From c1c001eba8d0fa4ca663298ba6e12695132c2951 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Tue, 17 Jan 2023 17:36:46 +0800
Subject: [PATCH 01/24] refactor: change time unit and API

---
 packages/core/src/Engine.ts                   |  6 +-
 packages/core/src/animation/Animator.ts       |  2 +-
 packages/core/src/base/Time.ts                | 77 +++++++++++--------
 .../core/src/particle/ParticleRenderer.ts     | 14 ++--
 4 files changed, 54 insertions(+), 45 deletions(-)

diff --git a/packages/core/src/Engine.ts b/packages/core/src/Engine.ts
index ed06e29a4f..148d7d5053 100644
--- a/packages/core/src/Engine.ts
+++ b/packages/core/src/Engine.ts
@@ -271,7 +271,7 @@ export class Engine extends EventDispatcher {
   resume(): void {
     if (!this._isPaused) return;
     this._isPaused = false;
-    this.time.reset();
+    this.time._reset();
     this._requestId = requestAnimationFrame(this._animate);
   }
 
@@ -280,7 +280,7 @@ export class Engine extends EventDispatcher {
    */
   update(): void {
     const time = this._time;
-    time.tick();
+    time._tick();
 
     const deltaTime = time.deltaTime;
     this._frameInProcess = true;
@@ -296,7 +296,7 @@ export class Engine extends EventDispatcher {
       scene._activeCameras.sort((camera1, camera2) => camera1.priority - camera2.priority);
 
       componentsManager.callScriptOnStart();
-      this.physicsManager._initialized && this.physicsManager._update(deltaTime / 1000.0);
+      this.physicsManager._initialized && this.physicsManager._update(deltaTime);
       this.inputManager._update();
       componentsManager.callScriptOnUpdate(deltaTime);
       componentsManager.callAnimationUpdate(deltaTime);
diff --git a/packages/core/src/animation/Animator.ts b/packages/core/src/animation/Animator.ts
index bcd9d8eba4..023f7e4bf1 100644
--- a/packages/core/src/animation/Animator.ts
+++ b/packages/core/src/animation/Animator.ts
@@ -176,7 +176,7 @@ export class Animator extends Component {
         continue;
       }
 
-      this._updateLayer(i, i === 0, deltaTime / 1000, animationUpdate);
+      this._updateLayer(i, i === 0, deltaTime, animationUpdate);
     }
   }
 
diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index f57e0769ea..6b10f6ac20 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -1,15 +1,16 @@
 /**
- * Tools for calculating the time per frame.
+ * Tools for get time information.
  */
 export class Time {
   /** @internal */
   _frameCount: number = 0;
 
   private _clock: { now: () => number };
+  private _time: number;
   private _timeScale: number;
   private _deltaTime: number;
   private _startTime: number;
-  private _lastTickTime: number;
+  private _lastSystemTime: number;
 
   /*
    * The total number of frames since the start of the engine.
@@ -19,68 +20,76 @@ export class Time {
   }
 
   /**
-   * Constructor of the Time.
+   * The interval in seconds from the last frame to the current frame.
    */
-  constructor() {
-    this._clock = performance ? performance : Date;
-
-    this._timeScale = 1.0;
-    this._deltaTime = 0.0001;
-
-    const now = this._clock.now();
-    this._startTime = now;
-    this._lastTickTime = now;
+  get deltaTime(): number {
+    return this._deltaTime;
   }
 
-  reset() {
-    this._lastTickTime = this._clock.now();
+  /**
+   * The unscaled interval in seconds from the last frame to the current frame.
+   */
+  get unscaledDeltaTime(): number {
+    return this._deltaTime / this._timeScale;
   }
 
   /**
-   * Current Time
+   * The time in seconds at the beginning of this frame.
    */
-  get nowTime(): number {
-    return this._clock.now();
+  get time(): number {
+    return this._time;
   }
 
   /**
-   * Time between two ticks
+   * The elapsed time in seconds, after the engine is startup.
    */
-  get deltaTime(): number {
-    return this._deltaTime;
+  get timeSinceStartup(): number {
+    return this._time - this._startTime;
   }
 
   /**
-   * Scaled delta time.
+   * The scale of time.
    */
   get timeScale(): number {
     return this._timeScale;
   }
-  set timeScale(s) {
-    this._timeScale = s;
+
+  set timeScale(value) {
+    this._timeScale = value;
   }
 
   /**
-   * Unscaled delta time.
+   * Constructor of the Time.
    */
-  get unscaledDeltaTime(): number {
-    return this._deltaTime / this._timeScale;
+  constructor() {
+    this._clock = performance ? performance : Date;
+
+    this._timeScale = 1.0;
+    this._deltaTime = 0.0001;
+
+    const now = this._clock.now() / 1000;
+    this._startTime = now;
+    this._lastSystemTime = now;
   }
 
   /**
-   * The elapsed time, after the clock is initialized.
+   * @internal
    */
-  get timeSinceStartup(): number {
-    return this.nowTime - this._startTime;
+  _reset() {
+    this._lastSystemTime = this._clock.now() / 1000;
   }
 
