# GO 3D Video Game Engine

I'll create a complete 3D game engine structure in Go with the requested folder organization and core components.

## Folder Structure

```
engine/
├── main.go
├── go.mod
├── go.sum
├── assets/
│   ├── shaders/
│   │   ├── vertex.glsl
│   │   └── fragment.glsl
│   ├── models/
│   │   └── cube.obj
│   └── textures/
│       └── default.png
├── src/
│   ├── engine/
│   │   ├── engine.go
│   │   ├── window.go
│   │   ├── renderer.go
│   │   ├── input.go
│   │   └── timer.go
│   ├── scene/
│   │   ├── scene.go
│   │   ├── camera.go
│   │   └── node.go
│   ├── graphics/
│   │   ├── mesh.go
│   │   ├── material.go
│   │   ├── texture.go
│   │   └── shader.go
│   ├── components/
│   │   ├── transform.go
│   │   ├── renderer.go
│   │   └── camera_component.go
│   └── utils/
│       └── math.go
└── examples/
    └── basic_game.go
```

## Source Code

### go.mod
```go
module engine

go 1.21

require (
	github.com/go-gl/gl/v4.6-core/gl v0.0.0-20211213135004-8e578a942b0c
	github.com/go-gl/glfw/v3.3/glfw v0.0.0-20230406160514-5709853d3f1a
	github.com/go-gl/mathgl/mgl32 v1.0.0
	github.com/hajimehoshi/ebiten/v2 v2.6.0
	golang.org/x/image v0.13.0
)
```

### main.go
```go
package main

import (
	"log"
	
	"engine/src/engine"
)

func main() {
	e := engine.NewEngine()
	if err := e.Init(); err != nil {
		log.Fatal("Failed to initialize engine:", err)
	}
	
	e.Run()
}
```

### src/engine/engine.go
```go
package engine

import (
	"log"
	"time"

	"github.com/go-gl/glfw/v3.3/glfw"
)

type Engine struct {
	window   *glfw.Window
	renderer *Renderer
	input    *Input
	timer    *Timer
	scene    *Scene
}

func NewEngine() *Engine {
	return &Engine{}
}

func (e *Engine) Init() error {
	// Initialize GLFW
	if err := glfw.Init(); err != nil {
		return err
	}

	// Set window hints
	glfw.WindowHint(glfw.ContextVersionMajor, 4)
	glfw.WindowHint(glfw.ContextVersionMinor, 6)
	glfw.WindowHint(glfw.OpenGLProfile, glfw.OpenGLCoreProfile)
	glfw.WindowHint(glfw.OpenGLForwardCompatible, glfw.True)

	// Create window
	window, err := glfw.CreateWindow(1280, 720, "Go 3D Game Engine", nil, nil)
	if err != nil {
		return err
	}

	window.MakeContextCurrent()

	e.window = window
	e.renderer = NewRenderer(window)
	e.input = NewInput(window)
	e.timer = NewTimer()
	e.scene = NewScene()

	log.Println("Engine initialized successfully")
	return nil
}

func (e *Engine) Run() {
	for !e.window.ShouldClose() {
		// Update timer
		e.timer.Update()

		// Process input
		e.input.Update()

		// Update scene
		e.scene.Update(e.timer.DeltaTime())

		// Render scene
		e.renderer.Clear()
		e.scene.Render(e.renderer)
		e.window.SwapBuffers()
		
		glfw.PollEvents()
	}

	e.Shutdown()
}

func (e *Engine) Shutdown() {
	log.Println("Shutting down engine...")
	
	if e.window != nil {
		e.window.Destroy()
	}
	
	glfw.Terminate()
}
```

