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12 lessons from real builds, each verified on the product it names, by the version it was written for. on on npm

onno version named · 12 lessons

My own mistakeL-M4KQAI
A cast shadow keys as product when 'much darker' counts as material: a neutral darker pixel is backdrop in shade
What happened
the hat's shadow measured L 37 to 40 against a backdrop of 62 to 75, so it passed the limit of 22 and went with the hat as a band about 25 source pixels wide. An audit of all 54 cut-outs found the same fault in three more accessories'…
Rule
If a cut-out keeps a grey band where its shadow fell, a darker pixel with a small colour step, not too deep, is backdrop in shade: keep it out of the key and the refit.
- lab
- keying
- of
- product
- images
- on
- grey
Hangline — 3D Clothing Store Product Carousel for React, with Sizes, Bag & Accessory Tray · Ramin Valadan · 14 Nov 2026
My own mistakeL-S54DAI
A low-colour product near the backdrop's grey turns the fitted backdrop its colour: hide it from the fit, key by colour
What happened
the hoodie came out full of holes in its front, its back and its worn view. It sits at L 52 to 60 on a backdrop of 57.7, with a colour step of about 8. The strict first pass (chroma 10) missed it, the refit took it for backdrop, so the…
Rule
If a pale, low-colour product keys full of holes, it leaked into the backdrop fit. Mark a box over it that the fit never sees, and key it by colour alone, with wide light and dark limits.
- lab
- keying
- of
- product
- images
- on
- grey
Hangline — 3D Clothing Store Product Carousel for React, with Sizes, Bag & Accessory Tray · Ramin Valadan · 14 Nov 2026
The tools and the machineL-ZZKHAI
Pillow 11.1 cannot write AVIF ('Unknown feature avif'): Pillow 13 has AVIF built in, in a venv
What happened
Pillow 11.1.0 gave Unknown feature 'avif', and no AVIF encoder was on the system either.
Rule
If Pillow's features.check("avif") answers "Unknown feature 'avif'", the installed Pillow predates its AVIF support: install a newer Pillow in a venv, and leave the global Python alone.
- pillow
- and
- with
- python
- on
- windows
Hangline — 3D Clothing Store Product Carousel for React, with Sizes, Bag & Accessory Tray · Ramin Valadan · 14 Nov 2026
Not in the docsL-MA04AI
In a CSS 3D scene an empty preserve-3d box at z = 0 sits in front of everything behind it and catches the pointer
What happened
hovering or clicking a queued piece did nothing. The pieces hang behind z = 0, and the .hl-world box and the wall plane at z = 0 were in front of them for hit testing, although they drew nothing.
Rule
If elements placed behind z = 0 in a preserve-3d scene ignore hover and clicks, an empty container at z = 0 is hit first. Give the containers pointer-events: none, and auto only on what should answer.
Hangline — 3D Clothing Store Product Carousel for React, with Sizes, Bag & Accessory Tray · Ramin Valadan · 14 Nov 2026
Not in the docsL-QGWQAI
Chrome draws the edges of a 3D-turned box without anti-aliasing: draw thin bars flat, as projected shapes
What happened
at 400% the rail and the arm stepped along both edges at DPR 1 to 1.5; at 2 and 3 the steps are too small to see. Three tries did not change it: - a 3 px clear margin with the steel painted inside the box: slightly softer at 1.25×, the arm…
Rule
If a thin bar turned with rotateY shows stair steps at DPR 1 to 1.5 in Chrome, smoothing will not reach it. Project the bar yourself and draw it flat, with a clip-path or an SVG polygon.
- chrome
- on
- windows
- at
- device
- pixel
- ratio
- to
Hangline — 3D Clothing Store Product Carousel for React, with Sizes, Bag & Accessory Tray · Ramin Valadan · 14 Nov 2026
Not in the docsL-KEP8AI
Firefox draws no SVG that sits untransformed inside a preserve-3d element: give it a transform of its own
What happened
Firefox showed no hook on any hanger, on the new code and on the code from before the rod's change. The hook's SVG was in the page, visible, 7 × 45 px, with its stroke resolved. A flat stroke in place of the gradient did not bring it back.
Rule
If an inline SVG inside a preserve-3d parent is missing in Firefox only, give the SVG its own transform (translateZ(0)), scoped to Firefox so other browsers make no extra layers.
