Before writing a single line of OpenGL code, we need to understand what we are building and why. An engine is not a rendering demo. It is not a collection of random utilities. It is a coherent system designed to support predictable, maintainable, extensible development.

This article defines the architectural mindset that will guide the entire series.

In the context of small games and simulations, understanding the distinction between libraries, frameworks, and engines is crucial.

• A library provides isolated functionality (e.g., math, image loading).
• A framework provides structure but expects you to fill in the logic.
• An engine provides a complete runtime environment
  • rendering
  • input
  • timing
  • simulation
  • resource management
  • tools

For small games and physics simulations, the engine must be lightweight, modular, and predictable.

Because the goal is engineering mastery, not just producing a game. Building your own engine will help you master:

• how rendering pipelines work
• how simulation loops are structured
• how systems communicate
• how to design modular software
• how to reason about performance and determinism

This series is about learning the craft, not competing with AAA engines.

We target:

• simple 2D/3D games
• real time physics simulations
• educational visualization tools

This means:

• no massive asset pipelines
• no complex animation systems
• no editor tooling (yet)
• no multi threaded rendering (yet)

We focus on clarity, architecture, and correctness.

Every subsystem must be isolated:

• math
• platform
• renderer
• resources
• simulation
• tools

No subsystem should “know too much” about another. This prevents tight coupling and makes the engine maintainable.

Physics simulations require reproducibility:

• same inputs → same outputs
• fixed timestep
• predictable update order

Determinism is a design constraint, not an afterthought.

Engine modules should be testable without a GPU or window:

• math
• simulation
• resource management
• input mapping

This requires clean separation between logic and platform.

The engine must be:

• readable
• debuggable
• extendable
• stable

This is achieved through:

• consistent naming
• clear module boundaries
• minimal global state
• predictable data flow

Rendering does not handle physics. Physics does not handle input. Input does not handle resources.

Each module has a single responsibility.

Responsible for:

• window creation
• OpenGL context
• input events
• timing

This layer isolates OS specific details.

Responsible for:

• shaders
• buffers
• textures
• materials
• draw submission

The renderer is data driven and GPU centric.

Responsible for:

• physics
• collisions
• integration
• world updates

Simulation is deterministic and independent of rendering.

Responsible for:

• loading assets
• caching resources
• managing lifetimes

This layer prevents duplication and ensures consistency.

Optional but useful:

• debug overlays
• profiling
• visualization helpers

Tools improve development workflow.

An engine is a collection of systems that:

• communicate through well defined interfaces
• avoid hidden dependencies
• operate predictably

This mindset prevents spaghetti architecture.

The engine must evolve:

• new rendering techniques
• new physics features
• new tools
• new platforms

Design choices must anticipate future growth.

Tight coupling kills engines. We avoid:

• global state
• cross module includes
• “god classes”
• implicit dependencies

Instead, we use:

• clear interfaces
• dependency injection
• module boundaries
• explicit ownership rules

We don’t go full ECS here, but we adopt:

• contiguous data where possible
• predictable memory access
• minimal branching in hot paths

This improves performance and clarity.

By the end of the series, we will have:

• a modular OpenGL engine
• a deterministic simulation loop
• a clean rendering pipeline
• a minimal scene system
• a physics module
• a small game
• a physics visualization tool

Everything will be:

• modern
• clean
• architecturally sound
• easy to extend
• easy to understand

This is not a toy — it is a real engine, designed with professional engineering principles.