Bug 1697981 - Do not allocate CompositorWindow for Software WebRender r=nical

Since Bug 1688096 fix, WebRender and Software WebRender could be used at the same time.

Differential Revision: https://phabricator.services.mozilla.com/D108141

gfx/layers/ipc/CompositorBridgeParent.cpp

@@ -1771,9 +1771,16 @@ PWebRenderBridgeParent* CompositorBridgeParent::AllocPWebRenderBridgeParent(
   MOZ_ASSERT(mWidget);
 
 #ifdef XP_WIN
-  if (mWidget && (DeviceManagerDx::Get()->CanUseDComp() ||
-                  gfxVars::UseWebRenderFlipSequentialWin())) {
-    mWidget->AsWindows()->EnsureCompositorWindow();
+  if (mWidget && mWidget->AsWindows()) {
+    const auto options = mWidget->GetCompositorOptions();
+    if (!options.UseSoftwareWebRender() &&
+        (DeviceManagerDx::Get()->CanUseDComp() ||
+         gfxVars::UseWebRenderFlipSequentialWin())) {
+      mWidget->AsWindows()->EnsureCompositorWindow();
+    } else if (options.UseSoftwareWebRender() &&
+               mWidget->AsWindows()->GetCompositorHwnd()) {
+      mWidget->AsWindows()->DestroyCompositorWindow();
+    }
   }
 #endif
 

gfx/webrender_bindings/RenderCompositorANGLE.cpp

@@ -307,16 +307,16 @@ bool RenderCompositorANGLE::CreateSwapChain(nsACString& aError) {
       mUseTripleBuffering = useTripleBuffering;
     } else if (useFlipSequential) {
       gfxCriticalNoteOnce << "FLIP_SEQUENTIAL is not supported. Fallback";
-
-      if (mWidget->AsWindows()->GetCompositorHwnd()) {
-        // Destroy compositor window.
-        mWidget->AsWindows()->DestroyCompositorWindow();
-        hwnd = mWidget->AsWindows()->GetHwnd();
-      }
     }
   }
 
   if (!mSwapChain) {
+    if (mWidget->AsWindows()->GetCompositorHwnd()) {
+      // Destroy compositor window.
+      mWidget->AsWindows()->DestroyCompositorWindow();
+      hwnd = mWidget->AsWindows()->GetHwnd();
+    }
+
     DXGI_SWAP_CHAIN_DESC swapDesc{};
     swapDesc.BufferDesc.Width = 0;
     swapDesc.BufferDesc.Height = 0;