From c91f6d64f59303dc7a4017b8c45629aa23c0a504 Mon Sep 17 00:00:00 2001
From: Martin Valigursky <mvaligursky@snapchat.com>
Date: Wed, 5 Jun 2024 10:49:06 +0100
Subject: [PATCH] Particle system uses uint16 indices instead of uint32

---
 .../graphics/particles-mesh.example.mjs       |  2 +-
 src/scene/particle-system/particle-emitter.js | 20 +++++++++++++------
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/examples/src/examples/graphics/particles-mesh.example.mjs b/examples/src/examples/graphics/particles-mesh.example.mjs
index 78417bf2b25..eae2fdba9db 100644
--- a/examples/src/examples/graphics/particles-mesh.example.mjs
+++ b/examples/src/examples/graphics/particles-mesh.example.mjs
@@ -145,7 +145,7 @@ assetListLoader.load(() => {
 
     // when texture is loaded add particlesystem component to entity
     entity.addComponent('particlesystem', {
-        numParticles: 150,
+        numParticles: 25,
         lifetime: 1,
         rate: 0.01,
         scaleGraph: new pc.Curve([0, 0.2, 1, 0.7]),
diff --git a/src/scene/particle-system/particle-emitter.js b/src/scene/particle-system/particle-emitter.js
index a5115f6a4f8..94635615899 100644
--- a/src/scene/particle-system/particle-emitter.js
+++ b/src/scene/particle-system/particle-emitter.js
@@ -13,7 +13,7 @@ import {
     BUFFER_DYNAMIC,
     CULLFACE_NONE,
     FILTER_LINEAR, FILTER_NEAREST,
-    INDEXFORMAT_UINT32,
+    INDEXFORMAT_UINT16,
     PIXELFORMAT_RGBA8, PIXELFORMAT_RGBA32F,
     PRIMITIVE_TRIANGLES,
     SEMANTIC_ATTR0, SEMANTIC_ATTR1, SEMANTIC_ATTR2, SEMANTIC_ATTR3, SEMANTIC_ATTR4, SEMANTIC_TEXCOORD0,
@@ -576,7 +576,15 @@ class ParticleEmitter {
 
         particleTexHeight = (this.useCpu || this.pack8) ? 4 : 2;
 
-        this.useMesh = !!this.mesh;
+        this.useMesh = false;
+        if (this.mesh) {
+            const totalVertCount = this.numParticles * this.mesh.vertexBuffer.numVertices;
+            if (totalVertCount > 65535) {
+                Debug.warn('WARNING: particle system can\'t render mesh particles because numParticles * numVertices is more than 65k. Reverting to quad particles.');
+            } else {
+                this.useMesh = true;
+            }
+        }
 
         this.numParticlesPot = math.nextPowerOfTwo(this.numParticles);
         this.rebuildGraphs();
@@ -982,7 +990,7 @@ class ParticleEmitter {
                 this.vertexBuffer = new VertexBuffer(this.graphicsDevice, particleFormat, psysVertCount, {
                     usage: BUFFER_DYNAMIC
                 });
-                this.indexBuffer = new IndexBuffer(this.graphicsDevice, INDEXFORMAT_UINT32, psysIndexCount);
+                this.indexBuffer = new IndexBuffer(this.graphicsDevice, INDEXFORMAT_UINT16, psysIndexCount);
             } else {
                 const elements = [{
                     semantic: SEMANTIC_ATTR0,
@@ -1010,7 +1018,7 @@ class ParticleEmitter {
                 this.vertexBuffer = new VertexBuffer(this.graphicsDevice, particleFormat, psysVertCount, {
                     usage: BUFFER_DYNAMIC
                 });
-                this.indexBuffer = new IndexBuffer(this.graphicsDevice, INDEXFORMAT_UINT32, psysIndexCount);
+                this.indexBuffer = new IndexBuffer(this.graphicsDevice, INDEXFORMAT_UINT16, psysIndexCount);
             }
 
             // Fill the vertex buffer
@@ -1057,8 +1065,8 @@ class ParticleEmitter {
 
             // Fill the index buffer
             let dst = 0;
-            const indices = new Uint32Array(this.indexBuffer.lock());
-            if (this.useMesh) meshData = new Uint32Array(this.mesh.indexBuffer[0].lock());
+            const indices = new Uint16Array(this.indexBuffer.lock());
+            if (this.useMesh) meshData = new Uint16Array(this.mesh.indexBuffer[0].lock());
             for (let i = 0; i < numParticles; i++) {
                 if (!this.useMesh) {
                     const baseIndex = i * 4;