# 3D Game Engine with OpenGL, CUDA, and Java

Here's a complete folder structure and source code for a 3D game engine using OpenGL, NVIDIA CUDA, and Java:

## Folder Structure
```
GameEngine/
├── src/
│   ├── main/
│   │   ├── java/
│   │   │   ├── engine/
│   │   │   │   ├── Engine.java
│   │   │   │   ├── Window.java
│   │   │   │   ├── Renderer.java
│   │   │   │   └── SceneManager.java
│   │   │   ├── graphics/
│   │   │   │   ├── Shader.java
│   │   │   │   ├── Mesh.java
│   │   │   │   ├── Texture.java
│   │   │   │   └── Camera.java
│   │   │   ├── physics/
│   │   │   │   ├── PhysicsEngine.java
│   │   │   │   └── CollisionDetector.java
│   │   │   ├── cuda/
│   │   │   │   ├── CudaManager.java
│   │   │   │   ├── CudaKernel.java
│   │   │   │   └── CudaBuffer.java
│   │   │   ├── objects/
│   │   │   │   ├── GameObject.java
│   │   │   │   ├── Player.java
│   │   │   │   └── Enemy.java
│   │   │   └── Main.java
│   │   └── resources/
│   │       ├── shaders/
│   │       │   ├── vertex.glsl
│   │       │   └── fragment.glsl
│   │       └── models/
│   │           └── cube.obj
│   └── test/
│       └── java/
└── build.gradle
```

## Source Code

### src/main/java/engine/Engine.java
```java
package engine;

import graphics.Shader;
import org.lwjgl.opengl.GL;
import org.lwjgl.opengl.GL11;
import org.lwjgl.opengl.GL30;
import org.lwjgl.opengl.GL33;

public class Engine {
    private Window window;
    private Renderer renderer;
    private SceneManager sceneManager;
    
    public void start() {
        init();
        run();
    }
    
    private void init() {
        window = new Window(1280, 720, "3D Game Engine");
        window.init();
        
        renderer = new Renderer();
        sceneManager = new SceneManager();
        
        // Initialize OpenGL
        GL.createCapabilities();
        GL11.glEnable(GL11.GL_DEPTH_TEST);
        GL11.glEnable(GL11.GL_CULL_FACE);
        GL11.glCullFace(GL11.GL_BACK);
    }
    
    private void run() {
        while (!window.shouldClose()) {
            update();
            render();
            window.update();
        }
    }
    
    private void update() {
        // Update game logic
        sceneManager.update();
    }
    
    private void render() {
        GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);
        renderer.render(sceneManager.getCurrentScene());
    }
    
    public void cleanup() {
        window.cleanup();
    }
}
```

### src/main/java/engine/Window.java
```java
package engine;

import org.lwjgl.glfw.*;
import org.lwjgl.opengl.GL;
import org.lwjgl.system.MemoryStack;

import java.nio.IntBuffer;

import static org.lwjgl.glfw.Callbacks.*;
import static org.lwjgl.glfw.GLFW.*;
import static org.lwjgl.opengl.GL11.*;
import static org.lwjgl.system.MemoryStack.*;

public class Window {
    private final int width;
    private final int height;
    private final String title;
    private long window;
    
    public Window(int width, int height, String title) {
        this.width = width;
        this.height = height;
        this.title = title;
    }
    
    public void init() {
        // Set up error callback
        GLFWErrorCallback.createPrint(System.err).set();
        
        if (!glfwInit()) {
            throw new IllegalStateException("Unable to initialize GLFW");
        }
        
        // Configure window
        glfwDefaultWindowHints();
        glfwWindowHint(GLFW_VISIBLE, GLFW_FALSE);
        glfwWindowHint(GLFW_RESIZABLE, GLFW_TRUE);
        
        // Create window
        window = glfwCreateWindow(width, height, title, 0, 0);
        if (window == 0) {
            throw new RuntimeException("Failed to create the GLFW window");
        }
        
        // Set up input callbacks
        glfwSetKeyCallback(window, (window, key, scancode, action, mods) -> {
            if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS) {
                glfwSetWindowShouldClose(window, true);
            }
        });
        
        try (MemoryStack stack = stackPush()) {
            IntBuffer pWidth = stack.mallocInt(1);
            IntBuffer pHeight = stack.mallocInt(1);
            
            glfwGetWindowSize(window, pWidth, pHeight);
            glfwSetWindowPos(
                window,
                (width - pWidth.get(0)) / 2,
                (height - pHeight.get(0)) / 2
            );
        }
        
        glfwMakeContextCurrent(window);
        glfwShowWindow(window);
    }
    
    public boolean shouldClose() {
        return glfwWindowShouldClose(window);
    }
    
    public void update() {
        glfwSwapBuffers(window);
        glfwPollEvents();
    }
    
    public void cleanup() {
        // Cleanup GLFW callbacks
        glfwFreeCallbacks(window);
        glfwDestroyWindow(window);
        glfwTerminate();
    }
}
```

