3D Paper Material

3D Paper Material

Paper is a fibre field cut out by a torn outline: a height map of laid fibres and formation clouds gives the surface, an alpha mask with pulled-out fibres gives the edge, offset copies give the thickness, and the back light is transmitted by how thin the formation is at each pixel. Drop any one and the sheet is a white plane.

Reach for paper-cinder-transition when the paper burns or is revealed by fire; this skill is the unburnt sheet. It is a hung or laid sheet in a scene. A page-turning book needs a bend rig this skill does not provide.

Read demo.html for a working build: MeshPhysicalMaterial patched with onBeforeCompile, maps baked once into half-float targets, masks painted with Canvas 2D. Its NOISE GLSL, formation, kozo-fibre and bark-fleck expressions, back-light transmission, tearLine and the fray loop are ported unchanged from the Kibori workshop page (kibori.html, washiMat, footTear).

The pipeline

1. Bake fibres (GPU, once). One full-screen pass writes R height, G formation, B fibre, A fleck to a half-float target. Height is 0.5 + fibre*0.34 + (tooth-0.5)*0.1 - fleck*0.2 - crease*0.55. Keep samples: 0 on the target and mipmaps on.
2. Warp the lattice. Domain-warp the fibre coordinates by 0.014 unit and rotate them by (gnoise(q*2.1)-0.5)*1.5 rad. Add a finer, fainter fibre set at 2.7x frequency (max 0.55).
3. Paint the mask (Canvas 2D, on stock change). R thin strip inside the tear, G silhouette plus fray fibres, B ink with a low-alpha bleed halo, A the silhouette blurred by a shadow drawn off to the side (edge age). Read back with getImageData and write into a DataTexture, rows flipped, alpha as data.
4. Shape the sheet. A 168 x 240 plane: hung bow, a mountain crease, pin dimples, and a cylinder roll (radius 0.23, angle 2.6*curl) that keeps length. Add three copies offset along the normal by thick/3, 2thick/3, thick.
5. Shade. Albedo from formation and fibre, ink over it, toast and foxing by the age mask. Height goes through a world-unit bump (see gotchas). Alpha is coverage, not a cut.
6. Transmit. emissive += L * tr, where tr = 0.74 + (0.5-form)*0.85 + (0.5-lowfbm)*0.45 - fibre*0.22 - fleck*0.45, times stock gain, plus the thin strip, minus ink. L is the garden behind: sky, sun patch, black bamboo stems sampled through a mip bias of 1.4.
7. Macro. Re-bake a second height target and mask over a 0.5 unit window at the focus point and blend it over the base by window edge. Never tile a small texture.

Constants that landed

Scale: 1 unit = 134.8 mm (A4 is 1.55 x 2.2). Base bake 990 px/unit = 7.3 px/mm; macro window 1536 px over 0.5 unit = 22.8 px/mm. Tear samples 3400 per unit. Camera 28 degree FOV; macro distance 0.46-0.50.

Rules and the failure each prevents

• Cut the outline from four independent tear lines, never a rectangle with a wobble. A single sine or noise edge reads as a CSS wave; tearLine runs straight, turns, runs again. Give cut sides amplitude 3-4, torn sides 60-100.
• Pull fibres past the edge and paint them as partial coverage. A hard alpha edge reads as scissors. Fibres are 0.3-0.7 px wide at 30-75% alpha; on a dark wall they show as pale hairs.
• Stack three offset copies behind the front layer, tinted 0.8-0.94 of the paper. One quad has no thickness and shows nothing side-on. Keep the offset at 0.0045-0.011 unit; more reads as cardboard.
• Warp and rotate the fibre lattice. Two orthogonal ridged families read as scratched glass or a crosshatch, especially raking-lit.
• Drive transmission from the same fields as the albedo. A flat emissive constant reads as a lamp inside a card; thin formation must glow, fibre bundles and ink must hold light back.
• Fade the toast band to zero beyond the edge. Toasting the fray turns pulled-out fibres brown-black against a dark wall.
• Bleed ink with a halo below the ink threshold and let fibre and formation carry it over. A blurred halo alone is out-of-focus ink; smoothstep(0.62,0.85, halo + fibre*0.4 + (0.5-form)*0.5) wicks along strands. Guard the term with smoothstep(0.03,0.16, halo) or fibres far from any ink go black.
• Round the bark flecks. Kibori's cell hash gives squares at macro; multiply by an ellipse smoothstep(0.5,0.12,length((fract(q*cell)-0.5)*vec2(1,1.9))).
• Bake a window for macro. A base map at 7 px/mm turns to fog at 22 px/mm; a tiled 512 px paper tile shows its seam.