Bug 1875369 [Linux] Get renderer again after WillPaintWindow() r=emilio

WillPaintWindow() spins event loop which can lead to any action related to nsWindow - it can be hid, shown or destroyed.
If the nsWindow visibility is changed, compositor/renderer is deleted and we need to get it again.

Differential Revision: https://phabricator.services.mozilla.com/D200272

widget/gtk/nsWindow.cpp

@@ -3753,6 +3753,26 @@ void nsWindow::CreateCompositorVsyncDispatcher() {
 }
 #endif
 
+void nsWindow::RequestRepaint(LayoutDeviceIntRegion& aRepaintRegion) {
+  WindowRenderer* renderer = GetWindowRenderer();
+  WebRenderLayerManager* layerManager = renderer->AsWebRender();
+  KnowsCompositor* knowsCompositor = renderer->AsKnowsCompositor();
+
+  if (knowsCompositor && layerManager && mCompositorSession) {
+    if (!mConfiguredClearColor && !IsPopup()) {
+      layerManager->WrBridge()->SendSetDefaultClearColor(LookAndFeel::Color(
+          LookAndFeel::ColorID::Window, PreferenceSheet::ColorSchemeForChrome(),
+          LookAndFeel::UseStandins::No));
+      mConfiguredClearColor = true;
+    }
+
+    // We need to paint to the screen even if nothing changed, since if we
+    // don't have a compositing window manager, our pixels could be stale.
+    layerManager->SetNeedsComposite(true);
+    layerManager->SendInvalidRegion(aRepaintRegion.ToUnknownRegion());
+  }
+}
+
 gboolean nsWindow::OnExposeEvent(cairo_t* cr) {
   // This might destroy us.
   NotifyOcclusionState(OcclusionState::VISIBLE);
@@ -3777,8 +3797,7 @@ gboolean nsWindow::OnExposeEvent(cairo_t* cr) {
   }
 #endif
 
-  nsIWidgetListener* listener = GetListener();
+  if (!GetListener()) {
-  if (!listener) {
     return FALSE;
   }
 
@@ -3795,44 +3814,29 @@ gboolean nsWindow::OnExposeEvent(cairo_t* cr) {
   LayoutDeviceIntRegion region = exposeRegion;
   region.ScaleRoundOut(scale, scale);
 
-  WindowRenderer* renderer = GetWindowRenderer();
+  RequestRepaint(region);
-  WebRenderLayerManager* layerManager = renderer->AsWebRender();
-  KnowsCompositor* knowsCompositor = renderer->AsKnowsCompositor();
-
-  if (knowsCompositor && layerManager && mCompositorSession) {
-    if (!mConfiguredClearColor && !IsPopup()) {
-      layerManager->WrBridge()->SendSetDefaultClearColor(LookAndFeel::Color(
-          LookAndFeel::ColorID::Window, PreferenceSheet::ColorSchemeForChrome(),
-          LookAndFeel::UseStandins::No));
-      mConfiguredClearColor = true;
-    }
-
-    // We need to paint to the screen even if nothing changed, since if we
-    // don't have a compositing window manager, our pixels could be stale.
-    layerManager->SetNeedsComposite(true);
-    layerManager->SendInvalidRegion(region.ToUnknownRegion());
-  }
 
   RefPtr<nsWindow> strongThis(this);
 
   // Dispatch WillPaintWindow notification to allow scripts etc. to run
-  // before we paint
+  // before we paint. It also spins event loop which may show/hide the window
-  {
+  // so we may have new renderer etc.
-    listener->WillPaintWindow(this);
+  GetListener()->WillPaintWindow(this);
 
   // If the window has been destroyed during the will paint notification,
   // there is nothing left to do.
-    if (!mGdkWindow) {
+  if (!mGdkWindow || mIsDestroyed) {
     return TRUE;
   }
 
-    // Re-get the listener since the will paint notification might have
+  // Re-get all rendering components since the will paint notification
-    // killed it.
+  // might have killed it.
-    listener = GetListener();
+  nsIWidgetListener* listener = GetListener();
-    if (!listener) {
+  if (!listener) return FALSE;
-      return FALSE;
+
-    }
+  WindowRenderer* renderer = GetWindowRenderer();
-  }
+  WebRenderLayerManager* layerManager = renderer->AsWebRender();
+  KnowsCompositor* knowsCompositor = renderer->AsKnowsCompositor();
 
   if (knowsCompositor && layerManager && layerManager->NeedsComposite()) {
     layerManager->ScheduleComposite(wr::RenderReasons::WIDGET);

widget/gtk/nsWindow.h

@@ -986,6 +986,8 @@ class nsWindow final : public nsBaseWidget {
 
   void EmulateResizeDrag(GdkEventMotion* aEvent);
 
+  void RequestRepaint(LayoutDeviceIntRegion& aRepaintRegion);
+
 #ifdef MOZ_X11
   typedef enum {GTK_WIDGET_COMPOSIDED_DEFAULT = 0,
                 GTK_WIDGET_COMPOSIDED_DISABLED = 1,