   /**
-   * Call every frame, update delta time and other data.
+   * @internal
    */
-  public tick(): void {
-    const now = this.nowTime;
-    this._deltaTime = (now - this._lastTickTime) * this._timeScale;
-    this._lastTickTime = now;
+  _tick(): void {
+    const systemTime = this._clock.now() / 1000;
+    const deltaTime = (systemTime - this._lastSystemTime) * this._timeScale;
+
+    this._deltaTime = deltaTime;
+    this._time += deltaTime;
     this._frameCount++;
+
+    this._lastSystemTime = systemTime;
   }
 }
diff --git a/packages/core/src/particle/ParticleRenderer.ts b/packages/core/src/particle/ParticleRenderer.ts
index 1fa9331dfa..fdf84abf5e 100644
--- a/packages/core/src/particle/ParticleRenderer.ts
+++ b/packages/core/src/particle/ParticleRenderer.ts
@@ -1,4 +1,6 @@
-import { MathUtil, Vector3, Color } from "@oasis-engine/math";
+import { Color, MathUtil, Vector3 } from "@oasis-engine/math";
+import { GLCapabilityType } from "../base/Constant";
+import { ignoreClone } from "../clone/CloneManager";
 import { Buffer } from "../graphic/Buffer";
 import { BufferBindFlag } from "../graphic/enums/BufferBindFlag";
 import { BufferUsage } from "../graphic/enums/BufferUsage";
@@ -6,14 +8,12 @@ import { IndexFormat } from "../graphic/enums/IndexFormat";
 import { VertexElementFormat } from "../graphic/enums/VertexElementFormat";
 import { VertexElement } from "../graphic/VertexElement";
 import { Material } from "../material/Material";
+import { BufferMesh } from "../mesh/BufferMesh";
+import { MeshRenderer } from "../mesh/MeshRenderer";
+import { CullMode, Shader } from "../shader";
 import { BlendFactor } from "../shader/enums/BlendFactor";
 import { RenderQueueType } from "../shader/enums/RenderQueueType";
-import { Shader, CullMode } from "../shader";
 import { Texture } from "../texture";
-import { MeshRenderer } from "../mesh/MeshRenderer";
-import { GLCapabilityType } from "../base/Constant";
-import { BufferMesh } from "../mesh/BufferMesh";
-import { ignoreClone } from "../clone/CloneManager";
 
 enum DirtyFlagType {
   Position = 0x1,
@@ -560,7 +560,7 @@ export class ParticleRenderer extends MeshRenderer {
       this._updateDirtyFlag = 0;
     }
 
-    this._time += deltaTime / 1000;
+    this._time += deltaTime;
     this.shaderData.setFloat("u_time", this._time);
   }
 

From a133e1ae7e6d4dabb6d6f47ef529983f3ccaef2b Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Tue, 17 Jan 2023 17:43:19 +0800
Subject: [PATCH 02/24] refactor: opt code

---
 packages/core/src/base/Time.ts | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index 6b10f6ac20..99612756ce 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -9,7 +9,6 @@ export class Time {
   private _time: number;
   private _timeScale: number;
   private _deltaTime: number;
-  private _startTime: number;
   private _lastSystemTime: number;
 
   /*
@@ -40,13 +39,6 @@ export class Time {
     return this._time;
   }
 
-  /**
-   * The elapsed time in seconds, after the engine is startup.
-   */
-  get timeSinceStartup(): number {
-    return this._time - this._startTime;
-  }
-
   /**
    * The scale of time.
    */
@@ -68,7 +60,6 @@ export class Time {
     this._deltaTime = 0.0001;
 
     const now = this._clock.now() / 1000;
-    this._startTime = now;
     this._lastSystemTime = now;
   }
 

From e76dee803af618ede76b5ea9034d60dae52924d4 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Tue, 17 Jan 2023 17:51:41 +0800
Subject: [PATCH 03/24] refactor: opt code

---
 packages/core/src/base/Time.ts | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index 99612756ce..10ec39f950 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -33,12 +33,19 @@ export class Time {
   }
 
   /**
-   * The time in seconds at the beginning of this frame.
+   * The time in seconds of this frame.
    */
   get time(): number {
     return this._time;
   }
 
+  /**
+   * The unscaled time in seconds of this frame.
+   */
+  get unscaledTime(): number {
+    return this._time / this._timeScale;
+  }
+
   /**
    * The scale of time.
    */

From 7ec6903def601358d8d07ef83e21340fd74f037a Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Tue, 17 Jan 2023 17:58:10 +0800
Subject: [PATCH 04/24] refactor: opt code

---
 packages/core/src/base/Time.ts | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index 10ec39f950..11f462740d 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -6,9 +6,11 @@ export class Time {
   _frameCount: number = 0;
 
   private _clock: { now: () => number };
-  private _time: number;
-  private _timeScale: number;
-  private _deltaTime: number;
+  private _time: number = 0;
+  private _unscaledTime: number = 0;
+  private _deltaTime: number = 0;
+  private _unscaledDeltaTime: number = 0;
+  private _timeScale: number = 1.0;
   private _lastSystemTime: number;
 
   /*
@@ -62,10 +64,6 @@ export class Time {
    */
   constructor() {
     this._clock = performance ? performance : Date;
-
-    this._timeScale = 1.0;
-    this._deltaTime = 0.0001;
-
     const now = this._clock.now() / 1000;
     this._lastSystemTime = now;
   }

From 9577271996e0521eef828179f9bbcc9d38db3a2d Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Thu, 16 Mar 2023 11:23:13 +0800
Subject: [PATCH 05/24] refactor: opt code

