Bug 1581448 - Add support for specifying extra per-primitive flags in WR display lists r=kvark,nical

This patch replaces the is_backface_visible bool in the common
per-primitive data in the display list with a PrimitiveFlags
enumeration. This will allow Gecko to specify extra information
about certain primitive, such as tagging scroll bars.

Differential Revision: https://phabricator.services.mozilla.com/D45970

--HG--
extra : moz-landing-system : lando

gfx/webrender_bindings/src/bindings.rs

@@ -2357,6 +2357,17 @@ pub extern "C" fn wr_dp_push_iframe(state: &mut WrState,
     );
 }
 
+// A helper fn to construct a PrimitiveFlags
+fn prim_flags(
+    is_backface_visible: bool,
+) -> PrimitiveFlags {
+    if is_backface_visible {
+        PrimitiveFlags::IS_BACKFACE_VISIBLE
+    } else {
+        PrimitiveFlags::empty()
+    }
+}
+
 #[no_mangle]
 pub extern "C" fn wr_dp_push_rect(state: &mut WrState,
                                   rect: LayoutRect,
@@ -2376,7 +2387,7 @@ pub extern "C" fn wr_dp_push_rect(state: &mut WrState,
         clip_rect: clip_rect.unwrap_or(LayoutRect::zero()),
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -2406,7 +2417,7 @@ pub extern "C" fn wr_dp_push_rect_with_parent_clip(
         clip_rect: clip_rect.unwrap(),
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -2458,7 +2469,7 @@ pub extern "C" fn wr_dp_push_backdrop_filter_with_parent_clip(
         clip_rect: clip_rect.unwrap(),
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -2486,7 +2497,7 @@ pub extern "C" fn wr_dp_push_clear_rect(state: &mut WrState,
         clip_rect: clip_rect.unwrap(),
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible: true,
+        flags: prim_flags(true),
         hit_info: state.current_tag,
     };
 
@@ -2512,7 +2523,7 @@ pub extern "C" fn wr_dp_push_hit_test(state: &mut WrState,
         clip_rect: clip_rect.unwrap(),
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -2539,7 +2550,7 @@ pub extern "C" fn wr_dp_push_clear_rect_with_parent_clip(
         clip_rect: clip_rect.unwrap(),
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible: true,
+        flags: prim_flags(true),
         hit_info: state.current_tag,
     };
 
@@ -2566,7 +2577,7 @@ pub extern "C" fn wr_dp_push_image(state: &mut WrState,
         clip_rect: clip,
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -2606,7 +2617,7 @@ pub extern "C" fn wr_dp_push_repeating_image(state: &mut WrState,
         clip_rect: clip,
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -2650,7 +2661,7 @@ pub extern "C" fn wr_dp_push_yuv_planar_image(state: &mut WrState,
         clip_rect: clip,
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -2686,7 +2697,7 @@ pub extern "C" fn wr_dp_push_yuv_NV12_image(state: &mut WrState,
         clip_rect: clip,
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -2721,7 +2732,7 @@ pub extern "C" fn wr_dp_push_yuv_interleaved_image(state: &mut WrState,
         clip_rect: clip,
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -2757,7 +2768,7 @@ pub extern "C" fn wr_dp_push_text(state: &mut WrState,
         clip_rect: clip,
         spatial_id: space_and_clip.spatial_id,
         clip_id: space_and_clip.clip_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag
     };
 
@@ -2813,7 +2824,7 @@ pub extern "C" fn wr_dp_push_line(state: &mut WrState,
         clip_rect: *clip,
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -2858,7 +2869,7 @@ pub extern "C" fn wr_dp_push_border(state: &mut WrState,
         clip_rect: clip,
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -2907,7 +2918,7 @@ pub extern "C" fn wr_dp_push_border_image(state: &mut WrState,
         clip_rect: clip,
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -2965,7 +2976,7 @@ pub extern "C" fn wr_dp_push_border_gradient(state: &mut WrState,
         clip_rect: clip,
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -3027,7 +3038,7 @@ pub extern "C" fn wr_dp_push_border_radial_gradient(state: &mut WrState,
         clip_rect: clip,
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -3070,7 +3081,7 @@ pub extern "C" fn wr_dp_push_linear_gradient(state: &mut WrState,
         clip_rect: clip,
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -3114,7 +3125,7 @@ pub extern "C" fn wr_dp_push_radial_gradient(state: &mut WrState,
         clip_rect: clip,
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 
@@ -3147,7 +3158,7 @@ pub extern "C" fn wr_dp_push_box_shadow(state: &mut WrState,
         clip_rect: clip,
         clip_id: space_and_clip.clip_id,
         spatial_id: space_and_clip.spatial_id,
-        is_backface_visible,
+        flags: prim_flags(is_backface_visible),
         hit_info: state.current_tag,
     };
 

gfx/wr/webrender/src/hit_test.rs

@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use api::{BorderRadius, ClipMode, HitTestFlags, HitTestItem, HitTestResult, ItemTag};
+use api::{BorderRadius, ClipMode, HitTestFlags, HitTestItem, HitTestResult, ItemTag, PrimitiveFlags};
 use api::PipelineId;
 use api::units::*;
 use crate::clip::{ClipChainId, ClipDataStore, ClipNode, ClipItemKind, ClipStore};
@@ -104,7 +104,7 @@ impl HitTestingItem {
             rect: info.rect,
             clip_rect: info.clip_rect,
             tag,
-            is_backface_visible: info.is_backface_visible,
+            is_backface_visible: info.flags.contains(PrimitiveFlags::IS_BACKFACE_VISIBLE),
             spatial_node_index,
             clip_chain_range,
         }

gfx/wr/webrender/src/internal_types.rs

@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use api::{ColorF, DebugCommand, DocumentId, ExternalImageData, ExternalImageId};
+use api::{ColorF, DebugCommand, DocumentId, ExternalImageData, ExternalImageId, PrimitiveFlags};
 use api::{ImageFormat, ItemTag, NotificationRequest, Shadow, FilterOp, MAX_BLUR_RADIUS};
 use api::units::*;
 use api;
@@ -554,7 +554,7 @@ pub struct LayoutPrimitiveInfo {
     /// but that's an ongoing project, so for now it exists and is used :(
     pub rect: LayoutRect,
     pub clip_rect: LayoutRect,
-    pub is_backface_visible: bool,
+    pub flags: PrimitiveFlags,
     pub hit_info: Option<ItemTag>,
 }
 
