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Shadow Geometry: Umbra and Penumbra — 3D

3D shadow-puppet stage — an extended lamp sampled across many point sources casts a real umbra and penumbra onto a screen as you drag the occluding object, sizes scaling by similar-triangles geometric optics.

Physics & Mechanics3DModerate60 FPS📱 Mobile-adapted⇄ 2D version

Details

CategoryPhysics & Mechanics

RenderingThree.js · WebGL

DifficultyModerate

Target FPS60

ControlsSliders for lamp size, lamp-to-screen distance, lamp-to-object distance, and object size, plus a sample-count toggle button; drag the pumpkin object to reposition it in x/y, drag empty space to orbit the camera, scroll to zoom, and a reset button.

shadow-geometryumbrapenumbraopticshalloween

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⚙ Under the hood

An extended lamp sampled across many point sources casts a real umbra and penumbra onto a screen as you drag the occluding object, sizes scaling by similar-triangles geometric optics.

shadow-geometryumbrapenumbraopticshalloween

3D · Three.js / WebGL renderer · 60 FPS target · runs fully client-side, no install