Move density normalization into the shader

[Alek99]

Summary

• upload wire-native log-u8 density attachments directly to R8 textures
• animate exposure with a u_normScale shader uniform instead of decoding, requantizing, allocating, and re-uploading the full grid every frame
• preserve the old visual order by requantizing each of four fetched texels before manual bilinear interpolation; settled scale=1 frames retain hardware LINEAR sampling
• make the standalone re-bin worker return log-u8 directly
• keep cached/home density windows GPU-only: texture + metadata, with zero retained CPU grid bytes
• reuse the pinned home texture instead of allocating/re-uploading it

Context recovery rebuilds home from the canonical payload, then the existing view-request path refines the current window.

Verification

• complete suite with only the confirmed base marker deselected: 2212 passed, 66 skipped, 1 deselected in 75.77s
• the deselected minified-bundle marker fails identically on untouched main and is corrected in draft PR Avoid full payload reships for restyles and unchanged columns #189
• focused real-Chromium shader, worker, cache-eviction, drilldown-alignment, and context-loss probes: 16 passed
• shader vs independently CPU-requantized reference: 0 pixel mismatches
• manual four-texel sampling vs hardware LINEAR at scale 1: 0 pixel mismatches, max delta 0
• 61-frame exposure lifecycle: 0 texImage2D calls
• real context loss/fresh-canvas rebuild: pixel-identical
• worker re-bin: exactly one upload, no retained encoded/f32 cache
• ruff check .: passed
• ruff format --check .: 343 files already formatted
• tsc -p js/tsconfig.json --noEmit: passed
• node js/build.mjs --check: shipped bundles fresh
• git diff --check: passed

Local real-Chromium benchmark

500,000 source points, 824×488 density grid (402,112 cells), 120 exposure frames under SwiftShader:

Measurement	Result
normalization texture uploads	0
retained CPU cache bytes	0 B
former f32 cache footprint	2,394,880 B
shader draw median / p95 / max	0.10 / 0.30 / 0.30 ms
removed CPU requantization loop	0.397 ms/frame
worker result bytes	402,112 B
animation completed	yes

Closes #166

[codspeed-hq]

Merging this PR will not alter performance

✅ 97 untouched benchmarks
⏩ 1 skipped benchmark¹

---

_{Comparing agent/density-normalization-shader (cba3b49) with main (2a7d898)}

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. ↩

[greptile-apps]

Greptile Summary

This PR moves density normalization into the fragment shader and removes retained CPU density grids. The main changes are:

• Upload log-u8 density data directly to R8 textures.
• Animate exposure with a shader uniform instead of repeated texture uploads.
• Return compact log-u8 grids from the re-bin worker.
• Keep cached density windows as textures and metadata only.
• Reuse the pinned home texture and rebuild it from the canonical payload after context loss.

Confidence Score: 5/5

This looks safe to merge.

No blocking issues found in the changed code.

T-Rex Logs

What T-Rex did

• The quantitative probe was run against the committed head standalone bundle in real Chromium/SwiftShader and produced the complete JSON payload.
• Before/after Playwright recordings were generated from repository-generated standalone HTML, bundled JavaScript, styles, and a 90,000-point density chart, and the visuals were verified to be identical, with 1,556 colors and 29,965 non-white screenshot pixels, while browser console and page-error logs were empty, establishing the zero-upload lifecycle change as validated by the browser probe.

_{Ran code and verified through T-Rex}

Important Files Changed

Filename	Overview
js/src/40_gl.ts	Adds shader-side texel requantization and manual bilinear sampling during exposure animation.
js/src/45_lod.ts	Adds compact encoding and normalization helpers while changing density caches to texture-only ownership.
js/src/46_worker.ts	Encodes worker re-bin output as log-u8 before transferring it to the main thread.
js/src/50_chartview.ts	Uploads encoded density bytes directly and supplies the normalization scale during drawing.
js/src/54_kernel.ts	Consumes compact worker results and restores the home view by reusing its pinned texture.
tests/test_density_shader_normalization.py	Adds browser coverage for shader parity, upload-free animation, compact caching, and context recovery.
tests/test_density_texture_eviction.py	Covers texture eviction and verifies that density cache entries do not retain CPU grids.
benchmarks/bench_density_normalization.py	Adds a Chromium benchmark for draw time, texture uploads, worker output size, and retained cache bytes.

_{Reviews (1): Last reviewed commit: "Move density normalization into the shad..." | Re-trigger Greptile}