---
 packages/core/src/RenderPipeline/BasicRenderPipeline.ts | 2 +-
 packages/core/src/base/Time.ts                          | 4 +---
 packages/core/src/shadow/ShadowUtils.ts                 | 2 +-
 3 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/packages/core/src/RenderPipeline/BasicRenderPipeline.ts b/packages/core/src/RenderPipeline/BasicRenderPipeline.ts
index c81fc45a21..fa801ac6c8 100644
--- a/packages/core/src/RenderPipeline/BasicRenderPipeline.ts
+++ b/packages/core/src/RenderPipeline/BasicRenderPipeline.ts
@@ -319,7 +319,7 @@ export class BasicRenderPipeline {
           continue;
         }
       }
-      renderer._renderFrameCount = engine.time._frameCount;
+      renderer._renderFrameCount = engine.time.frameCount;
       renderer._prepareRender(context);
     }
   }
diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index 11f462740d..1e85991490 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -2,9 +2,7 @@
  * Tools for get time information.
  */
 export class Time {
-  /** @internal */
-  _frameCount: number = 0;
-
+  private _frameCount: number = 0;
   private _clock: { now: () => number };
   private _time: number = 0;
   private _unscaledTime: number = 0;
diff --git a/packages/core/src/shadow/ShadowUtils.ts b/packages/core/src/shadow/ShadowUtils.ts
index 15ed27d7fc..4d5cba711e 100644
--- a/packages/core/src/shadow/ShadowUtils.ts
+++ b/packages/core/src/shadow/ShadowUtils.ts
@@ -186,7 +186,7 @@ export class ShadowUtils {
         renderer.castShadows &&
         ShadowUtils.cullingRenderBounds(renderer.bounds, shadowSliceData.cullPlaneCount, shadowSliceData.cullPlanes)
       ) {
-        renderer._renderFrameCount = renderer.engine.time._frameCount;
+        renderer._renderFrameCount = renderer.engine.time.frameCount;
         renderer._prepareRender(context);
       }
     }

From 271a85c097c4b18e3f751d322b4118279076488d Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Thu, 16 Mar 2023 11:50:40 +0800
Subject: [PATCH 06/24] refactor: opt code

---
 packages/core/src/base/Time.ts | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index 1e85991490..3efda50a13 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -3,11 +3,10 @@
  */
 export class Time {
   private _frameCount: number = 0;
-  private _clock: { now: () => number };
-  private _time: number = 0;
-  private _unscaledTime: number = 0;
   private _deltaTime: number = 0;
   private _unscaledDeltaTime: number = 0;
+  private _time: number = 0;
+  private _unscaledTime: number = 0;
   private _timeScale: number = 1.0;
   private _lastSystemTime: number;
 
@@ -29,7 +28,7 @@ export class Time {
    * The unscaled interval in seconds from the last frame to the current frame.
    */
   get unscaledDeltaTime(): number {
-    return this._deltaTime / this._timeScale;
+    return this._unscaledDeltaTime;
   }
 
   /**
@@ -43,7 +42,7 @@ export class Time {
    * The unscaled time in seconds of this frame.
    */
   get unscaledTime(): number {
-    return this._time / this._timeScale;
+    return this._unscaledTime;
   }
 
   /**
@@ -61,29 +60,30 @@ export class Time {
    * Constructor of the Time.
    */
   constructor() {
-    this._clock = performance ? performance : Date;
-    const now = this._clock.now() / 1000;
-    this._lastSystemTime = now;
+    this._lastSystemTime = performance.now() / 1000;
   }
 
   /**
    * @internal
    */
   _reset() {
-    this._lastSystemTime = this._clock.now() / 1000;
+    this._lastSystemTime = performance.now() / 1000;
   }
 
   /**
    * @internal
    */
   _tick(): void {
-    const systemTime = this._clock.now() / 1000;
-    const deltaTime = (systemTime - this._lastSystemTime) * this._timeScale;
+    const currentSystemTime = performance.now() / 1000;
+    const unscaledDeltaTime = currentSystemTime - this._lastSystemTime;
+    const deltaTime = unscaledDeltaTime * this._timeScale;
 
+    this._unscaledDeltaTime = unscaledDeltaTime;
+    this._unscaledTime += unscaledDeltaTime;
     this._deltaTime = deltaTime;
     this._time += deltaTime;
     this._frameCount++;
 
-    this._lastSystemTime = systemTime;
+    this._lastSystemTime = currentSystemTime;
   }
 }

From 2df279744b85f8d6f382c9546b2131c3f98e3d08 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Thu, 16 Mar 2023 13:13:32 +0800
Subject: [PATCH 07/24] refactor: opt code

---
 packages/core/src/Engine.ts    | 2 +-
 packages/core/src/base/Time.ts | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/core/src/Engine.ts b/packages/core/src/Engine.ts
index 82cfae07a0..a4f9a6f22d 100644
--- a/packages/core/src/Engine.ts
+++ b/packages/core/src/Engine.ts
@@ -306,7 +306,7 @@ export class Engine extends EventDispatcher {
     }
 
     const time = this._time;
-    time._tick();
+    time._update();
 
     const deltaTime = time.deltaTime;
     this._frameInProcess = true;
diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index 3efda50a13..7e7724a986 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -73,7 +73,7 @@ export class Time {
   /**
    * @internal
    */
-  _tick(): void {
+  _update(): void {
     const currentSystemTime = performance.now() / 1000;
     const unscaledDeltaTime = currentSystemTime - this._lastSystemTime;
     const deltaTime = unscaledDeltaTime * this._timeScale;

From 431ea46d638e3ade44f215f8c8ee6f24df7433fe Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Thu, 16 Mar 2023 15:31:31 +0800
Subject: [PATCH 08/24] refactor: opt code

---
 packages/core/src/Scene.ts     |  3 +++
 packages/core/src/base/Time.ts | 26 ++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/packages/core/src/Scene.ts b/packages/core/src/Scene.ts
index 9df66943f1..477b3357a0 100644
--- a/packages/core/src/Scene.ts
+++ b/packages/core/src/Scene.ts
@@ -379,8 +379,11 @@ export class Scene extends EngineObject {
    */
   _updateShaderData(): void {
     const shaderData = this.shaderData;
+    const time = this._engine.time;
     const lightManager = this._engine._lightManager;
 
