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

Here's a comprehensive folder structure and source code for a 3D video game engine that integrates Rust, NVIDIA CUDA, and DirectX 12:

## Folder Structure
```
game_engine/
├── Cargo.toml
├── src/
│   ├── main.rs
│   ├── engine/
│   │   ├── mod.rs
│   │   ├── core/
│   │   │   ├── mod.rs
│   │   │   ├── renderer.rs
│   │   │   ├── input.rs
│   │   │   └── timer.rs
│   │   ├── graphics/
│   │   │   ├── mod.rs
│   │   │   ├── dx12_renderer.rs
│   │   │   └── cuda_renderer.rs
│   │   ├── assets/
│   │   │   ├── mod.rs
│   │   │   ├── mesh.rs
│   │   │   ├── texture.rs
│   │   │   └── shader.rs
│   │   └── scene/
│   │       ├── mod.rs
│   │       ├── scene_graph.rs
│   │       └── camera.rs
│   └── utils/
│       ├── mod.rs
│       ├── math.rs
│       └── logger.rs
├── shaders/
│   ├── vertex.hlsl
│   ├── pixel.hlsl
│   └── compute.hlsl
├── cuda/
│   ├── kernels.cu
│   └── cuda_bindings.rs
└── build/
    ├── build.rs
    └── config.toml
```

## Cargo.toml
```toml
[package]
name = "game_engine"
version = "0.1.0"
edition = "2021"

[dependencies]
winit = "0.28"
windows = { version = "0.51", features = ["Win32_Foundation", "Win32_UI_WindowsAndMessaging", "Win32_Graphics_Direct3D12"] }
d3d12 = "0.1"
nvapi = "0.1"
bytemuck = "1.12"
serde = { version = "1.0", features = ["derive"] }
log = "0.4"
env_logger = "0.10"
image = "0.24"

[build-dependencies]
cc = "1.0"
```

## src/main.rs
```rust
use engine::core::renderer::Renderer;
use engine::scene::scene_graph::SceneGraph;

mod engine;

fn main() {
    env_logger::init();
    
    let mut renderer = Renderer::new();
    let mut scene = SceneGraph::new();
    
    // Initialize the engine
    if let Err(e) = renderer.initialize() {
        eprintln!("Failed to initialize renderer: {}", e);
        return;
    }
    
    // Main game loop
    loop {
        // Process input
        // Update game logic
        // Render scene
        
        renderer.render(&scene);
        
        // Handle frame timing
        std::thread::sleep(std::time::Duration::from_millis(16)); // ~60 FPS
    }
}
```

## src/engine/mod.rs
```rust
pub mod core;
pub mod graphics;
pub mod assets;
pub mod scene;
pub mod utils;
```

## src/engine/core/renderer.rs
```rust
use crate::engine::graphics::dx12_renderer::Dx12Renderer;
use crate::engine::graphics::cuda_renderer::CudaRenderer;
use crate::engine::scene::scene_graph::SceneGraph;

pub struct Renderer {
    dx12_renderer: Dx12Renderer,
    cuda_renderer: CudaRenderer,
}

impl Renderer {
    pub fn new() -> Self {
        Self {
            dx12_renderer: Dx12Renderer::new(),
            cuda_renderer: CudaRenderer::new(),
        }
    }

    pub fn initialize(&mut self) -> Result<(), Box<dyn std::error::Error>> {
        self.dx12_renderer.initialize()?;
        self.cuda_renderer.initialize()?;
        Ok(())
    }

    pub fn render(&mut self, scene: &SceneGraph) {
        // Use DirectX 12 for rendering
        self.dx12_renderer.render(scene);
        
        // Use CUDA for compute-intensive tasks
        self.cuda_renderer.render(scene);
    }
}
```

## src/engine/core/input.rs
```rust
use winit::event::{Event, KeyboardInput, VirtualKeyCode, ElementState};

pub struct InputManager {
    pub keys_pressed: Vec<VirtualKeyCode>,
    pub mouse_position: (f32, f32),
}

impl InputManager {
    pub fn new() -> Self {
        Self {
            keys_pressed: Vec::new(),
            mouse_position: (0.0, 0.0),
        }
    }

    pub fn handle_event(&mut self, event: &Event<()>) {
        match event {
            Event::WindowEvent { event, .. } => {
                match event {
                    winit::event::WindowEvent::KeyboardInput { input, .. } => {
                        if let Some(keycode) = input.virtual_keycode {
                            match input.state {
                                ElementState::Pressed => {
                                    self.keys_pressed.push(keycode);
                                }
                                ElementState::Released => {
                                    self.keys_pressed.retain(|&k| k != keycode);
                                }
                            }
                        }
                    }
                    winit::event::WindowEvent::CursorMoved { position, .. } => {
                        self.mouse_position = (position.x as f32, position.y as f32);
                    }
                    _ => {}
                }
            }
            _ => {}
        }
    }

    pub fn is_key_pressed(&self, key: VirtualKeyCode) -> bool {
        self.keys_pressed.contains(&key)
    }
}
```

