# Banana Jelly Material Study (WebGPU)

- Author: @N1njaCodex
- Card: Creator prompt
- Theme: Jelly & soft-body
- Stack: Not rebuilt
- Interaction: Drag
- Licence: Credited link (Shared publicly by the author; full text with credit, removed on request)
- Verified: not yet
- Original post: https://x.com/N1njaCodex/status/2107187133173678156

## Original prompt

```text
Build "Banana Jelly" — a single self-contained HTML file (no external requests, no libraries, no build step at runtime) using native WebGPU + WGSL. It is one entry in an editorial "MATERIAL STUDIES" series: an interactive, physically simulated banana plant whose every part is rendered as translucent coloured jelly. Simulation in JS, rendering in WebGPU; the page must stay smooth (sim < 2 ms/frame).

PAGE / LAYOUT (editorial, warm paper)
- Background paper #ece9e3 fading to a slightly darker floor; ink #241f1d; accent #c99a06 (banana gold); hairline rules #d5d0c8.
- Top-left: small caps eyebrow "MATERIAL STUDIES", huge italic serif H1 "Banana / Jelly." (Iowan Old Style / Palatino / Georgia stack), short rule, caption "A little sway. A little slip. A whole bunch."
- Top-right pill: green dot + "WEBGPU · LIVE" (or "WebGPU · Unavailable").
- Right floating glass panel (rgba paper, 1px border):
  • "THE TREE": dark button "Shake the tree" with a thin gold progress bar under it; tally row "On the bunch 31 · Fallen 0 · Peeled 0" (tabular mono numbers).
  • "PALETTE": three swatch buttons with a glossy jelly ball each — Cavendish (yellow), Red Dacca (red-purple), Blue Java (powder blue).
  • Sliders: Firmness 50, Internal damping 40, Breeze 30 (value shown in small mono at right).
  • Buttons: Reset · Pause · Reset view.
- Bottom-left: "HOW TO HOLD IT", italic line "Shake the bunch. Swing the heart. Throw one hard.", and a small grey line: "Drag a leaf or the stem to bend it · pull a banana off and fling it — a hard landing bursts the peel · drag the purple heart to swing it · drag empty space or right-drag to orbit · scroll or pinch to zoom".
- On wide screens, centre the plant in the free band between the masthead and the panel (shift the projection, fit the distance). Mobile: panel becomes a bottom sheet (closed by default, tap to open; the 3D view slides up so the plant stays visible), touch drag orbits, pinch zooms. No page scroll anywhere.
- Fallback card if navigator.gpu or the adapter is missing: "Banana Jelly." + explanation, pill shows "WebGPU · Unavailable". Zero console errors/warnings.

THE PLANT (must be LUSH — many big leaves, never a sparse/bald tree)
- A low round glossy cream jelly plinth/dish; plant rooted in its centre.
- Pseudostem: ~1.42 tall, 9 segments, radius 0.158→0.106, leaning slightly away from the bunch.
- Crown: 15 big paddle leaves spiralling by the golden angle (2.39996 rad). Young leaves stand almost upright, older ones arch out and droop (elevation 1.22→0.02 rad by age). Length 1.15–1.7, width ≈0.3·scale, sin^0.38 blade outline, slight V-fold/cup across the midrib, a few ragged wind-tear slits (tapered wedges, not many), slight edge ripple, old leaves yellowing a bit at the tips.
- Two pups (suckers) at the foot, each with 4 smaller leaves.
- Bunch stalk: from the top of the crown it rises slightly, arches over and hangs straight down (10 segments, length 1.18), then a thin neck and the HEART — a dark purple-maroon teardrop bud (cardiac flower) made of overlapping bracts, with one or two bracts lifted/curling back.
- 5 hands of bananas along the hanging stalk, fanned out on different sides (azimuth step 2.2 rad), counts 7,7,6,6,5 = 31 bananas, slightly larger near the top. Each banana: analytic curved arc, ridged (pentagonal-ish) cross-section, tapered dark stem end and dark tip, curving up toward the light; sparse dark freckles.

SIMULATION
- Whole plant = tree of nodes with position-based dynamics at fixed 240 Hz (4 solver iterations): length constraints + bend constraints toward a rest orientation stored relative to the parent frame (parallel-transported quaternion frames). Stiffness by order (stem stiff, leaf midribs springy, stalk flexible, neck soft).
- Gravity loads: every node carries the weight of its leaves/bananas. Pre-compensate the rest pose (iterate 3×: settle, measure sag, pre-bend rest orientations) so that, fully loaded, the plant sits exactly in its designed shape; when bananas fall, the lighter bunch lifts a little. Load changes are eased, not instantaneous.
