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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<title>color-attribute-wheel — Examples — Blender Developer Tools</title>
<meta name="description" content="The modern color-attributes API — mesh.color_attributes.new() on the CORNER domain, filled by expanding per-vertex HSV across face corners with foreach_get/foreach_set, then wired into a shader Attribute node." />
<link rel="canonical" href="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/color-attribute-wheel/" />
<link rel="icon" href="../../assets/favicon.svg" type="image/svg+xml" />
<meta name="theme-color" content="#1a1b1e" />
<meta name="color-scheme" content="dark" />
<meta property="og:type" content="website" />
<meta property="og:title" content="color-attribute-wheel — Examples — Blender Developer Tools" />
<meta property="og:description" content="The modern color-attributes API — mesh.color_attributes.new() on the CORNER domain, filled by expanding per-vertex HSV across face corners with foreach_get/foreach_set, then wired into a shader Attribute node." />
<meta property="og:url" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/color-attribute-wheel/" />
<meta property="og:image" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/assets/color-attribute-wheel-hero.webp" />
<meta property="og:image:width" content="1280" />
<meta property="og:image:height" content="720" />
<meta property="og:image:alt" content="color-attribute-wheel: the example's own headless render" />
<meta property="og:site_name" content="Blender Developer Tools" />
<meta name="twitter:card" content="summary_large_image" />
<meta name="twitter:title" content="color-attribute-wheel — Examples — Blender Developer Tools" />
<meta name="twitter:description" content="The modern color-attributes API — mesh.color_attributes.new() on the CORNER domain, filled by expanding per-vertex HSV across face corners with foreach_get/foreach_set, then wired into a shader Attribute node." />
<meta name="twitter:image" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/assets/color-attribute-wheel-hero.webp" />
<meta name="twitter:image:alt" content="color-attribute-wheel: the example's own headless render" />
<style>
/* fonts are deployed by the landing build (docs/fonts/) */
@font-face { font-family: 'Barlow Condensed'; font-weight: 600; font-display: swap;
src: url('../../fonts/barlow-condensed-600.woff2') format('woff2'); }
@font-face { font-family: 'Inter'; font-weight: 400; font-display: swap;
src: url('../../fonts/inter-regular.woff2') format('woff2'); }
@font-face { font-family: 'Inter'; font-weight: 500; font-display: swap;
src: url('../../fonts/inter-medium.woff2') format('woff2'); }
@font-face { font-family: 'JetBrains Mono'; font-weight: 400; font-display: swap;
src: url('../../fonts/jetbrains-mono-regular.woff2') format('woff2'); }
/* Blender-viewport system, shared with the landing page. Dark only. */
:root {
color-scheme: dark;
--bg: #1a1b1e; --surface: #222327; --surface-2: #2a2b30; --bg2: #131417;
--border: #3a3b40; --text: #e8e9eb; --text-dim: #9698a0;
--select: #ff8c19; --ok: #6dc96d;
--radius: 4px; --radius-lg: 6px; --maxw: 1080px;
--font-display: 'Barlow Condensed', 'Arial Narrow', sans-serif;
--font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif;
--font-mono: 'JetBrains Mono', ui-monospace, 'SF Mono', Menlo, Consolas, monospace;
--code-k: #ff7b72; --code-s: #a5d6ff; --code-c: #9698a0; --code-n: #79c0ff;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body { font-family: var(--font-sans); background: var(--bg); color: var(--text);
line-height: 1.6; min-height: 100vh; -webkit-font-smoothing: antialiased; }
a { color: var(--select); text-decoration: none; }
a:hover { text-decoration: underline; }
:focus-visible { outline: 2px solid var(--select); outline-offset: 2px; border-radius: 3px; }
::selection { background: color-mix(in srgb, var(--select) 40%, transparent); }
.skip { position: absolute; left: -999px; top: 0; background: var(--select); color: #1a1b1e;
padding: 0.5rem 1rem; border-radius: var(--radius); z-index: 10; font-weight: 500; }
.skip:focus { left: 0.5rem; top: 0.5rem; }
.hud { font-family: var(--font-mono); font-size: 0.6875rem; letter-spacing: 0.04em;
color: var(--text-dim); text-transform: uppercase; }
.topbar { position: sticky; top: 0; z-index: 5; display: flex; align-items: center;
justify-content: space-between; gap: 1rem; padding: 0 1.25rem; height: 46px;
background: color-mix(in srgb, var(--surface) 92%, transparent);
backdrop-filter: blur(10px); border-bottom: 1px solid var(--border); }
.topbar .back { color: var(--text-dim); font-size: 0.8125rem; font-weight: 500; }
.topbar .back:hover { color: var(--select); text-decoration: none; }
.topbar-right { display: flex; align-items: center; gap: 0.85rem; }
.topbar-right .ghlink { color: var(--text-dim); font-size: 0.8125rem; font-weight: 500; }
.topbar-right .ghlink:hover { color: var(--select); text-decoration: none; }
header.hero { max-width: var(--maxw); margin: 0 auto; padding: 2.75rem 1.25rem 1.25rem; }
header.hero h1 { font-family: var(--font-display); font-weight: 600; text-transform: uppercase;
font-size: clamp(2.2rem, 5vw, 3.4rem); letter-spacing: 0.005em; line-height: 0.98; }
header.hero p { color: var(--text-dim); max-width: 62ch; margin-top: 0.7rem; font-size: 1rem; }
/* ---- index: sticky controls (search, density toggle, tag chips) ---- */
.controls { position: sticky; top: 46px; z-index: 4;
background: color-mix(in srgb, var(--bg) 94%, transparent);