@@ -563,7 +563,7 @@ impl LayoutPrimitiveInfo {
         Self {
             rect,
             clip_rect,
-            is_backface_visible: true,
+            flags: PrimitiveFlags::default(),
             hit_info: None,
         }
     }

gfx/wr/webrender/src/picture.rs

@@ -4,7 +4,7 @@
 
 use api::{MixBlendMode, PipelineId, PremultipliedColorF, FilterPrimitiveKind};
 use api::{PropertyBinding, PropertyBindingId, FilterPrimitive, FontRenderMode};
-use api::{DebugFlags, RasterSpace, ImageKey, ColorF};
+use api::{DebugFlags, RasterSpace, ImageKey, ColorF, PrimitiveFlags};
 use api::units::*;
 use crate::box_shadow::{BLUR_SAMPLE_SCALE};
 use crate::clip::{ClipStore, ClipChainInstance, ClipDataHandle, ClipChainId};
@@ -2283,7 +2283,7 @@ impl PrimitiveList {
         prim_instance: PrimitiveInstance,
         prim_size: LayoutSize,
         spatial_node_index: SpatialNodeIndex,
-        is_backface_visible: bool,
+        prim_flags: PrimitiveFlags,
         insert_position: PrimitiveListPosition,
     ) {
         let mut flags = ClusterFlags::empty();
@@ -2300,7 +2300,7 @@ impl PrimitiveList {
             _ => {}
         }
 
-        if is_backface_visible {
+        if prim_flags.contains(PrimitiveFlags::IS_BACKFACE_VISIBLE) {
             flags.insert(ClusterFlags::IS_BACKFACE_VISIBLE);
         }
 
@@ -2345,13 +2345,13 @@ impl PrimitiveList {
         prim_instance: PrimitiveInstance,
         prim_size: LayoutSize,
         spatial_node_index: SpatialNodeIndex,
-        is_backface_visible: bool,
+        flags: PrimitiveFlags,
     ) {
         self.push(
             prim_instance,
             prim_size,
             spatial_node_index,
-            is_backface_visible,
+            flags,
             PrimitiveListPosition::Begin,
         )
     }
@@ -2362,13 +2362,13 @@ impl PrimitiveList {
         prim_instance: PrimitiveInstance,
         prim_size: LayoutSize,
         spatial_node_index: SpatialNodeIndex,
-        is_backface_visible: bool,
+        flags: PrimitiveFlags,
     ) {
         self.push(
             prim_instance,
             prim_size,
             spatial_node_index,
-            is_backface_visible,
+            flags,
             PrimitiveListPosition::End,
         )
     }
@@ -2583,7 +2583,7 @@ impl PicturePrimitive {
         context_3d: Picture3DContext<OrderedPictureChild>,
         frame_output_pipeline_id: Option<PipelineId>,
         apply_local_clip_rect: bool,
-        is_backface_visible: bool,
+        flags: PrimitiveFlags,
         requested_raster_space: RasterSpace,
         prim_list: PrimitiveList,
         spatial_node_index: SpatialNodeIndex,
@@ -2600,7 +2600,7 @@ impl PicturePrimitive {
             frame_output_pipeline_id,
             extra_gpu_data_handles: SmallVec::new(),
             apply_local_clip_rect,
-            is_backface_visible,
+            is_backface_visible: flags.contains(PrimitiveFlags::IS_BACKFACE_VISIBLE),
             requested_raster_space,
             spatial_node_index,
             local_rect: LayoutRect::zero(),

gfx/wr/webrender/src/prim_store/backdrop.rs

@@ -2,6 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+use api::PrimitiveFlags;
 use api::units::*;
 use crate::clip_scroll_tree::SpatialNodeIndex;
 use crate::intern::{Internable, InternDebug, Handle as InternHandle};
@@ -34,13 +35,13 @@ pub type BackdropKey = PrimKey<Backdrop>;
 
 impl BackdropKey {
     pub fn new(
-        is_backface_visible: bool,
+        flags: PrimitiveFlags,
         prim_size: LayoutSize,
         backdrop: Backdrop,
     ) -> Self {
         BackdropKey {
             common: PrimKeyCommonData {
-                is_backface_visible,
+                flags,
                 prim_size: prim_size.into(),
             },
             kind: backdrop,
@@ -86,7 +87,7 @@ impl InternablePrimitive for Backdrop {
         info: &LayoutPrimitiveInfo,
     ) -> BackdropKey {
         BackdropKey::new(
-            info.is_backface_visible,
+            info.flags,
             info.rect.size,
             self
         )

gfx/wr/webrender/src/prim_store/gradient.rs

@@ -4,7 +4,7 @@
 
 use api::{
     ColorF, ColorU, ExtendMode, GradientStop,
-    PremultipliedColorF, LineOrientation,
+    PremultipliedColorF, LineOrientation, PrimitiveFlags,
 };
 use api::units::{LayoutPoint, LayoutSize, LayoutVector2D};
 use crate::scene_building::IsVisible;
@@ -78,13 +78,13 @@ pub struct LinearGradientKey {
 
 impl LinearGradientKey {
     pub fn new(
-        is_backface_visible: bool,
+        flags: PrimitiveFlags,
         prim_size: LayoutSize,
         linear_grad: LinearGradient,
     ) -> Self {
         LinearGradientKey {
             common: PrimKeyCommonData {
-                is_backface_visible,
+                flags,
                 prim_size: prim_size.into(),
             },
             extend_mode: linear_grad.extend_mode,
@@ -308,7 +308,7 @@ impl InternablePrimitive for LinearGradient {
         info: &LayoutPrimitiveInfo,
     ) -> LinearGradientKey {
         LinearGradientKey::new(
-            info.is_backface_visible,
+            info.flags,
             info.rect.size,
             self
         )
@@ -384,13 +384,13 @@ pub struct RadialGradientKey {
 