+    time._updateSceneShaderData(shaderData);
+
     lightManager._updateShaderData(this.shaderData);
     const sunLightIndex = lightManager._getSunLightIndex();
     if (sunLightIndex !== -1) {
diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index 7e7724a986..57c346f2aa 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -1,7 +1,14 @@
+import { Vector4 } from "@oasis-engine/math";
+import { ShaderData } from "../shader/ShaderData";
+import { ShaderProperty } from "../shader/ShaderProperty";
+
 /**
  * Tools for get time information.
  */
 export class Time {
+  private static _timeProperty = ShaderProperty.getByName("u_Time");
+  private static _deltaTimeProperty = ShaderProperty.getByName("u_DeltaTime");
+
   private _frameCount: number = 0;
   private _deltaTime: number = 0;
   private _unscaledDeltaTime: number = 0;
@@ -10,6 +17,9 @@ export class Time {
   private _timeScale: number = 1.0;
   private _lastSystemTime: number;
 
+  private _timeValue: Vector4 = new Vector4();
+  private _deltaTimeValue: Vector4 = new Vector4();
+
   /*
    * The total number of frames since the start of the engine.
    */
@@ -86,4 +96,20 @@ export class Time {
 
     this._lastSystemTime = currentSystemTime;
   }
+
+  /**
+   * @internal
+   */
+  _updateSceneShaderData(shaderData: ShaderData): void {
+    const timeValue = this._timeValue;
+    const deltaTimeValue = this._deltaTimeValue;
+
+    const time = this._time;
+    timeValue.set(time, Math.sin(time), Math.cos(time), 0);
+    shaderData.setVector4(Time._timeProperty, timeValue);
+
+    const deltaTime = this._deltaTime;
+    deltaTimeValue.set(deltaTime, 0, 0, 0);
+    shaderData.setVector4(Time._deltaTimeProperty, deltaTimeValue);
+  }
 }

From 545511e2c4f9387260690a758fb48e3211ac2431 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Thu, 16 Mar 2023 17:54:57 +0800
Subject: [PATCH 09/24] refactor: opt code

---
 packages/core/src/base/Time.ts | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index 57c346f2aa..b71a7b63cd 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -12,8 +12,8 @@ export class Time {
   private _frameCount: number = 0;
   private _deltaTime: number = 0;
   private _unscaledDeltaTime: number = 0;
-  private _time: number = 0;
-  private _unscaledTime: number = 0;
+  private _elapsedTime: number = 0;
+  private _unscaledElapsedTime: number = 0;
   private _timeScale: number = 1.0;
   private _lastSystemTime: number;
 
@@ -42,17 +42,17 @@ export class Time {
   }
 
   /**
-   * The time in seconds of this frame.
+   * The elapsed time in seconds of this frame.
    */
-  get time(): number {
-    return this._time;
+  get elapsedTime(): number {
+    return this._elapsedTime;
   }
 
   /**
-   * The unscaled time in seconds of this frame.
+   * The unscaled elapsed time in seconds of this frame.
    */
-  get unscaledTime(): number {
-    return this._unscaledTime;
+  get unscaledElapsedTime(): number {
+    return this._unscaledElapsedTime;
   }
 
   /**
@@ -89,9 +89,9 @@ export class Time {
     const deltaTime = unscaledDeltaTime * this._timeScale;
 
     this._unscaledDeltaTime = unscaledDeltaTime;
-    this._unscaledTime += unscaledDeltaTime;
+    this._unscaledElapsedTime += unscaledDeltaTime;
     this._deltaTime = deltaTime;
-    this._time += deltaTime;
+    this._elapsedTime += deltaTime;
     this._frameCount++;
 
     this._lastSystemTime = currentSystemTime;
@@ -104,7 +104,7 @@ export class Time {
     const timeValue = this._timeValue;
     const deltaTimeValue = this._deltaTimeValue;
 
-    const time = this._time;
+    const time = this._elapsedTime;
     timeValue.set(time, Math.sin(time), Math.cos(time), 0);
     shaderData.setVector4(Time._timeProperty, timeValue);
 

From fa849dc5795274e04286113dbef071f4575afa8c Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Thu, 16 Mar 2023 17:59:24 +0800
Subject: [PATCH 10/24] refactor: opt code

---
 packages/core/src/Engine.ts | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/packages/core/src/Engine.ts b/packages/core/src/Engine.ts
index a4f9a6f22d..23f425eedc 100644
--- a/packages/core/src/Engine.ts
+++ b/packages/core/src/Engine.ts
@@ -68,7 +68,7 @@ export class Engine extends EventDispatcher {
 
   /* @internal */
   _renderElementPool: ClassPool<RenderElement> = new ClassPool(RenderElement);
-   /* @internal */
+  /* @internal */
   _meshRenderDataPool: ClassPool<MeshRenderData> = new ClassPool(MeshRenderData);
   /* @internal */
   _spriteRenderDataPool: ClassPool<SpriteRenderData> = new ClassPool(SpriteRenderData);
@@ -158,21 +158,21 @@ export class Engine extends EventDispatcher {
   }
 
   /**
-   * Get the resource manager.
+   * The resource manager.
    */
   get resourceManager(): ResourceManager {
     return this._resourceManager;
   }
 
   /**
-   * Get the scene manager.
+   * The scene manager.
    */
   get sceneManager(): SceneManager {
     return this._sceneManager;
   }
 
   /**
-   * Get the Time class.
+   * The time information of the engine.
    */
   get time(): Time {
     return this._time;

From ae073a631b1c5ff44adb65e21cdb847c4236fb41 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Thu, 16 Mar 2023 18:30:56 +0800
Subject: [PATCH 11/24] refactor: opt code

