From fd7e0afdbfd7816f5b54421fbc169dca9910883b Mon Sep 17 00:00:00 2001
From: Bobby Holley <bobbyholley@gmail.com>
Date: Tue, 11 Dec 2018 14:38:31 -0800
Subject: [PATCH] Bug 1513308 - Lazily initialize DirectX devices for
 WebRender. r=mattwoodrow

---
 dom/canvas/CanvasRenderingContext2D.cpp |  2 ++
 gfx/thebes/gfxPlatform.cpp              |  7 +++++++
 gfx/thebes/gfxPlatform.h                |  2 ++
 gfx/thebes/gfxWindowsPlatform.cpp       | 15 +++++++++++++--
 gfx/thebes/gfxWindowsPlatform.h         |  3 +++
 5 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/dom/canvas/CanvasRenderingContext2D.cpp b/dom/canvas/CanvasRenderingContext2D.cpp
index f5b75835765fc..a74c6e4f6f6b6 100644
--- a/dom/canvas/CanvasRenderingContext2D.cpp
+++ b/dom/canvas/CanvasRenderingContext2D.cpp
@@ -1495,6 +1495,8 @@ CanvasRenderingContext2D::RenderingMode CanvasRenderingContext2D::EnsureTarget(
     return aRenderingMode;
   }
 
+  gfxPlatform::GetPlatform()->EnsureDevicesInitialized();
+
   // This would make no sense, so make sure we don't get ourselves in a mess
   MOZ_ASSERT(mRenderingMode != RenderingMode::DefaultBackendMode);
 
diff --git a/gfx/thebes/gfxPlatform.cpp b/gfx/thebes/gfxPlatform.cpp
index 2f9d4e2a79547..e1f62c2f4c229 100644
--- a/gfx/thebes/gfxPlatform.cpp
+++ b/gfx/thebes/gfxPlatform.cpp
@@ -911,6 +911,13 @@ void gfxPlatform::Init() {
 #endif
   gPlatform->InitAcceleration();
   gPlatform->InitWebRenderConfig();
+  // When using WebRender, we defer initialization of the D3D11 devices until
+  // the (rare) cases where they're used. Note that the GPU process where WebRender
+  // runs doesn't initialize gfxPlatform and performs explicit initialization of
+  // the bits it needs.
+  if (!gfxVars::UseWebRender()) {
+    gPlatform->EnsureDevicesInitialized();
+  }
   gPlatform->InitOMTPConfig();
 
   if (gfxConfig::IsEnabled(Feature::GPU_PROCESS)) {
diff --git a/gfx/thebes/gfxPlatform.h b/gfx/thebes/gfxPlatform.h
index 7e6cfd5a52743..49baa1d6ba063 100644
--- a/gfx/thebes/gfxPlatform.h
+++ b/gfx/thebes/gfxPlatform.h
@@ -738,6 +738,8 @@ class gfxPlatform : public mozilla::layers::MemoryPressureListener {
   virtual void OnMemoryPressure(
       mozilla::layers::MemoryPressureReason aWhy) override;
 
+  virtual void EnsureDevicesInitialized() {};
+
  protected:
   gfxPlatform();
   virtual ~gfxPlatform();
diff --git a/gfx/thebes/gfxWindowsPlatform.cpp b/gfx/thebes/gfxWindowsPlatform.cpp
index 22d4c688d14f1..f299bcd979803 100644
--- a/gfx/thebes/gfxWindowsPlatform.cpp
+++ b/gfx/thebes/gfxWindowsPlatform.cpp
@@ -424,7 +424,6 @@ void gfxWindowsPlatform::InitAcceleration() {
   DeviceManagerDx::Init();
 
   InitializeConfig();
-  InitializeDevices();
   UpdateANGLEConfig();
   UpdateRenderMode();
 
@@ -497,7 +496,9 @@ bool gfxWindowsPlatform::HandleDeviceReset() {
   gfxConfig::Reset(Feature::DIRECT2D);
 
   InitializeConfig();
-  InitializeDevices();
+  if (mInitializedDevices) {
+    InitializeDevices();
+  }
   UpdateANGLEConfig();
   return true;
 }
@@ -1470,6 +1471,16 @@ void gfxWindowsPlatform::InitializeD3D11Config() {
                         uint32_t(aDevice));
 }
 
+// Supports lazy device initialization on Windows, so that WebRender can avoid
+// initializing GPU state and allocating swap chains for most non-GPU processes.
+void gfxWindowsPlatform::EnsureDevicesInitialized() {
+  if (!mInitializedDevices) {
+    InitializeDevices();
+    UpdateBackendPrefs();
+    mInitializedDevices = true;
+  }
+}
+
 void gfxWindowsPlatform::InitializeDevices() {
   if (XRE_IsParentProcess()) {
     // If we're the UI process, and the GPU process is enabled, then we don't
diff --git a/gfx/thebes/gfxWindowsPlatform.h b/gfx/thebes/gfxWindowsPlatform.h
index b3e8d10ae956f..20ee1eb092918 100644
--- a/gfx/thebes/gfxWindowsPlatform.h
+++ b/gfx/thebes/gfxWindowsPlatform.h
@@ -105,6 +105,8 @@ class gfxWindowsPlatform : public gfxPlatform {
     return (gfxWindowsPlatform*)gfxPlatform::GetPlatform();
   }
 
+  virtual void EnsureDevicesInitialized() override;
+
   virtual gfxPlatformFontList* CreatePlatformFontList() override;
 
   virtual already_AddRefed<gfxASurface> CreateOffscreenSurface(
@@ -259,6 +261,7 @@ class gfxWindowsPlatform : public gfxPlatform {
   DWRITE_MEASURING_MODE mMeasuringMode;
 
   RefPtr<mozilla::layers::ReadbackManagerD3D11> mD3D11ReadbackManager;
+  bool mInitializedDevices = false;
 };
 
 #endif /* GFX_WINDOWS_PLATFORM_H */