 impl RadialGradientKey {
     pub fn new(
-        is_backface_visible: bool,
+        flags: PrimitiveFlags,
         prim_size: LayoutSize,
         radial_grad: RadialGradient,
     ) -> Self {
         RadialGradientKey {
             common: PrimKeyCommonData {
-                is_backface_visible,
+                flags,
                 prim_size: prim_size.into(),
             },
             extend_mode: radial_grad.extend_mode,
@@ -538,7 +538,7 @@ impl InternablePrimitive for RadialGradient {
         info: &LayoutPrimitiveInfo,
     ) -> RadialGradientKey {
         RadialGradientKey::new(
-            info.is_backface_visible,
+            info.flags,
             info.rect.size,
             self,
         )

gfx/wr/webrender/src/prim_store/image.rs

@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use api::{
-    AlphaType, ColorDepth, ColorF, ColorU,
+    AlphaType, ColorDepth, ColorF, ColorU, PrimitiveFlags,
     ImageKey as ApiImageKey, ImageRendering,
     PremultipliedColorF, Shadow, YuvColorSpace, ColorRange, YuvFormat,
 };
@@ -85,13 +85,13 @@ pub type ImageKey = PrimKey<Image>;
 
 impl ImageKey {
     pub fn new(
-        is_backface_visible: bool,
+        flags: PrimitiveFlags,
         prim_size: LayoutSize,
         image: Image,
     ) -> Self {
         ImageKey {
             common: PrimKeyCommonData {
-                is_backface_visible,
+                flags,
                 prim_size: prim_size.into(),
             },
             kind: image,
@@ -327,7 +327,7 @@ impl InternablePrimitive for Image {
         info: &LayoutPrimitiveInfo,
     ) -> ImageKey {
         ImageKey::new(
-            info.is_backface_visible,
+            info.flags,
             info.rect.size,
             self
         )
@@ -393,14 +393,14 @@ pub type YuvImageKey = PrimKey<YuvImage>;
 
 impl YuvImageKey {
     pub fn new(
-        is_backface_visible: bool,
+        flags: PrimitiveFlags,
         prim_size: LayoutSize,
         yuv_image: YuvImage,
     ) -> Self {
 
         YuvImageKey {
             common: PrimKeyCommonData {
-                is_backface_visible,
+                flags,
                 prim_size: prim_size.into(),
             },
             kind: yuv_image,
@@ -509,7 +509,7 @@ impl InternablePrimitive for YuvImage {
         info: &LayoutPrimitiveInfo,
     ) -> YuvImageKey {
         YuvImageKey::new(
-            info.is_backface_visible,
+            info.flags,
             info.rect.size,
             self,
         )

gfx/wr/webrender/src/prim_store/mod.rs

@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use api::{BorderRadius, ClipMode, ColorF};
-use api::{ImageRendering, RepeatMode};
+use api::{ImageRendering, RepeatMode, PrimitiveFlags};
 use api::{PremultipliedColorF, PropertyBinding, Shadow, GradientStop};
 use api::{BoxShadowClipMode, LineStyle, LineOrientation, BorderStyle};
 use api::{PrimitiveKeyKind};
@@ -389,7 +389,7 @@ impl GpuCacheAddress {
 #[derive(MallocSizeOf)]
 pub struct PrimitiveSceneData {
     pub prim_size: LayoutSize,
-    pub is_backface_visible: bool,
+    pub flags: PrimitiveFlags,
 }
 
 #[cfg_attr(feature = "capture", derive(Serialize))]
@@ -653,7 +653,7 @@ impl From<WorldPoint> for PointKey {
 #[cfg_attr(feature = "replay", derive(Deserialize))]
 #[derive(Debug, Clone, Eq, MallocSizeOf, PartialEq, Hash)]
 pub struct PrimKeyCommonData {
-    pub is_backface_visible: bool,
+    pub flags: PrimitiveFlags,
     pub prim_size: SizeKey,
 }
 
@@ -662,7 +662,7 @@ impl PrimKeyCommonData {
         info: &LayoutPrimitiveInfo,
     ) -> Self {
         PrimKeyCommonData {
-            is_backface_visible: info.is_backface_visible,
+            flags: info.flags,
             prim_size: info.rect.size.into(),
         }
     }
@@ -686,13 +686,13 @@ pub struct PrimitiveKey {
 
 impl PrimitiveKey {
     pub fn new(
-        is_backface_visible: bool,
+        flags: PrimitiveFlags,
         prim_size: LayoutSize,
         kind: PrimitiveKeyKind,
     ) -> Self {
         PrimitiveKey {
             common: PrimKeyCommonData {
-                is_backface_visible,
+                flags,
                 prim_size: prim_size.into(),
             },
             kind,
@@ -736,7 +736,7 @@ impl From<PrimitiveKeyKind> for PrimitiveTemplateKind {
 #[cfg_attr(feature = "replay", derive(Deserialize))]
 #[derive(MallocSizeOf)]
 pub struct PrimTemplateCommonData {
-    pub is_backface_visible: bool,
+    pub flags: PrimitiveFlags,
     pub may_need_repetition: bool,
     pub prim_size: LayoutSize,
     pub opacity: PrimitiveOpacity,
@@ -750,7 +750,7 @@ pub struct PrimTemplateCommonData {
 impl PrimTemplateCommonData {
     pub fn with_key_common(common: PrimKeyCommonData) -> Self {
         PrimTemplateCommonData {
-            is_backface_visible: common.is_backface_visible,
+            flags: common.flags,
             may_need_repetition: true,
             prim_size: common.prim_size.into(),
             gpu_cache_handle: GpuCacheHandle::new(),
@@ -853,7 +853,7 @@ impl InternablePrimitive for PrimitiveKeyKind {
         info: &LayoutPrimitiveInfo,
     ) -> PrimitiveKey {
         PrimitiveKey::new(
-            info.is_backface_visible,
+            info.flags,
             info.rect.size,
             self,
         )

gfx/wr/webrender/src/prim_store/picture.rs

@@ -4,7 +4,7 @@
 
 use api::{
     ColorU, MixBlendMode, FilterPrimitiveInput, FilterPrimitiveKind, ColorSpace,
-    PropertyBinding, PropertyBindingId, CompositeOperator,
+    PropertyBinding, PropertyBindingId, CompositeOperator, PrimitiveFlags,
 };
 use api::units::{Au, LayoutSize, LayoutVector2D};
 use crate::scene_building::IsVisible;
@@ -239,14 +239,14 @@ pub type PictureKey = PrimKey<Picture>;
 
 impl PictureKey {
     pub fn new(
-        is_backface_visible: bool,
+        flags: PrimitiveFlags,
         prim_size: LayoutSize,
         pic: Picture,
     ) -> Self {
 
