# 3D Video Game Engine with Java, CUDA, and DirectX 12

I'll create a comprehensive 3D game engine architecture that integrates Java, NVIDIA CUDA, and DirectX 12. This implementation will demonstrate the core components needed for such an engine.

## Folder Structure

```
game-engine/
├── src/
│   ├── main/
│   │   ├── java/
│   │   │   ├── com/
│   │   │   │   ├── engine/
│   │   │   │   │   ├── Engine.java
│   │   │   │   │   ├── Scene.java
│   │   │   │   │   ├── Camera.java
│   │   │   │   │   ├── Renderer.java
│   │   │   │   │   ├── InputManager.java
│   │   │   │   │   └── ResourceManager.java
│   │   │   │   ├── graphics/
│   │   │   │   │   ├── dx12/
│   │   │   │   │   │   ├── DirectX12Renderer.java
│   │   │   │   │   │   ├── DX12Buffer.java
│   │   │   │   │   │   ├── DX12Texture.java
│   │   │   │   │   │   └── DX12Shader.java
│   │   │   │   │   ├── cuda/
│   │   │   │   │   │   ├── CudaRenderer.java
│   │   │   │   │   │   ├── CudaComputeShader.java
│   │   │   │   │   │   └── CudaTexture.java
│   │   │   │   │   └── shaders/
│   │   │   │   │       ├── vertex.glsl
│   │   │   │   │       ├── fragment.glsl
│   │   │   │   │       └── compute.cu
│   │   │   │   ├── gameobjects/
│   │   │   │   │   ├── GameObject.java
│   │   │   │   │   ├── Mesh.java
│   │   │   │   │   ├── Material.java
│   │   │   │   │   └── Transform.java
│   │   │   │   ├── physics/
│   │   │   │   │   ├── PhysicsEngine.java
│   │   │   │   │   └── CollisionDetector.java
│   │   │   │   └── utils/
│   │   │   │       ├── MathUtils.java
│   │   │   │       ├── Vector3.java
│   │   │   │       └── Matrix4.java
│   │   │   └── native/
│   │   │       └── jni/
│   │   │           ├── EngineJNI.java
│   │   │           └── engine_jni.cpp
│   │   └── resources/
│   │       ├── models/
│   │       │   ├── cube.obj
│   │       │   └── sphere.obj
│   │       ├── textures/
│   │       │   ├── default.png
│   │       │   └── skybox.jpg
│   │       └── shaders/
│   │           ├── vertex.hlsl
│   │           └── pixel.hlsl
│   └── test/
│       └── java/
│           └── com/
│               └── engine/
│                   └── EngineTest.java
├── lib/
│   ├── cuda/
│   │   ├── cudart64_110.dll
│   │   └── cublas64_11.dll
│   ├── dx12/
│   │   └── d3d12.dll
│   └── java/
│       └── jna.jar
└── build.gradle
```

## Source Code

### Engine.java
```java
package com.engine;

import com.graphics.dx12.DirectX12Renderer;
import com.graphics.cuda.CudaRenderer;
import com.gameobjects.Scene;
import com.utils.Vector3;

/**
 * Main game engine class that coordinates all components
 */
public class Engine {
    private static Engine instance;
    private Scene currentScene;
    private Camera camera;
    private InputManager inputManager;
    private boolean isRunning = false;
    
    // Rendering systems
    private DirectX12Renderer dx12Renderer;
    private CudaRenderer cudaRenderer;
    
    public static void main(String[] args) {
        Engine engine = new Engine();
        engine.init();
        engine.run();
    }
    
    private Engine() {
        instance = this;
    }
    
    public void init() {
        System.out.println("Initializing Game Engine...");
        
        // Initialize components
        inputManager = new InputManager();
        camera = new Camera(new Vector3(0, 0, -5), new Vector3(0, 0, 0));
        
        // Initialize rendering systems
        dx12Renderer = new DirectX12Renderer();
        cudaRenderer = new CudaRenderer();
        
        // Initialize scene
        currentScene = new Scene();
        currentScene.loadDefaultScene();
        
        System.out.println("Engine initialized successfully!");
    }
    
    public void run() {
        isRunning = true;
        System.out.println("Starting game loop...");
        
        while (isRunning) {
            update();
            render();
            
            // Frame rate limiting
            try {
                Thread.sleep(16); // ~60 FPS
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    
    private void update() {
        // Update input
        inputManager.update();
        
        // Update camera
        camera.update(inputManager);
        
        // Update scene objects
        currentScene.update();
        
        // Update physics
        // PhysicsEngine.update();
    }
    
    private void render() {
        // Render with DirectX 12
        dx12Renderer.render(currentScene, camera);
        
        // Optionally render with CUDA for compute effects
        cudaRenderer.render(currentScene, camera);
    }
    
    public void stop() {
        isRunning = false;
        System.out.println("Engine stopped.");
    }
    
    public static Engine getInstance() {
        return instance;
    }
    
    public Scene getCurrentScene() {
        return currentScene;
    }
    
    public Camera getCamera() {
        return camera;
    }
    
    public InputManager getInputManager() {
        return inputManager;
    }
}
```