## src/engine/core/timer.rs
```rust
use std::time::{Instant, Duration};

pub struct Timer {
    start_time: Instant,
    last_frame_time: Duration,
}

impl Timer {
    pub fn new() -> Self {
        Self {
            start_time: Instant::now(),
            last_frame_time: Duration::from_secs(0),
        }
    }

    pub fn update(&mut self) {
        self.last_frame_time = self.start_time.elapsed();
        self.start_time = Instant::now();
    }

    pub fn delta_time(&self) -> f32 {
        self.last_frame_time.as_secs_f32()
    }

    pub fn elapsed_seconds(&self) -> f32 {
        self.start_time.elapsed().as_secs_f32()
    }
}
```

## src/engine/graphics/dx12_renderer.rs
```rust
use windows::Win32::Graphics::Direct3D12::*;
use windows::Win32::Graphics::Direct3D::D3D_FEATURE_LEVEL_11_0;
use windows::Win32::Foundation::{RECT, BOOL};
use windows::Win32::UI::WindowsAndMessaging::GetClientRect;
use winit::window::Window;

use crate::engine::scene::scene_graph::SceneGraph;

pub struct Dx12Renderer {
    device: Option<ID3D12Device>,
    command_queue: Option<ID3D12CommandQueue>,
    swap_chain: Option<ID3D12SwapChain>,
    rtv_descriptor_heap: Option<ID3D12DescriptorHeap>,
    frame_resources: Vec<FrameResource>,
    current_frame_index: usize,
}

struct FrameResource {
    command_allocator: Option<ID3D12CommandAllocator>,
    fence: Option<ID3D12Fence>,
    fence_value: u64,
    fence_event: Option<HANDLE>,
}

impl Dx12Renderer {
    pub fn new() -> Self {
        Self {
            device: None,
            command_queue: None,
            swap_chain: None,
            rtv_descriptor_heap: None,
            frame_resources: Vec::new(),
            current_frame_index: 0,
        }
    }

    pub fn initialize(&mut self) -> Result<(), Box<dyn std::error::Error>> {
        unsafe {
            // Create device
            let device = create_device()?;
            self.device = Some(device);
            
            // Create command queue
            let command_queue = create_command_queue(&self.device.as_ref().unwrap())?;
            self.command_queue = Some(command_queue);
            
            // Create swap chain
            let swap_chain = create_swap_chain(&self.device.as_ref().unwrap(), &self.command_queue.as_ref().unwrap())?;
            self.swap_chain = Some(swap_chain);
            
            // Create frame resources
            self.frame_resources = create_frame_resources(&self.device.as_ref().unwrap())?;
        }
        
        Ok(())
    }

    pub fn render(&mut self, scene: &SceneGraph) {
        unsafe {
            let frame_index = self.current_frame_index;
            let frame_resource = &mut self.frame_resources[frame_index];
            
            // Reset command allocator
            let command_allocator = frame_resource.command_allocator.as_ref().unwrap();
            command_allocator.Reset()?;
            
            // Create command list
            let command_list = create_command_list(
                &self.device.as_ref().unwrap(),
                &command_allocator,
                &self.command_queue.as_ref().unwrap()
            )?;
            
            // Begin recording commands
            command_list.Close()?;
            
            // Execute command list
            let command_queue = self.command_queue.as_ref().unwrap();
            command_queue.ExecuteCommandLists(&[Some(command_list.clone())]);
            
            // Present frame
            self.swap_chain.as_ref().unwrap().Present(1, 0);
        }
        
        self.current_frame_index = (self.current_frame_index + 1) % 3;
    }
}

unsafe fn create_device() -> Result<ID3D12Device, Box<dyn std::error::Error>> {
    let device: ID3D12Device = D3D12CreateDevice(
        None,
        D3D_FEATURE_LEVEL_11_0,
        &ID3D12Device::IID,
    )?;
    
    Ok(device)
}

unsafe fn create_command_queue(device: &ID3D12Device) -> Result<ID3D12CommandQueue, Box<dyn std::error::Error>> {
    let queue_desc = D3D12_COMMAND_QUEUE_DESC {
        Type: D3D12_COMMAND_LIST_TYPE_DIRECT,
        Priority: 0,
        Flags: D3D12_COMMAND_QUEUE_FLAG_NONE,
        NodeMask: 0,
    };
    
    let command_queue: ID3D12CommandQueue = device.CreateCommandQueue(&queue_desc)?;
    Ok(command_queue)
}

unsafe fn create_swap_chain(
    device: &ID3D12Device,
    command_queue: &ID3D12CommandQueue
) -> Result<ID3D12SwapChain, Box<dyn std::error::Error>> {
    // Create swap chain description
    let swap_chain_desc = DXGI_SWAP_CHAIN_DESC {
        BufferDesc: DXGI_MODE_DESC {
            Width: 1920,
            Height: 1080,
            RefreshRate: DXGI_RATIONAL { Numerator: 60, Denominator: 1 },
            Format: DXGI_FORMAT_R8G8B8A8_UNORM,
            ScanlineOrdering: DXGI_MODE_SCANLINE_ORDER_UNSPECIFIED,
            Scaling: DXGI_MODE_SCALING_UNSPECIFIED,
        },
        SampleDesc: DXGI_SAMPLE_DESC {
            Count: 1,
            Quality: 0,
        },
        BufferUsage: DXGI_USAGE_RENDER_TARGET_OUTPUT,
        BufferCount: 3,
        OutputWindow: HWND::default(),
        Windowed: BOOL(1),
        SwapEffect: DXGI_SWAP_EFFECT_FLIP_DISCARD,
        Flags: DXGI_SWAP_CHAIN_FLAG_ALLOW_MODE_SWITCH,
    };
    
    let swap_chain: ID3D12SwapChain = CreateDXGIFactory1()?
        .CreateSwapChainForHwnd(
            command_queue,
            HWND::default(),
            &swap_chain_desc,
            None,
            None
        )?;
    
    Ok(swap_chain)
}

unsafe fn create_frame_resources(device: &ID3D12Device) -> Result<Vec<FrameResource>, Box<dyn std::error::Error>> {
    let mut resources = Vec::new();
    
    for _ in 0..3 {
        let command_allocator: ID3D12CommandAllocator = device.CreateCommandAllocator(D3D12_COMMAND_LIST_TYPE_DIRECT)?;
        
        let fence: ID3D12Fence = device.CreateFence(0, D3D12_FENCE_FLAG_NONE)?;
        
        resources.push(FrameResource {
            command_allocator: Some(command_allocator),
            fence: Some(fence),
            fence_value: 0,
            fence_event: None,
        });
    }
    
    Ok(resources)
}

unsafe fn create_command_list(
    device: &ID3D12Device,
    allocator: &ID3D12CommandAllocator,
    queue: &ID3D12CommandQueue
) -> Result<ID3D12GraphicsCommandList, Box<dyn std::error::Error>> {
    let command_list: ID3D12GraphicsCommandList = device.CreateCommandList(
        0,
        D3D12_COMMAND_LIST_TYPE_DIRECT,
        allocator,
        None,
        &ID3D12GraphicsCommandList::IID,
    )?;
    
    Ok(command_list)
}
```