         PictureKey {
             common: PrimKeyCommonData {
-                is_backface_visible,
+                flags,
                 prim_size: prim_size.into(),
             },
             kind: pic,
@@ -288,7 +288,7 @@ impl InternablePrimitive for Picture {
         info: &LayoutPrimitiveInfo,
     ) -> PictureKey {
         PictureKey::new(
-            info.is_backface_visible,
+            info.flags,
             info.rect.size,
             self,
         )

gfx/wr/webrender/src/scene_building.rs

@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use api::{AlphaType, BorderDetails, BorderDisplayItem, BuiltDisplayListIter};
+use api::{AlphaType, BorderDetails, BorderDisplayItem, BuiltDisplayListIter, PrimitiveFlags};
 use api::{ClipId, ColorF, CommonItemProperties, ComplexClipRegion, ComponentTransferFuncType, RasterSpace};
 use api::{DisplayItem, DisplayItemRef, ExtendMode, ExternalScrollId, FilterData};
 use api::{FilterOp, FilterPrimitive, FontInstanceKey, GlyphInstance, GlyphOptions, GradientStop};
@@ -668,7 +668,7 @@ impl<'a> SceneBuilder<'a> {
                     ),
                     LayoutSize::zero(),
                     clip_chain_instance.spatial_node_index,
-                    true,
+                    PrimitiveFlags::IS_BACKFACE_VISIBLE,
                 );
 
                 remaining_prims.add_prim_to_start(
@@ -678,7 +678,7 @@ impl<'a> SceneBuilder<'a> {
                     ),
                     LayoutSize::zero(),
                     clip_chain_instance.spatial_node_index,
-                    true,
+                    PrimitiveFlags::IS_BACKFACE_VISIBLE,
                 );
             }
         }
@@ -688,7 +688,7 @@ impl<'a> SceneBuilder<'a> {
         // Now, create a picture with tile caching enabled that will hold all
         // of the primitives selected as belonging to the main scroll root.
         let pic_key = PictureKey::new(
-            true,
+            PrimitiveFlags::IS_BACKFACE_VISIBLE,
             LayoutSize::zero(),
             Picture {
                 composite_mode_key: PictureCompositeKey::Identity,
@@ -700,7 +700,7 @@ impl<'a> SceneBuilder<'a> {
             .intern(&pic_key, || {
                 PrimitiveSceneData {
                     prim_size: LayoutSize::zero(),
-                    is_backface_visible: true,
+                    flags: PrimitiveFlags::IS_BACKFACE_VISIBLE,
                 }
             }
             );
@@ -732,7 +732,7 @@ impl<'a> SceneBuilder<'a> {
             Picture3DContext::Out,
             None,
             true,
-            true,
+            PrimitiveFlags::IS_BACKFACE_VISIBLE,
             RasterSpace::Screen,
             prim_list,
             main_scroll_root,
@@ -758,7 +758,7 @@ impl<'a> SceneBuilder<'a> {
             instance,
             LayoutSize::zero(),
             main_scroll_root,
-            true,
+            PrimitiveFlags::IS_BACKFACE_VISIBLE,
         );
     }
 
@@ -1110,7 +1110,7 @@ impl<'a> SceneBuilder<'a> {
         let layout = LayoutPrimitiveInfo {
             rect: snap_to_device.snap_rect(&rect),
             clip_rect: snap_to_device.snap_rect(&clip_rect),
-            is_backface_visible: common.is_backface_visible,
+            flags: common.flags,
             hit_info: common.hit_info,
         };
 
@@ -1594,7 +1594,7 @@ impl<'a> SceneBuilder<'a> {
             .intern(&prim_key, || {
                 PrimitiveSceneData {
                     prim_size: info.rect.size,
-                    is_backface_visible: info.is_backface_visible,
+                    flags: info.flags,
                 }
             });
 
@@ -1659,7 +1659,7 @@ impl<'a> SceneBuilder<'a> {
         prim_instance: PrimitiveInstance,
         prim_size: LayoutSize,
         spatial_node_index: SpatialNodeIndex,
-        is_backface_visible: bool,
+        flags: PrimitiveFlags,
     ) {
         // Add primitive to the top-most stacking context on the stack.
         if prim_instance.is_chased() {
@@ -1671,7 +1671,7 @@ impl<'a> SceneBuilder<'a> {
             prim_instance,
             prim_size,
             spatial_node_index,
-            is_backface_visible,
+            flags,
         );
     }
 
@@ -1762,7 +1762,7 @@ impl<'a> SceneBuilder<'a> {
             prim_instance,
             info.rect.size,
             clip_and_scroll.spatial_node_index,
-            info.is_backface_visible,
+            info.flags,
         );
     }
 
@@ -1821,7 +1821,7 @@ impl<'a> SceneBuilder<'a> {
                     ExtendedPrimitiveInstance {
                         instance,
                         spatial_node_index: sc.spatial_node_index,
-                        is_backface_visible: sc.is_backface_visible,
+                        flags: sc.prim_flags,
                     }
                 });
                 (true, extra_instance)
@@ -1895,12 +1895,18 @@ impl<'a> SceneBuilder<'a> {
             |sc| sc.snap_to_device.clone(),
         );
 
