From 434e27bbe830a0e84f7f536f3dd073d5c3b0c83a Mon Sep 17 00:00:00 2001
From: Alejandro Alonso <alejandroalonsofernandez@gmail.com>
Date: Thu, 9 Apr 2026 16:18:04 +0200
Subject: [PATCH] :tada: Improve panning performance

---
 .../app/main/ui/workspace/viewport_wasm.cljs  |  4 +--
 frontend/src/app/render_wasm/api.cljs         | 35 +++++--------------
 render-wasm/src/render.rs                     | 12 +++++++
 render-wasm/src/render/surfaces.rs            |  9 +++++
 4 files changed, 31 insertions(+), 29 deletions(-)

diff --git a/frontend/src/app/main/ui/workspace/viewport_wasm.cljs b/frontend/src/app/main/ui/workspace/viewport_wasm.cljs
index ab06a89709..b45b7e492c 100644
--- a/frontend/src/app/main/ui/workspace/viewport_wasm.cljs
+++ b/frontend/src/app/main/ui/workspace/viewport_wasm.cljs
@@ -173,7 +173,6 @@
                                  (get base-objects parent-id)))))
 
         zoom              (d/check-num zoom 1)
-        prev-zoom         (mf/use-ref zoom)
 
         drawing-tool      (:tool drawing)
         drawing-obj       (:object drawing)
@@ -405,8 +404,7 @@
 
     (mf/with-effect [vbox zoom]
       (when (and @canvas-init? initialized?)
-        (wasm.api/set-view-box (mf/ref-val prev-zoom) zoom vbox))
-      (mf/set-ref-val! prev-zoom zoom))
+        (wasm.api/set-view-box zoom vbox)))
 
     (mf/with-effect [background]
       (when (and @canvas-init? initialized?)
diff --git a/frontend/src/app/render_wasm/api.cljs b/frontend/src/app/render_wasm/api.cljs
index a4993f3503..c3a783040b 100644
--- a/frontend/src/app/render_wasm/api.cljs
+++ b/frontend/src/app/render_wasm/api.cljs
@@ -989,34 +989,17 @@
               (render (js/performance.now))))]
     (fns/debounce do-render DEBOUNCE_DELAY_MS)))
 
-(def render-pan
-  (letfn [(do-render-pan [ts]
-            ;; Check if context is still initialized before executing
-            ;; to prevent errors when navigating quickly
-            (when wasm/context-initialized?
-              (perf/begin-measure "render-pan")
-              (render ts)
-              (perf/end-measure "render-pan")))]
-    (fns/throttle do-render-pan THROTTLE_DELAY_MS)))
-
 (defn set-view-box
-  [prev-zoom zoom vbox]
-  (let [is-pan (mth/close? prev-zoom zoom)]
-    (perf/begin-measure "set-view-box")
-    (h/call wasm/internal-module "_set_view_start")
-    (h/call wasm/internal-module "_set_view" zoom (- (:x vbox)) (- (:y vbox)))
+  [zoom vbox]
+  (perf/begin-measure "set-view-box")
+  (h/call wasm/internal-module "_set_view_start")
+  (h/call wasm/internal-module "_set_view" zoom (- (:x vbox)) (- (:y vbox)))
+  (perf/end-measure "set-view-box")
 
-    (if is-pan
-      (do (perf/end-measure "set-view-box")
-          (perf/begin-measure "set-view-box::pan")
-          (render-pan)
-          (render-finish)
-          (perf/end-measure "set-view-box::pan"))
-      (do (perf/end-measure "set-view-box")
-          (perf/begin-measure "set-view-box::zoom")
-          (h/call wasm/internal-module "_render_from_cache" 0)
-          (render-finish)
-          (perf/end-measure "set-view-box::zoom")))))
+  (perf/begin-measure "render-from-cache")
+  (h/call wasm/internal-module "_render_from_cache" 0)
+  (render-finish)
+  (perf/end-measure "render-from-cache"))
 
 (defn update-text-rect!
   [id]
diff --git a/render-wasm/src/render.rs b/render-wasm/src/render.rs
index c66bcdf2b3..acdd436e7c 100644
--- a/render-wasm/src/render.rs
+++ b/render-wasm/src/render.rs
@@ -337,6 +337,9 @@ pub(crate) struct RenderState {
     /// Preview render mode - when true, uses simplified rendering for progressive loading
     pub preview_mode: bool,
     pub export_context: Option<(Rect, f32)>,
+    /// Cleared at the beginning of a render pass; set to true after we clear Cache the first
+    /// time we are about to blit a tile into Cache for this pass.
+    pub cache_cleared_this_render: bool,
 }
 
 pub fn get_cache_size(viewbox: Viewbox, scale: f32) -> skia::ISize {
@@ -411,6 +414,7 @@ impl RenderState {
             ignore_nested_blurs: false,
             preview_mode: false,
             export_context: None,
+            cache_cleared_this_render: false,
         })
     }
 
@@ -665,6 +669,13 @@ impl RenderState {
     }
 
     pub fn apply_render_to_final_canvas(&mut self, rect: skia::Rect) -> Result<()> {
+        // Decide *now* (at the first real cache blit) whether we need to clear Cache.
+        // This avoids clearing Cache on renders that don't actually paint tiles (e.g. hover/UI),
+        // while still preventing stale pixels from surviving across full-quality renders.
+        if !self.options.is_fast_mode() && !self.cache_cleared_this_render {
+            self.surfaces.clear_cache(self.background_color);
+            self.cache_cleared_this_render = true;
+        }
         let tile_rect = self.get_current_aligned_tile_bounds()?;
         self.surfaces.cache_current_tile_texture(
             &self.tile_viewbox,
@@ -1497,6 +1508,7 @@ impl RenderState {
         performance::begin_measure!("render");
         performance::begin_measure!("start_render_loop");
 
+        self.cache_cleared_this_render = false;
         self.reset_canvas();
         let surface_ids = SurfaceId::Strokes as u32
             | SurfaceId::Fills as u32
diff --git a/render-wasm/src/render/surfaces.rs b/render-wasm/src/render/surfaces.rs
index 2ab32d1a61..3b7d4bcbbc 100644
--- a/render-wasm/src/render/surfaces.rs
+++ b/render-wasm/src/render/surfaces.rs
@@ -533,6 +533,15 @@ impl Surfaces {
         self.clear_all_dirty();
     }
 
+    /// Clears the whole cache surface without disturbing its configured transform.
+    pub fn clear_cache(&mut self, color: skia::Color) {
+        let canvas = self.cache.canvas();
+        canvas.save();
+        canvas.reset_matrix();
+        canvas.clear(color);
+        canvas.restore();
+    }
+
     pub fn cache_current_tile_texture(
         &mut self,
         tile_viewbox: &TileViewbox,