🎮 Jade 2D Game Engine

A custom 2D game engine built from scratch in Java, featuring a complete Entity Component System (ECS), batch rendering with OpenGL, an integrated Dear ImGui editor interface with docking, JBox2D physics, and scene serialization — developed as a Semester 4 Object-Oriented Programming (OOPS) project at UPES.

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✨ Features

🏗️ Engine Core

• Entity Component System (ECS) — Modular GameObject / Component / Transform architecture
• Scene Management — LevelEditorScene and LevelScene with hot-swapping support
• Delta-Time Game Loop — Consistent updates independent of frame rate
• Singleton Window Management — GLFW-based window with input callbacks

🎨 Rendering

• OpenGL 3.3 Core — Vertex-array based batch rendering pipeline
• Custom GLSL Shaders — Vertex + Fragment shader with a single-file #type parser
• Sprite Rendering — Color-based quads with dirty-flag optimization for GPU re-upload
• Framebuffer Object (FBO) — Off-screen rendering to texture at 1920×1080, displayed inside the editor viewport
• Camera System — Orthographic projection with position-based scrolling

🖥️ Editor (Dear ImGui)

• Docking Layout — Full-window ImGui dockspace (drag, resize, rearrange panels)
• Game Viewport — Live FBO texture display with 16:9 aspect ratio preservation
• Scene Hierarchy — Clickable tree-node list of all GameObjects in the active scene
• Inspector / Properties Panel — Edit Transform (position, scale, rotation) and SpriteRenderer (color picker, z-index) in real-time
• Engine Info Panel — Live FPS, frame time, and GameObject count
• Menu Bar — File (Save/Load Scene, Exit) and GameObject (Create Empty)

⚙️ Physics

• JBox2D Integration — 2D rigid-body physics world stepping
• Collider Components — Box2DCollider and CircleCollider
• RigidBody2D — Dynamic, Static, and Kinematic body types

💾 Serialization

• GSON-based save/load of scene data to level.json

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📐 Architecture

┌────────────────────────────────────────────────────┐
│                   Main.java                        │
│                  (Entry Point)                     │
└────────────────────┬───────────────────────────────┘
                     │
                     ▼
┌────────────────────────────────────────────────────┐
│               jade.Window (Singleton)              │
│  ┌──────────┐  ┌──────────┐  ┌──────────────────┐ │
│  │   GLFW   │  │  OpenGL  │  │   ImGuiLayer     │ │
│  │  Context  │  │ Renderer │  │  (Editor UI)     │ │
│  └──────────┘  └──────────┘  └──────────────────┘ │
└────────────────────┬───────────────────────────────┘
                     │
         ┌───────────┴───────────┐
         ▼                       ▼
┌─────────────────┐   ┌──────────────────┐
│  Scene (Active)  │   │   Framebuffer    │
│  ┌────────────┐  │   │   (Off-screen)   │
│  │ GameObject │  │   └──────────────────┘
│  │ ┌────────┐ │  │
│  │ │Compnent│ │  │
│  │ └────────┘ │  │
│  └────────────┘  │
│  ┌────────────┐  │
│  │  Renderer  │  │
│  │ (Batching) │  │
│  └────────────┘  │
└──────────────────┘

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🗂️ Project Structure

Game Engine In Java/
├── assets/
│   ├── images/               # Spritesheets and textures
│   ├── shaders/
│   │   └── default.glsl      # Vertex + Fragment shader
│   └── sounds/               # Audio assets
├── src/
│   └── main/java/
│       ├── Main.java              # Entry point
│       ├── jade/                  # Core engine package
│       │   ├── Window.java        # GLFW window + game loop
│       │   ├── Camera.java        # Orthographic camera
│       │   ├── GameObject.java    # Entity container
│       │   ├── Component.java     # Base component class
│       │   ├── Transform.java     # Position, scale, rotation
│       │   ├── KeyListener.java   # Keyboard input
│       │   ├── MouseListener.java # Mouse input
│       │   ├── Prefabs.java       # Factory methods
│       │   └── scenes/
│       │       ├── Scene.java              # Abstract scene base
│       │       ├── LevelEditorScene.java   # Editor workspace
│       │       └── LevelScene.java         # Runtime scene
│       ├── renderer/              # OpenGL rendering
│       │   ├── Shader.java        # GLSL compiler & uploader
│       │   ├── RenderBatch.java   # Batched sprite renderer
│       │   ├── Renderer.java      # Batch manager
│       │   ├── Framebuffer.java   # FBO for editor viewport
│       │   └── Texture.java       # Texture wrapper
│       ├── editor/                # Dear ImGui editor panels
│       │   ├── ImGuiLayer.java         # ImGui lifecycle + dockspace
│       │   ├── GameViewWindow.java     # FBO viewport display
│       │   ├── SceneHierarchyWindow.java # GameObject tree
│       │   └── PropertiesWindow.java   # Inspector panel
│       ├── components/            # Game components
│       │   ├── SpriteRenderer.java     # Color quad rendering
│       │   ├── Spritesheet.java        # Sprite atlas parsing
│       │   ├── StateMachine.java       # Animation states
│       │   ├── PlayerController.java   # Player input handler
│       │   ├── Blocks.java             # Block behaviors
│       │   ├── GoombaAI.java           # Enemy AI
│       │   ├── TurtleAI.java           # Enemy AI
│       │   └── ComponentDeserializer.java # GSON type adapter
│       ├── physics2d/             # Physics engine
│       │   ├── Physics2D.java          # JBox2D world wrapper
│       │   ├── RaycastInfo.java        # Raycast result data
│       │   └── components/
│       │       ├── RigidBody2D.java    # Physics body
│       │       ├── Box2DCollider.java  # AABB collider
│       │       └── CircleCollider.java # Circle collider
│       └── util/                  # Utilities
│           ├── Settings.java           # Engine constants
│           ├── Time.java               # Time utilities
│           └── AssetPool.java          # Resource caching
├── pom.xml                    # Maven build config
├── build.cmd                  # Build script
├── run_jar.bat                # Run script
└── level.json                 # Saved scene data

