feat: enable gravityModifier two constants mode (#1964)

Author: JujieX

packages/core/src/particle/enums/ParticleRandomSubSeeds.ts

@@ -15,5 +15,6 @@ export enum ParticleRandomSubSeeds {
   SizeOverLifetime = 0x591bc05c,
   RotationOverLifetime = 0x40eb95e4,
   TextureSheetAnimation = 0xbc524e5,
-  Shape = 0xaf502044
+  Shape = 0xaf502044,
+  GravityModifier = 0xa47b8c4d
 }

packages/core/src/particle/modules/MainModule.ts

@@ -98,6 +98,9 @@ export class MainModule implements ICustomClone {
   @ignoreClone
   readonly _startRotationRand = new Rand(0, ParticleRandomSubSeeds.StartRotation);
 
+  @ignoreClone
+  readonly _gravityModifierRand = new Rand(0, ParticleRandomSubSeeds.GravityModifier);
+
   @ignoreClone
   private _generator: ParticleGenerator;
   @ignoreClone
@@ -196,7 +199,7 @@ export class MainModule implements ICustomClone {
     }
 
     const particleGravity = this._gravity;
-    const gravityModifierValue = this.gravityModifier.evaluate(undefined, undefined);
+    const gravityModifierValue = this.gravityModifier.evaluate(undefined, this._gravityModifierRand.random());
     Vector3.scale(renderer.scene.physics.gravity, gravityModifierValue, particleGravity);
 
     shaderData.setVector3(MainModule._gravity, particleGravity);