orca/config/patches/xterm-src/@xterm__addon-webgl@0.20.0-beta.329.src.patch

diff --git a/src/CellColorResolver.ts b/src/CellColorResolver.ts
index 49fdf5b1bb4d6c1f602e36470248a10a690a3479..384f4db6f22d0691f66938d42333d1b0424ee513 100644
--- a/src/CellColorResolver.ts
+++ b/src/CellColorResolver.ts
@@ -18,6 +18,15 @@ let $isSelected = false;
 let $colors: ReadonlyColorSet | undefined;
 let $variantOffset = 0;
 
+function isTranslucentDefaultBackground(bg: number, colors: ReadonlyColorSet): boolean {
+  const mode = bg & Attributes.CM_MASK;
+  if (mode === Attributes.CM_DEFAULT || (colors.background.rgba & 0xFF) === 0xFF) {
+    return false;
+  }
+  const rgb = mode === Attributes.CM_RGB ? bg & Attributes.RGB_MASK : colors.ansi[bg & Attributes.PCOLOR_MASK].rgba >>> 8;
+  return rgb === colors.background.rgba >>> 8;
+}
+
 export class CellColorResolver {
   /**
    * The shared result of the {@link resolve} call. This is only safe to use immediately after as
@@ -59,6 +68,12 @@ export class CellColorResolver {
     $colors = this._themeService.colors;
     $variantOffset = 0;
 
+    // Orca: a translucent terminal paints its backdrop once; an explicit background equal to the
+    // default background is that backdrop, not an opaque fill. The buffer keeps the original color.
+    if (!(cell.fg & FgFlags.INVERSE) && this._optionService.rawOptions.allowTransparency && isTranslucentDefaultBackground(cell.bg, $colors)) {
+      this.result.bg &= ~(Attributes.CM_MASK | Attributes.RGB_MASK);
+    }
+
     const code = cell.getCode();
     if (code !== NULL_CELL_CODE && cell.extended.underlineStyle === UnderlineStyle.DOTTED) {
       const lineWidth = Math.max(1, Math.floor(this._optionService.rawOptions.fontSize * this._coreBrowserService.dpr / 15));
diff --git a/src/GlyphRenderer.ts b/src/GlyphRenderer.ts
index 742f0879ff4f04509e4a07c8efdf0d5743fe8ee5..21347443255cba3011e534248557239931ab7d47 100644
--- a/src/GlyphRenderer.ts
+++ b/src/GlyphRenderer.ts
@@ -61,6 +61,8 @@ function createFragmentShaderSource(maxFragmentShaderTextureUnits: number): stri
   for (let i = 1; i < maxFragmentShaderTextureUnits; i++) {
     textureConditionals += ` else if (v_texpage == ${i}) { outColor = texture(u_texture[${i}], v_texcoord); }`;
   }
+  // A v_texpage beyond the sampler budget matches no branch above. Leaving outColor unwritten
+  // is undefined behaviour in GLSL ES and paints garbage, so fall through to transparent.
   return (`#version 300 es
 precision lowp float;
 
@@ -74,7 +76,7 @@ out vec4 outColor;
 void main() {
   if (v_texpage == 0) {
     outColor = texture(u_texture[0], v_texcoord);
-  } ${textureConditionals}
+  } ${textureConditionals} else { outColor = vec4(0.0, 0.0, 0.0, 0.0); }
 }`);
 }
 
@@ -102,6 +104,7 @@ export class GlyphRenderer extends Disposable {
   private _atlas: ITextureAtlas | undefined;
   private _lastSeenPageLayoutVersion: number = -1;
   private _pageOverflowWarned: boolean = false;
+  private _uploadedTextureCount: number = 0;
   private _activeBuffer: number = 0;
   private readonly _vertices: IVertices = {
     count: 0,
@@ -387,6 +390,15 @@ export class GlyphRenderer extends Disposable {
         this._bindAtlasPageTexture(gl, this._atlas, i);
       }
     }
+    // Merging or evicting pages shrinks the page list, release the textures of pages that no
+    // longer exist as they would otherwise keep their full size in GPU memory until reused.
+    for (let i = pageCount; i < this._uploadedTextureCount; i++) {
+      gl.activeTexture(gl.TEXTURE0 + i);
+      gl.bindTexture(gl.TEXTURE_2D, this._atlasTextures[i].texture);
+      gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 1, 1, 0, gl.RGBA, gl.UNSIGNED_BYTE, new Uint8Array([255, 0, 0, 255]));
+      this._atlasTextures[i].version = -1;
+    }
+    this._uploadedTextureCount = pageCount;
 