---
 packages/core/src/base/Time.ts | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index b71a7b63cd..c0e3e59393 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -28,28 +28,28 @@ export class Time {
   }
 
   /**
-   * The interval in seconds from the last frame to the current frame.
+   * The delta time in seconds from the last frame to the current frame.
    */
   get deltaTime(): number {
     return this._deltaTime;
   }
 
   /**
-   * The unscaled interval in seconds from the last frame to the current frame.
+   * The unscaled delta time in seconds from the last frame to the current frame.
    */
   get unscaledDeltaTime(): number {
     return this._unscaledDeltaTime;
   }
 
   /**
-   * The elapsed time in seconds of this frame.
+   * The elapsed time in seconds since the start of the engine.
    */
   get elapsedTime(): number {
     return this._elapsedTime;
   }
 
   /**
-   * The unscaled elapsed time in seconds of this frame.
+   * The unscaled elapsed time in seconds since the start of the engine.
    */
   get unscaledElapsedTime(): number {
     return this._unscaledElapsedTime;

From 2109bb3046dee3ac54c1b1d8d8b090b5e6785b13 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Thu, 16 Mar 2023 18:48:29 +0800
Subject: [PATCH 12/24] refactor: opt code

---
 packages/core/src/Script.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/core/src/Script.ts b/packages/core/src/Script.ts
index 4c03aa12f2..2d6d4c8b36 100644
--- a/packages/core/src/Script.ts
+++ b/packages/core/src/Script.ts
@@ -51,13 +51,13 @@ export class Script extends Component {
 
   /**
    * The main loop, called frame by frame.
-   * @param deltaTime - The deltaTime when the script update.
+   * @param deltaTime - The delta time since last frame in seconds
    */
   onUpdate(deltaTime: number): void {}
 
   /**
    * Called after the onUpdate finished, called frame by frame.
-   * @param deltaTime - The deltaTime when the script update.
+   * @param deltaTime - The delta time since last frame in seconds
    */
   onLateUpdate(deltaTime: number): void {}
 

From 91bd941713d59231c608d5a21aff06c093c75db8 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Fri, 17 Mar 2023 11:50:38 +0800
Subject: [PATCH 13/24] refactor: opt code

---
 packages/core/src/base/Time.ts              | 36 ++++++++++-----------
 packages/core/src/physics/PhysicsManager.ts | 23 +------------
 2 files changed, 19 insertions(+), 40 deletions(-)

diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index c0e3e59393..093105e2d6 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -3,7 +3,7 @@ import { ShaderData } from "../shader/ShaderData";
 import { ShaderProperty } from "../shader/ShaderProperty";
 
 /**
- * Tools for get time information.
+ * Provide time related information.
  */
 export class Time {
   private static _timeProperty = ShaderProperty.getByName("u_Time");
@@ -14,12 +14,22 @@ export class Time {
   private _unscaledDeltaTime: number = 0;
   private _elapsedTime: number = 0;
   private _unscaledElapsedTime: number = 0;
-  private _timeScale: number = 1.0;
   private _lastSystemTime: number;
 
   private _timeValue: Vector4 = new Vector4();
   private _deltaTimeValue: Vector4 = new Vector4();
 
+  /**
+   * Maximum delta time allowed per frame in seconds.
+   *
+   * @remarks
+   * When the frame rate is low or stutter occurs, `deltaTime` will not exceed this value.
+   */
+  maximumDeltaTime: number = 0.333333;
+
+  /** The scale of time. */
+  timeScale: number = 1.0;
+
   /*
    * The total number of frames since the start of the engine.
    */
@@ -42,30 +52,19 @@ export class Time {
   }
 
   /**
-   * The elapsed time in seconds since the start of the engine.
+   * The amount of elapsed time in seconds since the start of the engine.
    */
   get elapsedTime(): number {
     return this._elapsedTime;
   }
 
   /**
-   * The unscaled elapsed time in seconds since the start of the engine.
+   * The amount of unscaled elapsed time in seconds since the start of the engine.
    */
   get unscaledElapsedTime(): number {
     return this._unscaledElapsedTime;
   }
 
-  /**
-   * The scale of time.
-   */
-  get timeScale(): number {
-    return this._timeScale;
-  }
-
-  set timeScale(value) {
-    this._timeScale = value;
-  }
-
   /**
    * Constructor of the Time.
    */
@@ -85,11 +84,12 @@ export class Time {
    */
   _update(): void {
     const currentSystemTime = performance.now() / 1000;
-    const unscaledDeltaTime = currentSystemTime - this._lastSystemTime;
-    const deltaTime = unscaledDeltaTime * this._timeScale;
-
+    
+    const unscaledDeltaTime = currentSystemTime - this._lastSystemTime;    
     this._unscaledDeltaTime = unscaledDeltaTime;
     this._unscaledElapsedTime += unscaledDeltaTime;
+
+    const deltaTime = Math.min(unscaledDeltaTime, this.maximumDeltaTime) * this.timeScale;
     this._deltaTime = deltaTime;
     this._elapsedTime += deltaTime;
     this._frameCount++;
diff --git a/packages/core/src/physics/PhysicsManager.ts b/packages/core/src/physics/PhysicsManager.ts
index b4e2e2e2d4..93eaaf35d6 100644
--- a/packages/core/src/physics/PhysicsManager.ts
+++ b/packages/core/src/physics/PhysicsManager.ts
@@ -127,15 +127,6 @@ export class PhysicsManager {
   /** The fixed time step in seconds at which physics are performed. */
   fixedTimeStep: number = 1 / 60;
 
