Bug 1635584 - Make BackdropFilter's Availability Depend on WebRender r=emilio

- Enable BackdropFilter pref by default
  - Add function IsBackdropFilterAavailable()
  - Use IsBackdropFilterAvailable for relevant WebIDL instead of pref
  - Add test for BackdropFilter availability

Differential Revision: https://phabricator.services.mozilla.com/D73967

dom/bindings/GenerateCSS2PropertiesWebIDL.py

@@ -23,8 +23,14 @@ def generate(output, idlFilename, dataFile):
         # (e.g. on nsComputedDOMStyle).
         extendedAttrs = ["CEReactions", "Throws",
                          "SetterNeedsSubjectPrincipal=NonSystem"]
+
         if p.pref != "":
-            extendedAttrs.append('Pref="%s"' % p.pref)
+            # BackdropFilter is a special case where we want WebIDL to check
+            # a function instead of checking the pref directly.
+            if p.method == "BackdropFilter":
+                extendedAttrs.append('Func="nsCSSProps::IsBackdropFilterAvailable"')
+            else:
+                extendedAttrs.append('Pref="%s"' % p.pref)
 
         prop = p.method
 

gfx/thebes/gfxPlatform.cpp

@@ -807,6 +807,12 @@ static void FrameRatePrefChanged(const char* aPref, void*) {
   }
 }
 
+static void RecomputeBackdropFilterEnabledState() {
+  NS_DispatchToMainThread(NS_NewRunnableFunction("RecomputeEnabledState", [] {
+    nsCSSProps::RecomputeEnabledState("layout.css.backdrop-filter.enabled");
+  }));
+}
+
 void gfxPlatform::Init() {
   MOZ_RELEASE_ASSERT(!XRE_IsGPUProcess(), "GFX: Not allowed in GPU process.");
   MOZ_RELEASE_ASSERT(!XRE_IsRDDProcess(), "GFX: Not allowed in RDD process.");
@@ -1078,6 +1084,8 @@ void gfxPlatform::Init() {
   if (obs) {
     obs->NotifyObservers(nullptr, "gfx-features-ready", nullptr);
   }
+
+  RecomputeBackdropFilterEnabledState();
 }
 
 void gfxPlatform::ReportTelemetry() {
@@ -3278,8 +3286,9 @@ void gfxPlatform::NotifyGPUProcessDisabled() {
             FeatureStatus::Unavailable, "GPU Process is disabled",
             NS_LITERAL_CSTRING("FEATURE_FAILURE_GPU_PROCESS_DISABLED"));
     gfxVars::SetUseWebRender(false);
-  }
 
+    RecomputeBackdropFilterEnabledState();
+  }
   gfxVars::SetRemoteCanvasEnabled(false);
 }
 

layout/style/nsCSSProps.cpp

@@ -14,12 +14,14 @@
 #include "mozilla/ArrayUtils.h"
 #include "mozilla/Casting.h"
 
+#include "gfxPlatform.h"
 #include "nsLayoutUtils.h"
 #include "nsIWidget.h"
 #include "nsStyleConsts.h"  // For system widget appearance types
 
 #include "mozilla/dom/Animation.h"
 #include "mozilla/dom/AnimationEffectBinding.h"  // for PlaybackDirection
+#include "mozilla/gfx/gfxVars.h"                 // for UseWebRender
 #include "mozilla/LookAndFeel.h"                 // for system colors
 
 #include "nsString.h"
@@ -63,12 +65,19 @@ static nsStaticCaseInsensitiveNameTable* CreateStaticTable(
 }
 
 void nsCSSProps::RecomputeEnabledState(const char* aPref, void*) {
+  DebugOnly<bool> foundPref = false;
   for (const PropertyPref* pref = kPropertyPrefTable;
        pref->mPropID != eCSSProperty_UNKNOWN; pref++) {
     if (!aPref || !strcmp(aPref, pref->mPref)) {
+      foundPref = true;
       gPropertyEnabled[pref->mPropID] = Preferences::GetBool(pref->mPref);
+      if (pref->mPropID == eCSSProperty_backdrop_filter) {
+        gPropertyEnabled[pref->mPropID] &=
+            gfxPlatform::Initialized() && gfx::gfxVars::UseWebRender();
+      }
     }
   }
+  MOZ_ASSERT(foundPref);
 }
 
 void nsCSSProps::AddRefTable(void) {

layout/style/nsCSSProps.h

@@ -117,6 +117,19 @@ class nsCSSProps {
   }
 
  private:
+  // A table for shorthand properties.  The appropriate index is the
+  // property ID minus eCSSProperty_COUNT_no_shorthands.
+  static const nsCSSPropertyID* const
+      kSubpropertyTable[eCSSProperty_COUNT - eCSSProperty_COUNT_no_shorthands];
+
+ public:
+  /**
+   * Returns true if the backdrop-filter pref and WebRender are enabled.
+   */
+  static bool IsBackdropFilterAvailable(JSContext*, JSObject*) {
+    return IsEnabled(eCSSProperty_backdrop_filter);
+  }
+
   /**
    * Recoumputes the enabled state of a pref. If aPrefName is nullptr,
    * recomputes the state of all prefs in gPropertyEnabled.
@@ -125,12 +138,6 @@ class nsCSSProps {
   static void RecomputeEnabledState(const char* aPrefName,
                                     void* aClosure = nullptr);
 
-  // A table for shorthand properties.  The appropriate index is the
-  // property ID minus eCSSProperty_COUNT_no_shorthands.
-  static const nsCSSPropertyID* const
-      kSubpropertyTable[eCSSProperty_COUNT - eCSSProperty_COUNT_no_shorthands];
-
- public:
   static const nsCSSPropertyID* SubpropertyEntryFor(nsCSSPropertyID aProperty) {
     MOZ_ASSERT(eCSSProperty_COUNT_no_shorthands <= aProperty &&
                    aProperty < eCSSProperty_COUNT,

layout/style/test/mochitest.ini

@@ -85,6 +85,7 @@ support-files = file_animations_with_disabled_properties.html
 [test_asyncopen.html]
 [test_at_rule_parse_serialize.html]
 [test_attribute_selector_eof_behavior.html]
+[test_backdrop_filter_enabled_state.html]
 [test_background_blend_mode.html]
 [test_border_device_pixel_rounding_initial_style.html]
 [test_box_size_keywords.html]

layout/style/test/test_backdrop_filter_enabled_state.html

@@ -0,0 +1,25 @@
+<!DOCTYPE HTML>
+<head>
+  <meta charset=utf-8>
+  <title>Test Backdrop-Filter Enabled State</title>
+  <link rel="author" title="Erik Nordin" href="mailto:nordzilla@mozilla.com">
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+</head>
+<script>
+SimpleTest.waitForExplicitFinish();
+
+const webRenderEnabled = SpecialPowers.Cc["@mozilla.org/gfx/info;1"].getService(
+  SpecialPowers.Ci.nsIGfxInfo
+).WebRenderEnabled;
+
+(async function() {
+  for (let enabled of [true, false]) {
+    await SpecialPowers.pushPrefEnv({"set": [["layout.css.backdrop-filter.enabled", enabled]]});
+    is(webRenderEnabled && enabled, CSS.supports("backdrop-filter: initial"),
+      "backdrop-filter is available only if backdrop-filter pref is set and WebRender is enabled");
+  }
+  SimpleTest.finish();
+}());
+
+</script>
+