✦ Isekai Gemcraft ✦

異世界魔法石工坊

You are the cutter, not the audience.
A gemstone faceting-machine simulator that runs in your browser.

Tilt angle × 96-tooth index gear × depth stop — then press, blind. Release to reveal.

▶ PLAY IN BROWSER

Free · no install · desktop & mobile · English / 繁體中文 (toggle in-game)

Isekai Gemcraft — magical faceting machine

✦ TRAILER COMING SOON ✦

Real machine, real cuts, mostly permanent

🗡

Blind cutting

The view masks while you grind. Longer press cuts deeper — you only see the result after you release.

d = r·sinθ + h·cosθ ✦ t ⟼ 96−t ✦ Σ facets = 57 ✦ ∠40.75° ⊕ idx 12 ✦ d = r·sinθ + h·cosθ ✦ t ⟼ 96−t ✦ Σ facets = 57 ✦ ∠40.75° ⊕ idx 12 ✦ clip(n,d) ⊨ dot(n,v) ≤ d ✦ culet ⟹ 0.735R ✦ 96T ≡ 3.75°/t ✦ clip(n,d) ⊨ dot(n,v) ≤ d ✦ culet ⟹ 0.735R ✦ 96T ≡ 3.75°/t ✦ ⟨P1 45°⟩⟨C1 40°⟩⟨T 0°⟩ ✦ dev 0.0° ✦ yield 27.4% ✦ ⟨P1 45°⟩⟨C1 40°⟩⟨T 0°⟩ ✦ dev 0.0° ✦ yield 27.4% ✦ ❖ mast 73.5%R ❖ 8-fold ❖ q̂ = tilt ⊗ spin ❖ lap ⊥ world ❖ mast 73.5%R ❖ 8-fold ❖ q̂ = tilt ⊗ spin ❖ lap ⊥ world ❖

📜

Real faceting charts

Five cut designs executed tier by tier, exactly like a physical faceting diagram: angle + index + depth stop, with a guided instruction sheet and compass rings.

B+ A+ S+

⚖

Overdramatic appraisal

An otherworld master grades your symmetry, yield and diagram accuracy — with a professionally sharp tongue. Every stone joins your collection tray.

👁

Time-magic rewind

Every stone carries exactly 3 rewinds. Each one makes the last cut "never observed" — a narrow, sci-fi-flavored mercy for the one time you fat-finger the depth stop. Burn through all three and the simulator goes back to remembering everything.

Screenshots

White diamond Asscher step cut hovering over the lap — Asscher step cut (49 facets) — vertical girdle blades shape the octagon

Purple Portuguese cut gemstone above the grinding lap — Portuguese cut (97 facets) — 16-fold symmetry, three staggered rows

The diagram library

Diagram	Facets	Symmetry	Difficulty
Simple Sun	17	8-fold	⭐ start here
Standard Round Brilliant	57	8-fold	challenge
Asscher Step Cut	49	8-fold + girdle blades	intermediate
Portuguese	97	16-fold staggered	hard
Trillion	16	3-fold	quick

How it works

The stone is a convex polytope — a raw vertex/face list. Every cut is one half-space plane clip, computed exactly: no voxels, no CSG library, no mesh booleans. Facets stay perfectly planar at any count (the Portuguese cut runs 121 faces), and re-cutting the same plane removes nothing — which is precisely the property that makes depth-stop faceting and one-tap symmetric array cuts work, same as on a physical machine.

Every diagram ships with a built-in #dev console auditor: it re-derives each facet's expected normal and plane distance straight from the diagram's own angle/index/depth table, then diffs that against the actual cut geometry. All five built-in diagrams report a 100% facet match at 0.0° deviation — not "close enough," exact.

The cut plane is always "world down"; the stone's tilt and index spin are quaternions, and the plane is transformed into stone-local coordinates. Real-time convex clipping, procedural gemstone faceting, computational geometry in the browser — in one HTML file with Three.js r128. View source, it's all there.

Open source

The diagram system is data-driven — contributing a new cut design is a data entry plus one picker card. The built-in auditor must report a 100% facet match before merge.

★ GitHub Contribute a diagram