⚡ Present viewport before interest-area tile work

Defer the interest-ring until visible tiles are done, present via
FrameType::ViewportReady, then fill interest on later Partial frames
so large files show the viewport without waiting on off-screen work.

frontend/src/app/render_wasm/api.cljs

@@ -362,6 +362,19 @@
 (def ^:const FRAME_TYPE_NONE 0)     ;; This type should never "leak".
 (def ^:const FRAME_TYPE_PARTIAL 1)  ;; A frame needs more render calls to end.
 (def ^:const FRAME_TYPE_FULL 2)     ;; A frame was full.
+(def ^:const FRAME_TYPE_VIEWPORT_READY 3) ;; Viewport presented; interest tiles may still be pending.
+
+(defn- needs-more-render-frames?
+  "True when WASM still has progressive tile work (visible or interest ring)."
+  []
+  (or (= wasm/internal-frame-type FRAME_TYPE_PARTIAL)
+      (= wasm/internal-frame-type FRAME_TYPE_VIEWPORT_READY)))
+
+(defn- frame-presented-target?
+  "True when this frame recomposited Target (full or early viewport present)."
+  []
+  (not= wasm/internal-frame-type FRAME_TYPE_PARTIAL))
+
 (def ^:const RENDER-FLAG-SYNC-TILES 4) ;; Rebuild tile index without ending fast mode (pan/zoom pause).
 
 (defn- internal-render
@@ -371,7 +384,7 @@
    (internal-render timestamp wasm/internal-frame-type))
   ([timestamp flags]
    (set! wasm/internal-frame-type (h/call wasm/internal-module "_render" timestamp flags))
-   (when (= wasm/internal-frame-type FRAME_TYPE_PARTIAL)
+   (when (needs-more-render-frames?)
      (request-render "frame-type-partial"))))
 
 (defn- build-reload-payload
@@ -468,13 +481,13 @@
       (when (is-text-editor-wasm-enabled @st/state)
         (text-editor/text-editor-update-blink timestamp)
         ;; Only repaint the overlay when this frame recomposited Target (a full
-        ;; frame). A partial frame is flushed but not presented — Target still
-        ;; shows the last presented frame with the overlay already on it — so
-        ;; repainting the translucent selection over it stacks another layer
-        ;; every progressive frame: it darkens, then snaps back when the final
-        ;; frame presents from the clean Backbuffer (the blink at the end of a
-        ;; zoom over a selection, gh-10709).
-        (when (not= wasm/internal-frame-type FRAME_TYPE_PARTIAL)
+        ;; frame or early viewport present). A partial frame is flushed but not
+        ;; presented - Target still shows the last presented frame with the
+        ;; overlay already on it - so repainting the translucent selection over
+        ;; it stacks another layer every progressive frame: it darkens, then
+        ;; snaps back when the final frame presents from the clean Backbuffer
+        ;; (the blink at the end of a zoom over a selection, gh-10709).
+        (when (frame-presented-target?)
           (text-editor/text-editor-render-overlay))
         ;; Drain editor events. Only content/layout changes need a full shape
         ;; re-render; selection/style changes are already reflected by the
@@ -1376,14 +1389,14 @@
 
 (defn- render-text-editor-overlay-after-frame!
   "Repaint the overlay after a direct `internal-render`, but only when that
-   render recomposited Target (a full frame). A partial frame is only flushed —
-   Target keeps the last presented frame with the overlay already on it — so
-   repainting the translucent selection then stacks another layer and it visibly
-   darkens across the progressive frames before snapping back on the final
-   present (the blink at the end of a zoom over a selection, gh-10709). The
-   final full frame's own repaint keeps the overlay in place."
+   render recomposited Target (a full frame or early viewport present). A partial
+   frame is only flushed - Target keeps the last presented frame with the overlay
+   already on it - so repainting the translucent selection then stacks another
+   layer and it visibly darkens across the progressive frames before snapping
+   back on the final present (the blink at the end of a zoom over a selection,
+   gh-10709). The final full frame's own repaint keeps the overlay in place."
   []
-  (when (not= wasm/internal-frame-type FRAME_TYPE_PARTIAL)
+  (when (frame-presented-target?)
     (render-text-editor-overlay-if-active!)))
 