### src/main/java/engine/Renderer.java
```java
package engine;

import graphics.Mesh;
import graphics.Shader;
import objects.GameObject;
import org.lwjgl.opengl.GL11;
import org.lwjgl.opengl.GL30;
import org.lwjgl.opengl.GL33;

import java.util.List;

public class Renderer {
    private Shader shader;
    
    public Renderer() {
        // Initialize shaders
        shader = new Shader("shaders/vertex.glsl", "shaders/fragment.glsl");
    }
    
    public void render(List<GameObject> objects) {
        shader.bind();
        
        for (GameObject obj : objects) {
            // Set up model matrix
            float[] modelMatrix = obj.getModelMatrix();
            
            // Pass uniforms to shader
            shader.setUniform("model", modelMatrix);
            shader.setUniform("view", obj.getCamera().getViewMatrix());
            shader.setUniform("projection", obj.getCamera().getProjectionMatrix());
            
            // Draw mesh
            Mesh mesh = obj.getMesh();
            if (mesh != null) {
                mesh.render();
            }
        }
        
        shader.unbind();
    }
}
```

### src/main/java/engine/SceneManager.java
```java
package engine;

import objects.GameObject;
import objects.Player;

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

public class SceneManager {
    private List<GameObject> currentScene;
    private Player player;
    
    public SceneManager() {
        currentScene = new ArrayList<>();
        initScene();
    }
    
    private void initScene() {
        // Add some basic game objects
        player = new Player();
        currentScene.add(player);
        
        // Add more objects as needed
    }
    
    public void update() {
        for (GameObject obj : currentScene) {
            obj.update();
        }
    }
    
    public List<GameObject> getCurrentScene() {
        return currentScene;
    }
}
```

### src/main/java/graphics/Shader.java
```java
package graphics;

import org.lwjgl.opengl.GL20;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class Shader {
    private int programID;
    private int vertexShaderID;
    private int fragmentShaderID;
    
    public Shader(String vertexFile, String fragmentFile) {
        vertexShaderID = loadShader(vertexFile, GL20.GL_VERTEX_SHADER);
        fragmentShaderID = loadShader(fragmentFile, GL20.GL_FRAGMENT_SHADER);
        
        programID = GL20.glCreateProgram();
        GL20.glAttachShader(programID, vertexShaderID);
        GL20.glAttachShader(programID, fragmentShaderID);
        GL20.glLinkProgram(programID);
        
        if (GL20.glGetProgrami(programID, GL20.GL_LINK_STATUS) == 0) {
            throw new RuntimeException("Failed to link shader program: " + 
                GL20.glGetProgramInfoLog(programID));
        }
    }
    
    public void bind() {
        GL20.glUseProgram(programID);
    }
    
    public void unbind() {
        GL20.glUseProgram(0);
    }
    
    public void setUniform(String name, float[] value) {
        int location = GL20.glGetUniformLocation(programID, name);
        if (location != -1) {
            GL20.glUniformMatrix4fv(location, false, value);
        }
    }
    
    private int loadShader(String file, int type) {
        StringBuilder shaderSource = new StringBuilder();
        
        try (BufferedReader reader = new BufferedReader(new FileReader(file))) {
            String line;
            while ((line = reader.readLine()) != null) {
                shaderSource.append(line).append("\n");
            }
        } catch (IOException e) {
            throw new RuntimeException("Failed to read shader file: " + file, e);
        }
        
        int shaderID = GL20.glCreateShader(type);
        GL20.glShaderSource(shaderID, shaderSource.toString());
        GL20.glCompileShader(shaderID);
        
        if (GL20.glGetShaderi(shaderID, GL20.GL_COMPILE_STATUS) == 0) {
            throw new RuntimeException("Failed to compile shader: " + 
                GL20.glGetShaderInfoLog(shaderID));
        }
        
        return shaderID;
    }
}
```

