Don't change the overlay surface size

Author: Emmanuel Garcia

shell/platform/darwin/ios/framework/Source/FlutterOverlayView.mm

@@ -39,6 +39,7 @@ - (instancetype)init {
   if (self) {
     self.layer.opaque = NO;
     self.userInteractionEnabled = NO;
+    self.autoresizingMask = (UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight);
   }
 
   return self;

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews.mm

@@ -26,31 +26,50 @@
     std::shared_ptr<IOSContext> ios_context) {
   if (available_layer_index_ >= layers_.size()) {
     std::shared_ptr<FlutterPlatformViewLayer> layer;
+    fml::scoped_nsobject<FlutterOverlayView> overlay_view;
+    fml::scoped_nsobject<FlutterOverlayView> overlay_view_wrapper;
 
     if (!gr_context) {
-      fml::scoped_nsobject<FlutterOverlayView> overlay_view([[FlutterOverlayView alloc] init]);
-      overlay_view.get().autoresizingMask =
-          (UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight);
+      overlay_view.reset([[FlutterOverlayView alloc] init]);
+      overlay_view_wrapper.reset([[FlutterOverlayView alloc] init]);
+
       std::unique_ptr<IOSSurface> ios_surface =
           [overlay_view.get() createSurface:std::move(ios_context)];
       std::unique_ptr<Surface> surface = ios_surface->CreateGPUSurface();
 
       layer = std::make_shared<FlutterPlatformViewLayer>(
-          std::move(overlay_view), std::move(ios_surface), std::move(surface));
+          std::move(overlay_view), std::move(overlay_view_wrapper), std::move(ios_surface),
+          std::move(surface));
     } else {
       CGFloat screenScale = [UIScreen mainScreen].scale;
-      fml::scoped_nsobject<FlutterOverlayView> overlay_view(
-          [[FlutterOverlayView alloc] initWithContentsScale:screenScale]);
-      overlay_view.get().autoresizingMask =
-          (UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight);
+      overlay_view.reset([[FlutterOverlayView alloc] initWithContentsScale:screenScale]);
+      overlay_view_wrapper.reset([[FlutterOverlayView alloc] initWithContentsScale:screenScale]);
+
       std::unique_ptr<IOSSurface> ios_surface =
           [overlay_view.get() createSurface:std::move(ios_context)];
       std::unique_ptr<Surface> surface = ios_surface->CreateGPUSurface(gr_context);
 
