Bug 1734505 - Add Feature::WINDOW_OCCLUSION r=gfx-reviewers,nical

With Feature::WINDOW_OCCLUSION, about:support could show if window occlusion is enabled. And Feature::WINDOW_OCCLUSION could be used to override windows occlusion setting. It could be used for Bug 1733955.

Differential Revision: https://phabricator.services.mozilla.com/D127752

gfx/config/gfxFeature.h

@@ -38,6 +38,7 @@ namespace gfx {
   _(WEBGPU, Feature, "WebGPU")                                           \
   _(X11_EGL, Feature, "X11 EGL")                                         \
   _(DMABUF, Feature, "DMABUF")                                           \
+  _(WINDOW_OCCLUSION, Feature, "WINDOW_OCCLUSION")                       \
   /* Add new entries above this comment */
 
 enum class Feature : uint32_t {

gfx/thebes/gfxPlatform.cpp

@@ -27,6 +27,7 @@
 #include "mozilla/StaticPrefs_layers.h"
 #include "mozilla/StaticPrefs_media.h"
 #include "mozilla/StaticPrefs_webgl.h"
+#include "mozilla/StaticPrefs_widget.h"
 #include "mozilla/Telemetry.h"
 #include "mozilla/TimeStamp.h"
 #include "mozilla/Unused.h"
@@ -899,6 +900,7 @@ void gfxPlatform::Init() {
 
   gPlatform->InitWebGLConfig();
   gPlatform->InitWebGPUConfig();
+  gPlatform->InitWindowOcclusionConfig();
 
   // When using WebRender, we defer initialization of the D3D11 devices until
   // the (rare) cases where they're used. Note that the GPU process where
@@ -2758,6 +2760,31 @@ void gfxPlatform::InitWebGPUConfig() {
   }
 }
 
+void gfxPlatform::InitWindowOcclusionConfig() {
+  if (!XRE_IsParentProcess()) {
+    return;
+  }
+#ifdef XP_WIN
+  FeatureState& feature = gfxConfig::GetFeature(Feature::WINDOW_OCCLUSION);
+  feature.SetDefaultFromPref(
+      StaticPrefs::
+          GetPrefName_widget_windows_window_occlusion_tracking_enabled(),
+      true,
+      StaticPrefs::
+          GetPrefDefault_widget_windows_window_occlusion_tracking_enabled());
+
+  const char* env = PR_GetEnv("MOZ_WINDOW_OCCLUSION");
+  if (env) {
+    if (*env == '1') {
+      feature.UserForceEnable("Force enabled by envvar");
+    } else {
+      feature.UserDisable("Force disabled by envvar",
+                          "FEATURE_FAILURE_OCCL_ENV"_ns);
+    }
+  }
+#endif
+}
+
 bool gfxPlatform::CanUseHardwareVideoDecoding() {
   // this function is called from the compositor thread, so it is not
   // safe to init the prefs etc. from here.

gfx/thebes/gfxPlatform.h

@@ -811,6 +811,7 @@ class gfxPlatform : public mozilla::layers::MemoryPressureListener {
   virtual void InitWebRenderConfig();
   virtual void InitWebGLConfig();
   virtual void InitWebGPUConfig();
+  virtual void InitWindowOcclusionConfig();
 
   virtual void GetPlatformDisplayInfo(mozilla::widget::InfoObject& aObj) {}
 

widget/windows/WinWindowOcclusionTracker.cpp

@@ -14,6 +14,7 @@
 #include "base/thread.h"
 #include "base/message_loop.h"
 #include "base/platform_thread.h"
+#include "gfxConfig.h"
 #include "nsThreadUtils.h"
 #include "mozilla/DataMutex.h"
 #include "mozilla/gfx/Logging.h"
@@ -349,7 +350,7 @@ void WinWindowOcclusionTracker::Start() {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_ASSERT(!sTracker);
 
-  if (!StaticPrefs::widget_windows_window_occlusion_tracking_enabled()) {
+  if (!gfx::gfxConfig::IsEnabled(gfx::Feature::WINDOW_OCCLUSION)) {
     return;
   }