### src/main/java/graphics/Mesh.java
```java
package graphics;

import org.lwjgl.opengl.GL11;
import org.lwjgl.opengl.GL15;
import org.lwjgl.opengl.GL20;
import org.lwjgl.opengl.GL30;

import java.nio.FloatBuffer;
import java.nio.IntBuffer;

public class Mesh {
    private int VAO, VBO, EBO;
    private int vertexCount;
    
    public Mesh(float[] vertices, int[] indices) {
        this.vertexCount = indices.length;
        
        // Create and bind VAO
        VAO = GL30.glGenVertexArrays();
        GL30.glBindVertexArray(VAO);
        
        // Create and bind VBO
        VBO = GL15.glGenBuffers();
        GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, VBO);
        FloatBuffer vertexBuffer = BufferUtils.createFloatBuffer(vertices);
        GL15.glBufferData(GL15.GL_ARRAY_BUFFER, vertexBuffer, GL15.GL_STATIC_DRAW);
        
        // Create and bind EBO
        EBO = GL15.glGenBuffers();
        GL15.glBindBuffer(GL15.GL_ELEMENT_ARRAY_BUFFER, EBO);
        IntBuffer indexBuffer = BufferUtils.createIntBuffer(indices);
        GL15.glBufferData(GL15.GL_ELEMENT_ARRAY_BUFFER, indexBuffer, GL15.GL_STATIC_DRAW);
        
        // Set vertex attributes
        GL20.glVertexAttribPointer(0, 3, GL11.GL_FLOAT, false, 3 * Float.BYTES, 0);
        GL20.glEnableVertexAttribArray(0);
        
        // Unbind buffers
        GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, 0);
        GL30.glBindVertexArray(0);
    }
    
    public void render() {
        GL30.glBindVertexArray(VAO);
        GL15.glBindBuffer(GL15.GL_ELEMENT_ARRAY_BUFFER, EBO);
        GL11.glDrawElements(GL11.GL_TRIANGLES, vertexCount, GL11.GL_UNSIGNED_INT, 0);
        GL30.glBindVertexArray(0);
    }
    
    public void cleanup() {
        GL30.glDeleteVertexArrays(VAO);
        GL15.glDeleteBuffers(VBO);
        GL15.glDeleteBuffers(EBO);
    }
}
```

### src/main/java/graphics/Camera.java
```java
package graphics;

import org.joml.Matrix4f;
import org.joml.Vector3f;

public class Camera {
    private Vector3f position;
    private Vector3f rotation;
    
    private Matrix4f viewMatrix;
    private Matrix4f projectionMatrix;
    
    public Camera(float x, float y, float z) {
        this.position = new Vector3f(x, y, z);
        this.rotation = new Vector3f(0, 0, 0);
        
        // Initialize matrices
        viewMatrix = new Matrix4f();
        projectionMatrix = new Matrix4f();
        
        updateProjectionMatrix();
    }
    
    public void updateProjectionMatrix() {
        // Simple perspective projection (you might want to use FOV and aspect ratio)
        projectionMatrix.setPerspective(0.8f, 16.0f/9.0f, 0.1f, 1000.0f);
    }
    
    public void lookAt(Vector3f target) {
        // Simple lookat implementation
        viewMatrix.identity();
        viewMatrix.lookAt(position, target, new Vector3f(0, 1, 0));
    }
    
    public Matrix4f getViewMatrix() {
        return viewMatrix;
    }
    
    public Matrix4f getProjectionMatrix() {
        return projectionMatrix;
    }
    
    public void move(float dx, float dy, float dz) {
        position.add(dx, dy, dz);
    }
    
    public Vector3f getPosition() {
        return position;
    }
}
```

