Isekai Gemcraft

Isekai Gemcraft is Penny Yu's browser faceting simulator, presenting a magical workshop around mechanics drawn from a physical gemstone-cutting machine. Players choose a crystal, mount the rough stone, set a tilt angle between zero and ninety degrees, rotate it through a 96-tooth index gear, and press it against a grinding lap. Cutting uses real-time convex polytope clipping, so every resulting facet remains planar rather than being approximated with voxels or decorative textures.

Five guided designs range from a seventeen-facet tutorial stone to round brilliant, Asscher, Portuguese, and trillion cuts. Diagram steps specify the required angle, index, and depth, with compass rings and optional symmetric-array actions assisting repetitive facets. Free-cutting mode removes the guide for open experimentation. Players can change coarse, fine, and polishing laps, tint stones with solid or two-tone colors, adjust lighting, submit finished work for appraisal, and preserve stones in a daily collection with favorites and JSON import or export. The bilingual, touch-capable single-file Three.js project is released under GPL-3.0.

Choose a rough stone and start with the Simple Sun tutorial if you are unfamiliar with faceting. Use the protractor control to set the tilt angle and the 96-position index gear to rotate the stone. Set the target depth, then press and hold the grinding control; the view is intentionally masked while material is removed. Release to inspect the new facet. A longer press cuts deeper until the depth stop reaches its target.

Follow each diagram's angle, index, and lap instructions, using the compass rings or symmetric-array action when several equivalent facets are required. Begin with a coarse lap, refine the surfaces with a fine lap, and finish with polish before submitting the gem for appraisal. Three rewind charges can undo early mistakes; after they are spent, later cuts remain permanent. Free-cutting mode removes diagram safeguards for custom shapes.