TL;DR

• Symptom: text longer than ~260 characters rendered garbage every few glyphs—but only on WebGL.
• Root cause: Nova’s fallback renderer packed vertices into a 1 D RGBA texture wider than WebGL’s 8 192-pixel limit.
• Fix: tiled the buffer into 8 192-pixel rows and made the shader use the same row width.

The Bug: Long Text Goes Glitch-City

QA noticed that any dialog exceeding about 260 chars ≈ 1 024 glyphs shredded itself
on WebGL — characters would vanish or swap every ~20 glyphs.
The Editor looked fine… until we forced
SystemSettings.UseFallbackRendering = true and the corruption showed up there
too.

// WebGL console
Texture has out of range width (got 12800 max supported 8192)

Root Cause: Oversized & Misaligned Fallback Buffers

Nova switches to a texture-buffer fallback when SSBOs aren’t available
(WebGL). One glyph vertex = 64 bytes = 4 float4 pixels. A modest
<TextBlock> with 3224 vertices became a
12896 px × 1 texture—well above WebGL’s limit.

After we clamped the width to 8192 px, another artefact surfaced:
the shader still believed rows were 16 384 px wide, so edits wrote to
one row and the GPU read from another.

The Fix in Two Commits

1 — Tile the Buffer Texture

int maxEdge = 8192;
int width   = Mathf.Min(numPixels, maxEdge);
int height  = Mathf.CeilToInt((float)numPixels / width);
texture = new Texture2D(width, height, TextureFormat.RGBAFloat, false, true);

2 — Sync the Shader Constant

#if defined(NOVA_FALLBACK_RENDERING)
  #if defined(UNITY_WEBGL) || defined(UNITY_EDITOR)
    #define MAX_TEXTURE_DIMENSION 8192u
  #else
    #define MAX_TEXTURE_DIMENSION 16384u
  #endif
#endif

We also patched SetData() to honour
shaderBufferStartIndex * 4 for RGBA paths so runtime edits no longer
stomp earlier glyphs.

Results

✅ WebGL build: zero artefacts, zero crashes.
✅ Stand-alone desktop builds keep the 16 384-px SSBO path.
Editor is showing the strange behaviour still. But not a priority currently for a fix.