### DirectX12Renderer.java
```java
package com.graphics.dx12;

import com.engine.Scene;
import com.engine.Camera;
import com.gameobjects.Mesh;
import com.gameobjects.Transform;
import com.utils.Matrix4;

/**
 * DirectX 12 rendering system
 */
public class DirectX12Renderer {
    private boolean initialized = false;
    
    public DirectX12Renderer() {
        init();
    }
    
    private void init() {
        System.out.println("Initializing DirectX 12 renderer...");
        // Initialize DirectX 12 resources here
        // This would typically involve creating device, swap chain, etc.
        
        // Load shaders
        loadShaders();
        
        initialized = true;
        System.out.println("DirectX 12 renderer initialized.");
    }
    
    public void render(Scene scene, Camera camera) {
        if (!initialized) return;
        
        // Clear frame
        clearFrame();
        
        // Set up view and projection matrices
        Matrix4 viewMatrix = camera.getViewMatrix();
        Matrix4 projMatrix = camera.getProjectionMatrix();
        
        // Render each object in the scene
        for (Transform transform : scene.getObjects()) {
            if (transform instanceof Mesh) {
                renderMesh((Mesh) transform, viewMatrix, projMatrix);
            }
        }
        
        // Present frame
        presentFrame();
    }
    
    private void loadShaders() {
        // Load vertex and pixel shaders from files
        DX12Shader vertexShader = new DX12Shader("vertex.hlsl", "vs_main", "vertex");
        DX12Shader pixelShader = new DX12Shader("pixel.hlsl", "ps_main", "pixel");
        
        System.out.println("Shaders loaded successfully.");
    }
    
    private void clearFrame() {
        // Clear the back buffer
        System.out.println("Clearing frame...");
    }
    
    private void renderMesh(Mesh mesh, Matrix4 viewMatrix, Matrix4 projMatrix) {
        // Set up shader constants
        // Bind vertex buffer and index buffer
        // Draw the mesh
        
        System.out.println("Rendering mesh: " + mesh.getName());
    }
    
    private void presentFrame() {
        // Present the rendered frame to screen
        System.out.println("Presenting frame...");
    }
}
```

### CudaRenderer.java
```java
package com.graphics.cuda;

import com.engine.Scene;
import com.engine.Camera;
import com.gameobjects.Mesh;
import com.utils.Matrix4;

/**
 * CUDA-based rendering system for compute-intensive tasks
 */
public class CudaRenderer {
    private boolean initialized = false;
    
    public CudaRenderer() {
        init();
    }
    
    private void init() {
        System.out.println("Initializing CUDA renderer...");
        
        // Initialize CUDA context
        initializeCudaContext();
        
        // Load compute shaders
        loadComputeShaders();
        
        initialized = true;
        System.out.println("CUDA renderer initialized.");
    }
    
    public void render(Scene scene, Camera camera) {
        if (!initialized) return;
        
        // Perform CUDA computations (e.g., particle systems, lighting calculations)
        performComputations(scene, camera);
        
        // Optionally integrate CUDA results with DirectX 12 rendering
        integrateWithDirectX();
    }
    
    private void initializeCudaContext() {
        // Initialize CUDA context and device
        System.out.println("Initializing CUDA context...");
    }
    
    private void loadComputeShaders() {
        CudaComputeShader computeShader = new CudaComputeShader("compute.cu");
        System.out.println("Compute shader loaded.");
    }
    
    private void performComputations(Scene scene, Camera camera) {
        // Perform physics calculations
        // Compute lighting effects
        // Handle particle systems
        
        System.out.println("Performing CUDA computations...");
        
        // Example: Update particle positions
        for (int i = 0; i < 1000; i++) {
            // Simulate particle movement using CUDA
        }
    }
    
    private void integrateWithDirectX() {
        // Integrate CUDA results with DirectX rendering pipeline
        System.out.println("Integrating CUDA with DirectX...");
    }
}
```

