Add vectorized per-item style channels [codex]

[sselvakumaran]

unifies style attributes so per-item attributes can vary (mainly to allow setting alpha per-item; but also adds changes to color, line-height, etc.)

[codspeed-hq]

Merging this PR will not alter performance

✅ 94 untouched benchmarks
⏩ 1 skipped benchmark¹

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_{Comparing set_alpha (a6b0378) with main (c2a61d8)}

Footnotes

1. 1 benchmark was skipped, so the baseline result was used instead. If it was deleted from the codebase, click here and archive it to remove it from the performance reports. ↩

[Alek99]

Review findings:

• [P1] js/src/50_chartview.js:2330: the simple scatter path does not exclude g.styleBuf. Constant-color/size circles with vector opacity, artist alpha, symbol, or stroke width are sent to _drawSimplePoints, which binds only x/y and scalar opacity; the new channels are ignored.
• [P1] python/xy/_raster.py:1500 / python/xy/_svg.py:2129: scalar stroke= remains in style, but the new static paths only inspect trace["stroke"] and otherwise use the face paint. bar(color="red", stroke="blue") exports a red outline. For meshes this also forces one raster command per triangle with varying fills, matching the CodSpeed regression.
• [P1] js/src/40_gl.js:776 plus the SVG/PNG gradient branches: gradient rectangles bypass vector opacity/artist alpha; static paths also discard vector stroke/width (and PNG corner radii). Preserve the resolved instance channels in all three renderers.
• [P2] js/src/40_gl.js:253,580,790: constant outlines use a scalar premultiplied uniform, so per-item opacity/artist alpha affects fills but not scalar strokes. The match-fill fallback also uses a trace color rather than each direct face color.
• [P2] python/xy/_trace.py:87: style/stroke-only scatters aggregate at 200k rather than retaining direct rendering until the documented 2M per-item ceiling.
• [P2] python/xy/marks.py:1572: histogram scalar _artist_alpha is discarded; vector alpha works.
• [P2] js/src/50_chartview.js:3955: destruction omits the new rgba/style/stroke/radius buffers, leaking GPU allocations.
• Required checks are currently failing: protocol was bumped to 4 while repository smoke specs remain at 3, and docs lint finds the missing _artist_alpha scatter parameter documentation.

[greptile-apps]

Greptile Summary

This PR adds vectorized per-item styling across interactive and static chart rendering. The main changes are:

• Adds per-item color, opacity, alpha, stroke, width, symbol, and corner-radius channels.
• Extends WebGL shaders and buffers for the new style attributes.
• Aligns SVG, PNG, native, widget, streaming, and static-client output.
• Updates the wire protocol and native ABI versions.
• Adds rendering and Matplotlib compatibility tests.

Confidence Score: 5/5

This looks safe to merge.

The gradient rectangle and bar paths now apply per-item opacity and artist alpha. The packaged browser clients include the same shader update. No blocking issue remains in the changed code.

T-Rex Logs

What T-Rex did

• T-Rex confirmed that the scalar reference produced near-equal point counts across all five positions, with counts around 660 each.
• T-Rex observed that the vectorized output produced strongly varying per-item counts (114, 258, 788, 459, 834) and 551 distinct RGB values, indicating per-item alpha, color, stroke, and width variation.
• T-Rex ran Chromium navigation and capture, which exited with code 0, and the accessibility text identified a five-item data series.

_{Ran code and verified through T-Rex}

Important Files Changed

Filename	Overview
js/src/40_gl.js	Extends WebGL shaders with per-item paint and style attributes and preserves the alpha stack for gradient rectangles and bars.
js/src/50_chartview.js	Builds, binds, draws, and cleans up the new per-item style buffers across supported mark types.
python/xy/_paint.py	Centralizes direct-paint and alpha resolution for static exporters.
python/xy/_payload.py	Encodes vectorized paint and style channels in the updated chart payload.
python/xy/_svg.py	Applies per-item styles to SVG output.
python/xy/_raster.py	Applies per-item styles to raster output.
python/xy/static/index.js	Synchronizes the packaged browser client with the new shader and rendering behavior.
python/xy/static/standalone.js	Synchronizes the standalone browser client with the new shader and rendering behavior.
tests/pyplot/test_vectorized_styles.py	Covers vectorized style behavior through the Matplotlib compatibility layer.

_{Reviews (2): Last reviewed commit: "Preserve vector alpha for gradient recta..." | Re-trigger Greptile}