Bug 1642629 - Recycle a couple of vectors in PictureUpdateState. r=gw

Differential Revision: https://phabricator.services.mozilla.com/D79857

gfx/wr/webrender/src/frame_builder.rs

@@ -15,7 +15,7 @@ use crate::gpu_types::TransformData;
 use crate::internal_types::{FastHashMap, PlaneSplitter, SavedTargetIndex};
 use crate::picture::{PictureUpdateState, SurfaceInfo, ROOT_SURFACE_INDEX, SurfaceIndex, RecordedDirtyRegion};
 use crate::picture::{RetainedTiles, TileCacheInstance, DirtyRegion, SurfaceRenderTasks, SubpixelMode};
-use crate::picture::{BackdropKind, TileCacheLogger};
+use crate::picture::{BackdropKind, TileCacheLogger, PictureUpdateStateBuffers};
 use crate::prim_store::{SpaceMapper, PictureIndex, PrimitiveDebugId, PrimitiveScratchBuffer};
 use crate::prim_store::{DeferredResolve, PrimitiveVisibilityMask};
 use crate::profiler::{FrameProfileCounters, TextureCacheProfileCounters, ResourceProfileCounters};
@@ -121,10 +121,13 @@ pub struct FrameBuilder {
     /// that can optionally be consumed by this frame builder.
     pending_retained_tiles: RetainedTiles,
     pub globals: FrameGlobalResources,
-    // A vector that is cleared and re-built each frame. We keep it
-    // here to avoid reallocations.
+
+    // A few data structures that are cleared and re-built each frame.
+    // We keep them here to avoid reallocations.
     #[cfg_attr(any(feature = "capture", feature = "replay"), serde(skip))]
     surfaces: Vec<SurfaceInfo>,
+    #[cfg_attr(any(feature = "capture", feature = "replay"), serde(skip))]
+    picture_update_buffers: PictureUpdateStateBuffers,
 }
 
 pub struct FrameVisibilityContext<'a> {
@@ -242,6 +245,7 @@ impl FrameBuilder {
             pending_retained_tiles: RetainedTiles::new(),
             globals: FrameGlobalResources::empty(),
             surfaces: Vec::new(),
+            picture_update_buffers: PictureUpdateStateBuffers::default(),
         }
     }
 
@@ -262,6 +266,7 @@ impl FrameBuilder {
 
     pub fn memory_pressure(&mut self) {
         self.surfaces = Vec::new();
+        self.picture_update_buffers.memory_pressure();
     }
 
     /// Compute the contribution (bounding rectangles, and resources) of layers and their
@@ -350,6 +355,7 @@ impl FrameBuilder {
         // which surfaces have valid cached surfaces that don't need to
         // be rendered this frame.
         PictureUpdateState::update_all(
+            &mut self.picture_update_buffers,
             &mut self.surfaces,
             scene.root_pic_index,
             &mut scene.prim_store.pictures,

gfx/wr/webrender/src/picture.rs

@@ -3817,6 +3817,27 @@ impl TileCacheInstance {
     }
 }
 
+pub struct PictureUpdateStateBuffers {
+    surface_stack: Vec<SurfaceIndex>,
+    picture_stack: Vec<PictureInfo>,
+}
+
+impl Default for PictureUpdateStateBuffers {
+    fn default() -> Self {
+        PictureUpdateStateBuffers {
+            surface_stack: Vec::new(),
+            picture_stack: Vec::new(),
+        }
+    }
+}
+
+impl PictureUpdateStateBuffers {
+    pub fn memory_pressure(&mut self) {
+        self.surface_stack = Vec::new();
+        self.picture_stack = Vec::new();
+    }
+}
+
 /// Maintains a stack of picture and surface information, that
 /// is used during the initial picture traversal.
 pub struct PictureUpdateState<'a> {
@@ -3829,6 +3850,7 @@ pub struct PictureUpdateState<'a> {
 
 impl<'a> PictureUpdateState<'a> {
     pub fn update_all(
+        buffers: &mut PictureUpdateStateBuffers,
         surfaces: &'a mut Vec<SurfaceInfo>,
         pic_index: PictureIndex,
         picture_primitives: &mut [PicturePrimitive],
@@ -3843,12 +3865,14 @@ impl<'a> PictureUpdateState<'a> {
 
         let mut state = PictureUpdateState {
             surfaces,
-            surface_stack: vec![SurfaceIndex(0)],
-            picture_stack: Vec::new(),
+            surface_stack: buffers.surface_stack.take().cleared(),
+            picture_stack: buffers.picture_stack.take().cleared(),
             are_raster_roots_assigned: true,
             composite_state,
         };
 
+        state.surface_stack.push(SurfaceIndex(0));
+
         state.update(
             pic_index,
             picture_primitives,
@@ -3865,6 +3889,9 @@ impl<'a> PictureUpdateState<'a> {
                 ROOT_SPATIAL_NODE_INDEX,
             );
         }
+
+        buffers.surface_stack = state.surface_stack.take();
+        buffers.picture_stack = state.picture_stack.take();
     }
 
     /// Return the current surface

gfx/wr/webrender/src/util.rs

@@ -66,6 +66,9 @@ pub trait VecHelper<T> {
     /// Equivalent to `mem::replace(&mut vec, Vec::new())`
     fn take(&mut self) -> Self;
 
+    /// Call clear and return self (useful for chaining with calls that move the vector).
+    fn cleared(self) -> Self;
+
     /// Functionally equivalent to `mem::replace(&mut vec, Vec::new())` but tries
     /// to keep the allocation in the caller if it is empty or replace it with a
     /// pre-allocated vector.
@@ -99,6 +102,12 @@ impl<T> VecHelper<T> for Vec<T> {
         replace(self, Vec::new())
     }
 
+    fn cleared(mut self) -> Self {
+        self.clear();
+
+        self
+    }
+
     fn take_and_preallocate(&mut self) -> Self {
         let len = self.len();
         if len == 0 {