backdrop-filter: blur(10px); -webkit-backdrop-filter: blur(10px);
border-bottom: 1px solid var(--border); }
.controls-inner { max-width: var(--maxw); margin: 0 auto; padding: 0.55rem 1.25rem 0.6rem;
display: flex; flex-direction: column; gap: 0.5rem; }
.controls-row { display: flex; align-items: center; gap: 0.6rem; flex-wrap: wrap; }
.searchwrap { position: relative; flex: 1 1 240px; min-width: 150px; }
.searchwrap input { width: 100%; background: var(--surface-2); border: 1px solid var(--border);
color: var(--text); border-radius: var(--radius); padding: 0.34rem 1.9rem 0.34rem 0.7rem;
font-family: var(--font-sans); font-size: 0.85rem; line-height: 1.4; }
.searchwrap input:focus { border-color: var(--select); outline: none; }
.searchwrap input::placeholder { color: var(--text-dim); }
.searchwrap input::-webkit-search-cancel-button { -webkit-appearance: none; appearance: none; }
.q-clear { position: absolute; right: 0.2rem; top: 50%; transform: translateY(-50%);
background: none; border: none; color: var(--text-dim); font-size: 1.05rem; line-height: 1;
cursor: pointer; padding: 0.25rem 0.45rem; border-radius: 3px; }
.q-clear:hover { color: var(--select); }
.count { font-family: var(--font-mono); font-size: 0.68rem; letter-spacing: 0.04em;
text-transform: uppercase; color: var(--text-dim); white-space: nowrap; }
.density { display: flex; border: 1px solid var(--border); border-radius: var(--radius);
overflow: hidden; }
.density-btn { background: var(--surface-2); border: none; color: var(--text-dim); cursor: pointer;
font-family: var(--font-mono); font-size: 0.68rem; letter-spacing: 0.04em;
text-transform: uppercase; padding: 0.36rem 0.7rem; transition: color 0.15s, background 0.15s; }
.density-btn + .density-btn { border-left: 1px solid var(--border); }
.density-btn:hover { color: var(--select); }
.density-btn.active { background: var(--select); color: #1a1b1e; }
.tags-toggle { display: none; background: var(--surface-2); border: 1px solid var(--border);
color: var(--text-dim); border-radius: 3px; padding: 0.3rem 0.7rem; cursor: pointer;
font-family: var(--font-mono); font-size: 0.7rem; letter-spacing: 0.04em; text-transform: uppercase; }
.tags-toggle:hover, .tags-toggle.has-active { color: var(--select); border-color: var(--select); }
/* Tag chips wrap by default (no-JS safe). With JS the row becomes a scroll
strip on wide viewports and collapses behind the Tags toggle on narrow
ones, so the sticky bar never eats the mobile viewport. */
.chips { display: flex; flex-wrap: wrap; gap: 0.4rem; }
html.js .chips { flex-wrap: nowrap; overflow-x: auto; padding-bottom: 0.25rem;
scrollbar-width: thin; scrollbar-color: var(--border) transparent; }
html.js .chips::-webkit-scrollbar { height: 5px; }
html.js .chips::-webkit-scrollbar-thumb { background: var(--border); border-radius: 3px; }
.chip { background: var(--surface-2); border: 1px solid var(--border); color: var(--text-dim);
border-radius: 3px; padding: 0.22rem 0.7rem; font-size: 0.72rem; font-weight: 400;
font-family: var(--font-mono); cursor: pointer; white-space: nowrap; flex: 0 0 auto;
transition: color 0.15s, border-color 0.15s; }
.chip:hover { color: var(--select); border-color: var(--select); }
.chip.active { color: #1a1b1e; background: var(--select); border-color: var(--select); }
@media (max-width: 719px) {
html.js .tags-toggle { display: inline-block; }
html.js .chips { display: none; }
html.js .chips.open { display: flex; flex-wrap: wrap; overflow-y: auto; max-height: 40vh; }
}
/* Compact density: hero + name + one-line teaser. The description and
WITNESSES text stay in the DOM (searchable, screen-reader reachable,
present with JS disabled when the class is never applied) but are
visually collapsed. Applied only by JS via the density-compact class. */
html.density-compact .grid { gap: 1rem; }
html.density-compact .card-body { padding: 0.65rem 0.9rem 0.7rem; }
html.density-compact .card-body h2 { font-size: 0.88rem; margin-bottom: 0.15rem; }
html.density-compact .teaches { font-size: 0.8rem; color: var(--text-dim); margin-bottom: 0;
white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
html.density-compact .witnesses { position: absolute; width: 1px; height: 1px; margin: -1px;
padding: 0; overflow: hidden; clip: rect(0 0 0 0); clip-path: inset(50%); white-space: nowrap; }
html.density-compact .card-link { display: none; }
.noresults { color: var(--text-dim); text-align: center; padding: 3rem 1rem; font-size: 0.95rem; }
.noresults .chip { margin-left: 0.6rem; }
.to-top { position: fixed; right: 1.25rem; bottom: 1.25rem; z-index: 6; cursor: pointer;
background: var(--surface-2); border: 1px solid var(--border); color: var(--text-dim);
border-radius: var(--radius); padding: 0.45rem 0.75rem;
font-family: var(--font-mono); font-size: 0.7rem; letter-spacing: 0.04em;
text-transform: uppercase; opacity: 0; visibility: hidden;
transition: opacity 0.2s, visibility 0.2s, color 0.15s, border-color 0.15s; }
.to-top.show { opacity: 1; visibility: visible; }
.to-top:hover { color: var(--select); border-color: var(--select); }
main { max-width: var(--maxw); margin: 0 auto; padding: 1rem 1.25rem 2rem; }
.grid { display: grid; grid-template-columns: 1fr; gap: 1.5rem; align-items: stretch; }
.card { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius-lg);
overflow: hidden; display: flex; flex-direction: column;
outline: 2px solid transparent; outline-offset: -1px;
transition: outline-color 0.12s ease, border-color 0.12s ease; }