- Settle 2.5 s silently on load/reset (no tearing during settle).
- Breeze: smooth noise forcing on leaf nodes (gusts travelling through the crown), scaled by the slider; Breeze 0 = perfectly still.
- Blades and all meshes are skinned on the GPU from a storage buffer of node positions + frames (each vertex: two nodes, a fraction, an offset in the frame).
- Bananas on the bunch hang from their hand node with a small damped wobble spring (freq 3.2+2.2·firm Hz, damping from slider).
- Detachment: track each hand's smoothed acceleration; a banana tears off when the acceleration exceeds its strength (≈ 11+5·firm, varying per fruit), with fatigue accumulating on repeated shakes and a short per-hand cooldown — shaking should drop bananas progressively (a few per shake), never the whole bunch at once.
- "Shake the tree" applies a multi-second shake to the stem with a progress bar.
- Loose bananas are rigid bodies (3 spheres along the arc) with impulse contacts and friction against the plinth, floor, stem and each other; sleep when still; speed clamp.
- Peel bursts ONLY from impact: if a loose banana hits a surface with pre-contact normal speed above ~5.4+1.2·firm, it bursts. A fall from the bunch or a gentle drop never bursts it. Burst = the skin splits into 4 strips from the tip, which fold back around a hinge near the stem (arc fold then straight segment, sagging under gravity, slight per-strip variation), revealing creamy translucent flesh. Count it in "Peeled".

INTERACTION (pointer + touch)
- Pick bananas on the bunch: pulling it stretches its attachment; past ~0.075 of stretch held briefly it snaps off into your hand (only that one); keep the bunch from being yanked far (limited hold displacement, held fruit doesn't drag the bunch). Release with the pointer velocity to fling it.
- Drag the purple heart: it swings the stalk like a pendulum and keeps swinging after release; swinging must not shake bananas off.
- Drag a leaf or the stem: bends it, springs back on release.
- Drag empty space / right-drag: orbit; wheel/pinch: zoom; Reset view restores camera (az 0.55, el 0.2, FOV 36°).
- Firmness changes stiffness, tear strength and burst threshold; Internal damping changes wobble/swing damping; Pause freezes time; Reset regrows the full bunch.

RENDERING — the jelly look
- Everything is jelly: Beer–Lambert absorption by thickness (per-material sigma RGB), wrapped subsurface scatter, refraction of a soft studio environment, Fresnel rim + sharp specular, soft inner glow; leaves are thin translucent jelly with bright backlit veins/midrib and deeper colour toward the edges.
- Translucent leaves via weighted-blended OIT; bananas/stem/heart opaque-ish jelly with depth.
- Coloured shadow: a transmittance map rendered from the light (leaves tint the shadow green, bananas gold), blurred, projected onto the plinth and floor — a long soft coloured shadow to the right.
- Palettes (swap all tints live):
  • Cavendish — skin bright yellow (tint 1.0,0.8,0.08), green tips, creamy flesh, leaves fresh green (0.22,0.66,0.08), stem olive, heart deep purple-maroon, cream plinth.
  • Red Dacca — skin red-burgundy (0.82,0.1,0.16), pale peach flesh, leaves slightly warmer green, reddish stem, pinkish plinth.
  • Blue Java — skin powder blue-teal (0.56,0.8,0.86), white "ice-cream" flesh, blue-green leaves, cool grey-blue plinth.

QA (headless Chromium with SwiftShader WebGPU)
- Expose a debug hook (window.__bj: advance, shake, pick, project, setPalette, reset, setPause, counts) and verify: full bunch of 31 at start; ≥20 leaves; nothing falls when idle; breeze moves leaves and Breeze 0 is still; shaking drops some bananas without peeling them; fallen fruit comes to rest; counters update; reset restores; a pulled banana snaps off alone; a hard landing peels it, a gentle drop doesn't; heart swings as a pendulum without dropping fruit; leaves bend and spring back; palettes/sliders/pause/orbit/zoom work; stress test has no NaN; sim cost < 5 ms; no network requests; no console errors; mobile sheet + touch; fallback card.
```

Not rebuilt by 3dmotion yet. Credit stays with @N1njaCodex.

Prompt by @N1njaCodex (https://x.com/N1njaCodex/status/2107187133173678156) via 3dmotion.io/e/banana-jelly-material-study-webgpu