-  /**
-   * The max allowed time step in seconds one frame.
-   *
-   * @remarks
-   * When the frame rate is low or stutter occurs, the maximum execution time of physics will not exceed this value.
-   * So physics will slow down a bit when performance hitch occurs.
-   */
-  maxAllowedTimeStep: number = 1 / 3;
-
   /**
    * The gravity of physics scene.
    */
@@ -150,18 +141,6 @@ export class PhysicsManager {
     }
   }
 
-  /**
-   * @deprecated
-   * Please use `maxAllowedTimeStep` instead.
-   */
-  get maxSumTimeStep(): number {
-    return this.maxAllowedTimeStep;
-  }
-
-  set maxSumTimeStep(value: number) {
-    this.maxAllowedTimeStep = value;
-  }
-
   constructor(engine: Engine) {
     this._engine = engine;
 
@@ -302,7 +281,7 @@ export class PhysicsManager {
     const { fixedTimeStep: fixedTimeStep, _nativePhysicsManager: nativePhysicsManager } = this;
     const componentsManager = this._engine._componentsManager;
 
-    const simulateTime = Math.min(this.maxAllowedTimeStep, this._restTime + deltaTime);
+    const simulateTime = this._restTime + deltaTime;
     const step = Math.floor(simulateTime / fixedTimeStep);
     this._restTime = simulateTime - step * fixedTimeStep;
     for (let i = 0; i < step; i++) {

From b671bb8e688d03bfd4702f2e55f4e669669194ba Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Fri, 17 Mar 2023 12:07:27 +0800
Subject: [PATCH 14/24] refactor: opt code

---
 packages/core/src/base/Time.ts | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index 093105e2d6..25345c2bf4 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -23,7 +23,7 @@ export class Time {
    * Maximum delta time allowed per frame in seconds.
    *
    * @remarks
-   * When the frame rate is low or stutter occurs, `deltaTime` will not exceed this value.
+   * When the frame rate is low or stutter occurs, `deltaTime` will not exceed the value of `maximumDeltaTime` * `timeScale`.
    */
   maximumDeltaTime: number = 0.333333;
 
@@ -84,8 +84,8 @@ export class Time {
    */
   _update(): void {
     const currentSystemTime = performance.now() / 1000;
-    
-    const unscaledDeltaTime = currentSystemTime - this._lastSystemTime;    
+
+    const unscaledDeltaTime = currentSystemTime - this._lastSystemTime;
     this._unscaledDeltaTime = unscaledDeltaTime;
     this._unscaledElapsedTime += unscaledDeltaTime;
 

From 6b9f1c06db7f4f32fb306c933ff000f810db4897 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Fri, 17 Mar 2023 12:54:13 +0800
Subject: [PATCH 15/24] refactor: opt code

---
 packages/core/src/physics/PhysicsManager.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/core/src/physics/PhysicsManager.ts b/packages/core/src/physics/PhysicsManager.ts
index 93eaaf35d6..eae49b5ff4 100644
--- a/packages/core/src/physics/PhysicsManager.ts
+++ b/packages/core/src/physics/PhysicsManager.ts
@@ -278,7 +278,7 @@ export class PhysicsManager {
    * @internal
    */
   _update(deltaTime: number): void {
-    const { fixedTimeStep: fixedTimeStep, _nativePhysicsManager: nativePhysicsManager } = this;
+    const { fixedTimeStep, _nativePhysicsManager: nativePhysicsManager } = this;
     const componentsManager = this._engine._componentsManager;
 
     const simulateTime = this._restTime + deltaTime;

From 200e9522ec8a6a647dfef01e5974a053e4d7e4b5 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Fri, 17 Mar 2023 13:01:26 +0800
Subject: [PATCH 16/24] refactor: opt code

---
 packages/core/src/base/Time.ts | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index 25345c2bf4..4533fd5267 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -6,7 +6,7 @@ import { ShaderProperty } from "../shader/ShaderProperty";
  * Provide time related information.
  */
 export class Time {
-  private static _timeProperty = ShaderProperty.getByName("u_Time");
+  private static _elapsedTimeProperty = ShaderProperty.getByName("u_ElapsedTime");
   private static _deltaTimeProperty = ShaderProperty.getByName("u_DeltaTime");
 
   private _frameCount: number = 0;
@@ -16,7 +16,7 @@ export class Time {
   private _unscaledElapsedTime: number = 0;
   private _lastSystemTime: number;
 
-  private _timeValue: Vector4 = new Vector4();
+  private _elapsedTimeValue: Vector4 = new Vector4();
   private _deltaTimeValue: Vector4 = new Vector4();
 
   /**
@@ -101,12 +101,12 @@ export class Time {
    * @internal
    */
   _updateSceneShaderData(shaderData: ShaderData): void {
-    const timeValue = this._timeValue;
+    const elapsedTimeValue = this._elapsedTimeValue;
     const deltaTimeValue = this._deltaTimeValue;
 
     const time = this._elapsedTime;
-    timeValue.set(time, Math.sin(time), Math.cos(time), 0);
-    shaderData.setVector4(Time._timeProperty, timeValue);
+    elapsedTimeValue.set(time, Math.sin(time), Math.cos(time), 0);
+    shaderData.setVector4(Time._elapsedTimeProperty, elapsedTimeValue);
 
     const deltaTime = this._deltaTime;
     deltaTimeValue.set(deltaTime, 0, 0, 0);

From de62310af863b24264934b581ba2ca0cedf62f34 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Fri, 17 Mar 2023 15:12:47 +0800
Subject: [PATCH 17/24] feat: rename time property name

