Bug 1517723 - Update webrender to commit a40a5ffd1649d6bf6f55b76c7d633e4d157d4478 (WR PR #3467). r=kats

https://github.com/servo/webrender/pull/3467

Differential Revision: https://phabricator.services.mozilla.com/D15722

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

gfx/webrender_bindings/revision.txt

@@ -1 +1 @@
-8a7212b628ae39e7251201b0a9761c74bab42c5d
+a40a5ffd1649d6bf6f55b76c7d633e4d157d4478

gfx/wr/webrender/src/picture.rs

@@ -113,6 +113,9 @@ pub struct Tile {
     pub local_rect: LayoutRect,
     /// The valid rect within this tile.
     valid_rect: WorldRect,
+    /// The currently visible rect within this tile, updated per frame.
+    /// If None, this tile is not currently visible.
+    visible_rect: Option<WorldRect>,
     /// Uniquely describes the content of this tile, in a way that can be
     /// (reasonably) efficiently hashed and compared.
     descriptor: TileDescriptor,
@@ -136,6 +139,7 @@ impl Tile {
             local_rect: LayoutRect::zero(),
             world_rect: WorldRect::zero(),
             valid_rect: WorldRect::zero(),
+            visible_rect: None,
             handle: TextureCacheHandle::invalid(),
             descriptor: TileDescriptor::new(),
             is_valid: false,
@@ -491,6 +495,17 @@ impl TileCache {
             .intersection(&device_world_rect)
             .expect("todo: handle clipped device rect");
 
+        // Expand the needed device rect vertically by a small number of tiles. This
+        // ensures that as tiles are scrolled in/out of view, they are retained for
+        // a while before being discarded.
+        // TODO(gw): On some pages it might be worth also inflating horizontally.
+        //           (is this locale specific?). It might be possible to make a good
+        //           guess based on the size of the picture rect for the tile cache.
+        let needed_device_rect = needed_device_rect.inflate(
+            0.0,
+            3.0 * TILE_SIZE_HEIGHT as f32,
+        );
+
         let p0 = needed_device_rect.origin;
         let p1 = needed_device_rect.bottom_right();
 
@@ -554,6 +569,8 @@ impl TileCache {
                     .unmap(&tile.world_rect)
                     .expect("bug: can't unmap world rect");
 
+                tile.visible_rect = tile.world_rect.intersection(&frame_context.screen_world_rect);
+
                 self.tiles.push(tile);
             }
         }
@@ -610,7 +627,6 @@ impl TileCache {
         resource_cache: &ResourceCache,
         opacity_binding_store: &OpacityBindingStorage,
         image_instances: &ImageInstanceStorage,
-        screen_world_rect: &WorldRect,
     ) {
         if !self.needs_update {
             return;
@@ -766,10 +782,13 @@ impl TileCache {
                         );
 
                         if let Some(clip_world_rect) = self.map_local_to_world.map(&local_rect) {
-                            world_clip_rect = match world_clip_rect.intersection(&clip_world_rect) {
-                                Some(rect) => rect,
-                                None => return,
-                            };
+                            // Even if this ends up getting clipped out by the current clip
+                            // stack, we want to ensure the primitive gets added to the tiles
+                            // below, to ensure invalidation isn't tripped up by the wrong
+                            // number of primitives that affect this tile.
+                            world_clip_rect = world_clip_rect
+                                .intersection(&clip_world_rect)
+                                .unwrap_or(WorldRect::zero());
                         }
 
                         false
@@ -819,14 +838,31 @@ impl TileCache {
                 let index = (y * self.tile_count.width + x) as usize;
                 let tile = &mut self.tiles[index];
 
+                // TODO(gw): For now, we need to always build the dependencies each
+                //           frame, so can't early exit here. In future, we should
+                //           support retaining the tile descriptor from when the
+                //           tile goes off-screen, which will mean we can then
+                //           compare against that next time it becomes visible.
+                let visible_rect = match tile.visible_rect {
+                    Some(visible_rect) => visible_rect,
+                    None => WorldRect::zero(),
+                };
+
                 // Work out the needed rect for the primitive on this tile.
                 // TODO(gw): We should be able to remove this for any tile that is not
                 //           a partially clipped tile, which would be a significant
                 //           optimization for the common case (non-clipped tiles).
-                let needed_rect = match world_clip_rect.intersection(&tile.world_rect).and_then(|r| r.intersection(screen_world_rect)) {
-                    Some(rect) => rect.translate(&-tile.world_rect.origin.to_vector()),
-                    None => continue,
-                };
+
+                // Get the required tile-local rect that this primitive occupies.
+                // Ensure that even if it's currently clipped out of this tile,
+                // we still insert a rect of zero size, so that the tile descriptor's
+                // needed rects array matches.
+                let needed_rect = world_clip_rect
+                    .intersection(&visible_rect)
+                    .map(|rect| {
+                        rect.translate(&-tile.world_rect.origin.to_vector())
+                    })
+                    .unwrap_or(WorldRect::zero());
 
                 tile.descriptor.needed_rects.push(needed_rect);
 
@@ -930,10 +966,7 @@ impl TileCache {
                 tile.is_valid = false;
             }
 
-            let visible_rect = match tile
-                .world_rect
-                .intersection(&frame_context.screen_world_rect)
-            {
+            let visible_rect = match tile.visible_rect {
                 Some(rect) => rect,
                 None => continue,
             };
@@ -2010,7 +2043,6 @@ impl PicturePrimitive {
                 resource_cache,
                 opacity_binding_store,
                 image_instances,
-                &frame_context.screen_world_rect,
             );
         }
     }