[FIX] Fix particle emission rate when looping (playcanvas#8263)

willeastcott · web-flow · commit 039772aed75d · 2025-12-19T09:33:27.000Z
diff --git a/src/scene/particle-system/cpu-updater.js b/src/scene/particle-system/cpu-updater.js
@@ -141,7 +141,7 @@ class ParticleCPUUpdater {
             const a2 = 1.0;
             particleTex[i * particleTexChannels + 3 + emitter.numParticlesPot * particleTexChannels * 2] = a2;
 
-            const maxNegLife = Math.max(emitter.lifetime, (emitter.numParticles - 1.0) * (Math.max(emitter.rate, emitter.rate2)));
+            const maxNegLife = Math.max(emitter.lifetime, emitter.numParticles * (Math.max(emitter.rate, emitter.rate2)));
             const maxPosLife = emitter.lifetime + 1.0;
             startSpawnTime = (startSpawnTime + maxNegLife) / (maxNegLife + maxPosLife);
             const rgba3 = encodeFloatRGBA(startSpawnTime);
@@ -396,7 +396,7 @@ class ParticleCPUUpdater {
                     // respawn particle by moving it's life back to zero.
                     // OR below zero, if there are still unspawned particles to be emitted before this one.
                     // such thing happens when you have an enormous amount of particles with short lifetime.
-                    life -= Math.max(particleLifetime, (emitter.numParticles - 1) * particleRate);
+                    life -= Math.max(particleLifetime, emitter.numParticles * particleRate);
 
                     // dead particles in a single-shot system continue their paths, but marked as invisible.
                     // it is necessary for keeping correct separation between particles, based on emission rate.
diff --git a/src/scene/shader-lib/glsl/chunks/particle/frag/particleInputRgba8.js b/src/scene/shader-lib/glsl/chunks/particle/frag/particleInputRgba8.js
@@ -35,7 +35,7 @@ void readInput(float uv) {
     inShow = tex2.a > 0.5;
 
     inLife = decodeFloatRGBA(tex3);
-    float maxNegLife = max(lifetime, (numParticles - 1.0) * (rate+rateDiv));
+    float maxNegLife = max(lifetime, numParticles * (rate+rateDiv));
     float maxPosLife = lifetime+1.0;
     inLife = inLife * (maxNegLife + maxPosLife) - maxNegLife;
 }
diff --git a/src/scene/shader-lib/glsl/chunks/particle/frag/particleOutputRgba8.js b/src/scene/shader-lib/glsl/chunks/particle/frag/particleOutputRgba8.js
@@ -22,7 +22,7 @@ void writeOutput() {
 
     outVel = (outVel / maxVel) + vec3(0.5); // TODO: mul
 
-    float maxNegLife = max(lifetime, (numParticles - 1.0) * (rate+rateDiv));
+    float maxNegLife = max(lifetime, numParticles * (rate+rateDiv));
     float maxPosLife = lifetime+1.0;
     outLife = (outLife + maxNegLife) / (maxNegLife + maxPosLife);
 
diff --git a/src/scene/shader-lib/glsl/chunks/particle/frag/particleUpdaterNoRespawn.js b/src/scene/shader-lib/glsl/chunks/particle/frag/particleUpdaterNoRespawn.js
@@ -1,6 +1,6 @@
 export default /* glsl */`
     if (outLife >= lifetime) {
-        outLife -= max(lifetime, (numParticles - 1.0) * particleRate);
+        outLife -= max(lifetime, numParticles * particleRate);
         visMode = -1.0;
     }
 `;
diff --git a/src/scene/shader-lib/glsl/chunks/particle/frag/particleUpdaterRespawn.js b/src/scene/shader-lib/glsl/chunks/particle/frag/particleUpdaterRespawn.js
@@ -1,6 +1,6 @@
 export default /* glsl */`
     if (outLife >= lifetime) {
-        outLife -= max(lifetime, (numParticles - 1.0) * particleRate);
+        outLife -= max(lifetime, numParticles * particleRate);
         visMode = 1.0;
     }
     visMode = outLife < 0.0? 1.0: visMode;
diff --git a/src/scene/shader-lib/wgsl/chunks/particle/frag/particleInputRgba8.js b/src/scene/shader-lib/wgsl/chunks/particle/frag/particleInputRgba8.js
@@ -40,7 +40,7 @@ fn readInput(uv: f32) {
     inShow = tex2.a > 0.5;
 