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🚀 Getting Started

Prerequisites

Tool	Version	Purpose
JDK	17+	Compilation & runtime
Maven	3.9+ (bundled via mvnw.cmd)	Dependency management
Windows	10/11	Native ImGui & LWJGL binaries

Build

# Clone the repository
git clone https://github.com/mayankmalik263/Game-Engine-In-Java.git
cd "Game Engine In Java"

# Build the fat JAR (includes all dependencies)
.\mvnw.cmd clean package -DskipTests

Run

# Option 1: Direct Java command
java --enable-native-access=ALL-UNNAMED -jar target\jade-engine-1.0.0-jar-with-dependencies.jar

# Option 2: Use the provided batch script
.\run_jar.bat

Note: The --enable-native-access=ALL-UNNAMED flag prevents JDK 17+ warnings related to LWJGL native library access.

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🕹️ Usage

Editor Controls

Action	How
Select GameObject	Click on a name in the Scene Hierarchy panel
Edit Transform	Drag the Position / Scale / Rotation fields in the Inspector
Change Color	Click the color swatch in the Inspector under SpriteRenderer
Create New Object	Menu Bar → GameObject → Create Empty
Save Scene	Menu Bar → File → Save Scene
Load Scene	Menu Bar → File → Load Scene
Rearrange Panels	Drag any panel tab to dock it anywhere

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🧱 OOP Principles Demonstrated

This project serves as a practical demonstration of core Object-Oriented Programming concepts:

Principle	Implementation
Encapsulation	Window singleton hides GLFW internals; Framebuffer encapsulates OpenGL FBO state
Inheritance	Scene → LevelEditorScene / LevelScene; Component → SpriteRenderer / RigidBody2D / PlayerController
Polymorphism	scene.update(dt) dispatches to the correct scene subclass; component.update(dt) dispatches per-component
Abstraction	Component defines a contract (start(), update()); Scene abstracts initialization via init()

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📦 Dependencies

Library	Version	Purpose
LWJGL	3.3.3	OpenGL, GLFW windowing, STB image loading
imgui-java	1.86.11	Dear ImGui bindings for Java (GLFW + GL3 backend)
JOML	1.10.8	Math library (matrices, vectors)
JBox2D	2.2.1.1	2D rigid-body physics simulation
GSON	2.11.0	JSON serialization for scene save/load
JUnit 5	5.11.0	Unit testing framework

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🧪 Testing

# Run the unit test suite
.\mvnw.cmd test

Tests cover core systems including GameObject, Transform, Camera, and Physics2D.

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🛠️ Rendering Pipeline

┌─────────────────────────────────────────────────┐
│                  Game Loop                       │
│                                                  │
│  1. glfwPollEvents()                            │
│                                                  │
│  2. ┌─── PASS 1: Scene → Framebuffer ─────────┐ │
│     │  framebuffer.bind()                      │ │
│     │  glClear(COLOR | DEPTH)                  │ │
│     │  scene.update(dt)                        │ │
│     │    └─ renderer.render(camera)            │ │
│     │        └─ for each RenderBatch:          │ │
│     │            shader.use()                  │ │
│     │            upload projection & view      │ │
│     │            glDrawElements(...)           │ │
│     │  framebuffer.unbind()                    │ │
│     └──────────────────────────────────────────┘ │
│                                                  │
│  3. ┌─── PASS 2: ImGui → Screen ──────────────┐ │
│     │  glClear(COLOR)                          │ │
│     │  imGuiLayer.update(dt, scene, textureId) │ │
│     │    ├─ dockSpaceOverViewport()            │ │
│     │    ├─ GameViewWindow (FBO texture)       │ │
│     │    ├─ SceneHierarchyWindow               │ │
│     │    ├─ PropertiesWindow                   │ │
│     │    └─ Engine Info                        │ │
│     └──────────────────────────────────────────┘ │
│                                                  │
│  4. glfwSwapBuffers()                           │
└─────────────────────────────────────────────────┘

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📄 License

This project is developed for educational purposes as part of a university course. Feel free to use it as a learning resource.

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🙏 Acknowledgments

• GamesWithGabe — The original tutorial series that inspired this engine's architecture
• LWJGL — Lightweight Java Game Library
• Dear ImGui — Immediate-mode GUI library by Omar Cornut
• SpaiR/imgui-java — Java bindings for Dear ImGui

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Built with ☕ Java | 🎓 UPES Semester 4 OOP Project