tl;dr: A developer built a 3D software renderer from scratch for the Playdate handheld, which has no GPU and a 1-bit display, using Quake's BSP format to leverage precomputed visibility (PVS) and lighting via existing tools like TrenchBroom. Key techniques include a 16-bit reciprocal z-buffer, perspective-correct texture mapping with cheap reciprocal approximations, 8x8 Bayer dithering for faux-grayscale lighting, and half-resolution (200x120) rendering scaled up. The final look is a cel-shaded, high-contrast style inspired by Obra Dinn, chosen because fully textured scenes became too noisy on a 1-bit screen.