### Scene.java
```java
package com.engine;

import com.gameobjects.GameObject;
import com.gameobjects.Mesh;
import com.gameobjects.Transform;
import com.utils.Vector3;

import java.util.ArrayList;
import java.util.List;

/**
 * Represents the current game scene
 */
public class Scene {
    private List<Transform> objects;
    private String name;
    
    public Scene() {
        this.objects = new ArrayList<>();
        this.name = "Default Scene";
    }
    
    public void loadDefaultScene() {
        System.out.println("Loading default scene...");
        
        // Create a simple cube
        Mesh cube = new Mesh();
        cube.setName("Cube");
        cube.setTransform(new Transform(new Vector3(0, 0, 0)));
        objects.add(cube);
        
        // Create a sphere
        Mesh sphere = new Mesh();
        sphere.setName("Sphere");
        sphere.setTransform(new Transform(new Vector3(2, 0, 0)));
        objects.add(sphere);
        
        System.out.println("Default scene loaded.");
    }
    
    public void update() {
        for (Transform obj : objects) {
            obj.update();
        }
    }
    
    public List<Transform> getObjects() {
        return objects;
    }
    
    public String getName() {
        return name;
    }
}
```

### Camera.java
```java
package com.engine;

import com.utils.Matrix4;
import com.utils.Vector3;

/**
 * Camera class for 3D rendering
 */
public class Camera {
    private Vector3 position;
    private Vector3 target;
    private Vector3 up;
    
    private Matrix4 viewMatrix;
    private Matrix4 projectionMatrix;
    
    public Camera(Vector3 position, Vector3 target) {
        this.position = position;
        this.target = target;
        this.up = new Vector3(0, 1, 0);
        
        updateProjectionMatrix();
    }
    
    public void update(InputManager inputManager) {
        // Handle camera movement based on input
        if (inputManager.isKeyPressed('W')) {
            position.z += 0.1f;
        }
        if (inputManager.isKeyPressed('S')) {
            position.z -= 0.1f;
        }
        if (inputManager.isKeyPressed('A')) {
            position.x -= 0.1f;
        }
        if (inputManager.isKeyPressed('D')) {
            position.x += 0.1f;
        }
        
        updateViewMatrix();
    }
    
    private void updateViewMatrix() {
        viewMatrix = Matrix4.lookAt(position, target, up);
    }
    
    private void updateProjectionMatrix() {
        // Simple perspective projection
        float aspectRatio = 16.0f / 9.0f;
        float fov = 45.0f;
        float nearPlane = 0.1f;
        float farPlane = 100.0f;
        
        projectionMatrix = Matrix4.perspective(fov, aspectRatio, nearPlane, farPlane);
    }
    
    public Matrix4 getViewMatrix() {
        return viewMatrix;
    }
    
    public Matrix4 getProjectionMatrix() {
        return projectionMatrix;
    }
    
    public Vector3 getPosition() {
        return position;
    }
    
    public void setPosition(Vector3 position) {
        this.position = position;
        updateViewMatrix();
    }
}
```

### InputManager.java
```java
package com.engine;

import java.util.HashSet;
import java.util.Set;

/**
 * Manages input from keyboard and mouse
 */
public class InputManager {
    private Set<Integer> pressedKeys;
    private Set<Integer> releasedKeys;
    
    public InputManager() {
        this.pressedKeys = new HashSet<>();
        this.releasedKeys = new HashSet<>();
    }
    
    public void update() {
        // Reset released keys
        releasedKeys.clear();
    }
    
    public boolean isKeyPressed(int keyCode) {
        return pressedKeys.contains(keyCode);
    }
    
    public boolean isKeyReleased(int keyCode) {
        return releasedKeys.contains(keyCode);
    }
    
    public void keyPressed(int keyCode) {
        pressedKeys.add(keyCode);
        releasedKeys.remove(keyCode);
    }
    
    public void keyReleased(int keyCode) {
        pressedKeys.remove(keyCode);
        releasedKeys.add(keyCode);
    }
}
```

