Bug 1924152 - Support rendering without presenting. r=gw

The goal for this initial implementation is to be able to render picture snapshots without presenting the frame, but it could be extended to supporting some picture cache slices without presenting (for example if we know that the picture is not affected by scrolling or animated properties and want to start rendering it early).

Differential Revision: https://phabricator.services.mozilla.com/D234162

Author: nical

webrender/src/frame_builder.rs

@@ -274,6 +274,7 @@ impl FrameBuilder {
     fn build_layer_screen_rects_and_cull_layers(
         &mut self,
         scene: &mut BuiltScene,
+        present: bool,
         global_screen_world_rect: WorldRect,
         resource_cache: &mut ResourceCache,
         gpu_cache: &mut GpuCache,
@@ -294,6 +295,8 @@ impl FrameBuilder {
     ) {
         profile_scope!("build_layer_screen_rects_and_cull_layers");
 
+        let render_picture_cache_slices = present;
+
         let root_spatial_node_index = spatial_tree.root_reference_frame_index();
 
         const MAX_CLIP_COORD: f32 = 1.0e9;
@@ -427,6 +430,9 @@ impl FrameBuilder {
             }
 
             for pic_index in scene.tile_cache_pictures.iter().rev() {
+                if !render_picture_cache_slices {
+                    break;
+                }
                 let pic = &mut scene.prim_store.pictures[pic_index.0];
 
                 match pic.raster_config {
@@ -583,6 +589,10 @@ impl FrameBuilder {
         frame_state.push_dirty_region(default_dirty_region);
 
         for pic_index in &scene.tile_cache_pictures {
+            if !render_picture_cache_slices {
+                break;
+            }
+
             prepare_picture(
                 *pic_index,
                 &mut scene.prim_store,
@@ -617,6 +627,7 @@ impl FrameBuilder {
     pub fn build(
         &mut self,
         scene: &mut BuiltScene,
+        present: bool,
         resource_cache: &mut ResourceCache,
         gpu_cache: &mut GpuCache,
         rg_builder: &mut RenderTaskGraphBuilder,
@@ -682,6 +693,7 @@ impl FrameBuilder {
 
         self.build_layer_screen_rects_and_cull_layers(
             scene,
+            present,
             screen_world_rect,
             resource_cache,
             gpu_cache,
@@ -772,33 +784,35 @@ impl FrameBuilder {
                 passes.push(pass);
             }
 
-            let mut ctx = RenderTargetContext {
-                global_device_pixel_scale,
-                clip_store: &scene.clip_store,
-                prim_store: &scene.prim_store,
-                resource_cache,
-                use_dual_source_blending,
-                use_advanced_blending: scene.config.gpu_supports_advanced_blend,
-                break_advanced_blend_batches: !scene.config.advanced_blend_is_coherent,
-                batch_lookback_count: scene.config.batch_lookback_count,
-                spatial_tree,
-                data_stores,
-                surfaces: &scene.surfaces,
-                scratch: &mut scratch.primitive,
-                screen_world_rect,
-                globals: &self.globals,
-                tile_caches,
-                root_spatial_node_index: spatial_tree.root_reference_frame_index(),
-                frame_memory: &mut frame_memory,
-            };
+            if present {
+                let mut ctx = RenderTargetContext {
+                    global_device_pixel_scale,
+                    clip_store: &scene.clip_store,
+                    prim_store: &scene.prim_store,
+                    resource_cache,
+                    use_dual_source_blending,
+                    use_advanced_blending: scene.config.gpu_supports_advanced_blend,
+                    break_advanced_blend_batches: !scene.config.advanced_blend_is_coherent,
+                    batch_lookback_count: scene.config.batch_lookback_count,
+                    spatial_tree,
+                    data_stores,
+                    surfaces: &scene.surfaces,
+                    scratch: &mut scratch.primitive,
+                    screen_world_rect,
+                    globals: &self.globals,
+                    tile_caches,
+                    root_spatial_node_index: spatial_tree.root_reference_frame_index(),
+                    frame_memory: &mut frame_memory,
+                };
 
