Bug 1530915 - Change external scroll offset to be a vector. r=emilio

Change the external scroll offset to be a vector, rather than a
point. This can also be updated gecko-side in future, but for
now is converted to a vector at the API boundary.

Also plumb through the external scroll offset so that it is stored
inside the ScrollFrameInfo in a spatial node. This will allow
modifying the transforms that the clip-scroll tree creates to
take into account the external scroll offset in future.

Differential Revision: https://phabricator.services.mozilla.com/D21319

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

gfx/webrender_bindings/src/bindings.rs

@@ -2220,7 +2220,9 @@ pub extern "C" fn wr_dp_define_scroll_layer(state: &mut WrState,
         vec![],
         None,
         ScrollSensitivity::Script,
-        scroll_offset,
+        // TODO(gw): We should also update the Gecko-side APIs to provide
+        //           this as a vector rather than a point.
+        scroll_offset.to_vector(),
     );
 
     WrSpaceAndClip::from_webrender(space_and_clip)

gfx/wr/examples/scrolling.rs

@@ -56,7 +56,7 @@ impl Example for App {
                 vec![],
                 None,
                 ScrollSensitivity::ScriptAndInputEvents,
-                LayoutPoint::zero(),
+                LayoutVector2D::zero(),
             );
 
             // now put some content into it.
@@ -88,7 +88,7 @@ impl Example for App {
                 vec![],
                 None,
                 ScrollSensitivity::ScriptAndInputEvents,
-                LayoutPoint::zero(),
+                LayoutVector2D::zero(),
             );
 
             // give it a giant gray background just to distinguish it and to easily

gfx/wr/webrender/src/clip_scroll_tree.rs

@@ -433,6 +433,7 @@ impl ClipScrollTree {
         content_size: &LayoutSize,
         scroll_sensitivity: ScrollSensitivity,
         frame_kind: ScrollFrameKind,
+        external_scroll_offset: LayoutVector2D,
     ) -> SpatialNodeIndex {
         let node = SpatialNode::new_scroll_frame(
             pipeline_id,
@@ -442,6 +443,7 @@ impl ClipScrollTree {
             content_size,
             scroll_sensitivity,
             frame_kind,
+            external_scroll_offset,
         );
         self.add_spatial_node(node)
     }

gfx/wr/webrender/src/display_list_flattener.rs

@@ -631,6 +631,7 @@ impl<'a> DisplayListFlattener<'a> {
             &content_size,
             info.scroll_sensitivity,
             ScrollFrameKind::Explicit,
+            info.external_scroll_offset,
         );
     }
 
@@ -786,6 +787,7 @@ impl<'a> DisplayListFlattener<'a> {
             &pipeline.content_size,
             ScrollSensitivity::ScriptAndInputEvents,
             ScrollFrameKind::PipelineRoot,
+            LayoutVector2D::zero(),
         );
 
         self.rf_mapper.push_scope();
@@ -1803,6 +1805,7 @@ impl<'a> DisplayListFlattener<'a> {
             content_size,
             ScrollSensitivity::ScriptAndInputEvents,
             ScrollFrameKind::PipelineRoot,
+            LayoutVector2D::zero(),
         );
     }
 
@@ -1900,6 +1903,7 @@ impl<'a> DisplayListFlattener<'a> {
         content_size: &LayoutSize,
         scroll_sensitivity: ScrollSensitivity,
         frame_kind: ScrollFrameKind,
+        external_scroll_offset: LayoutVector2D,
     ) -> SpatialNodeIndex {
         let node_index = self.clip_scroll_tree.add_scroll_frame(
             parent_node_index,
@@ -1909,6 +1913,7 @@ impl<'a> DisplayListFlattener<'a> {
             content_size,
             scroll_sensitivity,
             frame_kind,
+            external_scroll_offset,
         );
         self.id_to_index_mapper.map_spatial_node(new_node_id, node_index);
         node_index

gfx/wr/webrender/src/spatial_node.rs

@@ -125,6 +125,7 @@ impl SpatialNode {
         content_size: &LayoutSize,
         scroll_sensitivity: ScrollSensitivity,
         frame_kind: ScrollFrameKind,
+        external_scroll_offset: LayoutVector2D,
     ) -> Self {
         let node_type = SpatialNodeType::ScrollFrame(ScrollFrameInfo::new(
                 *frame_rect,
@@ -135,6 +136,7 @@ impl SpatialNode {
                 ),
                 external_id,
                 frame_kind,
+                external_scroll_offset,
             )
         );
 
