Developer builds a real-time 3D shader demo for The Game Boy Color — you can download the ROM or experience the 3D teapot in your browser

A clever developer has successfully gotten a Game Boy Color (GBC) to execute an interactive, user-driven, real-time 3D shader demo. Danny Spencer posted a video, blog post, along with downloadable ROMs and source code, and even embedded the demo in an online GBC emulator, allowing anyone curious to try out his Lambert-shaded 3D teapot.

It is always fascinating to see developers squeeze the last ounce of performance out of the available hardware. So, seeing this interactive spinning teapot demo for the GBC is super cool. Moreover, Spencer lays out all the details behind this accomplishment.

Running this real-time shader on the GBC wouldn’t be much of a challenge if the handheld had a strong processor. Nintendo’s second portable device, however, was nowhere near powerful. It kept the Sharp SM83 SoC, the same one used in the original Game Boy, but increased it to “dual-speed mode” at just over 8 MHz. This mode-switching, single-to-dual-speed chip was excellent for backward compatibility, though.

While the additional speed helps with this real-time 3D demo, the GBC’s processing remains severely inadequate for executing a user-interactive shader. Spencer dedicates a substantial part of his blog to showing how the SM83’s absence of a multiply instruction was cleverly circumvented through logarithms and lookup tables. To minimize computational load, the developer transformed the vectors into spherical coordinates and then implemented the Lambert shader with a spherical dot product. Much more detail on the programming, math, and rendering can be found in the linked blog post.

Download and explore the demo

Spencer has posted the gbshader code and associated materials on GitHub. There you’ll also find links to download GBC ROM releases for this interactive 3D shader demo.

Most readers will find it easiest to run the shader demo through the embedded emulator in the blog post. You can use the arrow keys to reposition the light source and simultaneously adjust the teapot’s viewing angle. On my computer keyboard, I could tweak both settings at once to manage the animation and lighting.

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