UnityTowerDefense/Assets/_Project/Scripts/VFX/CoinBurstVfx.cs

// Assets/_Project/Scripts/VFX/CoinBurstVfx.cs
using UnityEngine;

namespace TD.VFX
{
    /// <summary>
    /// Self-contained, code-configured gold-coin burst used as the zero-art placeholder for the
    /// tower-sell effect. Configures its own <see cref="ParticleSystem"/> for a short radial
    /// spray of gold specks thrown up in random arcs under gravity, then destroys itself.
    /// </summary>
    /// <remarks>
    /// Instantiated at runtime by <see cref="SellEffectSpawner"/> when no authored VFX prefab is
    /// assigned. It can also be dropped on a prefab in the editor and tuned. Replace with an
    /// authored particle / VFX-graph prefab (assigned on the spawner) when art is ready — nothing
    /// else needs to change.
    /// </remarks>
    [RequireComponent(typeof(ParticleSystem))]
    public class CoinBurstVfx : MonoBehaviour
    {
        [Tooltip("How many coin specks to throw.")]
        [SerializeField] private int coinCount = 14;

        [Tooltip("Longest a speck lives (seconds). The whole effect self-destructs shortly after.")]
        [SerializeField] private float lifetime = 0.6f;

        [Tooltip("Gold tint applied to the specks.")]
        [SerializeField] private Color coinColor = new Color(1f, 0.84f, 0.2f, 1f);

        private void Awake()
        {
            var ps = GetComponent<ParticleSystem>();
            if (ps == null) ps = gameObject.AddComponent<ParticleSystem>();
            Configure(ps);
        }

        private void Configure(ParticleSystem ps)
        {
            // Reconfiguring modules requires the system to be stopped first.
            ps.Stop(true, ParticleSystemStopBehavior.StopEmittingAndClear);

            var main = ps.main;
            main.duration          = 0.1f;
            main.loop              = false;
            main.playOnAwake       = false;
            main.startLifetime     = new ParticleSystem.MinMaxCurve(lifetime * 0.6f, lifetime);
            main.startSpeed        = new ParticleSystem.MinMaxCurve(2.5f, 5f);
            main.startSize         = new ParticleSystem.MinMaxCurve(0.07f, 0.16f);
            main.startRotation     = new ParticleSystem.MinMaxCurve(0f, Mathf.PI * 2f);
            main.startColor        = coinColor;
            main.gravityModifier   = 2.5f; // arc up then fall back down quickly
            main.simulationSpace   = ParticleSystemSimulationSpace.World;
            main.maxParticles      = 64;
            main.stopAction        = ParticleSystemStopAction.None;

            var emission = ps.emission;
            emission.enabled      = true;
            emission.rateOverTime = 0f; // burst only, no continuous stream
            emission.SetBursts(new[] { new ParticleSystem.Burst(0f, (short)coinCount) });

            // Hemisphere pointing up → specks spray outward and upward in random directions.
            var shape = ps.shape;
            shape.enabled   = true;
            shape.shapeType = ParticleSystemShapeType.Hemisphere;
            shape.radius    = 0.12f;

            // Fade the specks out over the back half of their life so they "decay quickly".
            var col = ps.colorOverLifetime;
            col.enabled = true;
            var grad = new Gradient();
            grad.SetKeys(
                new[] { new GradientColorKey(coinColor, 0f), new GradientColorKey(coinColor, 1f) },
                new[]
                {
                    new GradientAlphaKey(1f, 0f),
                    new GradientAlphaKey(1f, 0.55f),
                    new GradientAlphaKey(0f, 1f),
                });
            col.color = new ParticleSystem.MinMaxGradient(grad);

            // Give the specks a visible, transparent-capable material even with no assigned art.
            var renderer = GetComponent<ParticleSystemRenderer>();
            if (renderer != null)
            {
                renderer.renderMode = ParticleSystemRenderMode.Billboard;
                if (renderer.sharedMaterial == null)
                {
                    Shader shader = Shader.Find("Universal Render Pipeline/Particles/Unlit")
                                    ?? Shader.Find("Sprites/Default")
                                    ?? Shader.Find("Legacy Shaders/Particles/Alpha Blended Premultiply");
                    if (shader != null)
                        renderer.material = new Material(shader) { color = coinColor };
                }
            }

            ps.Play();

            // Tear down after the last speck has died (plus a small margin).
            Destroy(gameObject, lifetime + 0.25f);
        }
    }
}