🔧 Rebuild indices on zoom change, not pan

render-wasm/src/main.rs

@@ -251,11 +251,16 @@ pub extern "C" fn set_view_end() {
         state.render_state.options.set_fast_mode(false);
         // We can have renders in progress
         state.render_state.cancel_animation_frame();
+        // Only rebuild tile indices when zoom has changed.
+        // During pan-only operations, shapes stay in the same tiles
+        // because tile_size = 1/scale * TILE_SIZE (depends only on zoom).
+        if state.render_state.zoom_changed() {
             if state.render_state.options.is_profile_rebuild_tiles() {
                 state.rebuild_tiles();
             } else {
                 state.rebuild_tiles_shallow();
             }
+        }
     });
 }
 

render-wasm/src/render.rs

@@ -2057,6 +2057,12 @@ impl RenderState {
         self.cached_viewbox.zoom() * self.options.dpr()
     }
 
+    /// Returns true if the zoom level has changed since the last cached viewbox.
+    /// Used to optimize pan-only operations where tile indices don't need to be rebuilt.
+    pub fn zoom_changed(&self) -> bool {
+        (self.viewbox.zoom - self.cached_viewbox.zoom).abs() > f32::EPSILON
+    }
+
     pub fn mark_touched(&mut self, uuid: Uuid) {
         self.touched_ids.insert(uuid);
     }