-            self.build_composite_pass(
-                scene,
-                &mut ctx,
-                gpu_cache,
-                &mut deferred_resolves,
-                &mut composite_state,
-            );
+                self.build_composite_pass(
+                    scene,
+                    &mut ctx,
+                    gpu_cache,
+                    &mut deferred_resolves,
+                    &mut composite_state,
+                );
+            }
         }
 
         profile.end_time(profiler::FRAME_BATCHING_TIME);
@@ -822,6 +836,7 @@ impl FrameBuilder {
                 device_origin,
                 scene.output_rect.size(),
             ),
+            present,
             passes,
             transform_palette: transform_palette.finish(),
             render_tasks,
@@ -1274,6 +1289,7 @@ pub fn build_render_pass(
 pub struct Frame {
     /// The rectangle to show the frame in, on screen.
     pub device_rect: DeviceIntRect,
+    pub present: bool,
     pub passes: FrameVec<RenderPass>,
 
     pub transform_palette: FrameVec<TransformData>,

webrender/src/render_api.rs

@@ -122,6 +122,9 @@ pub enum GenerateFrame {
         /// An id that allows tracking the frame transaction through the various
         /// frame stages. Specified by the caller of generate_frame().
         id: u64,
+        /// If false, (a subset of) the frame will be rendered, but nothing will
+        /// be presented on the window.
+        present: bool,
     },
     /// Don't generate a frame even if something has changed.
     No,
@@ -136,10 +139,19 @@ impl GenerateFrame {
         }
     }
 
+    /// If false, a frame may be (partially) generated but it will not be
+    /// presented to the window.
+    pub fn present(&self) -> bool {
+        match self {
+            GenerateFrame::Yes { present, .. } => *present,
+            GenerateFrame::No => false,
+        }
+    }
+
     /// Return the frame ID, if a frame is generated.
     pub fn id(&self) -> Option<u64> {
         match self {
-            GenerateFrame::Yes { id } => Some(*id),
+            GenerateFrame::Yes { id, .. } => Some(*id),
             GenerateFrame::No => None,
         }
     }
@@ -363,8 +375,8 @@ impl Transaction {
     /// as to when happened.
     ///
     /// [notifier]: trait.RenderNotifier.html#tymethod.new_frame_ready
-    pub fn generate_frame(&mut self, id: u64, reasons: RenderReasons) {
-        self.generate_frame = GenerateFrame::Yes{ id };
+    pub fn generate_frame(&mut self, id: u64, present: bool, reasons: RenderReasons) {
+        self.generate_frame = GenerateFrame::Yes{ id, present };
         self.render_reasons |= reasons;
     }
 

webrender/src/render_backend.rs

@@ -515,6 +515,7 @@ impl Document {
         debug_flags: DebugFlags,
         tile_caches: &mut FastHashMap<SliceId, Box<TileCacheInstance>>,
         frame_stats: Option<FullFrameStats>,
+        present: bool,
         render_reasons: RenderReasons,
         frame_memory: FrameMemory,
     ) -> RenderedDocument {
@@ -529,6 +530,7 @@ impl Document {
         let frame = {
             let frame = self.frame_builder.build(
                 &mut self.scene,
+                present,
                 resource_cache,
                 gpu_cache,
                 &mut self.rg_builder,
@@ -959,6 +961,7 @@ impl RenderBackend {
                 txn.frame_ops.take(),
                 txn.notifications.take(),
                 txn.render_frame,
+                txn.present,
                 RenderReasons::SCENE,
                 None,
                 txn.invalidate_rendered_frame,
@@ -1309,6 +1312,7 @@ impl RenderBackend {
                 txn.frame_ops.take(),
                 txn.notifications.take(),
                 txn.generate_frame.as_bool(),
+                txn.generate_frame.present(),
                 txn.render_reasons,
                 txn.generate_frame.id(),
                 txn.invalidate_rendered_frame,
@@ -1348,6 +1352,7 @@ impl RenderBackend {
                     Vec::default(),
                     Vec::default(),
                     false,
+                    false,
                     RenderReasons::empty(),
                     None,
                     false,
@@ -1370,6 +1375,7 @@ impl RenderBackend {
         mut frame_ops: Vec<FrameMsg>,
         mut notifications: Vec<NotificationRequest>,
         mut render_frame: bool,
+        present: bool,
         render_reasons: RenderReasons,
         generated_frame_id: Option<u64>,
         invalidate_rendered_frame: bool,
@@ -1469,6 +1475,7 @@ impl RenderBackend {
                     self.debug_flags,
                     &mut self.tile_caches,
                     frame_stats,
+                    present,
                     render_reasons,
                     frame_memory,
                 );
@@ -1675,6 +1682,7 @@ impl RenderBackend {
                     self.debug_flags,
                     &mut self.tile_caches,
                     None,
+                    true,
                     RenderReasons::empty(),
                     frame_memory,
                 );

webrender/src/renderer/mod.rs

@@ -1444,7 +1444,7 @@ impl Renderer {
         &mut self,
         doc_id: DocumentId,
         active_doc: &mut RenderedDocument,
-        device_size: Option<DeviceIntSize>,
+        mut device_size: Option<DeviceIntSize>,
         buffer_age: usize,
     ) -> Result<RenderResults, Vec<RendererError>> {
         profile_scope!("render");
@@ -1512,6 +1512,12 @@ impl Renderer {
             frame_id
         };
 