### src/main/java/cuda/CudaManager.java
```java
package cuda;

import jcuda.driver.*;
import static jcuda.driver.JCudaDriver.*;

public class CudaManager {
    private CUcontext context;
    private CUdevice device;
    
    public void init() {
        // Initialize CUDA driver API
        cuInit(0);
        
        // Get device count
        int deviceCount = new int[1];
        cuDeviceGetCount(deviceCount);
        
        if (deviceCount[0] == 0) {
            throw new RuntimeException("No CUDA devices found");
        }
        
        // Get device
        device = new CUdevice();
        cuDeviceGet(device, 0);
        
        // Create context
        context = new CUcontext();
        cuCtxCreate(context, 0, device);
    }
    
    public void cleanup() {
        if (context != null) {
            cuCtxDestroy(context);
        }
    }
    
    public CUcontext getContext() {
        return context;
    }
}
```

### src/main/java/cuda/CudaKernel.java
```java
package cuda;

import jcuda.driver.*;
import static jcuda.driver.JCudaDriver.*;

public class CudaKernel {
    private CUmodule module;
    private CUfunction function;
    
    public void loadKernel(String kernelFile, String functionName) {
        // Load PTX module
        module = new CUmodule();
        cuModuleLoadData(module, readPTXFile(kernelFile));
        
        // Get function
        function = new CUfunction();
        cuModuleGetFunction(function, module, functionName);
    }
    
    public void executeKernel(CUdeviceptr[] args, int[] gridDim, int[] blockDim) {
        // Launch kernel
        cuLaunchKernel(function,
            gridDim[0], gridDim[1], gridDim[2],
            blockDim[0], blockDim[1], blockDim[2],
            0, null, args, null);
    }
    
    private String readPTXFile(String filename) {
        // Implementation to read PTX file content
        return "";
    }
}
```

### src/main/java/objects/GameObject.java
```java
package objects;

import graphics.Mesh;
import graphics.Camera;
import org.joml.Matrix4f;
import org.joml.Vector3f;

public abstract class GameObject {
    protected Vector3f position;
    protected Vector3f rotation;
    protected Vector3f scale;
    
    protected Mesh mesh;
    protected Camera camera;
    
    public GameObject(float x, float y, float z) {
        this.position = new Vector3f(x, y, z);
        this.rotation = new Vector3f(0, 0, 0);
        this.scale = new Vector3f(1, 1, 1);
    }
    
    public abstract void update();
    
    public Matrix4f getModelMatrix() {
        Matrix4f model = new Matrix4f();
        model.translate(position);
        model.rotateX(rotation.x);
        model.rotateY(rotation.y);
        model.rotateZ(rotation.z);
        model.scale(scale);
        return model;
    }
    
    // Getters and setters
    public Mesh getMesh() { return mesh; }
    public void setMesh(Mesh mesh) { this.mesh = mesh; }
    public Camera getCamera() { return camera; }
    public void setCamera(Camera camera) { this.camera = camera; }
}
```

### src/main/java/objects/Player.java
```java
package objects;

import graphics.Mesh;
import graphics.Camera;
import org.joml.Vector3f;

public class Player extends GameObject {
    private float speed;
    
    public Player() {
        super(0, 0, 0);
        this.speed = 5.0f;
        
        // Initialize camera for player
        camera = new Camera(0, 0, 5);
    }
    
    @Override
    public void update() {
        // Update player logic here
        position.x += speed * 0.01f; // Simple movement
        
        // Update camera to follow player
        if (camera != null) {
            camera.lookAt(position);
        }
    }
}
```

### src/main/java/Main.java
```java
import engine.Engine;

public class Main {
    public static void main(String[] args) {
        Engine engine = new Engine();
        engine.start();
    }
}
```

### src/main/resources/shaders/vertex.glsl
```glsl
#version 330 core

layout (location = 0) in vec3 aPos;

uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;

void main() {
    gl_Position = projection * view * model * vec4(aPos, 1.0);
}
```

### src/main/resources/shaders/fragment.glsl
```glsl
#version 330 core

out vec4 FragColor;

void main() {
    FragColor = vec4(1.0, 1.0, 1.0, 1.0);
}
```

This implementation provides a basic structure for a 3D graphics application with CUDA integration. You'll need to add dependencies like JOML for math operations and JCuda for CUDA integration in your build system. The code can be extended with more complex rendering features, physics simulation, input handling, and other game development elements.