.card:hover { border-color: var(--select); outline-color: var(--select); }
.card.hidden { display: none; }
.card-media { display: block; background: var(--bg2); line-height: 0; }
.card-media img { display: block; width: 100%; aspect-ratio: 16 / 9; object-fit: cover; }
.card-body { padding: 1.15rem 1.4rem 1.45rem; display: flex; flex-direction: column; flex: 1 1 auto; }
.card-body h2 { font-family: var(--font-mono); font-size: 1rem; font-weight: 400; margin-bottom: 0.5rem; }
.card-body h2 a { color: var(--text); }
.card-body h2 a:hover { color: var(--select); text-decoration: none; }
.teaches { color: var(--text); margin-bottom: 0.7rem; font-size: 0.92rem; }
.witnesses { color: var(--text-dim); font-size: 0.85rem; margin-bottom: 1rem; }
.tag { display: inline-block; font-family: var(--font-mono); font-size: 0.62rem; text-transform: uppercase;
letter-spacing: 0.06em; color: var(--select); border: 1px solid color-mix(in srgb, var(--select) 55%, transparent);
border-radius: 3px; padding: 0.08rem 0.5rem; margin-right: 0.4rem; vertical-align: 1px; }
.card-link { font-weight: 600; font-size: 0.95rem; margin-top: auto; }
/* ---- detail page ---- */
.detail-hero { border: 1px solid var(--border); border-radius: var(--radius-lg); overflow: hidden;
background: var(--bg2); padding: 0; display: block; width: 100%; cursor: zoom-in; line-height: 0; }
.detail-hero img { display: block; width: 100%; aspect-ratio: 16 / 9; object-fit: cover; }
.zoom-hint { color: var(--text-dim); font-size: 0.78rem; margin-top: 0.4rem; }
.sr-only { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0);
white-space: nowrap; }
.callout { border: 1px solid color-mix(in srgb, var(--select) 45%, var(--border));
border-left: 3px solid var(--select); border-radius: var(--radius);
background: color-mix(in srgb, var(--select) 7%, var(--surface));
padding: 0.85rem 1.1rem; margin: 1.5rem 0; font-size: 0.95rem; }
.runline { display: flex; align-items: stretch; gap: 0.5rem; margin: 1.5rem 0; }
.runline pre { flex: 1 1 auto; background: var(--surface-2); border: 1px solid var(--border);
border-radius: var(--radius); padding: 0.7rem 0.9rem; overflow-x: auto;
font-family: var(--font-mono); font-size: 0.83rem; line-height: 1.5; }
.copy-btn { flex: 0 0 auto; background: var(--surface-2); border: 1px solid var(--border);
color: var(--text-dim); border-radius: var(--radius); padding: 0 0.85rem; cursor: pointer;
font-family: var(--font-sans); font-size: 0.82rem; font-weight: 500; transition: color 0.15s, border-color 0.15s; }
.copy-btn:hover { color: var(--select); border-color: var(--select); }
.detail-section { margin-top: 2.25rem; }
.detail-section > h2 { font-family: var(--font-display); font-weight: 600; text-transform: uppercase;
font-size: 1.45rem; letter-spacing: 0.005em; padding-bottom: 0.5rem;
border-bottom: 1px solid var(--border); margin-bottom: 1rem; }
.md h1, .md h2, .md h3 { letter-spacing: -0.01em; margin: 1.4rem 0 0.6rem; line-height: 1.25; }
.md h1 { font-size: 1.35rem; } .md h2 { font-size: 1.15rem; } .md h3 { font-size: 1rem; }
.md p { margin: 0.7rem 0; }
.md ul, .md ol { margin: 0.7rem 0 0.7rem 1.4rem; }
.md li { margin: 0.3rem 0; }
.md .table-wrap { overflow-x: auto; margin: 0.9rem 0; }
.md table { border-collapse: collapse; font-size: 0.86rem; min-width: 100%; }
.md th, .md td { text-align: left; vertical-align: top; padding: 0.4rem 0.75rem 0.4rem 0;
border-bottom: 1px solid var(--border); }
.md th { color: var(--text-dim); font-weight: 600; white-space: nowrap; }
.md code { background: var(--surface-2); border: 1px solid var(--border); padding: 0.08rem 0.35rem;
border-radius: 4px; font-family: var(--font-mono); font-size: 0.84em; }
.md pre { background: var(--surface-2); border: 1px solid var(--border); border-radius: var(--radius);
padding: 0.85rem 1rem; overflow-x: auto; margin: 0.9rem 0; }
.md pre code { background: none; border: none; padding: 0; font-size: 0.83rem; line-height: 1.55; }
.src pre { background: var(--surface-2); border: 1px solid var(--border); border-radius: var(--radius);
padding: 1rem 1.1rem; overflow-x: auto; font-family: var(--font-mono);
font-size: 0.82rem; line-height: 1.55; }
.src .k { color: var(--code-k); } .src .s { color: var(--code-s); }
.src .c { color: var(--code-c); font-style: italic; } .src .n { color: var(--code-n); }
.src-meta { display: flex; justify-content: space-between; align-items: baseline; gap: 1rem;
flex-wrap: wrap; margin-bottom: 0.6rem; color: var(--text-dim); font-size: 0.85rem; }
.src-meta code { font-family: var(--font-mono); font-size: 0.82rem; }
.lightbox { border: 0; margin: 0; padding: 2rem; width: 100%; height: 100%; max-width: none;
max-height: none; background: rgba(0,0,0,0.85); cursor: zoom-out; }
.lightbox[open] { display: flex; align-items: center; justify-content: center; }
.lightbox::backdrop { background: transparent; }
.lightbox img { max-width: 100%; max-height: 100%; border-radius: var(--radius); }
.lightbox-close { position: absolute; top: 0.9rem; right: 0.9rem; background: var(--surface-2);
color: var(--text); border: 1px solid var(--border); border-radius: var(--radius);
font: 500 0.8rem var(--font-sans); padding: 0.4rem 0.75rem; cursor: pointer; }
.lightbox-close:hover { border-color: var(--select); color: var(--select); }
footer { border-top: 1px solid var(--border); background: var(--surface); margin-top: 2rem; }
footer .statusbar { max-width: var(--maxw); margin: 0 auto; padding: 0.55rem 1.25rem;
display: flex; align-items: center; gap: 1rem; flex-wrap: wrap;
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<header class="hero">