+        let prim_flags = if is_backface_visible {
+            PrimitiveFlags::IS_BACKFACE_VISIBLE
+        } else {
+            PrimitiveFlags::empty()
+        };
+
         // Push the SC onto the stack, so we know how to handle things in
         // pop_stacking_context.
         self.sc_stack.push(FlattenedStackingContext {
             prim_list: PrimitiveList::empty(),
             pipeline_id,
-            is_backface_visible,
+            prim_flags,
             requested_raster_space,
             spatial_node_index,
             clip_chain_id,
@@ -1939,7 +1945,7 @@ impl<'a> SceneBuilder<'a> {
                             prim,
                             LayoutSize::zero(),
                             stacking_context.spatial_node_index,
-                            true,
+                            PrimitiveFlags::IS_BACKFACE_VISIBLE,
                         );
                     }
 
@@ -1961,7 +1967,7 @@ impl<'a> SceneBuilder<'a> {
                             prim,
                             LayoutSize::zero(),
                             stacking_context.spatial_node_index,
-                            true,
+                            PrimitiveFlags::IS_BACKFACE_VISIBLE,
                         );
                     }
 
@@ -2018,7 +2024,7 @@ impl<'a> SceneBuilder<'a> {
             // Now, create a picture with tile caching enabled that will hold all
             // of the primitives selected as belonging to the main scroll root.
             let pic_key = PictureKey::new(
-                true,
+                PrimitiveFlags::IS_BACKFACE_VISIBLE,
                 LayoutSize::zero(),
                 Picture {
                     composite_mode_key: PictureCompositeKey::Identity,
@@ -2030,7 +2036,7 @@ impl<'a> SceneBuilder<'a> {
                 .intern(&pic_key, || {
                     PrimitiveSceneData {
                         prim_size: LayoutSize::zero(),
-                        is_backface_visible: true,
+                        flags: PrimitiveFlags::IS_BACKFACE_VISIBLE,
                     }
                 }
                 );
@@ -2054,7 +2060,7 @@ impl<'a> SceneBuilder<'a> {
                 Picture3DContext::Out,
                 None,
                 true,
-                true,
+                PrimitiveFlags::IS_BACKFACE_VISIBLE,
                 RasterSpace::Screen,
                 stacking_context.prim_list,
                 scroll_root,
@@ -2078,7 +2084,7 @@ impl<'a> SceneBuilder<'a> {
                 instance,
                 LayoutSize::zero(),
                 scroll_root,
-                true,
+                PrimitiveFlags::IS_BACKFACE_VISIBLE,
             );
             stacking_context.prim_list = prim_list;
         }
@@ -2091,7 +2097,7 @@ impl<'a> SceneBuilder<'a> {
                 leaf_context_3d,
                 leaf_output_pipeline_id,
                 true,
-                stacking_context.is_backface_visible,
+                stacking_context.prim_flags,
                 stacking_context.requested_raster_space,
                 stacking_context.prim_list,
                 stacking_context.spatial_node_index,
@@ -2107,7 +2113,7 @@ impl<'a> SceneBuilder<'a> {
         let mut cur_instance = create_prim_instance(
             leaf_pic_index,
             leaf_composite_mode.into(),
-            stacking_context.is_backface_visible,
+            stacking_context.prim_flags,
             ClipChainId::NONE,
             &mut self.interners,
         );
@@ -2123,7 +2129,7 @@ impl<'a> SceneBuilder<'a> {
             prims.push(ExtendedPrimitiveInstance {
                 instance: cur_instance,
                 spatial_node_index: stacking_context.spatial_node_index,
-                is_backface_visible: stacking_context.is_backface_visible,
+                flags: stacking_context.prim_flags,
             });
 
             let mut prim_list = PrimitiveList::empty();
@@ -2132,7 +2138,7 @@ impl<'a> SceneBuilder<'a> {
                     ext_prim.instance,
                     LayoutSize::zero(),
                     ext_prim.spatial_node_index,
-                    ext_prim.is_backface_visible,
+                    ext_prim.flags,
                 );
             }
 
@@ -2147,7 +2153,7 @@ impl<'a> SceneBuilder<'a> {
                     },
                     stacking_context.frame_output_pipeline_id,
                     true,
-                    stacking_context.is_backface_visible,
+                    stacking_context.prim_flags,
                     stacking_context.requested_raster_space,
                     prim_list,
                     stacking_context.spatial_node_index,
@@ -2159,7 +2165,7 @@ impl<'a> SceneBuilder<'a> {
             cur_instance = create_prim_instance(
                 current_pic_index,
                 PictureCompositeKey::Identity,
-                stacking_context.is_backface_visible,
+                stacking_context.prim_flags,
                 ClipChainId::NONE,
                 &mut self.interners,
             );
@@ -2171,7 +2177,7 @@ impl<'a> SceneBuilder<'a> {
             stacking_context.composite_ops.filters,
             stacking_context.composite_ops.filter_primitives,
             stacking_context.composite_ops.filter_datas,
-            stacking_context.is_backface_visible,
+            stacking_context.prim_flags,
             stacking_context.requested_raster_space,
             stacking_context.spatial_node_index,
             true,
@@ -2200,7 +2206,7 @@ impl<'a> SceneBuilder<'a> {
                 cur_instance.clone(),
                 LayoutSize::zero(),
                 stacking_context.spatial_node_index,
-                stacking_context.is_backface_visible,
+                stacking_context.prim_flags,
             );
 
             let blend_pic_index = PictureIndex(self.prim_store.pictures
@@ -2210,7 +2216,7 @@ impl<'a> SceneBuilder<'a> {
                     Picture3DContext::Out,
                     None,
                     true,
-                    stacking_context.is_backface_visible,
+                    stacking_context.prim_flags,
                     stacking_context.requested_raster_space,
                     prim_list,
                     stacking_context.spatial_node_index,
@@ -2223,7 +2229,7 @@ impl<'a> SceneBuilder<'a> {
             cur_instance = create_prim_instance(
                 blend_pic_index,
                 composite_mode.into(),
-                stacking_context.is_backface_visible,
+                stacking_context.prim_flags,
                 ClipChainId::NONE,
                 &mut self.interners,
             );
@@ -2260,7 +2266,7 @@ impl<'a> SceneBuilder<'a> {
                     cur_instance,
                     LayoutSize::zero(),
                     stacking_context.spatial_node_index,
-                    stacking_context.is_backface_visible,
+                    stacking_context.prim_flags,
                 );
                 None
             }
@@ -2277,7 +2283,7 @@ impl<'a> SceneBuilder<'a> {
             self.add_primitive_instance_to_3d_root(ExtendedPrimitiveInstance {
                 instance,
                 spatial_node_index: stacking_context.spatial_node_index,
-                is_backface_visible: stacking_context.is_backface_visible,
+                flags: stacking_context.prim_flags,
             });
         }
 
