layout: Refactor establishes_containing_block_for_all_descendants() (#36725)

Instead of grouping all the `will-change` conditions together, move each
one of them next to the condition for the relevant property.

This avoids the need to call `is_transformable()` multiple times, and
will also be needed for #35391.

Testing: unneeded (no change in behavior)

Signed-off-by: Oriol Brufau <obrufau@igalia.com>

components/layout/display_list/stacking_context.rs

@@ -530,7 +530,7 @@ impl StackingContext {
         if effects.filter.0.is_empty() &&
             effects.opacity == 1.0 &&
             effects.mix_blend_mode == ComputedMixBlendMode::Normal &&
-            !style.has_transform_or_perspective(FragmentFlags::empty()) &&
+            !style.has_effective_transform_or_perspective(FragmentFlags::empty()) &&
             style.clone_clip_path() == ClipPath::None
         {
             return false;
@@ -1584,7 +1584,10 @@ impl BoxFragment {
         &self,
         containing_block_rect: &PhysicalRect<Au>,
     ) -> Option<ReferenceFrameData> {
-        if !self.style.has_transform_or_perspective(self.base.flags) {
+        if !self
+            .style
+            .has_effective_transform_or_perspective(self.base.flags)
+        {
             return None;
         }
 

components/layout/style_ext.rs

@@ -320,7 +320,8 @@ pub(crate) trait ComputedValuesExt {
         containing_block_writing_mode: WritingMode,
     ) -> LogicalSides<LengthPercentageOrAuto<'_>>;
     fn is_transformable(&self, fragment_flags: FragmentFlags) -> bool;
-    fn has_transform_or_perspective(&self, fragment_flags: FragmentFlags) -> bool;
+    fn has_transform_or_perspective_style(&self) -> bool;
+    fn has_effective_transform_or_perspective(&self, fragment_flags: FragmentFlags) -> bool;
     fn z_index_applies(&self, fragment_flags: FragmentFlags) -> bool;
     fn effective_z_index(&self, fragment_flags: FragmentFlags) -> i32;
     fn effective_overflow(&self, fragment_flags: FragmentFlags) -> AxesOverflow;
@@ -522,15 +523,20 @@ impl ComputedValuesExt for ComputedValues {
         !self.is_inline_box(fragment_flags)
     }
 
-    /// Returns true if this style has a transform, or perspective property set and
+    /// Returns true if this style has a transform or perspective property set.
+    fn has_transform_or_perspective_style(&self) -> bool {
+        !self.get_box().transform.0.is_empty() ||
+            self.get_box().scale != GenericScale::None ||
+            self.get_box().rotate != GenericRotate::None ||
+            self.get_box().translate != GenericTranslate::None ||
+            self.get_box().perspective != Perspective::None
+    }
+
+    /// Returns true if this style has a transform or perspective property set, and
     /// it applies to this element.
-    fn has_transform_or_perspective(&self, fragment_flags: FragmentFlags) -> bool {
+    #[inline]
-        self.is_transformable(fragment_flags) &&
+    fn has_effective_transform_or_perspective(&self, fragment_flags: FragmentFlags) -> bool {
-            (!self.get_box().transform.0.is_empty() ||
+        self.is_transformable(fragment_flags) && self.has_transform_or_perspective_style()
-                self.get_box().scale != GenericScale::None ||
-                self.get_box().rotate != GenericRotate::None ||
-                self.get_box().translate != GenericTranslate::None ||
-                self.get_box().perspective != Perspective::None)
     }
 
     /// Whether the `z-index` property applies to this fragment.
@@ -705,7 +711,6 @@ impl ComputedValuesExt for ComputedValues {
         if self.is_transformable(fragment_flags) &&
             (!self.get_box().transform.0.is_empty() ||
                 self.get_box().transform_style == ComputedTransformStyle::Preserve3d ||
-                self.get_box().perspective != Perspective::None ||
                 will_change_bits
                     .intersects(WillChangeBits::TRANSFORM | WillChangeBits::PERSPECTIVE))
         {
@@ -795,29 +800,43 @@ impl ComputedValuesExt for ComputedValues {
         &self,
         fragment_flags: FragmentFlags,
     ) -> bool {
-        if self.has_transform_or_perspective(fragment_flags) {
-            return true;
-        }
-
-        if !self.get_effects().filter.0.is_empty() {
-            return true;
-        }
-
-        // See <https://drafts.csswg.org/css-transforms-2/#transform-style-property>.
-        if self.is_transformable(fragment_flags) &&
-            self.get_box().transform_style == ComputedTransformStyle::Preserve3d
-        {
-            return true;
-        }
         // From <https://www.w3.org/TR/css-will-change/#valdef-will-change-custom-ident>:
         // > If any non-initial value of a property would cause the element to generate a
         // > containing block for fixed positioned elements, specifying that property in will-change
         // > must cause the element to generate a containing block for fixed positioned elements.
         let will_change_bits = self.clone_will_change().bits;
-        if will_change_bits.intersects(WillChangeBits::FIXPOS_CB_NON_SVG) ||
+
-            (will_change_bits
+        // From <https://drafts.csswg.org/css-transforms-1/#transform-rendering>:
-                .intersects(WillChangeBits::TRANSFORM | WillChangeBits::PERSPECTIVE) &&
+        // > any value other than `none` for the `transform` property also causes the element
-                self.is_transformable(fragment_flags))
+        // > to establish a containing block for all descendants.
+        //
+        // From <https://www.w3.org/TR/css-transforms-2/#individual-transforms>
+        // > all other values […] create a stacking context and containing block for all
+        // > descendants, per usual for transforms.
+        //
+        // From <https://drafts.csswg.org/css-transforms-2/#perspective-property>:
+        // > The use of this property with any value other than `none` […] establishes a
+        // > containing block for all descendants, just like the `transform` property does.
+        //
+        // From <https://drafts.csswg.org/css-transforms-2/#transform-style-property>:
+        // > A computed value of `preserve-3d` for `transform-style` on a transformable element
+        // > establishes both a stacking context and a containing block for all descendants.
+        if self.is_transformable(fragment_flags) &&
+            (self.has_transform_or_perspective_style() ||
+                self.get_box().transform_style == ComputedTransformStyle::Preserve3d ||
+                will_change_bits
+                    .intersects(WillChangeBits::TRANSFORM | WillChangeBits::PERSPECTIVE))
+        {
+            return true;
+        }
+
+        // From <https://www.w3.org/TR/filter-effects-1/#propdef-filter>:
+        // > A value other than none for the filter property results in the creation of a containing
+        // > block for absolute and fixed positioned descendants unless the element it applies to is
+        // > a document root element in the current browsing context.
+        // FIXME(#35391): Need to check if this is the root element.
+        if !self.get_effects().filter.0.is_empty() ||
+            will_change_bits.intersects(WillChangeBits::FIXPOS_CB_NON_SVG)
         {
             return true;
         }