Architectural design is to solve a human problem and demands an in-depth understanding of the complex person-environment relations, which manifest a dynamic “entanglement” between humans and the physical environments. As James Gibson’s ecological theory postulates, humans can effectively perceive the 3D surroundings through 2D retinas because we move and look around in space and obtain constantly changing views as we carry out meaningful behaviors. However, when architects conceive and design our future living spaces, they do not have proper digital design tools to empathize with the end users. Introducing Project Fission and Downtown Explorer, this presentation highlights Unreal Engine’s tremendous potential in building immersive, real-time 3D tools that foreground humans’ dynamic visual relations with the built environment in the design process. Such tools seamlessly integrate the capacities of formal generation, visual simulation, and design evaluation without alienating designers from real-world visual experiences.