From 3bcb57545e3d2db44555f9128f4fefb66555fd98 Mon Sep 17 00:00:00 2001
From: Victor Sych <victor.sych@gmail.com>
Date: Thu, 21 May 2026 04:59:37 +0200
Subject: [PATCH] Re-upload atlas textures after page merges

---
 addons/addon-webgl/src/GlyphRenderer.ts     |  4 ++++
 addons/addon-webgl/src/RectangleRenderer.ts |  5 +++--
 addons/addon-webgl/src/WebglRenderer.ts     | 17 ++++++++---------
 3 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/addons/addon-webgl/src/GlyphRenderer.ts b/addons/addon-webgl/src/GlyphRenderer.ts
index b412f2d89..46b8efeb9 100644
--- a/addons/addon-webgl/src/GlyphRenderer.ts
+++ b/addons/addon-webgl/src/GlyphRenderer.ts
@@ -373,6 +373,10 @@ export class GlyphRenderer extends Disposable {
 
   public setAtlas(atlas: ITextureAtlas): void {
     this._atlas = atlas;
+    this.invalidateAtlasTextures();
+  }
+
+  public invalidateAtlasTextures(): void {
     for (const glTexture of this._atlasTextures) {
       glTexture.version = -1;
     }
diff --git a/addons/addon-webgl/src/RectangleRenderer.ts b/addons/addon-webgl/src/RectangleRenderer.ts
index 4ad8d66ff..81e129e5c 100644
--- a/addons/addon-webgl/src/RectangleRenderer.ts
+++ b/addons/addon-webgl/src/RectangleRenderer.ts
@@ -336,8 +336,9 @@ export class RectangleRenderer extends Disposable {
       }
     }
 
-    if (vertices.attributes.length < offset + 4) {
-      vertices.attributes = expandFloat32Array(vertices.attributes, this._terminal.rows * this._terminal.cols * INDICES_PER_RECTANGLE);
+    if (vertices.attributes.length < offset + INDICES_PER_RECTANGLE) {
+      // +1 for the viewport-clear rectangle at offset 0.
+      vertices.attributes = expandFloat32Array(vertices.attributes, (this._terminal.rows * this._terminal.cols + 1) * INDICES_PER_RECTANGLE);
     }
     $x1 = startX * this._dimensions.device.cell.width;
     $y1 = y * this._dimensions.device.cell.height;
diff --git a/addons/addon-webgl/src/WebglRenderer.ts b/addons/addon-webgl/src/WebglRenderer.ts
index 578955fc1..500308bd1 100644
--- a/addons/addon-webgl/src/WebglRenderer.ts
+++ b/addons/addon-webgl/src/WebglRenderer.ts
@@ -29,13 +29,7 @@ import { combinedDisposable, Disposable, MutableDisposable, toDisposable } from
 import { createRenderDimensions } from 'browser/renderer/shared/RendererUtils';
 
 const enum Constants {
-  /**
-   * Upper bound on how many times `renderRows` re-runs `_updateModel` after detecting a
-   * mid-update atlas page merge. A single retry should always suffice once every glyph
-   * needed by the frame is cached; the cap exists purely as a safety net against an
-   * unexpected runaway, not as a tuned value.
-   */
-  MERGE_RETRY_LIMIT = 3
+  MERGE_RETRY_LIMIT = 32
 }
 
 export class WebglRenderer extends Disposable implements IRenderer {
@@ -385,13 +379,18 @@ export class WebglRenderer extends Disposable implements IRenderer {
       this._updateModel(start, end);
     }
 
-    // A mid-update atlas page merge shifts cached glyphs to new texture pages, leaving
-    // stale texturePage values in the vertex buffer. Re-run a full update if that happened.
+    // A mid-update atlas page merge invalidates vertex data and may not bump the host
+    // page's version, so re-run the update and force a full texture rebind.
+    let merged = false;
     let mergeRetries = 0;
     while (this._charAtlas && this._glyphRenderer.value.beginFrame() && mergeRetries++ < Constants.MERGE_RETRY_LIMIT) {
+      merged = true;
       this._clearModel(true);
       this._updateModel(0, this._terminal.rows - 1);
     }
+    if (merged) {
+      this._glyphRenderer.value.invalidateAtlasTextures();
+    }
 
     // Render
     this._rectangleRenderer.value.renderBackgrounds();