## src/engine/graphics/cuda_renderer.rs
```rust
use nvapi::NvAPI_Status;
use std::ptr;

pub struct CudaRenderer {
    context: Option<*mut std::ffi::c_void>,
}

impl CudaRenderer {
    pub fn new() -> Self {
        Self {
            context: None,
        }
    }

    pub fn initialize(&mut self) -> Result<(), Box<dyn std::error::Error>> {
        // Initialize CUDA context
        unsafe {
            let status = nvapi::NvAPI_Initialize();
            if status != NvAPI_Status::NVAPI_OK {
                return Err("Failed to initialize NVIDIA API".into());
            }
            
            self.context = Some(ptr::null_mut());
        }
        
        Ok(())
    }

    pub fn render(&mut self, scene: &crate::engine::scene::scene_graph::SceneGraph) {
        // Perform CUDA-based rendering operations
        unsafe {
            if let Some(context) = self.context {
                // Example CUDA kernel launch
                // This would typically call a custom CUDA kernel to process scene data
                // For example: process_scene_with_cuda(context, scene);
            }
        }
    }
}

// Placeholder for actual CUDA kernel execution
unsafe fn process_scene_with_cuda(context: *mut std::ffi::c_void, scene: &crate::engine::scene::scene_graph::SceneGraph) {
    // In a real implementation, this would:
    // 1. Copy scene data to GPU memory
    // 2. Launch CUDA kernels for physics simulation or lighting calculations
    // 3. Copy results back to CPU memory if needed
    
    // This is where the actual CUDA kernel execution would happen
}
```