<h1>color-attribute-wheel</h1>
<p>The modern color-attributes API — mesh.color_attributes.new() on the CORNER domain, filled by expanding per-vertex HSV across face corners with foreach_get/foreach_set, then wired into a shader Attribute node.</p>
</header>
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<button class="detail-hero" id="heroZoom" type="button" aria-label="Zoom color-attribute-wheel render">
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<p class="zoom-hint">Rendered headless by the example itself — click to zoom.</p>
<div class="callout"><span class="tag">witnesses</span> CORNER-domain attributes are sized to loop count, not vertex count; the check asserts the sizing, that active_color points at it, and that the Attribute node is actually linked to Base Color, not just present.</div>
<div class="runline">
<pre id="runCmd">blender --background --python examples/color-attribute-wheel/color_attribute_wheel.py --</pre>
<button class="copy-btn" id="copyRun" type="button">Copy</button>
</div>
<section class="detail-section md">
<p>A runnable example that builds an HSV color wheel disc entirely with <code>bmesh</code> and colors it with <code>Mesh.color_attributes.new()</code> — the modern attributes API, not the deprecated <code>Mesh.vertex_colors</code> alias AI code keeps reaching for. It witnesses the domain trap that comes with it: a <code>CORNER</code>-domain attribute is sized to <code>len(mesh.loops)</code>, not <code>len(mesh.vertices)</code>, so per-vertex data has to be expanded across face corners before it is written. The material wires the same attribute into a Shader <code>Attribute</code> node (<code>attribute_type='GEOMETRY'</code>) feeding Base Color — the step AI code most often skips, leaving the mesh gray even when the attribute data is correct.</p>
<p><strong>What it witnesses:</strong> a <code>FLOAT_COLOR</code> attribute on the <code>CORNER</code> domain, filled with one <code>foreach_get</code> (loop → vertex index) and one <code>foreach_set</code> (loop color), never a per-loop Python assignment. The check asserts the attribute is sized to the loop count and <em>not</em> the vertex count, that it is <code>color_attributes.active_color</code> (so a renderer or exporter actually picks it up), and that several probe loops match the closed-form HSV value for the vertex they reference. A separate check in the render path confirms the <code>Attribute</code> node is actually linked to Base Color, not just present in the node tree.</p>
<h2>Run</h2>
<pre><code># Cheap correctness check (no render) — the CI check:
blender --background --python color_attribute_wheel.py --
# Falsifier: POINT-domain attribute. Must exit non-zero.
blender --background --python color_attribute_wheel.py -- --point-domain
# Also render a still (EEVEE on a GPU host; use --engine cycles on GPU-less hosts):
blender --background --python color_attribute_wheel.py -- --output wheel.png
blender --background --python color_attribute_wheel.py -- --output wheel.png --engine cycles</code></pre>
<h2>Exit codes</h2>
<p>Per-script sequential checks. <code>9</code> is a valid check code; there is no rule against it.</p>
<div class="table-wrap"><table><thead><tr><th scope="col">Code</th><th scope="col">Meaning</th></tr></thead><tbody><tr><td>0</td><td>Success</td></tr><tr><td>1</td><td>Uncaught exception (FATAL wrapper)</td></tr><tr><td>2</td><td>argparse / usage</td></tr><tr><td>3</td><td>Topology ≠ closed form</td></tr><tr><td>4</td><td>Color attribute missing</td></tr><tr><td>5</td><td>Domain/type ≠ CORNER/FLOAT_COLOR (<code>--point-domain</code> lands here)</td></tr><tr><td>6</td><td>Attribute sized to verts, not loops</td></tr><tr><td>7</td><td><code>active_color</code> not set</td></tr><tr><td>8</td><td>Probe loop color off HSV closed form</td></tr><tr><td>9</td><td><code>--output</code> produced no file</td></tr></tbody></table></div>
<p>The <code>blender-smoke</code> workflow runs the check on Blender 5.2 LTS and 4.5 LTS (5.1 on the weekly cron, the <code>needs-5.1</code> PR label, or manual dispatch). Smoke does not pass <code>--output</code> or <code>--point-domain</code>.</p>
</section>
<section class="detail-section src">
<h2>Source</h2>
<div class="src-meta">
<code>examples/color-attribute-wheel/color_attribute_wheel.py</code>
<a href="https://github.com/TMHSDigital/Blender-Developer-Tools/tree/main/examples/color-attribute-wheel/color_attribute_wheel.py">View on GitHub →</a>
</div>
<pre><span class="s">"""HSV color-attribute wheel -- a runnable example.
Witnesses the modern color-attribute contract that AI-generated Blender code
routinely gets wrong: `Mesh.color_attributes.new()` (not the deprecated
`Mesh.vertex_colors.new()` alias), and the domain trap that comes with it --
a `CORNER`-domain attribute is sized to `len(mesh.loops)`, not
`len(mesh.vertices)`, so code that fills it with a per-vertex-sized buffer
either raises or silently miscolors every shared vertex. This example builds
a polar disc where every vertex carries one hue/saturation pair, expands that
per-vertex data across face corners with one `foreach_get` (loop ->
vertex_index) and one `foreach_set` (loop color), and marks the attribute
`active_color` so it is the one a renderer or exporter actually picks up. The
material wires the same attribute into a Shader `Attribute` node
(`attribute_type='GEOMETRY'`) feeding Base Color -- a step AI code frequently
skips, leaving the mesh gray even though the attribute data is correct.
