{
    
    [Export] public bool AutoEnable { get; private set; } = true;
    
    public bool Enabled { get; private set; }
    
    [Export] public float MaxShadowScale = 1.2f;
    [Export] public float MinShadowScale = 0.5f;
    [Export] public float MaxShadowHeight = 5f;

    [Export(PropertyHint.Layers3DPhysics)] public uint CollisionMask { get; set; }

    private Node3D _mainObject;

    private Array<Rid> Exclusions = [];
    
    public void Init(Node3D mainObject)
    {
        _mainObject = mainObject;
        if (_mainObject is CharacterBody3D body)
        {
            Exclusions.Add(body.GetRid());
        }
    }

    public void Enable()
    {
        Enabled = true;
    }

    public void Disable()
    {
        Enabled = false;
    }

    public override void _Ready()
    {
        if (!AutoEnable) return;

        Init(GetParentNode3D());
        Enable();
    }

    public override void _PhysicsProcess(double delta)
    {
        if (!Enabled || _mainObject is null) return;
        
        // Raycast down to get ground height
        Vector3 origin = _mainObject.GlobalTransform.Origin;
        Vector3 from = origin + Vector3.Up * 0.5f;
        Vector3 to = origin + Vector3.Down * 20f;

        var spaceState = _mainObject.GetWorld3D().DirectSpaceState;

        var result = spaceState.IntersectRay(new PhysicsRayQueryParameters3D
        {
            From = from,
            To = to,
            CollideWithBodies = true,
            CollideWithAreas = false,
            CollisionMask = CollisionMask,
            Exclude = Exclusions
        });
        
        if (result.Count > 0)
        {
            Vector3 groundPos = (Vector3)result["position"];
            float height = origin.Y - groundPos.Y;

            // Clamp and scale
            float t = Mathf.Clamp(height / MaxShadowHeight, 0f, 1f);
            float scale = Mathf.Lerp(MaxShadowScale, MinShadowScale, t);

            this.GlobalPosition = new Vector3(origin.X, groundPos.Y + 0.01f, origin.Z);
            this.Scale = new Vector3(scale, scale, scale);
            this.Visible = true;
        }
        else
        {
            this.Visible = false;
        }
    }
}