GlyphRenderer sizes its GL texture array and fragment-shader sampler array to
exactly TextureAtlas.maxAtlasPages at construction, but _createNewPage pushes
past that cap whenever a 4-page same-size merge is impossible (heterogeneous
sizes, e.g. 1024+512+512+512). The next render throws TypeError: Cannot read
properties of undefined (reading 'version') and rendering freezes — the
single-terminal breakage vector for long heavy-CLI sessions (vscode#322756).
The test builds the renderer with maxAtlasPages=4 (same code path as the
production 8/16/32 values), churns distinct glyphs, and asserts no pageerror,
pages.length <= texture capacity, and an intact pinned header. RED today:
4x TypeError from GlyphRenderer.render.
Two terminals with equal configs share one TextureAtlas (CharAtlasCache).
When the atlas merges pages it raises a consume-once clear-model flag
(TextureAtlas.beginFrame); only the first terminal to render consumes it and
rebuilds its vertex model. Every other terminal keeps stale texture-page
indexes/coords and draws wrong glyphs on its next partial render even though
its buffer is intact.
The test churns terminal A to force merges, then gives terminal B a tiny
partial update: B's untouched header row garbles (signature diff ~130/255 vs
tolerance 14) while B's buffer still reads HEADER_REF. A DOM-renderer control
runs the same workload without GPU acceleration and passes: the corruption is
exclusive to the WebGL path.
RED on current code by design; the fix lands separately.
generateColoredAsciiFlood emitted a trailing \r\n after its final cell, so a
flood whose last line lands on the bottom row scrolled the screen. In the
alt-buffer repro this destroyed the pinned header row in the BUFFER, making
the 255/255 signature diff a content change, not renderer corruption. The
single-terminal merge path is actually healthy: with the scroll removed the
same 30-chunk merge-heavy workload renders the header with zero drift.
- generateColoredAsciiFlood: no linefeed after the final cell
- WebglReproExperiment: now a green guard; asserts row-1 buffer text first so
a content bug can never masquerade as corruption again
- WebglVisual: accurate comments; erase rewritten lines so leftover prefill
text doesn't look like corruption
- WebglSingleTermStress: replace stale EXPECTED-RED comment (test passes)
Anthony Kim
Jörg Breitbart
Daniel Imms