cirnogodot/Scripts/Resources/Loot/LootDropHelper.cs

using System.Collections.Generic;
using System.Linq;
using Godot;

namespace Cirno.Scripts.Resources.Loot;

/// <summary>
/// Shared logic for spawning and scattering <see cref="LootDrop"/> entries in the 3D world.
/// Used by both destructibles and enemies so the distribution behaviour stays consistent.
/// </summary>
public static class LootDropHelper
{
    /// <summary>
    /// Rolls each drop's chance, then spawns the resulting pickups scattered uniformly
    /// in a circle around <paramref name="center"/> with an outward + upward launch velocity
    /// so they arc through the air and fall to the floor.
    /// </summary>
    /// <param name="drops">The list of possible drops to evaluate.</param>
    /// <param name="anchor">Node used as the spawn parent / sibling reference.</param>
    /// <param name="center">World-space centre of the scatter circle.</param>
    /// <param name="scatterRadius">Radius of the circle in which items are spread.</param>
    /// <param name="launchUpSpeed">Initial upward speed applied to each pickup.</param>
    /// <param name="rng">Caller-owned RNG instance so seeds are consistent per object.</param>
    public static void SpawnDrops(
        IEnumerable<LootDrop> drops,
        Node3D anchor,
        Vector3 center,
        float scatterRadius,
        float launchUpSpeed,
        RandomNumberGenerator rng)
    {
        var dropList = drops?.ToList();
        if (dropList is not { Count: > 0 }) return;

        // Count total spawns up front so golden-angle spacing is proportional to the full set.
        var totalSpawns = dropList
            .Where(d => d?.Item is not null)
            .Sum(d => Mathf.Max(d.Count, 1));

        var itemIndex = 0;

        foreach (var drop in dropList)
        {
            if (drop?.Item is null) continue;

            var roll = rng.RandfRange(0f, 100f);
            if (roll > drop.Chance) continue;

            var spawnCount = Mathf.Max(drop.Count, 1);
            for (var i = 0; i < spawnCount; i++)
            {
                // Golden-angle placement gives uniform, non-clustering distribution.
                itemIndex++;
                var angle = itemIndex * Mathf.Tau / 1.618033988f;
                var radius = scatterRadius * Mathf.Sqrt((float)itemIndex / Mathf.Max(totalSpawns, 1));
                var offset = new Vector3(Mathf.Cos(angle) * radius, 0f, Mathf.Sin(angle) * radius);
                var spawnPos = center + offset;

                var lateralDir = offset.LengthSquared() > 0f ? offset.Normalized() : Vector3.Right;
                var launch = lateralDir * (scatterRadius * 0.5f) + Vector3.Up * launchUpSpeed;

                drop.Item.Spawn3D(anchor, spawnPosition: spawnPos, launchVelocity: launch);
            }
        }
    }
}