 (defn finalize-view-interaction!

render-wasm/src/render.rs

@@ -49,6 +49,10 @@ pub enum FrameType {
     None = 0,
     Partial = 1,
     Full = 2,
+    /// Viewport tiles are presented; interest-ring work may still be pending.
+    /// Frontend should keep requesting frames (like Partial) but may treat the
+    /// Target as freshly composited (like Full) for overlays.
+    ViewportReady = 3,
 }
 
 #[allow(dead_code)]
@@ -417,6 +421,9 @@ pub(crate) struct RenderState {
     /// are skipped. A full skip made flush_and_submit very slow (Skia ops-task
     /// ordering); doing it per shape was wasted GPU work.
     pub drop_shadows_ops_warmed: bool,
+    /// Visible tiles were already presented this pass; interest-ring fill may
+    /// still be running. Final Full should not re-present.
+    pub viewport_presented: bool,
 }
 
 pub struct InteractiveDragCrop {
@@ -601,6 +608,7 @@ impl RenderState {
             backbuffer_crop_cache: HashMap::default(),
             tile_atlas_flushed: false,
             drop_shadows_ops_warmed: false,
+            viewport_presented: false,
         })
     }
 
@@ -2195,6 +2203,7 @@ impl RenderState {
 
         // reorder by distance to the center.
         self.current_tile = None;
+        self.viewport_presented = false;
     }
 
     pub fn start_render_loop(
@@ -2366,9 +2375,14 @@ impl RenderState {
             self.render_shape_tree_partial(base_object, tree, timestamp, allow_stop)?;
 
         // `draw_atlas` needs a snapshot of the tile atlas. Partial frames are not
-        // presented (only flushed), so defer composition to the final frame and
-        // avoid re-snapshotting up to 4096² on every rAF during async tile work.
-        if !self.options.is_interactive_transform() && matches!(frame_type, FrameType::Full) {
+        // presented (only flushed), so defer composition until the viewport is
+        // ready and avoid re-snapshotting up to 4096² on every rAF during async
+        // tile work.
+        let should_compose = !self.options.is_interactive_transform()
+            && matches!(frame_type, FrameType::Full | FrameType::ViewportReady)
+            && !self.viewport_presented;
+
+        if should_compose {
             self.surfaces.draw_tile_atlas_to_backbuffer(
                 &self.viewbox,
                 &self.tile_viewbox,
@@ -2382,23 +2396,33 @@ impl RenderState {
             }
             FrameType::Partial => {
                 // Drain tile GPU work (Current / tile atlas / cache) without
-                // presenting Target and without re-snapshotting the tile atlas —
-                // composition stays deferred to Full (`01fc3c3e7d`). A Backbuffer
-                // flush alone left commands queued until present_frame's
-                // flush_and_submit, which stalled the browser on large files.
+                // presenting Target and without re-snapshotting the tile atlas.
+                // Composition stays deferred until ViewportReady/Full.
                 crate::get_gpu_state().context.flush_and_submit();
             }
-            FrameType::Full => {
-                // A full-quality frame is now complete. Rebuild the per-shape crop
-                // cache from the clean Backbuffer (no UI overlay yet) so that
-                // interactive drag backgrounds don't include the grid overlay.
+            FrameType::ViewportReady => {
+                // Visible tiles are done: present now so the user sees the
+                // viewport without waiting for interest-ring pre-render.
                 if !self.options.is_fast_mode() && !self.options.is_interactive_transform() {
                     self.rebuild_backbuffer_crop_cache(tree);
                 }
-                // present_frame: copy clean Backbuffer → Target, draw UI/debug
-                // overlays on Target only, then flush. Backbuffer stays overlay-free.
                 self.present_frame(tree);
+                self.viewport_presented = true;
                 wapi::notify_tiles_render_complete!();
+                crate::get_gpu_state().context.flush_and_submit();
+            }
+            FrameType::Full => {
+                if !self.viewport_presented {
+                    // A full-quality frame is now complete (no early viewport
+                    // present). Rebuild crop cache and present.
+                    if !self.options.is_fast_mode() && !self.options.is_interactive_transform() {
+                        self.rebuild_backbuffer_crop_cache(tree);
+                    }
+                    self.present_frame(tree);
+                    wapi::notify_tiles_render_complete!();
+                }
+                // If we already presented at ViewportReady, interest fill is
+                // done; Target already shows the viewport.
                 performance::end_measure!("render");
             }
         }
@@ -3776,8 +3800,18 @@ impl RenderState {
                         flattened: false,
                     }));
             } else {
-                // If there are no more pending tiles, stop.
-                should_stop = true;
+                // Visible tiles finished. Promote deferred interest-ring work
+                // so pan/zoom pre-render still happens, but yield first when
+                // allowed so continue_render_loop can present the viewport.
+                if self.pending_tiles.promote_deferred_interest() {
+                    if allow_stop {
+                        should_stop = true;
+                    }
+                    // Sync path (allow_stop=false): keep looping on interest
+                    // tiles in the same call without an early present.
+                } else {
+                    should_stop = true;
+                }
             }
         }
 