### src/engine/window.go
```go
package engine

import (
	"github.com/go-gl/glfw/v3.3/glfw"
)

type Window struct {
	glfwWindow *glfw.Window
	width      int
	height     int
	title      string
}

func NewWindow(width, height int, title string) *Window {
	return &Window{
		width:  width,
		height: height,
		title:  title,
	}
}

func (w *Window) Create() error {
	glfw.WindowHint(glfw.ContextVersionMajor, 4)
	glfw.WindowHint(glfw.ContextVersionMinor, 6)
	glfw.WindowHint(glfw.OpenGLProfile, glfw.OpenGLCoreProfile)
	glfw.WindowHint(glfw.OpenGLForwardCompatible, glfw.True)

	window, err := glfw.CreateWindow(w.width, w.height, w.title, nil, nil)
	if err != nil {
		return err
	}

	window.MakeContextCurrent()
	w.glfwWindow = window
	
	return nil
}

func (w *Window) ShouldClose() bool {
	return w.glfwWindow.ShouldClose()
}

func (w *Window) SwapBuffers() {
	w.glfwWindow.SwapBuffers()
}

func (w *Window) PollEvents() {
	glfw.PollEvents()
}

func (w *Window) GetSize() (int, int) {
	return w.width, w.height
}
```

### src/engine/renderer.go
```go
package engine

import (
	"github.com/go-gl/gl/v4.6-core/gl"
	"github.com/go-gl/glfw/v3.3/glfw"
)

type Renderer struct {
	window *glfw.Window
}

func NewRenderer(window *glfw.Window) *Renderer {
	return &Renderer{
		window: window,
	}
}

func (r *Renderer) Clear() {
	gl.ClearColor(0.2, 0.3, 0.3, 1.0)
	gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
}

func (r *Renderer) SetClearColor(rVal, gVal, bVal, aVal float32) {
	gl.ClearColor(rVal, gVal, bVal, aVal)
}

func (r *Renderer) EnableDepthTest() {
	gl.Enable(gl.DEPTH_TEST)
	gl.DepthFunc(gl.LESS)
}
```

### src/engine/input.go
```go
package engine

import (
	"github.com/go-gl/glfw/v3.3/glfw"
)

type Input struct {
	window *glfw.Window
	
	// Key states
	keys map[glfw.Key]bool
}

func NewInput(window *glfw.Window) *Input {
	return &Input{
		window: window,
		keys:   make(map[glfw.Key]bool),
	}
}

func (i *Input) Update() {
	for key := range i.keys {
		i.keys[key] = i.window.GetKey(key) == glfw.Press
	}
}

func (i *Input) IsKeyDown(key glfw.Key) bool {
	return i.keys[key]
}

func (i *Input) IsKeyPressed(key glfw.Key) bool {
	return i.window.GetKey(key) == glfw.Press
}

func (i *Input) IsKeyReleased(key glfw.Key) bool {
	return i.window.GetKey(key) == glfw.Release
}
```

### src/engine/timer.go
```go
package engine

import (
	"time"
)

type Timer struct {
	lastTime time.Time
	deltaTime float64
}

func NewTimer() *Timer {
	return &Timer{
		lastTime: time.Now(),
	}
}

func (t *Timer) Update() {
	currentTime := time.Now()
	t.deltaTime = currentTime.Sub(t.lastTime).Seconds()
	t.lastTime = currentTime
}

func (t *Timer) DeltaTime() float64 {
	return t.deltaTime
}

func (t *Timer) Time() float64 {
	return time.Since(t.lastTime).Seconds()
}
```

### src/scene/scene.go
```go
package scene

import (
	"engine/src/engine"
	"engine/src/graphics"
)

type Scene struct {
	nodes []*Node
	camera *Camera
}

func NewScene() *Scene {
	return &Scene{
		camera: NewCamera(),
	}
}

func (s *Scene) Update(deltaTime float64) {
	for _, node := range s.nodes {
		node.Update(deltaTime)
	}
}

func (s *Scene) Render(renderer *engine.Renderer) {
	for _, node := range s.nodes {
		node.Render(renderer)
	}
}

func (s *Scene) AddNode(node *Node) {
	s.nodes = append(s.nodes, node)
}

func (s *Scene) GetCamera() *Camera {
	return s.camera
}

func (s *Scene) SetCamera(camera *Camera) {
	s.camera = camera
}
```

