fix: capturePage not resolving with hidden windows

docs/api/browser-window.md

@@ -1441,7 +1441,7 @@ Returns `Boolean` - Whether the window's document has been edited.
 
 Returns `Promise<NativeImage>` - Resolves with a [NativeImage](native-image.md)
 
-Captures a snapshot of the page within `rect`. Omitting `rect` will capture the whole visible page.
+Captures a snapshot of the page within `rect`. Omitting `rect` will capture the whole visible page. If the page is not visible, `rect` may be empty.
 
 #### `win.loadURL(url[, options])`
 

shell/browser/api/electron_api_web_contents.cc

@@ -2634,6 +2634,18 @@ v8::Local<v8::Promise> WebContents::CapturePage(gin::Arguments* args) {
     return handle;
   }
 
+#if !defined(OS_MAC)
+  // If the view's renderer is suspended this may fail on Windows/Linux -
+  // bail if so. See CopyFromSurface in
+  // content/public/browser/render_widget_host_view.h.
+  auto* rfh = web_contents()->GetMainFrame();
+  if (rfh &&
+      rfh->GetVisibilityState() == blink::mojom::PageVisibilityState::kHidden) {
+    promise.Resolve(gfx::Image());
+    return handle;
+  }
+#endif  // defined(OS_MAC)
+
   // Capture full page if user doesn't specify a |rect|.
   const gfx::Size view_size =
       rect.IsEmpty() ? view->GetViewBounds().size() : rect.size();

spec-main/api-browser-window-spec.ts

@@ -1340,6 +1340,22 @@ describe('BrowserWindow module', () => {
       expect(image.isEmpty()).to.equal(true);
     });
 
+    it('resolves after the window is hidden', async () => {
+      const w = new BrowserWindow({ show: false });
+      w.loadFile(path.join(fixtures, 'pages', 'a.html'));
+      await emittedOnce(w, 'ready-to-show');
+      w.show();
+
+      const visibleImage = await w.capturePage();
+      expect(visibleImage.isEmpty()).to.equal(false);
+
+      w.hide();
+
+      const hiddenImage = await w.capturePage();
+      const isEmpty = process.platform !== 'darwin';
+      expect(hiddenImage.isEmpty()).to.equal(isEmpty);
+    });
+
     it('preserves transparency', async () => {
       const w = new BrowserWindow({ show: false, transparent: true });
       w.loadFile(path.join(fixtures, 'pages', 'theme-color.html'));