     // Draw the viewport
     gl.drawElementsInstanced(gl.TRIANGLE_STRIP, 4, gl.UNSIGNED_BYTE, 0, bufferLength / Constants.INDICES_PER_CELL);
diff --git a/src/RectangleRenderer.ts b/src/RectangleRenderer.ts
index eebfda3b3df9b4c8cefcc6a64692053ed5eaeefa..75e34767bd1e12802b72371fddb5fc9028814e11 100644
--- a/src/RectangleRenderer.ts
+++ b/src/RectangleRenderer.ts
@@ -226,7 +226,9 @@ export class RectangleRenderer extends Disposable {
         inverse = !!(fg & FgFlags.INVERSE);
         if (bg !== currentBg || (fg !== currentFg && (currentInverse || inverse))) {
           // A rectangle needs to be drawn if going from non-default to another color
-          if (currentBg !== 0 || (currentInverse && currentFg !== 0)) {
+          // Orca: style-only bg flags (dim, italic, extended) keep the default color, which the
+          // viewport clear already painted; filling it again ignored a translucent background.
+          if ((currentBg & Attributes.CM_MASK) !== Attributes.CM_DEFAULT || (currentInverse && currentFg !== 0)) {
             offset = rectangleCount++ * INDICES_PER_RECTANGLE;
             this._updateRectangle(vertices, offset, currentFg, currentBg, currentStartX, x, y);
           }
@@ -237,7 +239,7 @@ export class RectangleRenderer extends Disposable {
         }
       }
       // Finish rectangle if it's still going
-      if (currentBg !== 0 || (currentInverse && currentFg !== 0)) {
+      if ((currentBg & Attributes.CM_MASK) !== Attributes.CM_DEFAULT || (currentInverse && currentFg !== 0)) {
         offset = rectangleCount++ * INDICES_PER_RECTANGLE;
         this._updateRectangle(vertices, offset, currentFg, currentBg, currentStartX, terminal.cols, y);
       }
diff --git a/src/TextureAtlas.ts b/src/TextureAtlas.ts
index eff0d0e1c36906b1f14b85fb8db7907bf685c8a7..1fb0b7a971e33e1dbd2dcf9841645ca464617af2 100644
--- a/src/TextureAtlas.ts
+++ b/src/TextureAtlas.ts
@@ -3,6 +3,7 @@
  * @license MIT
  */
 
+import { FontWeight } from '@xterm/xterm';
 import { IColorContrastCache } from 'browser/Types';
 import { DIM_OPACITY, TEXT_BASELINE } from './Constants';
 import { tryDrawCustomGlyph } from './customGlyphs/CustomGlyphRasterizer';
@@ -114,21 +115,26 @@ export class TextureAtlas implements ITextureAtlas {
     this._onRemoveTextureAtlasCanvas.dispose();
   }
 
-  public warmUp(): void {
+  public warmUp(domContainer?: HTMLElement): void {
     if (!this._didWarmUp) {
-      this._doWarmUp();
+      this._doWarmUp(domContainer);
       this._didWarmUp = true;
     }
   }
 