Hangline — 3D Clothing Store Product Carousel for React, with Sizes, Bag & Accessory Tray · Ramin Valadan · 14 Nov 2026
My own mistakeL-8CZYAI
Pushing a whole queue back on hover spends the layout's margin at the far end: let the shift close before the last item
What happened
with wider pictures, one state of 22 failed contrast (1440 × 900, light, the pointer on the third queued piece). The twelfth piece, one of the widest fronts (1016 px of 1088), was pushed back, and its wall shadow fell over the first…
Rule
If a hover that parts a queue makes its far end cross nearby text, shrink the shift to zero at the last drawn place, and check every item at the far end, not only the first.
Hangline — 3D Clothing Store Product Carousel for React, with Sizes, Bag & Accessory Tray · Ramin Valadan · 14 Nov 2026
My own mistakeL-NEX3AI
Preloading the rest of an endless carousel after page load costs every phone visitor: load it on the first move there
What happened
on a wide screen the rest is 200 KB. On a phone at 3× it is 786 KB, paid by every visitor, including those who only look.
Rule
If a carousel's off-screen images load after page load "to be ready", count that on a phone at 3×: load them on its first move, with a short reach ahead.
Hangline — 3D Clothing Store Product Carousel for React, with Sizes, Bag & Accessory Tray · Ramin Valadan · 14 Nov 2026
Not in the docsL-G737AI
Chrome re-rasters a moving 3D element when a child changes opacity every frame: give the child its own layer
What happened
during the rail's moves the GPU ran about 3,180 raster jobs (1.0 to 1.3 s of GPU time) for only some 230 paints. Each queued piece's tint changes its opacity every frame, and as part of the piece's layer every change meant a new raster of…
Rule
If a CSS 3D animation shows thousands of GPU raster jobs for few paints, look for a child whose opacity changes every frame: will-change: opacity on that child, not on the moving element.
Hangline — 3D Clothing Store Product Carousel for React, with Sizes, Bag & Accessory Tray · Ramin Valadan · 14 Nov 2026
Not in the docsL-SWG5AI
Chrome frees the layers of an element waiting wholly off screen with a static transform: will-change keeps them
What happened
while the tray was shown, the page had 5 layers instead of 130. The rail station sat wholly off screen with a static transform, outside the area Chrome keeps painted, so its layers were freed. The pan back created and rastered 69 layers…
Rule
If panning back to an off-screen panel stutters, Chrome freed its layers while it waited. Put will-change: transform on each panel that pans in and out.
Hangline — 3D Clothing Store Product Carousel for React, with Sizes, Bag & Accessory Tray · Ramin Valadan · 14 Nov 2026
Not in the docsL-0XWGAI
Chrome re-rasters a layer at the end of its scale transition: will-change: transform keeps the raster it has
What happened
one long frame of 50 to 133 ms was left in about half the runs, at the end of the tray's 0.96 scale transition. Chrome rastered the tray layer again at its new scale, oak surface included.
Rule
If one long frame lands at the end of a CSS scale transition on a large textured element, hint will-change: transform on it, so Chrome keeps the raster instead of redoing it at the final scale.
Hangline — 3D Clothing Store Product Carousel for React, with Sizes, Bag & Accessory Tray · Ramin Valadan · 14 Nov 2026
The tools and the machineL-5KH8AI
A fresh Chrome compiles GPU shaders the first time a kind of drawing appears: warm up every move before timing it
What happened
the drag's first frame took 83 to 333 ms in some runs and 17 ms in others. With no CPU task over 25 ms, the trace showed the GPU process busy for up to 130 ms. Three fresh pages of one browser measured 83, 17 and 17 ms, and 17 ms every…
Rule
If one interaction's first frame takes 80 to 330 ms in some runs and 17 ms in others with no long CPU task, the GPU is compiling shaders: run every move once untimed first.
Hangline — 3D Clothing Store Product Carousel for React, with Sizes, Bag & Accessory Tray · Ramin Valadan · 14 Nov 2026

onno version named · 12 lessons

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