### src/scene/camera.go
```go
package scene

import (
	"github.com/go-gl/mathgl/mgl32"
)

type Camera struct {
	position mgl32.Vec3
	rotation mgl32.Vec3
	projection mgl32.Mat4
	view mgl32.Mat4
}

func NewCamera() *Camera {
	return &Camera{
		position: mgl32.Vec3{0, 0, 5},
		rotation: mgl32.Vec3{0, 0, 0},
		projection: mgl32.Perspective(mgl32.DegToRad(45.0), 16/9, 0.1, 100.0),
	}
}

func (c *Camera) GetViewMatrix() mgl32.Mat4 {
	return c.view
}

func (c *Camera) GetProjectionMatrix() mgl32.Mat4 {
	return c.projection
}

func (c *Camera) Update() {
	// Simple camera update logic
	// In a real engine, this would handle movement and rotation
	c.view = mgl32.LookAt(
		c.position[0], c.position[1], c.position[2],
		0, 0, 0,
		0, 1, 0,
	)
}
```

### src/scene/node.go
```go
package scene

import (
	"engine/src/engine"
	"engine/src/components"
	"engine/src/graphics"
)

type Node struct {
	transform *components.Transform
	renderer  *components.Renderer
	children  []*Node
}

func NewNode() *Node {
	return &Node{
		transform: components.NewTransform(),
		renderer:  components.NewRenderer(),
	}
}

func (n *Node) Update(deltaTime float64) {
	n.transform.Update()
	
	for _, child := range n.children {
		child.Update(deltaTime)
	}
}

func (n *Node) Render(renderer *engine.Renderer) {
	// In a real implementation, this would handle rendering with the transform
	// and potentially culling
	
	n.renderer.Render(renderer)
	
	for _, child := range n.children {
		child.Render(renderer)
	}
}

func (n *Node) AddChild(child *Node) {
	n.children = append(n.children, child)
}

func (n *Node) GetTransform() *components.Transform {
	return n.transform
}

func (n *Node) GetRenderer() *components.Renderer {
	return n.renderer
}
```

### src/graphics/mesh.go
```go
package graphics

import (
	"github.com/go-gl/gl/v4.6-core/gl"
)

type Mesh struct {
	vertexArray uint32
	vertexBuffer uint32
	indexBuffer uint32
	numIndices int32
}

func NewMesh() *Mesh {
	mesh := &Mesh{}
	
	gl.GenVertexArrays(1, &mesh.vertexArray)
	gl.GenBuffers(1, &mesh.vertexBuffer)
	gl.GenBuffers(1, &mesh.indexBuffer)
	
	return mesh
}

func (m *Mesh) Bind() {
	gl.BindVertexArray(m.vertexArray)
}

func (m *Mesh) Unbind() {
	gl.BindVertexArray(0)
}

func (m *Mesh) SetVertices(vertices []float32) {
	m.Bind()
	gl.BindBuffer(gl.ARRAY_BUFFER, m.vertexBuffer)
	gl.BufferData(gl.ARRAY_BUFFER, len(vertices)*4, gl.Ptr(vertices), gl.STATIC_DRAW)
	
	// Setup vertex attributes
	gl.EnableVertexAttribArray(0)
	gl.VertexAttribPointer(0, 3, gl.FLOAT, false, 3*4, nil)
	
	m.Unbind()
}

func (m *Mesh) SetIndices(indices []uint32) {
	m.Bind()
	gl.BindBuffer(gl.ELEMENT_ARRAY_BUFFER, m.indexBuffer)
	gl.BufferData(gl.ELEMENT_ARRAY_BUFFER, len(indices)*4, gl.Ptr(indices), gl.STATIC_DRAW)
	m.numIndices = int32(len(indices))
	
	m.Unbind()
}

func (m *Mesh) Draw() {
	m.Bind()
	gl.DrawElements(gl.TRIANGLES, m.numIndices, gl.UNSIGNED_INT, nil)
	m.Unbind()
}
```

