Axion Engine — Roadmap

Progressive milestones for building Axion. Each phase produces a runnable, demonstrable result. Aligned with TheCherno's Hazel engine series so YouTube tutorials map directly to these tasks.

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✅ Phase 0 — Foundation (DONE)

• CMake + vcpkg build system
• Engine library / Sandbox client separation
• Precompiled headers
• Logging system (spdlog wrapper, dual loggers)
• Window abstraction (GLFW)
• OpenGL 4.5 context (glad)
• Application class with main loop
• EntryPoint macro pattern
• Smart pointer aliases (Ref<T>, Scope<T>)

Deliverable: Window opens, displays a clear color, logs to console.

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✅ Phase 1 — Event System (DONE)

• Event base class with categories (Application, Input, Keyboard, Mouse)
• EventDispatcher for type-safe event handling
• Window events: ApplicationCloseEvent, ApplicationResizeEvent, WindowFocusEvent
• Key events: KeyPressedEvent, KeyReleased, KeyTypedEvent
• Mouse events: MouseButtonPressedEvent, MouseMovedEvent, MouseScrolledEvent
• Wire GLFW callbacks → push events into Window callback
• Application::OnEvent() receives events from window
• Add KeyCode.h / MouseCode.h (platform-agnostic input codes)

Deliverable: Pressing keys / clicking mouse logs events to console. Window resize updates viewport.

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🚧 Phase 2 — Input Polling (DONE)

• Input static class with IsKeyPressed(KeyCode), IsMouseButtonPressed, GetMousePosition
• Platform-specific implementation (WindowsInput.cpp or single GLFW backend)

Deliverable: Move a debug variable with WASD, log mouse coords.

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🚧 Phase 3 — Layer System

• Layer base class with OnAttach, OnDetach, OnUpdate, OnEvent, OnImGuiRender
• LayerStack (layers + overlays — overlays always on top)
• Application owns a LayerStack, iterates it each frame
• Events propagate top-to-bottom through layers (can be "handled" to stop)

Deliverable: Sandbox can push custom ExampleLayer that logs lifecycle events.

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🚧 Phase 4 — ImGui Integration

• ImGuiLayer as an overlay
• ImGui GLFW + OpenGL3 backend bindings
• Begin/end frame in correct loop positions
• Docking enabled (vcpkg already configured for this)
• Demo window toggle

Deliverable: ImGui demo window renders over the OpenGL viewport. Foundation for future editor.

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🚧 Phase 5 — Renderer Primitives (Triangle Era)

• Shader class (load from file, compile, uniform setters)
• VertexBuffer and IndexBuffer abstractions
• BufferLayout describing vertex attribute layout
• VertexArray (VAO wrapper)
• Render a colored triangle
• Render a square (with index buffer)

Deliverable: A rainbow triangle appears in the window. Foundational rite-of-passage.

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🚧 Phase 6 — Renderer Abstraction

• RendererAPI abstract class (Clear, SetClearColor, DrawIndexed, SetViewport)
• OpenGLRendererAPI concrete implementation
• RenderCommand static dispatcher
• Renderer class with BeginScene / Submit / EndScene
• OrthographicCamera (position, rotation, projection matrix)

Deliverable: Camera moves with WASD. Scene structure works for multiple objects.

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🚧 Phase 7 — Textures + 2D

• Texture2D abstract class
• OpenGLTexture2D using stb_image
• Texture units, binding, slot management
• Render a textured quad
• OrthographicCameraController (with zoom, aspect ratio, input handling)

Deliverable: Textured quad on screen, camera fully controllable.

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🚧 Phase 8 — 2D Batch Renderer

• Renderer2D::DrawQuad(position, size, color)
• Renderer2D::DrawQuad(position, size, texture)
• Dynamic vertex buffer
• Batch many quads in one draw call
• Texture atlas support
• Stats: draw calls, quad count

Deliverable: Render 10,000 sprites at 60fps. Stress test confirms batching works.

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🚧 Phase 9 — Entity Component System (ECS)

• Add entt to vcpkg
• Scene class wrapping entt::registry
• Entity wrapper class
• Core components: TransformComponent, SpriteRendererComponent, CameraComponent, TagComponent
• Scene rendering iterates entities with TransformComponent + SpriteRendererComponent
• Native scripting component (NativeScriptComponent)

Deliverable: Create entities, attach components, render them via scene.

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🚧 Phase 10 — Editor (Axion-Editor)

• Spin off Axion-Editor executable (separate from Sandbox)
• Viewport panel (renders scene to framebuffer → ImGui image)
• Scene hierarchy panel
• Properties / inspector panel
• Content browser (file system view)
• Gizmos for transform manipulation (ImGuizmo)
• Entity selection, picking via mouse

Deliverable: A standalone editor that looks/feels like a real game engine editor. HUGE portfolio piece.

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🚧 Phase 11 — Serialization

• Add yaml-cpp to vcpkg
• SceneSerializer — serialize scene to YAML
• Deserialize scene from YAML
• Editor: New Scene / Open Scene / Save / Save As menu
• File dialogs (native via Windows API)

Deliverable: Save a scene to disk, close editor, reopen, scene restored.

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🚧 Phase 12 — Framebuffers / Render Targets

• Framebuffer abstraction (color + depth attachments)
• Scene renders to framebuffer instead of screen
• Viewport panel displays framebuffer texture
• Multiple render targets for post-processing later

Deliverable: Editor viewport shows the rendered scene as an ImGui image.

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🚧 Phase 13 — Runtime / Editor split

• Scene play / stop / pause buttons in editor
• Runtime camera vs editor camera
• Scene copy on play (so changes during play don't persist)
• Native script binding (entity scripts run during play)

Deliverable: Editor + runtime distinction works like Unity.

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🚧 Phase 14 — 3D Era

• PerspectiveCamera + controller
• Depth testing enabled
• Render a cube
• Mesh loading via Assimp (.obj, .fbx, .gltf)
• MeshComponent
• Basic Phong lighting shader

Deliverable: A 3D cube rotates in the editor viewport with directional lighting.

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🚧 Phase 15 — Physics (2D first)

• Add box2d to vcpkg
• Rigidbody2DComponent, BoxCollider2DComponent, CircleCollider2DComponent
• Physics step in scene update
• Sync transforms between physics world and ECS

Deliverable: Drop boxes that fall and collide on play.

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🚧 Phase 16+ — Beyond

Any of:

• Audio system (OpenAL Soft or miniaudio)
• Scripting layer (Lua via sol2, or C# via Mono)
• 3D physics (Jolt or Bullet)
• PBR shading
• Skeletal animation
• Particle system
• Networking
• Vulkan renderer backend
• Asset packing / hot reload

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Reference

• TheCherno's Hazel series: https://www.youtube.com/playlist?list=PLlrATfBNZ98dC-V-N3m0Go4deliWHPFwT
• Hazel source: https://github.com/TheCherno/Hazel
• Game Programming Patterns: https://gameprogrammingpatterns.com
• learnopengl.com (graphics fundamentals)

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