-  private _doWarmUp(): void {
+  private _doWarmUp(domContainer: HTMLElement | undefined): void {
     // Pre-fill with ASCII 33-126, this is not urgent and done in idle callbacks
     this._warmUpQueue?.clear();
     const queue = this._warmUpQueue = new IdleTaskQueue(this._logService);
     for (let i = 33; i < 126; i++) {
       queue.enqueue(() => {
+        // Orca: a canvas outside the document ignores the page's font smoothing and rasterizes
+        // heavier glyphs that stay cached, so leave them to on-demand drawing until connected.
+        if (!domContainer?.isConnected) {
+          return;
+        }
         if (!this._cacheMap.get(i, DEFAULT_COLOR, DEFAULT_COLOR, DEFAULT_EXT)) {
-          const rasterizedGlyph = this._drawToCache(i, DEFAULT_COLOR, DEFAULT_COLOR, DEFAULT_EXT, false, undefined);
+          const rasterizedGlyph = this._drawToCache(i, DEFAULT_COLOR, DEFAULT_COLOR, DEFAULT_EXT, false, domContainer);
           this._cacheMap.set(i, DEFAULT_COLOR, DEFAULT_COLOR, DEFAULT_EXT, rasterizedGlyph);
         }
       });
@@ -138,21 +144,23 @@ export class TextureAtlas implements ITextureAtlas {
   private _pageLayoutVersion = 0;
   public get pageLayoutVersion(): number { return this._pageLayoutVersion; }
 
+  // Orca diagnostics: read by terminal-render-desync-weight-probe.ts to tell a real
+  // bold-collapse from a repaint problem. Canvas silently keeps its previous font when an
+  // assignment fails to parse, which rasterizes glyphs at a stale weight.
+  public fontProbeMismatchCount = 0;
+  public fontProbeLastMismatch: { desired: string, actual: string } | undefined;
+
   public clearTexture(): void {
-    if (this._pages[0].currentRow.x === 0 && this._pages[0].currentRow.y === 0) {
+    // Guard on every page rather than pages[0]: a merged page is never written through
+    // currentRow, so once one lands at index 0 the old check made every later clear a no-op.
+    if (this._pages.every(page => page.glyphs.length === 0 && page.currentRow.x === 0 && page.currentRow.y === 0)) {
       return;
     }
-    for (const page of this._pages) {
-      page.clear();
-    }
-    this._cacheMap.clear();
-    this._cacheMapCombined.clear();
-    this._didWarmUp = false;
-
-    // Invalidate renderer models so all texture pages are refreshed. The atlas may be shared, in
-    // which case the clearing renderer has cleared only its own model and every other owner still
-    // holds texture coords into the rows just wiped.
-    this._pageLayoutVersion++;
+    // Return the atlas to its constructor state instead of clearing in place: page.clear() leaves
+    // page.glyphs populated, which would keep the guard above from ever firing again. Eviction
+    // also bumps _pageLayoutVersion, so every renderer sharing this atlas rebuilds its model.
+    this._evictAllPages();
+    this._createNewPage();
   }
 
   private _createNewPage(): AtlasPage {
@@ -164,7 +172,7 @@ export class TextureAtlas implements ITextureAtlas {
       // Find the set of the largest 4 images, below the maximum size, with the highest
       // percentages used
       const pagesBySize = this._pages.filter(e => {
-        return e.canvas.width * 2 <= (TextureAtlas.maxTextureSize || Constants.FORCED_MAX_TEXTURE_SIZE);
+        return e.canvas.width * 2 <= Math.min(TextureAtlas.maxTextureSize || Constants.FORCED_MAX_TEXTURE_SIZE, Constants.FORCED_MAX_TEXTURE_SIZE);
       }).sort((a, b) => {
         if (b.canvas.width !== a.canvas.width) {
           return b.canvas.width - a.canvas.width;
@@ -468,6 +476,36 @@ export class TextureAtlas implements ITextureAtlas {
     return this._config.colors.contrastCache;
   }
 
