Bug 1582273. Pass scrollbar flags from gecko to webrender so it can identify them. r=gw

Differential Revision: https://phabricator.services.mozilla.com/D46587

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

gfx/webrender_bindings/WebRenderAPI.h

@@ -336,16 +336,17 @@ class MOZ_RAII AutoTransactionSender {
  */
 struct MOZ_STACK_CLASS StackingContextParams : public WrStackingContextParams {
   StackingContextParams()
-      : WrStackingContextParams{WrStackingContextClip::None(),
-                                nullptr,
-                                nullptr,
-                                wr::TransformStyle::Flat,
-                                wr::WrReferenceFrameKind::Transform,
-                                nullptr,
-                                /* is_backface_visible = */ true,
-                                /* cache_tiles = */ false,
-                                wr::MixBlendMode::Normal,
-                                /* is_backdrop_root = */ false} {}
+      : WrStackingContextParams{
+            WrStackingContextClip::None(),
+            nullptr,
+            nullptr,
+            wr::TransformStyle::Flat,
+            wr::WrReferenceFrameKind::Transform,
+            nullptr,
+            /* prim_flags = */ wr::PrimitiveFlags_IS_BACKFACE_VISIBLE,
+            /* cache_tiles = */ false,
+            wr::MixBlendMode::Normal,
+            /* is_backdrop_root = */ false} {}
 
   void SetPreserve3D(bool aPreserve) {
     transform_style =

gfx/webrender_bindings/src/bindings.rs

@@ -2065,7 +2065,7 @@ pub struct WrStackingContextParams {
     pub transform_style: TransformStyle,
     pub reference_frame_kind: WrReferenceFrameKind,
     pub scrolling_relative_to: *const u64,
-    pub is_backface_visible: bool,
+    pub prim_flags: PrimitiveFlags,
     /// True if picture caching should be enabled for this stacking context.
     pub cache_tiles: bool,
     pub mix_blend_mode: MixBlendMode,
@@ -2185,7 +2185,7 @@ pub extern "C" fn wr_dp_push_stacking_context(
          .dl_builder
          .push_stacking_context(bounds.origin,
                                 wr_spatial_id,
-                                params.is_backface_visible,
+                                params.prim_flags,
                                 wr_clip_id,
                                 params.transform_style,
                                 params.mix_blend_mode,

gfx/wr/webrender/src/scene_building.rs

@@ -361,7 +361,7 @@ impl<'a> SceneBuilder<'a> {
             root_pipeline.pipeline_id,
             CompositeOps::default(),
             TransformStyle::Flat,
-            /* is_backface_visible = */ true,
+            /* prim_flags = */ PrimitiveFlags::IS_BACKFACE_VISIBLE,
             /* create_tile_cache = */ false,
             ROOT_SPATIAL_NODE_INDEX,
             ClipChainId::NONE,
@@ -912,7 +912,7 @@ impl<'a> SceneBuilder<'a> {
         filters: ItemRange<FilterOp>,
         filter_datas: &[TempFilterData],
         filter_primitives: ItemRange<FilterPrimitive>,
-        is_backface_visible: bool,
+        prim_flags: PrimitiveFlags,
         apply_pipeline_clip: bool,
     ) {
         // Avoid doing unnecessary work for empty stacking contexts.
@@ -939,7 +939,7 @@ impl<'a> SceneBuilder<'a> {
             pipeline_id,
             composition_operations,
             stacking_context.transform_style,
-            is_backface_visible,
+            prim_flags,
             stacking_context.cache_tiles,
             spatial_node_index,
             clip_chain_id,
@@ -1373,7 +1373,7 @@ impl<'a> SceneBuilder<'a> {
                     item.filters(),
                     item.filter_datas(),
                     item.filter_primitives(),
-                    info.is_backface_visible,
+                    info.prim_flags,
                     apply_pipeline_clip,
                 );
                 return Some(subtraversal);
@@ -1771,7 +1771,7 @@ impl<'a> SceneBuilder<'a> {
         pipeline_id: PipelineId,
         composite_ops: CompositeOps,
         transform_style: TransformStyle,
-        is_backface_visible: bool,
+        prim_flags: PrimitiveFlags,
         create_tile_cache: bool,
         spatial_node_index: SpatialNodeIndex,
         clip_chain_id: ClipChainId,
@@ -1895,12 +1895,6 @@ 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 {

gfx/wr/webrender_api/src/display_item.rs

@@ -34,12 +34,15 @@ pub const MAX_BLUR_RADIUS: f32 = 300.;
 pub type ItemTag = (u64, u16);
 
 bitflags! {
+    #[repr(C)]
     #[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;
+        /// If set, this primitive represents a scroll bar container
+        const IS_SCROLLBAR_CONTAINER = 1 << 1;
+        /// If set, this primitive represents a scroll bar thumb
+        const IS_SCROLLBAR_THUMB = 1 << 2;
     }
 }
 