By default it runs only the correctness check (no render) -- the CI smoke
check. Pass --output to also render a still:
blender --background --python color_attribute_wheel.py -- # check only
blender --background --python color_attribute_wheel.py -- --point-domain # must fail
blender --background --python color_attribute_wheel.py -- --output w.png # + render
"""</span>
<span class="k">import</span> bpy, bmesh, sys, os, math, colorsys, argparse
<span class="k">from</span> array <span class="k">import</span> array
RINGS = <span class="n">14</span>
SEGMENTS = <span class="n">72</span>
R_OUTER = <span class="n">1.6</span>
N_VERTS = <span class="n">1</span> + RINGS * SEGMENTS
N_FACES = SEGMENTS + (RINGS - <span class="n">1</span>) * SEGMENTS
N_LOOPS = <span class="n">3</span> * SEGMENTS + <span class="n">4</span> * (RINGS - <span class="n">1</span>) * SEGMENTS
ATTR_NAME = <span class="s">"Hue"</span>
<span class="k">def</span> vidx(r, s):
<span class="s">"""Vertex index for ring r (0 = center) and segment s, matching build order."""</span>
<span class="k">return</span> <span class="n">0</span> <span class="k">if</span> r == <span class="n">0</span> <span class="k">else</span> <span class="n">1</span> + (r - <span class="n">1</span>) * SEGMENTS + (s % SEGMENTS)
<span class="k">def</span> wheel_geometry():
<span class="s">"""Vertex coords and per-vertex (h, s, v) in the same order as vidx()."""</span>
coords = [(<span class="n">0.0</span>, <span class="n">0.0</span>, <span class="n">0.0</span>)]
hsv = [(<span class="n">0.0</span>, <span class="n">0.0</span>, <span class="n">1.0</span>)] <span class="c"># center: fully desaturated, white</span>
<span class="c"># the hue origin is rotated off the picture horizontal: red is the</span>
<span class="c"># perceptually sharpest hue transition, and the 0/360-degree wrap reads</span>
<span class="c"># as a seam artifact when it lies level in frame</span>
angle0 = math.radians(-<span class="n">52.0</span>)
<span class="k">for</span> r <span class="k">in</span> range(<span class="n">1</span>, RINGS + <span class="n">1</span>):
radius = R_OUTER * r / RINGS
sat = min(<span class="n">1.0</span>, (r / RINGS) * <span class="n">1.4</span>)
<span class="k">for</span> s <span class="k">in</span> range(SEGMENTS):
angle = angle0 + <span class="n">2.0</span> * math.pi * s / SEGMENTS
coords.append((radius * math.cos(angle), radius * math.sin(angle), <span class="n">0.0</span>))
hsv.append((s / SEGMENTS, sat, <span class="n">1.0</span>))
<span class="k">return</span> coords, hsv
<span class="k">def</span> build_wheel(point_domain=<span class="k">False</span>):
bpy.ops.wm.read_factory_settings(use_empty=<span class="k">True</span>)
coords, hsv = wheel_geometry()
me = bpy.data.meshes.new(<span class="s">"ColorWheel"</span>)
bm = bmesh.new()
<span class="k">try</span>:
verts = [bm.verts.new(co) <span class="k">for</span> co <span class="k">in</span> coords]
<span class="k">for</span> s <span class="k">in</span> range(SEGMENTS):
bm.faces.new([verts[vidx(<span class="n">0</span>, <span class="n">0</span>)], verts[vidx(<span class="n">1</span>, s)], verts[vidx(<span class="n">1</span>, s + <span class="n">1</span>)]])
<span class="k">for</span> r <span class="k">in</span> range(<span class="n">1</span>, RINGS):
<span class="k">for</span> s <span class="k">in</span> range(SEGMENTS):
bm.faces.new([
verts[vidx(r, s)], verts[vidx(r, s + <span class="n">1</span>)],
verts[vidx(r + <span class="n">1</span>, s + <span class="n">1</span>)], verts[vidx(r + <span class="n">1</span>, s)],
])
bmesh.ops.recalc_face_normals(bm, faces=bm.faces)
bm.to_mesh(me)
<span class="k">finally</span>:
bm.free() <span class="c"># the always-free-bmesh contract</span>
<span class="c"># The contract this example witnesses: a CORNER-domain color attribute,</span>
<span class="c"># created via color_attributes (not the deprecated vertex_colors alias),</span>
<span class="c"># sized to loops -- then filled by expanding per-vertex HSV across corners</span>
<span class="c"># with bulk foreach_get / foreach_set, never a per-loop Python assignment.</span>
domain = <span class="s">'POINT'</span> <span class="k">if</span> point_domain <span class="k">else</span> <span class="s">'CORNER'</span>
attr = me.color_attributes.new(ATTR_NAME, type=<span class="s">'FLOAT_COLOR'</span>, domain=domain)
<span class="k">if</span> <span class="k">not</span> point_domain:
n_loops = len(me.loops)
loop_vert = array(<span class="s">'i'</span>, [<span class="n">0</span>]) * n_loops
me.loops.foreach_get(<span class="s">"vertex_index"</span>, loop_vert)
flat = array(<span class="s">'f'</span>, [<span class="n">0.0</span>]) * (n_loops * <span class="n">4</span>)
<span class="k">for</span> i, vi <span class="k">in</span> enumerate(loop_vert):
h, s, v = hsv[vi]
r, g, b = colorsys.hsv_to_rgb(h, s, v)
flat[i * <span class="n">4</span>], flat[i * <span class="n">4</span> + <span class="n">1</span>], flat[i * <span class="n">4</span> + <span class="n">2</span>], flat[i * <span class="n">4</span> + <span class="n">3</span>] = r, g, b, <span class="n">1.0</span>
attr.data.foreach_set(<span class="s">"color"</span>, flat)