+  /**
+   * Orca diagnostic. Canvas ignores a font assignment it cannot parse and silently keeps the
+   * previous value, so a bad family or weight rasterizes every glyph at a stale weight. Record
+   * the mismatch rather than correcting it: the goal is to tell that failure apart from a
+   * repaint bug when a terminal renders bold-collapsed.
+   */
+  private _probeRasterizationFontWeight(fontWeight: FontWeight): void {
+    const desired = String(fontWeight);
+    // Only numeric weights are comparable; keywords round-trip through Canvas unchanged.
+    if (!/^(?:[1-8]\d{2}|900)$/.test(desired)) {
+      return;
+    }
+    // Canvas normalizes font serialization: Chromium omits 400 and emits the keyword bold for 700.
+    const token = this._tmpCtx.font.match(
+      /(?:^|\s)(normal|bold|[1-9]\d{0,3})(?=\s+\d+(?:\.\d+)?px(?:\s|$))/
+    )?.[1] ?? '400';
+    const actual = token === 'normal' ? '400' : token === 'bold' ? '700' : token;
+    if (actual === desired) {
+      return;
+    }
+    this.fontProbeMismatchCount++;
+    this.fontProbeLastMismatch = { desired, actual: this._tmpCtx.font };
+    try {
+      (globalThis as { __orcaAtlasFontProbe?: (mismatch: { desired: string, actual: string }) => void })
+        .__orcaAtlasFontProbe?.(this.fontProbeLastMismatch);
+    } catch {
+      // Diagnostics only; a throwing listener must never break rasterization.
+    }
+  }
+
   private _drawToCache(codeOrChars: number | string, bg: number, fg: number, ext: number, restrictToCellHeight: boolean, domContainer: HTMLElement | undefined): IRasterizedGlyph {
     const chars = typeof codeOrChars === 'number' ? String.fromCharCode(codeOrChars) : codeOrChars;
 
@@ -539,6 +577,7 @@ export class TextureAtlas implements ITextureAtlas {
     const fontStyle = italic ? 'italic' : '';
     this._tmpCtx.font =
       `${fontStyle} ${fontWeight} ${this._config.fontSize * this._config.devicePixelRatio}px ${this._config.fontFamily}`;
+    this._probeRasterizationFontWeight(fontWeight);
     this._tmpCtx.textBaseline = TEXT_BASELINE;
 
     const powerlineGlyph = chars.length === 1 && isPowerlineGlyph(chars.charCodeAt(0));
diff --git a/src/Types.ts b/src/Types.ts
index bfd6fd76cebe8f55dce7bfad5406d4f7cd184320..0bd283ea7b2bb72d5d3f20b6e7e11e7cc44f283f 100644
--- a/src/Types.ts
+++ b/src/Types.ts
@@ -65,7 +65,7 @@ export interface ITextureAtlas extends IDisposable {
   /**
    * Warm up the texture atlas, adding common glyphs to avoid slowing early frame.
    */
-  warmUp(): void;
+  warmUp(domContainer?: HTMLElement): void;
 
   /**
    * Incremented whenever cached glyph texture page mappings may be stale, such as after atlas page
diff --git a/src/WebglRenderer.ts b/src/WebglRenderer.ts
index 2d0f5a3a8ee7fc0765a0179cee0102edb9376e4b..92f1c7241e887cd907d21d91aa26c0def02339f5 100644
--- a/src/WebglRenderer.ts
+++ b/src/WebglRenderer.ts
@@ -323,7 +323,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
       );
     }
     this._charAtlas = atlas;
-    this._charAtlas.warmUp();
+    this._charAtlas.warmUp(this._terminal.element);
     this._glyphRenderer.value?.setAtlas(this._charAtlas);
   }
 
@@ -393,7 +393,10 @@ export class WebglRenderer extends Disposable implements IRenderer {
     // 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) {
+    // Test the retry budget before beginFrame: beginFrame latches the page layout version it
+    // observed, so tripping the limit after consuming it would strand a stale model with no
+    // later frame able to notice it needs rebuilding.
+    while (this._charAtlas && mergeRetries++ < Constants.MERGE_RETRY_LIMIT && this._glyphRenderer.value.beginFrame()) {
       merged = true;
       this._clearModel(true);
       this._updateModel(0, this._terminal.rows - 1);
@@ -403,6 +406,20 @@ export class WebglRenderer extends Disposable implements IRenderer {
     }
 
