From faf5f72c1ff25a21a60eaa07f205a3eedd31a286 Mon Sep 17 00:00:00 2001
From: Jason Lin <lxj@google.com>
Date: Mon, 5 Sep 2022 13:17:45 +1000
Subject: [PATCH 1/2] Clear glyph render when the webgl model is cleared

---
 addons/xterm-addon-webgl/src/GlyphRenderer.ts | 26 +++++++++----------
 addons/xterm-addon-webgl/src/WebglRenderer.ts | 24 ++++++++++++-----
 2 files changed, 30 insertions(+), 20 deletions(-)

diff --git a/addons/xterm-addon-webgl/src/GlyphRenderer.ts b/addons/xterm-addon-webgl/src/GlyphRenderer.ts
index 85ef25f6..a7f4a700 100644
--- a/addons/xterm-addon-webgl/src/GlyphRenderer.ts
+++ b/addons/xterm-addon-webgl/src/GlyphRenderer.ts
@@ -238,21 +238,24 @@ export class GlyphRenderer  extends Disposable {
     // a_cellpos only changes on resize
   }
 
-  public clear(force?: boolean): void {
+  public clear(): void {
     const terminal = this._terminal;
     const newCount = terminal.cols * terminal.rows * INDICES_PER_CELL;
 
-    // Don't clear if not forced and the array length is correct
-    if (!force && this._vertices.count === newCount) {
-      return;
-    }
-
     // Clear vertices
-    this._vertices.count = newCount;
-    this._vertices.attributes = new Float32Array(newCount);
-    for (let i = 0; i < this._vertices.attributesBuffers.length; i++) {
-      this._vertices.attributesBuffers[i] = new Float32Array(newCount);
+    if (this._vertices.count !== newCount) {
+      this._vertices.attributes = new Float32Array(newCount);
+    } else {
+      this._vertices.attributes.fill(0);
     }
+    for (let i = 0; i < this._vertices.attributesBuffers.length; i++) {
+      if (this._vertices.count !== newCount) {
+        this._vertices.attributesBuffers[i] = new Float32Array(newCount);
+      } else {
+        this._vertices.attributesBuffers[i].fill(0);
+      }
+    }
+    this._vertices.count = newCount;
     let i = 0;
     for (let y = 0; y < terminal.rows; y++) {
       for (let x = 0; x < terminal.cols; x++) {
@@ -269,9 +272,6 @@ export class GlyphRenderer  extends Disposable {
     this.clear();
   }
 
-  public setColors(): void {
-  }
-
   public render(renderModel: IRenderModel): void {
     if (!this._atlas) {
       return;
diff --git a/addons/xterm-addon-webgl/src/WebglRenderer.ts b/addons/xterm-addon-webgl/src/WebglRenderer.ts
index 3ff0c237..b48ec7eb 100644
--- a/addons/xterm-addon-webgl/src/WebglRenderer.ts
+++ b/addons/xterm-addon-webgl/src/WebglRenderer.ts
@@ -163,12 +163,11 @@ export class WebglRenderer extends Disposable implements IRenderer {
     }
 
     this._rectangleRenderer.setColors();
-    this._glyphRenderer.setColors();
 
     this._refreshCharAtlas();
 
     // Force a full refresh
-    this._model.clear();
+    this._clearModel(true);
   }
 
   public onDevicePixelRatioChange(): void {
@@ -209,7 +208,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
     this._refreshCharAtlas();
 
     // Force a full refresh
-    this._model.clear();
+    this._clearModel(false);
   }
 
   public onCharSizeChanged(): void {
@@ -293,16 +292,27 @@ export class WebglRenderer extends Disposable implements IRenderer {
     this._glyphRenderer.setAtlas(this._charAtlas);
   }
 
+  /**
+   * Clear the model.
+   * @param clearGlyphRenderer Whether to also clear the glyph renderer. This
+   * should be true generally to make sure it is in the same state as the model.
+   */
+  private _clearModel(clearGlyphRenderer: boolean): void {
+    this._model.clear();
+    if (clearGlyphRenderer) {
+      this._glyphRenderer.clear();
+    }
+  }
+
   public clearCharAtlas(): void {
     this._charAtlas?.clearTexture();
-    this._model.clear();
+    this._clearModel(true);
     this._updateModel(0, this._terminal.rows - 1);
     this._requestRedrawViewport();
   }
 
   public clear(): void {
-    this._model.clear();
-    this._glyphRenderer.clear(true);
+    this._clearModel(true);
     for (const l of this._renderLayers) {
       l.reset(this._terminal);
     }
@@ -334,7 +344,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
 
     // Tell renderer the frame is beginning
     if (this._glyphRenderer.beginFrame()) {
-      this._model.clear();
+      this._clearModel(true);
       this._updateSelectionModel(undefined, undefined);
     }
 

From e5ad3ce9b98954a990895bf0115ff2aede682fdc Mon Sep 17 00:00:00 2001
From: Jason Lin <lxj@google.com>
Date: Mon, 5 Sep 2022 17:32:02 +1000
Subject: [PATCH 2/2] Polish

---
 addons/xterm-addon-webgl/src/WebglRenderer.ts | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/addons/xterm-addon-webgl/src/WebglRenderer.ts b/addons/xterm-addon-webgl/src/WebglRenderer.ts
index b48ec7eb..6420e812 100644
--- a/addons/xterm-addon-webgl/src/WebglRenderer.ts
+++ b/addons/xterm-addon-webgl/src/WebglRenderer.ts
@@ -207,7 +207,8 @@ export class WebglRenderer extends Disposable implements IRenderer {
 
     this._refreshCharAtlas();
 
-    // Force a full refresh
+    // Force a full refresh. Resizing `_glyphRenderer` should clear it already,
+    // so there is no need to clear it again here.
     this._clearModel(false);
   }