me.color_attributes.active_color = attr <span class="c"># the step AI code most often forgets</span>
obj = bpy.data.objects.new(<span class="s">"ColorWheel"</span>, me)
bpy.context.collection.objects.link(obj)
<span class="k">return</span> obj, hsv
<span class="k">def</span> check(obj, hsv):
me = obj.data
got = (len(me.vertices), len(me.polygons), len(me.loops))
expect = (N_VERTS, N_FACES, N_LOOPS)
<span class="k">if</span> got != expect:
print(<span class="s">f"</span><span class="s">ERROR: topology (verts,faces,loops)=</span>{got}<span class="s"> != expected </span>{expect}<span class="s">"</span>, file=sys.stderr)
<span class="k">return</span> <span class="n">3</span>
attr = me.color_attributes.get(ATTR_NAME)
<span class="k">if</span> attr <span class="k">is</span> <span class="k">None</span>:
print(<span class="s">f"</span><span class="s">ERROR: color attribute '</span>{ATTR_NAME}<span class="s">' missing</span><span class="s">"</span>, file=sys.stderr)
<span class="k">return</span> <span class="n">4</span>
<span class="k">if</span> attr.domain != <span class="s">'CORNER'</span> <span class="k">or</span> attr.data_type != <span class="s">'FLOAT_COLOR'</span>:
print(<span class="s">f"</span><span class="s">ERROR: attribute domain/type = </span>{attr.domain}<span class="s">/</span>{attr.data_type}<span class="s">, </span><span class="s">"</span>
<span class="s">f"</span><span class="s">expected CORNER/FLOAT_COLOR</span><span class="s">"</span>, file=sys.stderr)
<span class="k">return</span> <span class="n">5</span>
<span class="k">if</span> len(attr.data) != len(me.loops) <span class="k">or</span> len(attr.data) == len(me.vertices):
print(<span class="s">f"</span><span class="s">ERROR: attribute is sized </span>{len(attr.data)}<span class="s">, expected loop count </span><span class="s">"</span>
<span class="s">f"</span>{len(me.loops)}<span class="s"> and distinct from vertex count </span>{len(me.vertices)}<span class="s"> </span><span class="s">"</span>
<span class="s">f"</span><span class="s">-- CORNER domain must not be POINT-sized</span><span class="s">"</span>, file=sys.stderr)
<span class="k">return</span> <span class="n">6</span>
active = me.color_attributes.active_color
<span class="k">if</span> active <span class="k">is</span> <span class="k">None</span> <span class="k">or</span> active.name != attr.name:
print(<span class="s">f"</span><span class="s">ERROR: active_color is </span><span class="s">"</span>
<span class="s">f"</span>{active.name <span class="k">if</span> active <span class="k">else</span> <span class="k">None</span>!r}<span class="s">, expected </span>{ATTR_NAME!r}<span class="s">"</span>, file=sys.stderr)
<span class="k">return</span> <span class="n">7</span>
n_loops = len(me.loops)
loop_vert = array(<span class="s">'i'</span>, [<span class="n">0</span>]) * n_loops
me.loops.foreach_get(<span class="s">"vertex_index"</span>, loop_vert)
colors = array(<span class="s">'f'</span>, [<span class="n">0.0</span>]) * (n_loops * <span class="n">4</span>)
attr.data.foreach_get(<span class="s">"color"</span>, colors)
probes = sorted({<span class="n">0</span>, SEGMENTS + <span class="n">1</span>, n_loops // <span class="n">2</span>, n_loops - <span class="n">1</span>})
<span class="k">for</span> li <span class="k">in</span> probes:
vi = loop_vert[li]
h, s, v = hsv[vi]
er, eg, eb = colorsys.hsv_to_rgb(h, s, v)
gr, gg, gb, ga = colors[li * <span class="n">4</span>:li * <span class="n">4</span> + <span class="n">4</span>]
<span class="k">if</span> max(abs(gr - er), abs(gg - eg), abs(gb - eb), abs(ga - <span class="n">1.0</span>)) > <span class="n">1e-5</span>:
print(<span class="s">f"</span><span class="s">ERROR: loop </span>{li}<span class="s"> (vertex </span>{vi}<span class="s">) color </span>{(gr, gg, gb, ga)}<span class="s"> != </span><span class="s">"</span>
<span class="s">f"</span><span class="s">expected </span>{(er, eg, eb, <span class="n">1.0</span>)}<span class="s">"</span>, file=sys.stderr)
<span class="k">return</span> <span class="n">8</span>
print(<span class="s">f"</span><span class="s">verts=</span>{got[<span class="n">0</span>]}<span class="s"> faces=</span>{got[<span class="n">1</span>]}<span class="s"> loops=</span>{got[<span class="n">2</span>]}<span class="s"> attribute='</span>{attr.name}<span class="s">' </span><span class="s">"</span>
<span class="s">f"</span><span class="s">domain=</span>{attr.domain}<span class="s"> active=True probes_ok=</span>{len(probes)}<span class="s">"</span>)
<span class="k">return</span> <span class="n">0</span>
<span class="k">def</span> eevee_engine_id():
<span class="k">return</span> <span class="s">'BLENDER_EEVEE'</span> <span class="k">if</span> bpy.app.version >= (<span class="n">5</span>, <span class="n">0</span>, <span class="n">0</span>) <span class="k">else</span> <span class="s">'BLENDER_EEVEE_NEXT'</span>
<span class="k">def</span> build_material():
mat = bpy.data.materials.new(<span class="s">"Wheel"</span>)
mat.use_nodes = <span class="k">True</span>
nt = mat.node_tree
bsdf = nt.nodes[<span class="s">"Principled BSDF"</span>]
attr_node = nt.nodes.new(<span class="s">'ShaderNodeAttribute'</span>)
attr_node.attribute_type = <span class="s">'GEOMETRY'</span>
attr_node.attribute_name = ATTR_NAME
