From 2a925fcf65c4925ded102acbe036f5d246d0522b Mon Sep 17 00:00:00 2001
From: "eldar.zakaryaev" <eldar.zakaryaev@patternmasters.ru>
Date: Wed, 5 Jul 2023 11:11:44 +0300
Subject: [PATCH] Add using lengthScale to UIParticleSystem

---
 Runtime/Scripts/Effects/UIParticleSystem.cs | 31 +++++++++++++++++----
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/Runtime/Scripts/Effects/UIParticleSystem.cs b/Runtime/Scripts/Effects/UIParticleSystem.cs
index 4083b02..2b24889 100644
--- a/Runtime/Scripts/Effects/UIParticleSystem.cs
+++ b/Runtime/Scripts/Effects/UIParticleSystem.cs
@@ -16,6 +16,9 @@ namespace UnityEngine.UI.Extensions
         [Tooltip("Enables 3d rotation for the particles")]
         public bool use3dRotation = false;
 
+        [Tooltip("Enables using Renderer.lengthScale parameter")]
+        public bool _useLengthScale = false;
+        
         private Transform _transform;
         private ParticleSystem pSystem;
         private ParticleSystem.Particle[] particles;
@@ -26,6 +29,7 @@ namespace UnityEngine.UI.Extensions
         private Vector2 textureSheetAnimationFrameSize;
         private ParticleSystemRenderer pRenderer;
         private bool isInitialised = false;
+        private float _lengthScale;
 
         private Material currentMaterial;
 
@@ -91,7 +95,8 @@ namespace UnityEngine.UI.Extensions
                 pRenderer = pSystem.GetComponent<ParticleSystemRenderer>();
                 if (pRenderer != null)
                     pRenderer.enabled = false;
-
+                
+                _lengthScale = pRenderer.lengthScale;
                 if (material == null)
                 {
                     var foundShader = ShaderLibrary.GetShaderInstance("UI Extensions/Particles/Additive");
@@ -183,8 +188,6 @@ namespace UnityEngine.UI.Extensions
 #else
                 Vector2 position = (pSystem.simulationSpace == ParticleSystemSimulationSpace.Local ? particle.position : _transform.InverseTransformPoint(particle.position));
 #endif
-                float rotation = -particle.rotation * Mathf.Deg2Rad;
-                float rotation90 = rotation + Mathf.PI / 2;
                 Color32 color = particle.GetCurrentColor(pSystem);
                 float size = particle.GetCurrentSize(pSystem) * 0.5f;
 
@@ -280,13 +283,29 @@ namespace UnityEngine.UI.Extensions
                 _quad[3].color = color;
                 _quad[3].uv0 = temp;
 
+                
+                float rotation = -particle.rotation * Mathf.Deg2Rad;
+                var lengthScale = _lengthScale;
+                if (_useLengthScale) // this flag is mostly to secure old behaviour, it probably can be replaced with _lengthScale != 1
+                {
+                    // rotate towards velocity
+                    var normalizedVelocity = particle.velocity.normalized;
+                    rotation = Mathf.Atan2(normalizedVelocity.y, normalizedVelocity.x);
+                }
+                else
+                {
+                    lengthScale = 1f;
+                }
+                
+                float rotation90 = rotation + Mathf.PI / 2;
+
                 if (rotation == 0)
                 {
                     // no rotation
                     corner1.x = position.x - size;
-                    corner1.y = position.y - size;
+                    corner1.y = position.y - size * lengthScale;
                     corner2.x = position.x + size;
-                    corner2.y = position.y + size;
+                    corner2.y = position.y + size * lengthScale;
 
                     temp.x = corner1.x;
                     temp.y = corner1.y;
@@ -339,7 +358,7 @@ namespace UnityEngine.UI.Extensions
                     else
                     {
                         // apply rotation
-                        Vector2 right = new Vector2(Mathf.Cos(rotation), Mathf.Sin(rotation)) * size;
+                        Vector2 right = new Vector2(Mathf.Cos(rotation), Mathf.Sin(rotation)) * size * lengthScale;
                         Vector2 up = new Vector2(Mathf.Cos(rotation90), Mathf.Sin(rotation90)) * size;
 
                         _quad[0].position = position - right - up;