@@ -2606,7 +2612,6 @@ impl<'a> SceneBuilder<'a> {
                         blur_filter.sanitize();
                         let composite_mode = PictureCompositeMode::Filter(blur_filter);
                         let composite_mode_key = Some(composite_mode.clone()).into();
-                        let is_backface_visible = true; //TODO: double check this
 
                         // Pass through configuration information about whether WR should
                         // do the bounding rect inflation for text shadows.
@@ -2622,7 +2627,7 @@ impl<'a> SceneBuilder<'a> {
                                 Picture3DContext::Out,
                                 None,
                                 is_passthrough,
-                                is_backface_visible,
+                                PrimitiveFlags::IS_BACKFACE_VISIBLE,
                                 raster_space,
                                 prim_list,
                                 pending_shadow.clip_and_scroll.spatial_node_index,
@@ -2632,7 +2637,7 @@ impl<'a> SceneBuilder<'a> {
                         );
 
                         let shadow_pic_key = PictureKey::new(
-                            true,
+                            PrimitiveFlags::IS_BACKFACE_VISIBLE,
                             LayoutSize::zero(),
                             Picture { composite_mode_key },
                         );
@@ -2642,7 +2647,7 @@ impl<'a> SceneBuilder<'a> {
                             .intern(&shadow_pic_key, || {
                                 PrimitiveSceneData {
                                     prim_size: LayoutSize::zero(),
-                                    is_backface_visible: true,
+                                    flags: PrimitiveFlags::IS_BACKFACE_VISIBLE,
                                 }
                             }
                         );
@@ -2664,7 +2669,7 @@ impl<'a> SceneBuilder<'a> {
                             shadow_prim_instance,
                             LayoutSize::zero(),
                             pending_shadow.clip_and_scroll.spatial_node_index,
-                            true,
+                            PrimitiveFlags::IS_BACKFACE_VISIBLE,
                         );
                     }
                 }
@@ -2742,7 +2747,7 @@ impl<'a> SceneBuilder<'a> {
             shadow_prim_instance,
             info.rect.size,
             pending_primitive.clip_and_scroll.spatial_node_index,
-            info.is_backface_visible,
+            info.flags,
         );
     }
 
@@ -3298,7 +3303,7 @@ impl<'a> SceneBuilder<'a> {
         // a clip for each stacking context.
         for stacking_context in self.sc_stack.iter().rev().take_while(|sc| !sc.is_backdrop_root) {
             let clip_chain_id = stacking_context.clip_chain_id;
-            let is_backface_visible = stacking_context.is_backface_visible;
+            let prim_flags = stacking_context.prim_flags;
             let composite_mode = None;
 
             let mut prim_list = PrimitiveList::empty();
@@ -3306,7 +3311,7 @@ impl<'a> SceneBuilder<'a> {
                 instance,
                 LayoutSize::zero(),
                 backdrop_spatial_node_index,
-                is_backface_visible,
+                prim_flags,
             );
 
             backdrop_pic_index = PictureIndex(self.prim_store.pictures
@@ -3316,7 +3321,7 @@ impl<'a> SceneBuilder<'a> {
                     Picture3DContext::Out,
                     None,
                     true,
-                    is_backface_visible,
+                    prim_flags,
                     requested_raster_space,
                     prim_list,
                     backdrop_spatial_node_index,
@@ -3330,7 +3335,7 @@ impl<'a> SceneBuilder<'a> {
             instance = create_prim_instance(
                 backdrop_pic_index,
                 composite_mode.into(),
-                is_backface_visible,
+                prim_flags,
                 clip_chain_id,
                 &mut self.interners,
             );
@@ -3342,7 +3347,7 @@ impl<'a> SceneBuilder<'a> {
             filters,
             filter_primitives,
             filter_datas,
-            info.is_backface_visible,
+            info.flags,
             requested_raster_space,
             backdrop_spatial_node_index,
             false,
@@ -3365,7 +3370,7 @@ impl<'a> SceneBuilder<'a> {
                 filters,
                 filter_primitives,
                 filter_datas,
-                info.is_backface_visible,
+                info.flags,
                 requested_raster_space,
                 backdrop_spatial_node_index,
                 false,
@@ -3387,7 +3392,7 @@ impl<'a> SceneBuilder<'a> {
                 filtered_instance,
                 LayoutSize::zero(),
                 backdrop_spatial_node_index,
-                info.is_backface_visible,
+                info.flags,
             );
     }
 
@@ -3395,7 +3400,7 @@ impl<'a> SceneBuilder<'a> {
         let mut flattened_items = None;
         let mut backdrop_root =  None;
         let mut spatial_node_index = SpatialNodeIndex::INVALID;
-        let mut is_backface_visible = true;
+        let mut prim_flags = PrimitiveFlags::default();
         for sc in self.sc_stack.iter_mut().rev() {
             // Add child contents to parent stacking context
             if let Some((_, flattened_instance)) = flattened_items.take() {
@@ -3403,7 +3408,7 @@ impl<'a> SceneBuilder<'a> {
                     flattened_instance,
                     LayoutSize::zero(),
                     spatial_node_index,
-                    is_backface_visible,
+                    prim_flags,
                 );
             }
             flattened_items = sc.cut_item_sequence(
@@ -3413,7 +3418,7 @@ impl<'a> SceneBuilder<'a> {
                 Picture3DContext::Out,
             );
             spatial_node_index = sc.spatial_node_index;
-            is_backface_visible = sc.is_backface_visible;
+            prim_flags = sc.prim_flags;
             if sc.is_backdrop_root {
                 backdrop_root = Some(sc);
                 break;
@@ -3428,7 +3433,7 @@ impl<'a> SceneBuilder<'a> {
                 instance,
                 LayoutSize::zero(),
                 spatial_node_index,
-                is_backface_visible,
+                prim_flags,
             );
 
