Developed in collaboration with Louis Mercier (https://www.linkedin.com/in/louis-mercier-713657134/), we designed and built a custom C++ game engine through a deliberate architectural evolution, progressing from a simple text-based 2D prototype to a fully featured real-time engine with modern rendering and tooling. The project began as a TUI-driven engine built using traditional object-oriented design, focused on validating core ideas such as simulation flow, basic physics, and system ownership without graphical complexity. As the scope and ambitions grew, the architecture was reworked around an Entity Component System (ECS), enabling data-oriented design, better scalability, and clearer separation between data and behavior. This shift coincided with a migration to an SDL-based platform layer and an ImGui-powered editor, followed by the introduction of a BGFX-backed rendering pipeline. Rendering is orchestrated via a backend-agnostic FrameGraph owned by the Runtime, while a dedicated GraphicsRenderer acts as a thin BGFX facade responsible for GPU lifecycle, view management, and resource allocation. Distinct Game, Scene (editor), and Preview pipelines register their passes into the shared FrameGraph, ensuring consistency across gameplay, editor workflows, and off-screen rendering. The engine reflects an emphasis on intentional architectural decisions, extensibility, and parity between runtime and editor systems.