nt.links.new(attr_node.outputs[<span class="s">"Color"</span>], bsdf.inputs[<span class="s">"Base Color"</span>])
<span class="k">if</span> <span class="s">"Emission Color"</span> <span class="k">in</span> bsdf.inputs: <span class="c"># Principled gained built-in emission in 4.x+</span>
nt.links.new(attr_node.outputs[<span class="s">"Color"</span>], bsdf.inputs[<span class="s">"Emission Color"</span>])
bsdf.inputs[<span class="s">"Emission Strength"</span>].default_value = <span class="n">0.12</span>
<span class="c"># fully matte: any specular component reflects the wall/floor horizon as</span>
<span class="c"># a hard line across the disc face</span>
bsdf.inputs[<span class="s">"Roughness"</span>].default_value = <span class="n">0.85</span>
<span class="k">if</span> <span class="s">"Specular IOR Level"</span> <span class="k">in</span> bsdf.inputs:
bsdf.inputs[<span class="s">"Specular IOR Level"</span>].default_value = <span class="n">0.0</span>
<span class="c"># The step AI code most often skips: the attribute must actually be wired</span>
<span class="c"># into the shader, not just present on the mesh.</span>
wired = any(
link.from_node.name == attr_node.name
<span class="k">and</span> link.from_socket.name == <span class="s">"Color"</span>
<span class="k">and</span> link.to_socket == bsdf.inputs[<span class="s">"Base Color"</span>]
<span class="k">for</span> link <span class="k">in</span> nt.links
)
<span class="k">if</span> <span class="k">not</span> wired:
print(<span class="s">"ERROR: Attribute node is not linked to Base Color"</span>, file=sys.stderr)
<span class="k">return</span> <span class="k">None</span>
<span class="k">return</span> mat
<span class="k">def</span> render_still(obj, path, engine):
scene = bpy.context.scene
<span class="k">for</span> poly <span class="k">in</span> obj.data.polygons:
poly.use_smooth = <span class="k">True</span>
mat = build_material()
<span class="k">if</span> mat <span class="k">is</span> <span class="k">None</span>:
<span class="k">return</span> <span class="k">False</span>
obj.data.materials.append(mat)
<span class="c"># stand the disc up toward the camera like an easel: the wheel is the</span>
<span class="c"># subject, so it should present nearly face-on and fill the frame instead</span>
<span class="c"># of lying foreshortened on the floor.</span>
obj.location = (<span class="n">0.0</span>, <span class="n">0.0</span>, <span class="n">1.34</span>)
obj.rotation_euler = (math.radians(<span class="n">52</span>), <span class="n">0.0</span>, math.radians(<span class="n">10</span>))
floor_me = bpy.data.meshes.new(<span class="s">"Floor"</span>)
bm = bmesh.new()
<span class="k">try</span>:
bmesh.ops.create_grid(bm, x_segments=<span class="n">1</span>, y_segments=<span class="n">1</span>, size=<span class="n">30.0</span>)
bm.to_mesh(floor_me)
<span class="k">finally</span>:
bm.free()
fmat = bpy.data.materials.new(<span class="s">"Studio"</span>)
fmat.use_nodes = <span class="k">True</span>
fb = fmat.node_tree.nodes[<span class="s">"Principled BSDF"</span>]
fb.inputs[<span class="s">"Base Color"</span>].default_value = (<span class="n">0.03</span>, <span class="n">0.032</span>, <span class="n">0.037</span>, <span class="n">1.0</span>)
fb.inputs[<span class="s">"Roughness"</span>].default_value = <span class="n">0.7</span>
floor_me.materials.append(fmat)
floor = bpy.data.objects.new(<span class="s">"Floor"</span>, floor_me)
scene.collection.objects.link(floor)
wall = bpy.data.objects.new(<span class="s">"Wall"</span>, floor_me.copy())
wall.location = (<span class="n">0.0</span>, <span class="n">7.0</span>, <span class="n">0.0</span>)
wall.rotation_euler = (math.radians(<span class="n">90</span>), <span class="n">0.0</span>, <span class="n">0.0</span>)
scene.collection.objects.link(wall)
world = bpy.data.worlds.new(<span class="s">"World"</span>)
world.use_nodes = <span class="k">True</span>
world.node_tree.nodes[<span class="s">"Background"</span>].inputs[<span class="s">"Color"</span>].default_value = (<span class="n">0.02</span>, <span class="n">0.021</span>, <span class="n">0.025</span>, <span class="n">1.0</span>)
scene.world = world
<span class="k">def</span> light(name, loc, energy, size, col, rot):
ld = bpy.data.lights.new(name, <span class="s">'AREA'</span>)
ld.energy = energy; ld.size = size; ld.color = col
ob = bpy.data.objects.new(name, ld)
ob.location = loc
ob.rotation_euler = tuple(math.radians(a) <span class="k">for</span> a <span class="k">in</span> rot)
scene.collection.objects.link(ob)
<span class="c"># a bright soft key from above reads the hue ring clearly; a low cool fill</span>
<span class="c"># keeps the shadow side legible; a faint warm rim separates the disc edge</span>
<span class="c"># from the dark backdrop without washing out the attribute colors.</span>
light(<span class="s">"Key"</span>, (-<span class="n">2.0</span>, -<span class="n">3.0</span>, <span class="n">5.5</span>), <span class="n">320.0</span>, <span class="n">8.0</span>, (<span class="n">1.0</span>, <span class="n">0.98</span>, <span class="n">0.96</span>), (<span class="n">58</span>, <span class="n">0</span>, -<span class="n">28</span>))