         Some(pic_index)
@@ -3441,7 +3446,7 @@ impl<'a> SceneBuilder<'a> {
         mut filter_ops: Vec<Filter>,
         mut filter_primitives: Vec<FilterPrimitive>,
         filter_datas: Vec<FilterData>,
-        is_backface_visible: bool,
+        flags: PrimitiveFlags,
         requested_raster_space: RasterSpace,
         spatial_node_index: SpatialNodeIndex,
         inflate_if_required: bool,
@@ -3494,7 +3499,7 @@ impl<'a> SceneBuilder<'a> {
                 cur_instance.clone(),
                 LayoutSize::zero(),
                 spatial_node_index,
-                is_backface_visible,
+                flags,
             );
 
             let filter_pic_index = PictureIndex(self.prim_store.pictures
@@ -3504,7 +3509,7 @@ impl<'a> SceneBuilder<'a> {
                     Picture3DContext::Out,
                     None,
                     true,
-                    is_backface_visible,
+                    flags,
                     requested_raster_space,
                     prim_list,
                     spatial_node_index,
@@ -3519,7 +3524,7 @@ impl<'a> SceneBuilder<'a> {
             cur_instance = create_prim_instance(
                 current_pic_index,
                 composite_mode.into(),
-                is_backface_visible,
+                flags,
                 ClipChainId::NONE,
                 &mut self.interners,
             );
@@ -3565,7 +3570,7 @@ impl<'a> SceneBuilder<'a> {
                 cur_instance.clone(),
                 LayoutSize::zero(),
                 spatial_node_index,
-                is_backface_visible,
+                flags,
             );
 
             let filter_pic_index = PictureIndex(self.prim_store.pictures
@@ -3575,7 +3580,7 @@ impl<'a> SceneBuilder<'a> {
                     Picture3DContext::Out,
                     None,
                     true,
-                    is_backface_visible,
+                    flags,
                     requested_raster_space,
                     prim_list,
                     spatial_node_index,
@@ -3590,7 +3595,7 @@ impl<'a> SceneBuilder<'a> {
             cur_instance = create_prim_instance(
                 current_pic_index,
                 Some(composite_mode).into(),
-                is_backface_visible,
+                flags,
                 ClipChainId::NONE,
                 &mut self.interners,
             );
@@ -3622,7 +3627,7 @@ pub trait IsVisible {
 struct ExtendedPrimitiveInstance {
     instance: PrimitiveInstance,
     spatial_node_index: SpatialNodeIndex,
-    is_backface_visible: bool,
+    flags: PrimitiveFlags,
 }
 
 /// Properties of a stacking context that are maintained
@@ -3632,8 +3637,8 @@ struct FlattenedStackingContext {
     /// The list of primitive instances added to this stacking context.
     prim_list: PrimitiveList,
 
-    /// Whether this stacking context is visible when backfacing
+    /// Primitive instance flags for compositing this stacking context
-    is_backface_visible: bool,
+    prim_flags: PrimitiveFlags,
 
     /// Whether or not the caller wants this drawn in
     /// screen space (quality) or local space (performance)
@@ -3714,7 +3719,7 @@ impl FlattenedStackingContext {
         }
 
         // If backface visibility is explicitly set.
-        if !self.is_backface_visible {
+        if !self.prim_flags.contains(PrimitiveFlags::IS_BACKFACE_VISIBLE) {
             return false;
         }
 
@@ -3756,7 +3761,7 @@ impl FlattenedStackingContext {
                 flat_items_context_3d,
                 None,
                 true,
-                self.is_backface_visible,
+                self.prim_flags,
                 self.requested_raster_space,
                 mem::replace(&mut self.prim_list, PrimitiveList::empty()),
                 self.spatial_node_index,
@@ -3768,7 +3773,7 @@ impl FlattenedStackingContext {
         let prim_instance = create_prim_instance(
             pic_index,
             composite_mode.into(),
-            self.is_backface_visible,
+            self.prim_flags,
             self.clip_chain_id,
             interners,
         );
@@ -3836,12 +3841,12 @@ impl From<PendingPrimitive<TextRun>> for ShadowItem {
 fn create_prim_instance(
     pic_index: PictureIndex,
     composite_mode_key: PictureCompositeKey,
-    is_backface_visible: bool,
+    flags: PrimitiveFlags,
     clip_chain_id: ClipChainId,
     interners: &mut Interners,
 ) -> PrimitiveInstance {
     let pic_key = PictureKey::new(
-        is_backface_visible,
+        flags,
         LayoutSize::zero(),
         Picture { composite_mode_key },
     );
@@ -3851,7 +3856,7 @@ fn create_prim_instance(
         .intern(&pic_key, || {
             PrimitiveSceneData {
                 prim_size: LayoutSize::zero(),
-                is_backface_visible,
+                flags,
             }
         }
     );

gfx/wr/webrender_api/src/display_item.rs

@@ -33,6 +33,22 @@ pub const MAX_BLUR_RADIUS: f32 = 300.;
 /// events.
 pub type ItemTag = (u64, u16);
 