@@ -3795,6 +3829,12 @@ impl RenderState {
             self.cached_viewbox = self.viewbox;
         }
 
+        // Visible done with interest still queued and we yielded: present
+        // viewport now, keep Partial-like rAFs for the ring.
+        if allow_stop && !self.pending_tiles.list.is_empty() {
+            return Ok(FrameType::ViewportReady);
+        }
+
         Ok(FrameType::Full)
     }
 

render-wasm/src/tiles.rs

@@ -323,6 +323,8 @@ pub struct PendingTiles {
     pub visible_uncached: Vec<Tile>,
     pub interest_cached: Vec<Tile>,
     pub interest_uncached: Vec<Tile>,
+    /// Interest-ring tiles deferred until after the viewport has been presented.
+    deferred_interest: Vec<Tile>,
 }
 
 impl PendingTiles {
@@ -335,14 +337,16 @@ impl PendingTiles {
             visible_uncached: Vec::with_capacity(VIEWPORT_DEFAULT_CAPACITY),
             interest_cached: Vec::with_capacity(VIEWPORT_DEFAULT_CAPACITY),
             interest_uncached: Vec::with_capacity(VIEWPORT_DEFAULT_CAPACITY),
+            deferred_interest: Vec::with_capacity(VIEWPORT_DEFAULT_CAPACITY),
         }
     }
 
     pub fn update(&mut self, tile_viewbox: &TileViewbox, surfaces: &Surfaces, only_visible: bool) {
         self.list.clear();
+        self.deferred_interest.clear();
 
         // During interactive transform, skip the interest-area ring
-        // entirely — the user is dragging, every rAF is on the critical
+        // entirely: the user is dragging, every rAF is on the critical
         // path, and pre-rendering tiles outside the viewport is wasted
         // work that just gets evicted on the next pointer move. The ring
         // is repopulated naturally on gesture end / on idle rAFs.
@@ -394,10 +398,29 @@ impl PendingTiles {
             }
         }
 
-        self.list.extend(self.interest_uncached.iter());
-        self.list.extend(self.interest_cached.iter());
-        self.list.extend(self.visible_uncached.iter());
-        self.list.extend(self.visible_cached.iter());
+        // Visible tiles first. Interest-ring work is deferred so we can present
+        // as soon as the viewport is ready (see `promote_deferred_interest`).
+        // Interactive/`only_visible` already excludes the ring from `tile_rect`.
+        if only_visible {
+            self.list.extend(self.visible_uncached.iter());
+            self.list.extend(self.visible_cached.iter());
+        } else {
+            self.deferred_interest
+                .extend(self.interest_uncached.iter());
+            self.deferred_interest.extend(self.interest_cached.iter());
+            self.list.extend(self.visible_uncached.iter());
+            self.list.extend(self.visible_cached.iter());
+        }
+    }
+
+    /// Move deferred interest-ring tiles onto the pending list.
+    /// Returns true when there is interest work left to do.
+    pub fn promote_deferred_interest(&mut self) -> bool {
+        if self.deferred_interest.is_empty() {
+            return false;
+        }
+        self.list.append(&mut self.deferred_interest);
+        true
     }
 
     pub fn pop(&mut self) -> Option<Tile> {