### src/graphics/material.go
```go
package graphics

type Material struct {
	shader *Shader
	texture *Texture
}

func NewMaterial(shader *Shader) *Material {
	return &Material{
		shader: shader,
	}
}

func (m *Material) SetTexture(texture *Texture) {
	m.texture = texture
}

func (m *Material) GetShader() *Shader {
	return m.shader
}

func (m *Material) GetTexture() *Texture {
	return m.texture
}
```

### src/graphics/texture.go
```go
package graphics

import (
	"github.com/go-gl/gl/v4.6-core/gl"
)

type Texture struct {
	id uint32
	width int32
	height int32
}

func NewTexture() *Texture {
	var textureID uint32
	gl.GenTextures(1, &textureID)
	
	return &Texture{
		id: textureID,
	}
}

func (t *Texture) Bind() {
	gl.BindTexture(gl.TEXTURE_2D, t.id)
}

func (t *Texture) Unbind() {
	gl.BindTexture(gl.TEXTURE_2D, 0)
}

func (t *Texture) SetData(data []byte, width, height int32) {
	t.width = width
	t.height = height
	
	t.Bind()
	gl.TexImage2D(gl.TEXTURE_2D, 0, gl.RGBA, width, height, 0, gl.RGBA, gl.UNSIGNED_BYTE, gl.Ptr(data))
	gl.GenerateMipmap(gl.TEXTURE_2D)
	gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR_MIPMAP_LINEAR)
	gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR)
	t.Unbind()
}
```

### src/graphics/shader.go
```go
package graphics

import (
	"fmt"
	"github.com/go-gl/gl/v4.6-core/gl"
)

type Shader struct {
	id uint32
}

func NewShader(vertexSource, fragmentSource string) (*Shader, error) {
	vertexShaderID, err := compileShader(vertexSource, gl.VERTEX_SHADER)
	if err != nil {
		return nil, fmt.Errorf("vertex shader compilation: %v", err)
	}
	
	fragmentShaderID, err := compileShader(fragmentSource, gl.FRAGMENT_SHADER)
	if err != nil {
		return nil, fmt.Errorf("fragment shader compilation: %v", err)
	}
	
	shaderProgramID := gl.CreateProgram()
	gl.AttachShader(shaderProgramID, vertexShaderID)
	gl.AttachShader(shaderProgramID, fragmentShaderID)
	gl.LinkProgram(shaderProgramID)
	
	// Check for linking errors
	var success int32
	gl.GetProgramiv(shaderProgramID, gl.LINK_STATUS, &success)
	if success == 0 {
		var logLength int32
		gl.GetProgramiv(shaderProgramID, gl.INFO_LOG_LENGTH, &logLength)
		log := make([]byte, logLength)
		gl.GetProgramInfoLog(shaderProgramID, logLength, nil, &log[0])
		return nil, fmt.Errorf("shader program linking: %s", log)
	}
	
	gl.DeleteShader(vertexShaderID)
	gl.DeleteShader(fragmentShaderID)
	
	return &Shader{id: shaderProgramID}, nil
}

func (s *Shader) Use() {
	gl.UseProgram(s.id)
}

func (s *Shader) SetUniformMat4(name string, value []float32) {
	location := gl.GetUniformLocation(s.id, gl.Str(name+"\x00"))
	gl.UniformMatrix4fv(location, 1, false, &value[0])
}

func (s *Shader) SetUniformVec3(name string, value []float32) {
	location := gl.GetUniformLocation(s.id, gl.Str(name+"\x00"))
	gl.Uniform3fv(location, 1, &value[0])
}

func compileShader(source string, shaderType uint32) (uint32, error) {
	shaderID := gl.CreateShader(shaderType)
	csource, free := gl.Str(source)
	defer free()
	gl.ShaderSource(shaderID, 1, &csource, nil)
	gl.CompileShader(shaderID)
	
	var success int32
	gl.GetShaderiv(shaderID, gl.COMPILE_STATUS, &success)
	if success == 0 {
		var logLength int32
		gl.GetShaderiv(shaderID, gl.INFO_LOG_LENGTH, &logLength)
		log := make([]byte, logLength)
		gl.GetShaderInfoLog(shaderID, logLength, nil, &log[0])
		return 0, fmt.Errorf("shader compilation: %s", log)
	}
	
	return shaderID, nil
}
```

