3D Viewer Design

Design rules for any 3D viewport Claude generates inside Adom — CAD, EDA, mechanical, PCB, component preview, schematic 3D, molecule viewer, any WebGL canvas. The headline rule: always use the Adom Babylon viewer at `gallia/viewer/` as the baseline — don't rebuild from scratch, extend it. Covers engine choice (Babylon, never Three), canonical-viewer reuse + upstream contribution workflow, background color (gradient, never pure black/white), HDRI + hemispheric lighting, PBR material fixups, ArcRotateCamera defaults including zoom-to-mouse AND Shift+Alt+Click orbit-center recentering (Fusion 360 / Onshape style), ViewCube / view presets, **world- origin axis helpers (always on — critical because origins are where every Adom 3D integration bug hides)**, measurement markers, and AI-drivability hooks. Read this BEFORE you pick `scene.clearColor`, import any 3D library, or design any camera interaction. Trigger words: 3D viewer, 3D viewport, scene background, clear color, Babylon scene, adom 3d viewer, adom babylon viewer, canonical viewer, CAD background, PCB viewer, component viewer, GLB viewer, STEP viewer, 3D preview, viewport design, 3D scene setup, 3d bg color, HDRI, environmentSpecular.env, bottom light toggle, camera limits, zoom to mouse, zoom to cursor, orbit center, recenter rotation, shift alt click, fusion 360 orbit, onshape orbit, ViewCube, view cube, view presets, axis helper, axes helper, origin axes, show origin, world origin, mesh origin, coordinate system, xyz gizmo, measurement marker, Babylon vs Three.js.