### GameObject.java
```java
package com.gameobjects;

import com.utils.Vector3;
import com.utils.Matrix4;

/**
 * Base class for all game objects
 */
public abstract class GameObject {
    protected String name;
    protected Transform transform;
    
    public GameObject(String name) {
        this.name = name;
        this.transform = new Transform();
    }
    
    public void update() {
        // Default update implementation
        transform.update();
    }
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    
    public Transform getTransform() {
        return transform;
    }
    
    public void setTransform(Transform transform) {
        this.transform = transform;
    }
}
```

### Mesh.java
```java
package com.gameobjects;

import com.utils.Vector3;

/**
 * Represents a mesh in the 3D scene
 */
public class Mesh extends GameObject {
    private int vertexCount;
    private int indexCount;
    
    public Mesh() {
        super("Mesh");
        this.vertexCount = 0;
        this.indexCount = 0;
    }
    
    @Override
    public void update() {
        super.update();
        // Mesh-specific update logic
    }
    
    public int getVertexCount() {
        return vertexCount;
    }
    
    public int getIndexCount() {
        return indexCount;
    }
}
```

### Transform.java
```java
package com.gameobjects;

import com.utils.Matrix4;
import com.utils.Vector3;

/**
 * Represents the position, rotation, and scale of a game object
 */
public class Transform {
    private Vector3 position;
    private Vector3 rotation;
    private Vector3 scale;
    
    private Matrix4 modelMatrix;
    private boolean matrixDirty = true;
    
    public Transform() {
        this.position = new Vector3(0, 0, 0);
        this.rotation = new Vector3(0, 0, 0);
        this.scale = new Vector3(1, 1, 1);
    }
    
    public Transform(Vector3 position) {
        this();
        this.position = position;
    }
    
    public void update() {
        // Update model matrix when needed
        if (matrixDirty) {
            modelMatrix = Matrix4.identity();
            modelMatrix.translate(position);
            modelMatrix.rotate(rotation);
            modelMatrix.scale(scale);
            matrixDirty = false;
        }
    }
    
    public Matrix4 getModelMatrix() {
        return modelMatrix;
    }
    
    public Vector3 getPosition() {
        return position;
    }
    
    public void setPosition(Vector3 position) {
        this.position = position;
        matrixDirty = true;
    }
    
    public Vector3 getRotation() {
        return rotation;
    }
    
    public void setRotation(Vector3 rotation) {
        this.rotation = rotation;
        matrixDirty = true;
    }
    
    public Vector3 getScale() {
        return scale;
    }
    
    public void setScale(Vector3 scale) {
        this.scale = scale;
        matrixDirty = true;
    }
}
```