+bitflags! {
+    #[derive(Deserialize, MallocSizeOf, Serialize, PeekPoke)]
+    pub struct PrimitiveFlags: u8 {
+        /// The CSS backface-visibility property (yes, it can be really granular)
+        const IS_BACKFACE_VISIBLE = 1 << 0;
+        /// If set, this primitive represents part of a scroll bar
+        const IS_SCROLL_BAR = 1 << 1;
+    }
+}
+
+impl Default for PrimitiveFlags {
+    fn default() -> Self {
+        PrimitiveFlags::IS_BACKFACE_VISIBLE
+    }
+}
+
 /// A grouping of fields a lot of display items need, just to avoid
 /// repeating these over and over in this file.
 #[derive(Clone, Copy, Debug, Default, Deserialize, PartialEq, Serialize, PeekPoke)]
@@ -49,19 +65,22 @@ pub struct CommonItemProperties {
     /// dubious "common" field, but because it's an Option, it usually only
     /// wastes a single byte (for None).
     pub hit_info: Option<ItemTag>,
-    /// The CSS backface-visibility property (yes, it can be really granular)
+    /// Various flags describing properties of this primitive.
-    pub is_backface_visible: bool,
+    pub flags: PrimitiveFlags,
 }
 
 impl CommonItemProperties {
     /// Convenience for tests.
-    pub fn new(clip_rect: LayoutRect, space_and_clip: SpaceAndClipInfo) -> Self {
+    pub fn new(
+        clip_rect: LayoutRect,
+        space_and_clip: SpaceAndClipInfo,
+    ) -> Self {
         Self {
             clip_rect,
             spatial_id: space_and_clip.spatial_id,
             clip_id: space_and_clip.clip_id,
             hit_info: None,
-            is_backface_visible: true,
+            flags: PrimitiveFlags::default(),
         }
     }
 }

gfx/wr/wrench/src/rawtest.rs

@@ -118,7 +118,7 @@ impl<'a> RawtestHarness<'a> {
             clip_rect,
             clip_id: space_and_clip.clip_id,
             spatial_id: space_and_clip.spatial_id,
-            is_backface_visible: true,
+            flags: PrimitiveFlags::default(),
             hit_info: None,
         }
     }
@@ -133,7 +133,7 @@ impl<'a> RawtestHarness<'a> {
             clip_rect,
             clip_id,
             spatial_id,
-            is_backface_visible: true,
+            flags: PrimitiveFlags::default(),
             hit_info: None,
         }
     }
@@ -322,7 +322,7 @@ impl<'a> RawtestHarness<'a> {
             clip_rect: rect(0.0, 0.0, 800.0, 800.0),
             clip_id,
             spatial_id: root_space_and_clip.spatial_id,
-            is_backface_visible: true,
+            flags: PrimitiveFlags::default(),
             hit_info: None,
         };
 
@@ -954,7 +954,7 @@ impl<'a> RawtestHarness<'a> {
                     clip_rect: rect(110., 110., 50., 2.),
                     clip_id,
                     spatial_id,
-                    is_backface_visible: true,
+                    flags: PrimitiveFlags::default(),
                     hit_info: None,
                 };
                 builder.push_line(
@@ -1209,7 +1209,7 @@ impl<'a> RawtestHarness<'a> {
                 clip_rect: rect,
                 clip_id: temp_clip_id,
                 spatial_id: space_and_clip.spatial_id,
-                is_backface_visible: true,
+                flags: PrimitiveFlags::default(),
             },
             ColorF::new(1.0, 1.0, 1.0, 1.0),
         );
@@ -1229,7 +1229,7 @@ impl<'a> RawtestHarness<'a> {
                 clip_rect: rect,
                 clip_id: ClipId::ClipChain(clip_chain_id),
                 spatial_id: space_and_clip.spatial_id,
-                is_backface_visible: true,
+                flags: PrimitiveFlags::default(),
             },
             ColorF::new(1.0, 1.0, 1.0, 1.0),
         );

gfx/wr/wrench/src/yaml_frame_reader.rs

@@ -464,7 +464,7 @@ impl YamlFrameReader {
             clip_rect: LayoutRect::zero(),
             clip_id: ClipId::invalid(),
             spatial_id: SpatialId::new(0, PipelineId::dummy()),
-            is_backface_visible: true,
+            flags: PrimitiveFlags::default(),
             hit_info: None,
         };
         self.add_stacking_context_from_yaml(&mut builder, wrench, yaml, true, &mut info);
@@ -1643,12 +1643,21 @@ impl YamlFrameReader {
             }
 
             let space_and_clip = self.top_space_and_clip();
+            let mut flags = PrimitiveFlags::default();
+            if let Some(is_backface_visible) = item["backface-visible"].as_bool() {
+                if is_backface_visible {
+                    flags.insert(PrimitiveFlags::IS_BACKFACE_VISIBLE);
+                } else {
+                    flags.remove(PrimitiveFlags::IS_BACKFACE_VISIBLE);
+                }
+            }
+
             let mut info = CommonItemProperties {
                 clip_rect,
                 clip_id: space_and_clip.clip_id,
                 spatial_id: space_and_clip.spatial_id,
                 hit_info: self.to_hit_testing_tag(&item["hit-testing-tag"]),
-                is_backface_visible: item["backface-visible"].as_bool().unwrap_or(true),
+                flags,
             };
 
             match item_type {
@@ -2026,7 +2035,7 @@ impl YamlFrameReader {
         dl.push_stacking_context(
             bounds.origin,
             *self.spatial_id_stack.last().unwrap(),
-            info.is_backface_visible,
+            info.flags.contains(PrimitiveFlags::IS_BACKFACE_VISIBLE),
             clip_node_id,
             transform_style,
             mix_blend_mode,

gfx/wr/wrench/src/yaml_frame_writer.rs

@@ -203,7 +203,7 @@ fn maybe_radius_yaml(radius: &BorderRadius) -> Option<Yaml> {
 
 fn common_node(v: &mut Table, clip_id_mapper: &mut ClipIdMapper, info: &CommonItemProperties) {
     rect_node(v, "clip-rect", &info.clip_rect);
-    bool_node(v, "backface-visible", info.is_backface_visible);
+    bool_node(v, "backface-visible", info.flags.contains(PrimitiveFlags::IS_BACKFACE_VISIBLE));
 
     clip_and_scroll_node(v, clip_id_mapper, info.clip_id, info.spatial_id);