---
 packages/core/src/base/Time.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index 4533fd5267..0b998fda1f 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -6,8 +6,8 @@ import { ShaderProperty } from "../shader/ShaderProperty";
  * Provide time related information.
  */
 export class Time {
-  private static _elapsedTimeProperty = ShaderProperty.getByName("u_ElapsedTime");
-  private static _deltaTimeProperty = ShaderProperty.getByName("u_DeltaTime");
+  private static _elapsedTimeProperty = ShaderProperty.getByName("oasis_ElapsedTime");
+  private static _deltaTimeProperty = ShaderProperty.getByName("oasis_DeltaTime");
 
   private _frameCount: number = 0;
   private _deltaTime: number = 0;

From 2d9376d9040c9a44fff6d70ae2c4d16b0de4cec4 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Fri, 17 Mar 2023 16:29:41 +0800
Subject: [PATCH 18/24] test: add Time basic unit test

---
 tests/src/core/base/Time.test.ts              | 25 +++++++++++++++++++
 tests/src/core/physics/PhysicsManager.test.ts |  1 -
 2 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 tests/src/core/base/Time.test.ts

diff --git a/tests/src/core/base/Time.test.ts b/tests/src/core/base/Time.test.ts
new file mode 100644
index 0000000000..26a8b9ffc2
--- /dev/null
+++ b/tests/src/core/base/Time.test.ts
@@ -0,0 +1,25 @@
+import { WebGLEngine } from "@oasis-engine/rhi-webgl";
+import { expect } from "chai";
+
+describe("Time", () => {
+  it("Time basic", () => {
+    const engine = new WebGLEngine(document.createElement("canvas"));
+
+    expect(engine.time.frameCount).to.be.equal(0);
+    expect(engine.time.elapsedTime).to.be.equal(0);
+    expect(engine.time.deltaTime).to.be.equal(0);
+    expect(engine.time.unscaledElapsedTime).to.be.equal(0);
+    expect(engine.time.unscaledDeltaTime).to.be.equal(0);
+
+    expect(engine.time.timeScale).to.be.equal(1);
+    engine.time.timeScale = 2;
+    expect(engine.time.timeScale).to.be.equal(2);
+
+    expect(engine.time.maximumDeltaTime).to.be.equal(0.333333);
+    engine.time.maximumDeltaTime = 0.5;
+    expect(engine.time.maximumDeltaTime).to.be.equal(0.5);
+
+    engine.update();
+    expect(engine.time.frameCount).to.be.equal(1);
+  });
+});
diff --git a/tests/src/core/physics/PhysicsManager.test.ts b/tests/src/core/physics/PhysicsManager.test.ts
index b480646715..2b7aff8ee7 100644
--- a/tests/src/core/physics/PhysicsManager.test.ts
+++ b/tests/src/core/physics/PhysicsManager.test.ts
@@ -14,7 +14,6 @@ describe("physics manager test", () => {
     engine.physicsManager.initialize(LitePhysics);
 
     expect(engine.physicsManager.gravity.y).to.eq(-9.81);
-    expect(engine.physicsManager.maxSumTimeStep).to.eq(1 / 3);
     expect(engine.physicsManager.fixedTimeStep).to.eq(1 / 60);
   });
 

From 5ffb026e2ca944dca0d828f44bb96e38673a57b2 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Mon, 20 Mar 2023 11:43:23 +0800
Subject: [PATCH 19/24] refactor: opt code

---
 packages/core/src/Scene.ts | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/packages/core/src/Scene.ts b/packages/core/src/Scene.ts
index 477b3357a0..c188ab9689 100644
--- a/packages/core/src/Scene.ts
+++ b/packages/core/src/Scene.ts
@@ -379,12 +379,13 @@ export class Scene extends EngineObject {
    */
   _updateShaderData(): void {
     const shaderData = this.shaderData;
-    const time = this._engine.time;
-    const lightManager = this._engine._lightManager;
+    const engine = this._engine;
+    const lightManager = engine._lightManager;
 
-    time._updateSceneShaderData(shaderData);
+    engine.time._updateSceneShaderData(shaderData);
 
     lightManager._updateShaderData(this.shaderData);
+
     const sunLightIndex = lightManager._getSunLightIndex();
     if (sunLightIndex !== -1) {
       this._sunLight = lightManager._directLights.get(sunLightIndex);

From 93a7f0d24c8cbaa2f2f77add8f59a7302eb17e23 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Mon, 20 Mar 2023 12:09:11 +0800
Subject: [PATCH 20/24] refactor: opt code

---
 packages/core/src/base/Time.ts | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index 0b998fda1f..fc8fd7f65b 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -108,8 +108,7 @@ export class Time {
     elapsedTimeValue.set(time, Math.sin(time), Math.cos(time), 0);
     shaderData.setVector4(Time._elapsedTimeProperty, elapsedTimeValue);
 
-    const deltaTime = this._deltaTime;
-    deltaTimeValue.set(deltaTime, 0, 0, 0);
+    deltaTimeValue.set(this._deltaTime, 0, 0, 0);
     shaderData.setVector4(Time._deltaTimeProperty, deltaTimeValue);
   }
 }

From b5a740e0deb0c63f704c24a752584f34030cb02b Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Mon, 20 Mar 2023 12:10:25 +0800
Subject: [PATCH 21/24] refactor: opt code

---
 packages/core/src/base/Time.ts | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index fc8fd7f65b..8046696fbb 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -101,8 +101,7 @@ export class Time {
    * @internal
    */
   _updateSceneShaderData(shaderData: ShaderData): void {
-    const elapsedTimeValue = this._elapsedTimeValue;
-    const deltaTimeValue = this._deltaTimeValue;
+    const { _elapsedTimeValue: elapsedTimeValue, _deltaTimeValue: deltaTimeValue } = this;
 
     const time = this._elapsedTime;
     elapsedTimeValue.set(time, Math.sin(time), Math.cos(time), 0);