     let life_decoded = decodeFloatRGBA(tex3);
-    let maxNegLife = max(uniform.lifetime, (uniform.numParticles - 1.0) * (uniform.rate + uniform.rateDiv));
+    let maxNegLife = max(uniform.lifetime, uniform.numParticles * (uniform.rate + uniform.rateDiv));
     let maxPosLife = uniform.lifetime + 1.0;
     inLife = life_decoded * (maxNegLife + maxPosLife) - maxNegLife;
 }`;
diff --git a/src/scene/shader-lib/wgsl/chunks/particle/frag/particleOutputRgba8.js b/src/scene/shader-lib/wgsl/chunks/particle/frag/particleOutputRgba8.js
@@ -23,7 +23,7 @@ fn getOutput() -> vec4f {
 
     outVel = (outVel / uniform.maxVel) + vec3f(0.5); // TODO: mul
 
-    let maxNegLife = max(uniform.lifetime, (uniform.numParticles - 1.0) * (uniform.rate + uniform.rateDiv));
+    let maxNegLife = max(uniform.lifetime, uniform.numParticles * (uniform.rate + uniform.rateDiv));
     let maxPosLife = uniform.lifetime + 1.0;
     outLife = (outLife + maxNegLife) / (maxNegLife + maxPosLife);
 
diff --git a/src/scene/shader-lib/wgsl/chunks/particle/frag/particleUpdaterNoRespawn.js b/src/scene/shader-lib/wgsl/chunks/particle/frag/particleUpdaterNoRespawn.js
@@ -1,6 +1,6 @@
 export default /* wgsl */`
     if (outLife >= uniform.lifetime) {
-        outLife = outLife - max(uniform.lifetime, (uniform.numParticles - 1.0) * particleRate);
+        outLife = outLife - max(uniform.lifetime, uniform.numParticles * particleRate);
         visMode = -1.0;
     }
 `;
diff --git a/src/scene/shader-lib/wgsl/chunks/particle/frag/particleUpdaterRespawn.js b/src/scene/shader-lib/wgsl/chunks/particle/frag/particleUpdaterRespawn.js
@@ -1,6 +1,6 @@
 export default /* wgsl */`
     if (outLife >= uniform.lifetime) {
-        let subtractAmount = max(uniform.lifetime, (uniform.numParticles - 1.0) * particleRate);
+        let subtractAmount = max(uniform.lifetime, uniform.numParticles * particleRate);
         outLife = outLife - subtractAmount;
         visMode = 1.0;
     }

Original file line number	Diff line number	Diff line change
`@@ -35,7 +35,7 @@ void readInput(float uv) {`
`35`	`35`	`inShow = tex2.a > 0.5;`
`36`	`36`
`37`	`37`	`inLife = decodeFloatRGBA(tex3);`
`38`		`- float maxNegLife = max(lifetime, (numParticles - 1.0) * (rate+rateDiv));`
	`38`	`+ float maxNegLife = max(lifetime, numParticles * (rate+rateDiv));`
`39`	`39`	`float maxPosLife = lifetime+1.0;`
`40`	`40`	`inLife = inLife * (maxNegLife + maxPosLife) - maxNegLife;`
`41`	`41`	`}`
Original file line number	Diff line number	Diff line change
`@@ -1,6 +1,6 @@`
`1`	`1`	export default /* glsl */`
`2`	`2`	`if (outLife >= lifetime) {`
`3`		`- outLife -= max(lifetime, (numParticles - 1.0) * particleRate);`
	`3`	`+ outLife -= max(lifetime, numParticles * particleRate);`
`4`	`4`	`visMode = -1.0;`
`5`	`5`	`}`
`6`	`6`	`;
Original file line number	Diff line number	Diff line change
`@@ -1,6 +1,6 @@`
`1`	`1`	export default /* wgsl */`
`2`	`2`	`if (outLife >= uniform.lifetime) {`
`3`		`- outLife = outLife - max(uniform.lifetime, (uniform.numParticles - 1.0) * particleRate);`
	`3`	`+ outLife = outLife - max(uniform.lifetime, uniform.numParticles * particleRate);`
`4`	`4`	`visMode = -1.0;`
`5`	`5`	`}`
`6`	`6`	`;