+        if !active_doc.frame.present {
+            // Setting device_size to None is what ensures compositing/presenting
+            // the frame is skipped in the rest of this module.
+            device_size = None;
+        }
+
         if let Some(device_size) = device_size {
             // Inform the client that we are starting a composition transaction if native
             // compositing is enabled. This needs to be done early in the frame, so that
@@ -3494,7 +3500,7 @@ impl Renderer {
             // to the swapchain tile list
             match tile.kind {
                 TileKind::Opaque | TileKind::Alpha => {
-                    // Store (index of tile, index of layer) so we can segment them below 
+                    // Store (index of tile, index of layer) so we can segment them below
                     occlusion.add(&rect, is_opaque, idx); // (idx, input_layers.len() - 1));
                 }
                 TileKind::Clear => {

webrender/src/scene_builder_thread.rs

@@ -69,6 +69,7 @@ pub struct BuiltTransaction {
     pub interner_updates: Option<InternerUpdates>,
     pub spatial_tree_updates: Option<SpatialTreeUpdates>,
     pub render_frame: bool,
+    pub present: bool,
     pub invalidate_rendered_frame: bool,
     pub profile: TransactionProfile,
     pub frame_stats: FullFrameStats,
@@ -477,6 +478,7 @@ impl SceneBuilderThread {
             let txns = vec![Box::new(BuiltTransaction {
                 document_id: item.document_id,
                 render_frame: item.build_frame,
+                present: true,
                 invalidate_rendered_frame: false,
                 built_scene,
                 view: item.view,
@@ -664,6 +666,7 @@ impl SceneBuilderThread {
         Box::new(BuiltTransaction {
             document_id: txn.document_id,
             render_frame: txn.generate_frame.as_bool(),
+            present: txn.generate_frame.present(),
             invalidate_rendered_frame: txn.invalidate_rendered_frame,
             built_scene,
             view: doc.view,

wrench/src/rawtest.rs

@@ -97,7 +97,7 @@ impl<'a> RawtestHarness<'a> {
         );
         epoch.0 += 1;
 
-        txn.generate_frame(0, RenderReasons::TESTING);
+        txn.generate_frame(0, true, RenderReasons::TESTING);
         self.wrench.api.send_transaction(self.wrench.document_id, txn);
     }
 
@@ -1237,7 +1237,7 @@ impl<'a> RawtestHarness<'a> {
             Epoch(0),
             builder.end(),
         );
-        txn.generate_frame(0, RenderReasons::TESTING);
+        txn.generate_frame(0, true, RenderReasons::TESTING);
 
         self.wrench.api.send_transaction(self.wrench.document_id, txn);
 
@@ -1270,7 +1270,7 @@ impl<'a> RawtestHarness<'a> {
         // 6. rebuild the scene and compare again
         let mut txn = Transaction::new();
         txn.set_root_pipeline(captured.root_pipeline_id.unwrap());
-        txn.generate_frame(0, RenderReasons::TESTING);
+        txn.generate_frame(0, true, RenderReasons::TESTING);
         self.wrench.api.send_transaction(captured.document_id, txn);
         let pixels2 = self.render_and_get_pixels(window_rect);
         self.compare_pixels(pixels0, pixels2, window_rect.size());
@@ -1300,7 +1300,7 @@ impl<'a> RawtestHarness<'a> {
             Epoch(1),
             builder.end(),
         );
-        txn.generate_frame(0, RenderReasons::TESTING);
+        txn.generate_frame(0, true, RenderReasons::TESTING);
         self.wrench.api.send_transaction(doc_id, txn);
 
         // Ensure we get a notification from rendering the above, even though

wrench/src/wrench.rs

@@ -567,7 +567,7 @@ impl Wrench {
             txn.set_scroll_offsets(*id, offsets.clone());
         }
 
-        txn.generate_frame(0, RenderReasons::TESTING);
+        txn.generate_frame(0, true, RenderReasons::TESTING);
         self.api.send_transaction(self.document_id, txn);
     }
 
@@ -588,7 +588,7 @@ impl Wrench {
     pub fn refresh(&mut self) {
         self.begin_frame();
         let mut txn = Transaction::new();
-        txn.generate_frame(0, RenderReasons::TESTING);
+        txn.generate_frame(0, true, RenderReasons::TESTING);
         self.api.send_transaction(self.document_id, txn);
     }