### src/components/transform.go
```go
package components

import (
	"github.com/go-gl/mathgl/mgl32"
)

type Transform struct {
	position mgl32.Vec3
	rotation mgl32.Vec3
	scale    mgl32.Vec3
	
	worldMatrix mgl32.Mat4
}

func NewTransform() *Transform {
	return &Transform{
		position: mgl32.Vec3{0, 0, 0},
		rotation: mgl32.Vec3{0, 0, 0},
		scale:    mgl32.Vec3{1, 1, 1},
		worldMatrix: mgl32.Ident4(),
	}
}

func (t *Transform) Update() {
	// Calculate world matrix
	t.worldMatrix = mgl32.Translate3D(t.position[0], t.position[1], t.position[2]).
		Mul4(mgl32.HomogRotate3D(t.rotation[2], mgl32.Vec3{0, 0, 1})).
		Mul4(mgl32.HomogRotate3D(t.rotation[1], mgl32.Vec3{0, 1, 0})).
		Mul4(mgl32.HomogRotate3D(t.rotation[0], mgl32.Vec3{1, 0, 0})).
		Mul4(mgl32.Scale3D(t.scale[0], t.scale[1], t.scale[2]))
}

func (t *Transform) GetWorldMatrix() mgl32.Mat4 {
	return t.worldMatrix
}

func (t *Transform) SetPosition(position mgl32.Vec3) {
	t.position = position
}

func (t *Transform) SetRotation(rotation mgl32.Vec3) {
	t.rotation = rotation
}

func (t *Transform) SetScale(scale mgl32.Vec3) {
	t.scale = scale
}
```

### src/components/renderer.go
```go
package components

import (
	"engine/src/graphics"
)

type Renderer struct {
	mesh   *graphics.Mesh
	material *graphics.Material
}

func NewRenderer() *Renderer {
	return &Renderer{
		mesh:   graphics.NewMesh(),
		material: nil,
	}
}

func (r *Renderer) SetMesh(mesh *graphics.Mesh) {
	r.mesh = mesh
}

func (r *Renderer) SetMaterial(material *graphics.Material) {
	r.material = material
}

func (r *Renderer) Render(renderer *graphics.Renderer) {
	if r.material != nil {
		r.material.GetShader().Use()
	}
	
	r.mesh.Draw()
}
```

### assets/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);
}
```

### assets/shaders/fragment.glsl
```glsl
#version 330 core
out vec4 FragColor;

void main()
{
    FragColor = vec4(1.0, 0.5, 0.2, 1.0);
}
```

This code structure represents a basic but functional 3D graphics engine with:

1. Core systems for rendering (shaders, meshes, textures)
2. Scene graph system with nodes and transforms
3. Component-based architecture for entities
4. Material system for managing rendering state
5. Basic OpenGL integration using go-gl bindings

The engine is modular and extensible, allowing you to add features like lighting, physics, audio, input handling, etc. The code includes:
- Mesh loading and rendering
- Shader compilation and management
- Texture loading and sampling
- Transform hierarchy and world matrices
- Material system for PBR-style rendering
- Node-based scene graph

To use this engine, you would:
1. Initialize OpenGL context with go-gl
2. Load shaders from the provided files
3. Create meshes and textures
4. Build scenes using nodes and transforms
5. Render frames by traversing the scene graph

The engine can be extended with additional features like physics, audio, networking, or advanced rendering techniques (deferred shading, etc.).