@@ -670,7 +673,7 @@ pub struct ReferenceFrame {
 pub struct PushStackingContextDisplayItem {
     pub origin: LayoutPoint,
     pub spatial_id: SpatialId,
-    pub is_backface_visible: bool,
+    pub prim_flags: PrimitiveFlags,
     pub stacking_context: StackingContext,
 }
 

gfx/wr/webrender_api/src/display_list.rs

@@ -1254,7 +1254,7 @@ impl DisplayListBuilder {
         &mut self,
         origin: LayoutPoint,
         spatial_id: di::SpatialId,
-        is_backface_visible: bool,
+        prim_flags: di::PrimitiveFlags,
         clip_id: Option<di::ClipId>,
         transform_style: di::TransformStyle,
         mix_blend_mode: di::MixBlendMode,
@@ -1270,7 +1270,7 @@ impl DisplayListBuilder {
         let item = di::DisplayItem::PushStackingContext(di::PushStackingContextDisplayItem {
             origin,
             spatial_id,
-            is_backface_visible,
+            prim_flags,
             stacking_context: di::StackingContext {
                 transform_style,
                 mix_blend_mode,
@@ -1289,12 +1289,12 @@ impl DisplayListBuilder {
         &mut self,
         origin: LayoutPoint,
         spatial_id: di::SpatialId,
-        is_backface_visible: bool,
+        prim_flags: di::PrimitiveFlags,
     ) {
         self.push_simple_stacking_context_with_filters(
             origin,
             spatial_id,
-            is_backface_visible,
+            prim_flags,
             &[],
             &[],
             &[],
@@ -1306,7 +1306,7 @@ impl DisplayListBuilder {
         &mut self,
         origin: LayoutPoint,
         spatial_id: di::SpatialId,
-        is_backface_visible: bool,
+        prim_flags: di::PrimitiveFlags,
         filters: &[di::FilterOp],
         filter_datas: &[di::FilterData],
         filter_primitives: &[di::FilterPrimitive],
@@ -1314,7 +1314,7 @@ impl DisplayListBuilder {
         self.push_stacking_context(
             origin,
             spatial_id,
-            is_backface_visible,
+            prim_flags,
             None,
             di::TransformStyle::Flat,
             di::MixBlendMode::Normal,

layout/painting/nsDisplayList.cpp

@@ -6941,6 +6941,12 @@ bool nsDisplayOwnLayer::CreateWebRenderCommands(
   params.animation = prop.ptrOr(nullptr);
   params.clip =
       wr::WrStackingContextClip::ClipChain(aBuilder.CurrentClipChainId());
+  if (IsScrollbarContainer()) {
+    params.prim_flags |= wr::PrimitiveFlags_IS_SCROLLBAR_CONTAINER;
+  }
+  if (IsScrollThumbLayer()) {
+    params.prim_flags |= wr::PrimitiveFlags_IS_SCROLLBAR_THUMB;
+  }
   StackingContextHelper sc(aSc, GetActiveScrolledRoot(), mFrame, this, aBuilder,
                            params);
 
@@ -8626,7 +8632,9 @@ bool nsDisplayTransform::CreateWebRenderCommands(
   params.mBoundTransform = &newTransformMatrix;
   params.animation = animationsId ? &prop : nullptr;
   params.mTransformPtr = transformForSC;
-  params.is_backface_visible = !BackfaceIsHidden();
+  params.prim_flags = !BackfaceIsHidden()
+                          ? wr::PrimitiveFlags_IS_BACKFACE_VISIBLE
+                          : wr::PrimitiveFlags{0};
   params.mDeferredTransformItem = deferredTransformItem;
   params.mAnimated = animated;
   // Determine if we would have to rasterize any items in local raster space
@@ -9329,7 +9337,9 @@ bool nsDisplayPerspective::CreateWebRenderCommands(
   wr::StackingContextParams params;
   params.mTransformPtr = &perspectiveMatrix;
   params.reference_frame_kind = wr::WrReferenceFrameKind::Perspective;
-  params.is_backface_visible = !BackfaceIsHidden();
+  params.prim_flags = !BackfaceIsHidden()
+                          ? wr::PrimitiveFlags_IS_BACKFACE_VISIBLE
+                          : wr::PrimitiveFlags{0};
   params.SetPreserve3D(preserve3D);
   params.clip =
       wr::WrStackingContextClip::ClipChain(aBuilder.CurrentClipChainId());