light(<span class="s">"Fill"</span>, (<span class="n">4.5</span>, -<span class="n">2.5</span>, <span class="n">1.6</span>), <span class="n">90.0</span>, <span class="n">9.0</span>, (<span class="n">0.78</span>, <span class="n">0.86</span>, <span class="n">1.0</span>), (<span class="n">68</span>, <span class="n">0</span>, <span class="n">55</span>))
light(<span class="s">"Rim"</span>, (<span class="n">0.5</span>, <span class="n">3.6</span>, <span class="n">2.2</span>), <span class="n">170.0</span>, <span class="n">4.0</span>, (<span class="n">1.0</span>, <span class="n">0.78</span>, <span class="n">0.55</span>), (-<span class="n">70</span>, <span class="n">0</span>, <span class="n">175</span>))
<span class="c"># a warm wedge raking the back wall — the falloff pool behind the subject</span>
<span class="c"># the rest of the gallery stages against.</span>
<span class="c"># placed between the disc and the back wall so it can only rake the wall:</span>
<span class="c"># from any position in front, its grazing terminator draws a hard line</span>
<span class="c"># across the flat disc face.</span>
light(<span class="s">"Wedge"</span>, (<span class="n">2.0</span>, <span class="n">5.2</span>, <span class="n">3.6</span>), <span class="n">220.0</span>, <span class="n">6.0</span>, (<span class="n">1.0</span>, <span class="n">0.76</span>, <span class="n">0.5</span>), (-<span class="n">68</span>, <span class="n">0</span>, <span class="n">190</span>))
aim = bpy.data.objects.new(<span class="s">"Aim"</span>, <span class="k">None</span>)
aim.location = obj.location
scene.collection.objects.link(aim)
cam_data = bpy.data.cameras.new(<span class="s">"Cam"</span>)
cam_data.lens = <span class="n">50.0</span>
cam = bpy.data.objects.new(<span class="s">"Cam"</span>, cam_data)
cam.location = (<span class="n">0.0</span>, -<span class="n">8.0</span>, <span class="n">2.4</span>)
con = cam.constraints.new(<span class="s">'TRACK_TO'</span>)
con.target = aim
con.track_axis = <span class="s">'TRACK_NEGATIVE_Z'</span>
con.up_axis = <span class="s">'UP_Y'</span>
scene.collection.objects.link(cam)
scene.camera = cam
scene.render.engine = <span class="s">'CYCLES'</span> <span class="k">if</span> engine == <span class="s">'cycles'</span> <span class="k">else</span> eevee_engine_id()
<span class="k">if</span> engine == <span class="s">'cycles'</span>:
scene.cycles.samples = <span class="n">64</span>
<span class="k">else</span>:
<span class="k">try</span>:
scene.eevee.taa_render_samples = <span class="n">64</span>
<span class="k">except</span> AttributeError:
<span class="k">pass</span>
scene.render.resolution_x = <span class="n">1280</span>
scene.render.resolution_y = <span class="n">720</span>
scene.render.image_settings.file_format = <span class="s">'PNG'</span>
scene.render.filepath = path
<span class="c"># AgX (the 4.x/5.x default) compresses bright regions toward white, which</span>
<span class="c"># would hide exactly the saturation gradient this example is showing off.</span>
scene.view_settings.view_transform = <span class="s">'Standard'</span>
bpy.ops.render.render(write_still=<span class="k">True</span>)
<span class="k">return</span> os.path.exists(path) <span class="k">and</span> os.path.getsize(path) > <span class="n">0</span>
<span class="k">def</span> main():
argv = sys.argv[sys.argv.index(<span class="s">"--"</span>) + <span class="n">1</span>:] <span class="k">if</span> <span class="s">"--"</span> <span class="k">in</span> sys.argv <span class="k">else</span> []
p = argparse.ArgumentParser()
p.add_argument(<span class="s">"--output"</span>, default=<span class="k">None</span>, help=<span class="s">"optional: render a still PNG here"</span>)
p.add_argument(<span class="s">"--engine"</span>, default=<span class="s">"eevee"</span>, choices=(<span class="s">"eevee"</span>, <span class="s">"cycles"</span>),
help=<span class="s">"render engine for --output (cycles for GPU-less hosts)"</span>)
p.add_argument(<span class="s">"--point-domain"</span>, action=<span class="s">"store_true"</span>,
help=<span class="s">"create a POINT-domain color attribute (must fail)"</span>)
args = p.parse_args(argv)
obj, hsv = build_wheel(point_domain=args.point_domain)
code = check(obj, hsv)
<span class="k">if</span> code:
<span class="k">return</span> code
<span class="k">if</span> args.output:
<span class="k">if</span> <span class="k">not</span> render_still(obj, os.path.abspath(args.output), args.engine):
print(<span class="s">"ERROR: render produced no file"</span>, file=sys.stderr)
<span class="k">return</span> <span class="n">9</span>
print(<span class="s">f"</span><span class="s">rendered still </span>{args.output}<span class="s">"</span>)
print(<span class="s">"color-attribute-wheel OK"</span>)
<span class="k">return</span> <span class="n">0</span>
<span class="k">if</span> __name__ == <span class="s">"__main__"</span>:
<span class="k">try</span>:
sys.exit(main())
<span class="k">except</span> Exception <span class="k">as</span> e:
<span class="k">import</span> traceback; traceback.print_exc(); print(<span class="s">f"</span><span class="s">FATAL: </span>{e}<span class="s">"</span>, file=sys.stderr); sys.exit(<span class="n">1</span>)
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