## src/engine/assets/mesh.rs
```rust
use bytemuck::{Pod, Zeroable};

#[derive(Debug, Clone)]
pub struct Mesh {
    pub vertices: Vec<Vertex>,
    pub indices: Vec<u32>,
}

#[repr(C)]
#[derive(Copy, Clone, Debug, Pod, Zeroable)]
pub struct Vertex {
    pub position: [f32; 3],
    pub normal: [f32; 3],
    pub uv: [f32; 2],
}

impl Mesh {
    pub fn new(vertices: Vec<Vertex>, indices: Vec<u32>) -> Self {
        Self { vertices, indices }
    }

    pub fn empty() -> Self {
        Self {
            vertices: Vec::new(),
            indices: Vec::new(),
        }
    }
}
```

## src/engine/assets/texture.rs
```rust
use image::{ImageBuffer, Rgba};

pub struct Texture {
    pub width: u32,
    pub height: u32,
    pub data: Vec<u8>,
}

impl Texture {
    pub fn new(width: u32, height: u32, data: Vec<u8>) -> Self {
        Self { width, height, data }
    }

    pub fn from_image(image: ImageBuffer<Rgba<u8>, Vec<u8>>) -> Self {
        let (width, height) = image.dimensions();
        let data = image.into_raw();
        
        Self::new(width, height, data)
    }
}
```

## src/engine/assets/shader.rs
```rust
use std::path::Path;

pub struct Shader {
    pub name: String,
    pub bytecode: Vec<u8>,
}

impl Shader {
    pub fn new(name: &str, bytecode: Vec<u8>) -> Self {
        Self {
            name: name.to_string(),
            bytecode,
        }
    }

    pub fn from_file(path: impl AsRef<Path>) -> Result<Self, Box<dyn std::error::Error>> {
        let path = path.as_ref();
        let name = path.file_name().unwrap().to_string_lossy().to_string();
        let bytecode = std::fs::read(path)?;
        
        Ok(Self::new(&name, bytecode))
    }
}
```

## src/engine/scene/scene_graph.rs
```rust
use crate::engine::assets::mesh::Mesh;
use crate::engine::assets::texture::Texture;
use crate::engine::scene::camera::Camera;

#[derive(Debug)]
pub struct SceneGraph {
    pub camera: Camera,
    pub meshes: Vec<Mesh>,
    pub textures: Vec<Texture>,
}

impl SceneGraph {
    pub fn new() -> Self {
        Self {
            camera: Camera::new(),
            meshes: Vec::new(),
            textures: Vec::new(),
        }
    }

    pub fn add_mesh(&mut self, mesh: Mesh) {
        self.meshes.push(mesh);
    }

    pub fn add_texture(&mut self, texture: Texture) {
        self.textures.push(texture);
    }
}
```

## src/engine/scene/camera.rs
```rust
#[derive(Debug, Clone)]
pub struct Camera {
    pub position: [f32; 3],
    pub rotation: [f32; 3],
    pub fov: f32,
    pub near_plane: f32,
    pub far_plane: f32,
}

impl Camera {
    pub fn new() -> Self {
        Self {
            position: [0.0, 0.0, -5.0],
            rotation: [0.0, 0.0, 0.0],
            fov: 45.0,
            near_plane: 0.1,
            far_plane: 100.0,
        }
    }

    pub fn set_position(&mut self, x: f32, y: f32, z: f32) {
        self.position = [x, y, z];
    }

    pub fn set_rotation(&mut self, x: f32, y: f32, z: f32) {
        self.rotation = [x, y, z];
    }
}
```

## src/utils/math.rs
```rust
pub struct Vector3 {
    pub x: f32,
    pub y: f32,
    pub z: f32,
}

impl Vector3 {
    pub fn new(x: f32, y: f32, z: f32) -> Self {
        Self { x, y, z }
    }

    pub fn magnitude(&self) -> f32 {
        (self.x * self.x + self.y * self.y + self.z * self.z).sqrt()
    }

    pub fn normalize(&mut self) {
        let mag = self.magnitude();
        if mag > 0.0 {
            self.x /= mag;
            self.y /= mag;
            self.z /= mag;
        }
    }
}
```

## src/main.rs
```rust
use std::error::Error;

mod engine {
    pub mod assets;
    pub mod scene;
    pub mod graphics;
    pub mod utils;
}

fn main() -> Result<(), Box<dyn Error>> {
    println!("Initializing game engine...");
    
    // Initialize engine components here
    
    println!("Engine initialized successfully!");
    
    Ok(())
}
```

This implementation provides a foundation for a cross-platform game engine that combines:
1. DirectX 12 rendering with Rust bindings
2. CUDA integration for GPU acceleration
3. Modular asset management (meshes, textures, shaders)
4. Scene graph system with camera support
5. Math utilities for vector operations

The engine is structured to be extensible and can be expanded with additional features like audio, networking, or scripting systems. The actual DirectX and CUDA bindings would need to be implemented using appropriate Rust crates, which are not included in this example due to their complexity and dependency on system libraries.