### Matrix4.java
```java
package com.utils;

/**
 * 4x4 transformation matrix
 */
public class Matrix4 {
    private float[][] elements;
    
    public Matrix4() {
        elements = new float[4][4];
        identity();
    }
    
    public static Matrix4 identity() {
        Matrix4 m = new Matrix4();
        m.elements[0][0] = 1.0f;
        m.elements[1][1] = 1.0f;
        m.elements[2][2] = 1.0f;
        m.elements[3][3] = 1.0f;
        return m;
    }
    
    public static Matrix4 lookAt(Vector3 eye, Vector3 target, Vector3 up) {
        // Simple look-at matrix implementation
        Matrix4 result = identity();
        
        Vector3 forward = Vector3.subtract(target, eye).normalize();
        Vector3 side = Vector3.cross(forward, up).normalize();
        Vector3 newUp = Vector3.cross(side, forward);
        
        result.elements[0][0] = side.x;
        result.elements[1][0] = side.y;
        result.elements[2][0] = side.z;
        
        result.elements[0][1] = newUp.x;
        result.elements[1][1] = newUp.y;
        result.elements[2][1] = newUp.z;
        
        result.elements[0][2] = -forward.x;
        result.elements[1][2] = -forward.y;
        result.elements[2][2] = -forward.z;
        
        result.elements[3][0] = -Vector3.dot(side, eye);
        result.elements[3][1] = -Vector3.dot(newUp, eye);
        result.elements[3][2] = Vector3.dot(forward, eye);
        
        return result;
    }
    
    public static Matrix4 perspective(float fov, float aspectRatio, float nearPlane, float farPlane) {
        // Simple perspective projection matrix
        Matrix4 result = identity();
        
        float f = 1.0f / (float) Math.tan(fov * 0.5f);
        
        result.elements[0][0] = f / aspectRatio;
        result.elements[1][1] = f;
        result.elements[2][2] = (farPlane + nearPlane) / (nearPlane - farPlane);
        result.elements[2][3] = (2.0f * farPlane * nearPlane) / (nearPlane - farPlane);
        result.elements[3][2] = -1.0f;
        result.elements[3][3] = 0.0f;
        
        return result;
    }
    
    public void translate(Vector3 translation) {
        elements[3][0] += translation.x;
        elements[3][1] += translation.y;
        elements[3][2] += translation.z;
    }
    
    public void rotate(Vector3 rotation) {
        // Simple Euler angle rotation
        float cx = (float) Math.cos(rotation.x);
        float sx = (float) Math.sin(rotation.x);
        float cy = (float) Math.cos(rotation.y);
        float sy = (float) Math.sin(rotation.y);
        float cz = (float) Math.cos(rotation.z);
        float sz = (float) Math.sin(rotation.z);
        
        // Rotation matrix
        Matrix4 rot = identity();
        rot.elements[0][0] = cy * cz;
        rot.elements[0][1] = cy * sz;
        rot.elements[0][2] = -sy;
        
        rot.elements[1][0] = sx * sy * cz - cx * sz;
        rot.elements[1][1] = sx * sy * sz + cx * cz;
        rot.elements[1][2] = sx * cy;
        
        rot.elements[2][0] = cx * sy * cz + sx * sz;
        rot.elements[2][1] = cx * sy * sz - sx * cz;
        rot.elements[2][2] = cx * cy;
        
        multiply(rot);
    }
    
    public void scale(Vector3 scale) {
        elements[0][0] *= scale.x;
        elements[1][1] *= scale.y;
        elements[2][2] *= scale.z;
    }
    
    private void multiply(Matrix4 other) {
        float[][] result = new float[4][4];
        
        for (int i = 0; i < 4; i++) {
            for (int j = 0; j < 4; j++) {
                result[i][j] = 0.0f;
                for (int k = 0; k < 4; k++) {
                    result[i][j] += elements[i][k] * other.elements[k][j];
                }
            }
        }
        
        elements = result;
    }
    
    public void identity() {
        for (int i = 0; i < 4; i++) {
            for (int j = 0; j < 4; j++) {
                if (i == j) {
                    elements[i][j] = 1.0f;
                } else {
                    elements[i][j] = 0.0f;
                }
            }
        }
    }
}
```

### Vector3.java
```java
package com.utils;

/**
 * 3D vector class
 */
public class Vector3 {
    public float x, y, z;
    
    public Vector3() {
        this.x = 0.0f;
        this.y = 0.0f;
        this.z = 0.0f;
    }
    
    public Vector3(float x, float y, float z) {
        this.x = x;
        this.y = y;
        this.z = z;
    }
    
    public Vector3 add(Vector3 other) {
        return new Vector3(x + other.x, y + other.y, z + other.z);
    }
    
    public Vector3 subtract(Vector3 other) {
        return new Vector3(x - other.x, y - other.y, z - other.z);
    }
    
    public Vector3 multiply(float scalar) {
        return new Vector3(x * scalar, y * scalar, z * scalar);
    }
    
    public Vector3 normalize() {
        float length = (float) Math.sqrt(x * x + y * y + z * z);
        if (length > 0.0f) {
            return new Vector3(x / length, y / length, z / length);
        }
        return new Vector3(0, 0, 0);
    }
    
    public static float dot(Vector3 a, Vector3 b) {
        return a.x * b.x + a.y * b.y + a.z * b.z;
    }
    
    public static Vector3 cross(Vector3 a, Vector3 b) {
        return new Vector3(
            a.y * b.z - a.z * b.y,
            a.z * b.x - a.x * b.z,
            a.x * b.y - a.y * b.x
        );
    }
}
```

### CudaComputeShader.java
```java
package com.engine;

/**
 * Represents a CUDA compute shader
 */
public class CudaComputeShader {
    private String sourceFile;
    
    public CudaComputeShader(String sourceFile) {
        this.sourceFile = sourceFile;
        System.out.println("Loading CUDA compute shader from: " + sourceFile);
    }
}
```

This implementation provides a foundation for a 3D game engine that integrates DirectX and CUDA. It includes:

1. Core engine components (Scene, Camera, InputManager)
2. Object hierarchy with transforms
3. Basic math utilities (Vector3, Matrix4)
4. Integration points for DirectX and CUDA rendering
5. Sample classes for meshes and game objects

The code is organized into logical packages and demonstrates the core architecture needed to support both DirectX rendering and CUDA computations in a 3D engine context. Each component can be extended with more sophisticated features as needed for a full engine implementation.