Codex as a Full Custom Game Engine: The 'img2threejs' Skill Turns a Generated Image Into Playable 3D in Three Steps

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A widely shared demo (2,641 likes, 240K views) chains GPT imageGen → an img2threejs skill → GPT 5.6 Sol to convert a single generated 3D item image into a live Three.js scene, using Codex as the runtime rather than a code assistant. It's the clearest example yet of skills-as-compilers: a narrow, well-named skill collapsing a multi-day pipeline into a prompt. Builders should note the pattern — the leverage is in the skill definition, not the model.