@@ -655,6 +657,10 @@ pub struct ScrollFrameInfo {
     ///           to define scroll frames. However, that involves API changes
     ///           so we will use this as a temporary hack!
     pub frame_kind: ScrollFrameKind,
+
+    /// Amount that visual components attached to this scroll node have been
+    /// pre-scrolled in their local coordinates.
+    pub external_scroll_offset: LayoutVector2D,
 }
 
 /// Manages scrolling offset.
@@ -665,6 +671,7 @@ impl ScrollFrameInfo {
         scrollable_size: LayoutSize,
         external_id: Option<ExternalScrollId>,
         frame_kind: ScrollFrameKind,
+        external_scroll_offset: LayoutVector2D,
     ) -> ScrollFrameInfo {
         ScrollFrameInfo {
             viewport_rect,
@@ -673,6 +680,7 @@ impl ScrollFrameInfo {
             scrollable_size,
             external_id,
             frame_kind,
+            external_scroll_offset,
         }
     }
 
@@ -694,6 +702,7 @@ impl ScrollFrameInfo {
             scrollable_size: self.scrollable_size,
             external_id: self.external_id,
             frame_kind: self.frame_kind,
+            external_scroll_offset: self.external_scroll_offset,
         }
     }
 }

gfx/wr/webrender_api/src/display_item.rs

@@ -240,7 +240,7 @@ pub struct ScrollFrameDisplayItem {
     /// will have their coordinates shifted by this amount, and this offset
     /// should be added to those display item coordinates in order to get a
     /// normalized value that is consistent across display lists.
-    pub external_scroll_offset: LayoutPoint,
+    pub external_scroll_offset: LayoutVector2D,
 }
 
 #[derive(Clone, Copy, Debug, Deserialize, PartialEq, Serialize)]

gfx/wr/webrender_api/src/display_list.rs

@@ -1468,7 +1468,7 @@ impl DisplayListBuilder {
         complex_clips: I,
         image_mask: Option<di::ImageMask>,
         scroll_sensitivity: di::ScrollSensitivity,
-        external_scroll_offset: LayoutPoint,
+        external_scroll_offset: LayoutVector2D,
     ) -> di::SpaceAndClipInfo
     where
         I: IntoIterator<Item = di::ComplexClipRegion>,

gfx/wr/wrench/src/yaml_frame_reader.rs

@@ -1505,7 +1505,7 @@ impl YamlFrameReader {
             .expect("scroll frame must have a bounds");
         let content_size = yaml["content-size"].as_size().unwrap_or(clip_rect.size);
         let content_rect = LayoutRect::new(clip_rect.origin, content_size);
-        let external_scroll_offset = yaml["external-scroll-offset"].as_point().unwrap_or(LayoutPoint::zero());
+        let external_scroll_offset = yaml["external-scroll-offset"].as_vector().unwrap_or(LayoutVector2D::zero());
 
         let numeric_id = yaml["id"].as_i64().map(|id| id as u64);
 

gfx/wr/wrench/src/yaml_frame_writer.rs

@@ -1135,7 +1135,7 @@ impl YamlFrameWriter {
                     usize_node(&mut v, "id", clip_id_mapper.add_spatial_id(item.scroll_frame_id));
                     size_node(&mut v, "content-size", &base.rect().size);
                     rect_node(&mut v, "bounds", &base.clip_rect());
-                    point_node(&mut v, "external-scroll-offset", &item.external_scroll_offset);
+                    vector_node(&mut v, "external-scroll-offset", &item.external_scroll_offset);
 
                     let (complex_clips, complex_clip_count) = base.complex_clip();
                     if let Some(complex) = self.make_complex_clips_node(