     // Render
+    // A transparent framebuffer keeps the previous draw, so re-blending translucent
+    // backgrounds accumulated opacity on every redraw and flickered (Orca #6491).
+    if (this._terminal.options.allowTransparency) {
+      // Keep the RGB blend but write source alpha as-is; SRC_ALPHA on alpha
+      // itself would turn the configured opacity `a` into `a²`.
+      this._gl.blendFuncSeparate(
+        this._gl.SRC_ALPHA,
+        this._gl.ONE_MINUS_SRC_ALPHA,
+        this._gl.ONE,
+        this._gl.ONE_MINUS_SRC_ALPHA
+      );
+      this._gl.clearColor(0, 0, 0, 0);
+      this._gl.clear(this._gl.COLOR_BUFFER_BIT);
+    }
     this._rectangleRenderer.value.renderBackgrounds();
     this._glyphRenderer.value.render(this._model);
     if (!this._cursorBlinkStateManager.value || this._cursorBlinkStateManager.value.isCursorVisible) {
diff --git a/src/renderLayer/BaseRenderLayer.ts b/src/renderLayer/BaseRenderLayer.ts
index 5b11615328957b6f5d41a174284c11e061910d91..00f299659106716258ad7b02c2bfdddcc53e91fe 100644
--- a/src/renderLayer/BaseRenderLayer.ts
+++ b/src/renderLayer/BaseRenderLayer.ts
@@ -3,8 +3,6 @@
  * @license MIT
  */
 
-import { ReadonlyColorSet } from 'browser/Types';
-import { acquireTextureAtlas } from '../CharAtlasCache';
 import { IRenderDimensions } from 'browser/renderer/shared/Types';
 import { ICoreBrowserService, IThemeService } from 'browser/services/Services';
 import { Disposable, toDisposable } from 'common/Lifecycle';
@@ -14,7 +12,6 @@ import { Terminal } from '@xterm/xterm';
 import { IRenderLayer } from './Types';
 import { throwIfFalsy } from 'browser/renderer/shared/RendererUtils';
 import { TEXT_BASELINE } from '../Constants';
-import type { ITextureAtlas } from '../Types';
 
 export abstract class BaseRenderLayer extends Disposable implements IRenderLayer {
   private _canvas: HTMLCanvasElement;
@@ -26,8 +23,6 @@ export abstract class BaseRenderLayer extends Disposable implements IRenderLayer
   private _deviceCharLeft: number = 0;
   private _deviceCharTop: number = 0;
 
-  protected _charAtlas: ITextureAtlas | undefined;
-
   constructor(
     terminal: Terminal,
     private _container: HTMLElement,
@@ -44,8 +39,7 @@ export abstract class BaseRenderLayer extends Disposable implements IRenderLayer
     this._canvas.style.zIndex = zIndex.toString();
     this._initCanvas();
     this._container.appendChild(this._canvas);
-    this._register(this._themeService.onChangeColors(e => {
-      this._refreshCharAtlas(terminal, e);
+    this._register(this._themeService.onChangeColors(() => {
       this.reset(terminal);
     }));
     this._register(toDisposable(() => {
@@ -81,25 +75,10 @@ export abstract class BaseRenderLayer extends Disposable implements IRenderLayer
     this._initCanvas();
     this._container.replaceChild(this._canvas, oldCanvas);
 
-    // Regenerate char atlas and force a full redraw
-    this._refreshCharAtlas(terminal, this._themeService.colors);
+    // Force a full redraw
     this.handleGridChanged(terminal, 0, terminal.rows - 1);
   }
 
-  /**
-   * Refreshes the char atlas, aquiring a new one if necessary.
-   * @param terminal The terminal.
-   * @param colorSet The color set to use for the char atlas.
-   */
-  private _refreshCharAtlas(terminal: Terminal, colorSet: ReadonlyColorSet): void {
-    if (this._deviceCharWidth <= 0 && this._deviceCharHeight <= 0) {
-      return;
-    }
-
-    this._charAtlas = acquireTextureAtlas(terminal, this._optionsService.rawOptions, colorSet, this._deviceCellWidth, this._deviceCellHeight, this._deviceCharWidth, this._deviceCharHeight, this._coreBrowserService.dpr, 2048);
-    this._charAtlas.warmUp();
-  }
-
   public resize(terminal: Terminal, dim: IRenderDimensions): void {
     this._deviceCellWidth = dim.device.cell.width;
     this._deviceCellHeight = dim.device.cell.height;
@@ -116,8 +95,6 @@ export abstract class BaseRenderLayer extends Disposable implements IRenderLayer
     if (!this._alpha) {
       this._clearAll();
     }
-
-    this._refreshCharAtlas(terminal, this._themeService.colors);
   }
 
   public abstract reset(terminal: Terminal): void;