From 726e201314cf3d0e789c58df5341fe8b9c92ba61 Mon Sep 17 00:00:00 2001
From: German Khokhlov <ouchlock@gmail.com>
Date: Tue, 3 Nov 2026 23:33:50 +0400
Subject: [PATCH] Read a parked globe's WebGL context from the one it was built
 with instead of asking its canvas during a switch

Asking the canvas again during the switch made the reuse depend on getContext at that moment: with new contexts refused (qa-strict-failure-matrix, cold Navara to Cesium) the rollback to the parked Navara threw and left no globe.
---
 src/standalone/rendererCache.js       | 15 +++++++++------
 src/standalone/rendererCache.test.mjs | 18 ++++++++++++++++--
 2 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/src/standalone/rendererCache.js b/src/standalone/rendererCache.js
index 9347ab7a3..532220752 100644
--- a/src/standalone/rendererCache.js
+++ b/src/standalone/rendererCache.js
@@ -9,11 +9,8 @@ export function createRendererCache() {
     let entry = idle.get(kind);
     idle.delete(kind);
     // loseContext() takes effect before its queued DOM event is delivered.
-    // Check the existing context too, before resuming a parked render loop.
-    const canvas = entry?.scene.engine.host.canvas;
-    const context =
-      canvas?.getContext?.('webgl2') ?? canvas?.getContext?.('webgl');
-    if (entry && (entry.lost || context?.isContextLost())) {
+    // Check the context itself too, before resuming a parked render loop.
+    if (entry && (entry.lost || entry.context?.isContextLost?.())) {
       entry.dispose();
       entry = null;
     }
@@ -39,7 +36,13 @@ export function createRendererCache() {
           container,
           defer: (fn) => cleanups.push(fn),
         });
-        entry = { container, scene, dispose, lost: false };
+        // The context the globe draws with, read once while it is new: a
+        // switch reads its state and never asks the canvas again (a canvas
+        // asked for another context type would create one).
+        const canvas = scene.engine.host.canvas;
+        const context =
+          canvas.getContext?.('webgl2') ?? canvas.getContext?.('webgl') ?? null;
+        entry = { container, scene, dispose, lost: false, context };
         scene.engine.host.canvas.addEventListener(
           'webglcontextlost',
           () => {
diff --git a/src/standalone/rendererCache.test.mjs b/src/standalone/rendererCache.test.mjs
index 4b4b2cddc..2810f2aaf 100644
--- a/src/standalone/rendererCache.test.mjs
+++ b/src/standalone/rendererCache.test.mjs
@@ -27,7 +27,11 @@ test('a parked renderer is reused, but a lost context is disposed before rebuild
     defer(() => {
       released += 1;
     });
+    const canvas = new EventTarget();
+    const context = { lost: false, isContextLost: () => context.lost };
+    canvas.getContext = (type) => (type === 'webgl2' ? context : null);
     return {
+      context,
       suspend() {
         this.running = false;
       },
@@ -35,7 +39,7 @@ test('a parked renderer is reused, but a lost context is disposed before rebuild
         this.running = true;
       },
       engine: {
-        host: { container, canvas: new EventTarget() },
+        host: { container, canvas },
         render: { request() {} },
       },
     };
@@ -49,13 +53,23 @@ test('a parked renderer is reused, but a lost context is disposed before rebuild
   release();
   assert.equal(first.running, false);
   assert.equal(first.engine.host.container.isConnected, false);
+  // A parked renderer whose canvas no longer hands out contexts is still
+  // reused when its own context is alive.
+  first.engine.host.canvas.getContext = () => {
+    throw new Error('getContext called during a switch');
+  };
   assert.equal(await open(), first);
   assert.equal(first.running, true);
   assert.equal(first.engine.host.container.isConnected, true);
   cache.retain('navara');
   release();
   // The WebGL context is already lost, but its DOM event has not fired.
-  first.engine.host.canvas.getContext = () => ({ isContextLost: () => true });
+  // The switch reads the context the globe was built with and never asks
+  // the canvas again (a QA or driver failure of getContext must not decide).
+  first.context.lost = true;
+  first.engine.host.canvas.getContext = () => {
+    throw new Error('getContext called during a switch');
+  };
   const second = await open();
   assert.notEqual(second, first);
   assert.equal(released, 1);