From 12a8910667d9af6ef199580474479963a533d172 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Mon, 20 Mar 2023 12:29:16 +0800
Subject: [PATCH 22/24] refactor: opt code

---
 packages/core/src/base/Time.ts | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index 8046696fbb..0c672f6632 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -45,17 +45,17 @@ export class Time {
   }
 
   /**
-   * The unscaled delta time in seconds from the last frame to the current frame.
+   * The amount of elapsed time in seconds since the start of the engine.
    */
-  get unscaledDeltaTime(): number {
-    return this._unscaledDeltaTime;
+  get elapsedTime(): number {
+    return this._elapsedTime;
   }
 
   /**
-   * The amount of elapsed time in seconds since the start of the engine.
+   * The unscaled delta time in seconds from the last frame to the current frame.
    */
-  get elapsedTime(): number {
-    return this._elapsedTime;
+  get unscaledDeltaTime(): number {
+    return this._unscaledDeltaTime;
   }
 
   /**

From fa14bf9d1eb40be112e6a66d00b43b08b4480c70 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Mon, 20 Mar 2023 13:37:45 +0800
Subject: [PATCH 23/24] refactor: Optimization  time API

---
 packages/core/src/base/Time.ts | 35 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 18 deletions(-)

diff --git a/packages/core/src/base/Time.ts b/packages/core/src/base/Time.ts
index 0c672f6632..27ab6ed499 100644
--- a/packages/core/src/base/Time.ts
+++ b/packages/core/src/base/Time.ts
@@ -11,20 +11,15 @@ export class Time {
 
   private _frameCount: number = 0;
   private _deltaTime: number = 0;
-  private _unscaledDeltaTime: number = 0;
+  private _actualDeltaTime: number = 0;
   private _elapsedTime: number = 0;
-  private _unscaledElapsedTime: number = 0;
+  private _actualElapsedTime: number = 0;
   private _lastSystemTime: number;
 
   private _elapsedTimeValue: Vector4 = new Vector4();
   private _deltaTimeValue: Vector4 = new Vector4();
 
-  /**
-   * Maximum delta time allowed per frame in seconds.
-   *
-   * @remarks
-   * When the frame rate is low or stutter occurs, `deltaTime` will not exceed the value of `maximumDeltaTime` * `timeScale`.
-   */
+  /** Maximum delta time allowed per frame in seconds. */
   maximumDeltaTime: number = 0.333333;
 
   /** The scale of time. */
@@ -39,6 +34,8 @@ export class Time {
 
   /**
    * The delta time in seconds from the last frame to the current frame.
+   *
+   * @remarks When the frame rate is low or stutter occurs, `deltaTime` will not exceed the value of `maximumDeltaTime` * `timeScale`.
    */
   get deltaTime(): number {
     return this._deltaTime;
@@ -52,17 +49,19 @@ export class Time {
   }
 
   /**
-   * The unscaled delta time in seconds from the last frame to the current frame.
+   * The actual delta time in seconds from the last frame to the current frame.
+   *
+   * @remarks The actual delta time is not affected by `maximumDeltaTime` and `timeScale`.
    */
-  get unscaledDeltaTime(): number {
-    return this._unscaledDeltaTime;
+  get actualDeltaTime(): number {
+    return this._actualDeltaTime;
   }
 
   /**
-   * The amount of unscaled elapsed time in seconds since the start of the engine.
+   * The amount of actual elapsed time in seconds since the start of the engine.
    */
-  get unscaledElapsedTime(): number {
-    return this._unscaledElapsedTime;
+  get actualElapsedTime(): number {
+    return this._actualElapsedTime;
   }
 
   /**
@@ -85,11 +84,11 @@ export class Time {
   _update(): void {
     const currentSystemTime = performance.now() / 1000;
 
-    const unscaledDeltaTime = currentSystemTime - this._lastSystemTime;
-    this._unscaledDeltaTime = unscaledDeltaTime;
-    this._unscaledElapsedTime += unscaledDeltaTime;
+    const actualDeltaTime = currentSystemTime - this._lastSystemTime;
+    this._actualDeltaTime = actualDeltaTime;
+    this._actualElapsedTime += actualDeltaTime;
 
-    const deltaTime = Math.min(unscaledDeltaTime, this.maximumDeltaTime) * this.timeScale;
+    const deltaTime = Math.min(actualDeltaTime, this.maximumDeltaTime) * this.timeScale;
     this._deltaTime = deltaTime;
     this._elapsedTime += deltaTime;
     this._frameCount++;

From ffb52139615aed8d451a13b6bc4f97822c517e87 Mon Sep 17 00:00:00 2001
From: GuoLei1990 <gl3336563@163.com>
Date: Mon, 20 Mar 2023 13:45:33 +0800
Subject: [PATCH 24/24] refactor: fix unit test

---
 tests/src/core/base/Time.test.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/src/core/base/Time.test.ts b/tests/src/core/base/Time.test.ts
index 26a8b9ffc2..1c857e285f 100644
--- a/tests/src/core/base/Time.test.ts
+++ b/tests/src/core/base/Time.test.ts
@@ -8,8 +8,8 @@ describe("Time", () => {
     expect(engine.time.frameCount).to.be.equal(0);
     expect(engine.time.elapsedTime).to.be.equal(0);
     expect(engine.time.deltaTime).to.be.equal(0);
-    expect(engine.time.unscaledElapsedTime).to.be.equal(0);
-    expect(engine.time.unscaledDeltaTime).to.be.equal(0);
+    expect(engine.time.actualElapsedTime).to.be.equal(0);
+    expect(engine.time.actualDeltaTime).to.be.equal(0);
 
     expect(engine.time.timeScale).to.be.equal(1);
     engine.time.timeScale = 2;