Building a Tiny 3D Renderer for a Tiny Handheld
The author details their journey creating a 3D software renderer for the Playdate, pushing the limits of the tiny handheld's CPU to achieve 3DO/Saturn-era visuals. They delve into technical hurdles like 1-bit display lighting with dithering, custom perspective-correct texture mapping, and leveraging Quake's BSP format. This deep dive into performance optimization and creative problem-solving on constrained hardware resonates with the HN crowd.
The Lowdown
The author embarked on an ambitious project: building a 3D software renderer for the Playdate handheld. Facing a device with no dedicated 3D hardware and a 1-bit display, their journey involved extensive experimentation, optimization, and creative problem-solving to deliver playable real-time 3D graphics.
- Initial tests with a raycaster revealed the Playdate's significant performance limitations, confirming that all 3D rendering tasks would need to be handled by the CPU.
- The goal was to achieve perceived visuals akin to the 3DO or Sega Saturn era, despite vastly different underlying hardware architectures.
- To manage the CPU load, the renderer leveraged Quake's BSP (Binary Space Partitioning) map format, utilizing precompiled visibility data (PVS) for efficient culling of unseen geometry.
- A 16-bit reciprocal depth buffer (z-buffer) was implemented to handle depth sorting and enable dynamic objects and masked textures, providing more precision closer to the camera.
- Perspective-correct texture mapping was chosen over affine mapping to avoid visual warping, with an optimized approximation implemented to reduce the per-pixel division cost.
- Lighting on the 1-bit display was achieved using dithering with an 8x8 Bayer matrix, translating precomputed Quake lightmaps into perceived grayscale tones.
- Visual fidelity was prioritized, leading to a "1-bit cel-shading" aesthetic inspired by games like Return of the Obra Dinn and Jet Set Radio, which improved readability over noisy, fully textured scenes.
- Extensive optimization techniques were employed, including specific compiler flags, custom ARM Cortex-M7 assembler for critical functions, half-resolution rendering, precomputed values, and strategic use of code alignment and inlining, all rigorously benchmarked.
This project highlights the significant challenges and innovative solutions required to push the boundaries of hardware limitations. The author concludes by emphasizing the importance of iterative development, aiming for "good enough" to foster progress, and the critical role of benchmarking in effective optimization.