From aef5579f91874917bebd6c38f73e622bf8b3de18 Mon Sep 17 00:00:00 2001
From: Mistium <92952823+Mistium@users.noreply.github.com>
Date: Tue, 6 Oct 2026 19:25:30 +0100
Subject: [PATCH] Skip drawing while the GL context reports it is lost

The webglcontextlost event arrives as a separate task, so a frame can still be drawn after the browser has taken the context. If that frame creates the first wrapped texture, twgl's sampler check reads .constructor of the null sampler a lost context returns and throws. draw() now also asks the context itself.
---
 src/RenderWebGL.js            |  4 ++--
 test/unit/ContextLossTests.js | 17 ++++++++++++++++-
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/src/RenderWebGL.js b/src/RenderWebGL.js
index 633626748..acf2b8c7d 100644
--- a/src/RenderWebGL.js
+++ b/src/RenderWebGL.js
@@ -968,7 +968,7 @@ class RenderWebGL extends EventEmitter {
      * @returns {boolean} True while the WebGL context is lost and nothing can be drawn.
      */
     get isContextLost () {
-        return this._contextLost;
+        return this._contextLost || this._gl.isContextLost();
     }
 
     /**
@@ -1011,7 +1011,7 @@ class RenderWebGL extends EventEmitter {
     }
 
     draw() {
-        if (!this.dirty || this._contextLost) {
+        if (!this.dirty || this.isContextLost) {
             return;
         }
         this.dirty = false;
diff --git a/test/unit/ContextLossTests.js b/test/unit/ContextLossTests.js
index ae7c48796..a0e73ae02 100644
--- a/test/unit/ContextLossTests.js
+++ b/test/unit/ContextLossTests.js
@@ -10,7 +10,9 @@ const fakeRenderer = () => {
     renderer._allDrawables = [];
     renderer._drawList = [];
     renderer._contextLost = false;
-    renderer._gl = {};
+    renderer._gl = {
+        isContextLost: () => false
+    };
     renderer.dirty = true;
     renderer._listeners = {};
     renderer.emit = name => {
@@ -39,6 +41,19 @@ test('losing the context stops drawing and asks the browser to restore it', t =>
     t.end();
 });
 
+test('a context the browser has lost is not drawn before the lost event arrives', t => {
+    const renderer = fakeRenderer();
+    renderer._gl.isContextLost = () => true;
+    t.equal(renderer.isContextLost, true);
+
+    renderer._doExitDrawRegion = () => {
+        throw new Error('draw must not touch GL while the context is lost');
+    };
+    t.doesNotThrow(() => renderer.draw());
+    t.equal(renderer.dirty, true, 'the frame is still pending');
+    t.end();
+});
+
 test('restoring the context rebuilds renderer resources and tells every skin', t => {
     const renderer = fakeRenderer();
     renderer._contextLost = true;