       layer = std::make_shared<FlutterPlatformViewLayer>(
-          std::move(overlay_view), std::move(ios_surface), std::move(surface));
+          std::move(overlay_view), std::move(overlay_view_wrapper), std::move(ios_surface),
+          std::move(surface));
       layer->gr_context = gr_context;
     }
+    // The overlay view wrapper masks the overlay view.
+    // This is required to keep the backing surface size unchanged between frames.
+    //
+    // Otherwise, changing the size of the overlay would require a new surface,
+    // which can be very expensive.
+    //
+    // This is the case of an animation in which the overlay size is changing in every frame.
+    //
+    // +------------------------+
+    // |   overlay_view         |
+    // |    +--------------+    |              +--------------+
+    // |    |    wrapper   |    |  == mask =>  | overlay_view |
+    // |    +--------------+    |              +--------------+
+    // +------------------------+
+    overlay_view_wrapper.get().clipsToBounds = YES;
+    [overlay_view_wrapper.get() addSubview:overlay_view];
     layers_.push_back(layer);
   }
   auto layer = layers_[available_layer_index_];
@@ -424,7 +443,6 @@
     [sub_view removeFromSuperview];
   }
   views_.clear();
-  overlays_.clear();
   composition_order_.clear();
   active_composition_order_.clear();
   picture_recorders_.clear();
@@ -500,6 +518,10 @@
         // Get the intersection rect between the current rect
         // and the platform view rect.
         joined_rect.intersect(platform_view_rect);
+        // Subpixels in the platform may not align with the canvas subpixels.
+        // To workaround it, round the rect values.
+        joined_rect.setLTRB(std::round(joined_rect.left()), std::round(joined_rect.top()),
+                            std::round(joined_rect.right()), std::round(joined_rect.bottom()));
         // Clip the background canvas, so it doesn't contain any of the pixels drawn
         // on the overlay layer.
         background_canvas->clipRect(joined_rect, SkClipOp::kDifference);
@@ -545,10 +567,10 @@
       platform_view_root.layer.zPosition = zIndex++;
     }
     for (const std::shared_ptr<FlutterPlatformViewLayer>& layer : layers) {
-      if ([layer->overlay_view superview] != flutter_view) {
-        [flutter_view addSubview:layer->overlay_view];
+      if ([layer->overlay_view_wrapper superview] != flutter_view) {
+        [flutter_view addSubview:layer->overlay_view_wrapper];
       } else {
-        layer->overlay_view.get().layer.zPosition = zIndex++;
+        layer->overlay_view_wrapper.get().layer.zPosition = zIndex++;
       }
     }
     active_composition_order_.push_back(platform_view_id);
@@ -563,19 +585,23 @@
     int64_t view_id,
     int64_t overlay_id) {
   auto layer = layer_pool_->GetLayer(gr_context, ios_context);
+
+  auto overlay_view_wrapper = layer->overlay_view_wrapper.get();
   auto screenScale = [UIScreen mainScreen].scale;
-  // Set the size of the overlay UIView.
-  layer->overlay_view.get().frame = CGRectMake(rect.x() / screenScale,      //
-                                               rect.y() / screenScale,      //
-                                               rect.width() / screenScale,  //
-                                               rect.height() / screenScale  //
-  );
-  // Set a unique view identifier, so the overlay can be identified in unit tests.
-  layer->overlay_view.get().accessibilityIdentifier =
+  // Set the size of the overlay view wrapper.
+  // This wrapper view masks the overlay view.
+  overlay_view_wrapper.frame = CGRectMake(rect.x() / screenScale, rect.y() / screenScale,
+                                          rect.width() / screenScale, rect.height() / screenScale);
+  // Set a unique view identifier, so the overlay wrapper can be identified in unit tests.
+  overlay_view_wrapper.accessibilityIdentifier =
       [NSString stringWithFormat:@"platform_view[%lld].overlay[%lld]", view_id, overlay_id];
 
-  std::unique_ptr<SurfaceFrame> frame =
-      layer->surface->AcquireFrame(SkISize::Make(rect.width(), rect.height()));
+  auto overlay_view = layer->overlay_view.get();
+  // Set the size of the overlay view.
+  // This size is equal to the the device screen size.
+  overlay_view.frame = flutter_view_.get().bounds;
+
+  std::unique_ptr<SurfaceFrame> frame = layer->surface->AcquireFrame(frame_size_);
   // If frame is null, AcquireFrame already printed out an error message.
   if (!frame) {
     return layer;
@@ -594,11 +620,10 @@
 void FlutterPlatformViewsController::RemoveUnusedLayers() {
   auto layers = layer_pool_->GetUnusedLayers();
   for (const std::shared_ptr<FlutterPlatformViewLayer>& layer : layers) {
-    [layer->overlay_view removeFromSuperview];
+    [layer->overlay_view_wrapper removeFromSuperview];
   }
 
   std::unordered_set<int64_t> composition_order_set;
-
   for (int64_t view_id : composition_order_) {
     composition_order_set.insert(view_id);
   }
@@ -622,10 +647,6 @@
     views_.erase(viewId);
     touch_interceptors_.erase(viewId);
     root_views_.erase(viewId);
-    if (overlays_.find(viewId) != overlays_.end()) {
-      [overlays_[viewId]->overlay_view.get() removeFromSuperview];
-    }
-    overlays_.erase(viewId);
     current_composition_params_.erase(viewId);
     clip_count_.erase(viewId);
     views_to_recomposite_.erase(viewId);

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h

@@ -60,12 +60,14 @@ class IOSSurface;
 
 struct FlutterPlatformViewLayer {
   FlutterPlatformViewLayer(fml::scoped_nsobject<UIView> overlay_view,
+                           fml::scoped_nsobject<UIView> overlay_view_wrapper,
                            std::unique_ptr<IOSSurface> ios_surface,
                            std::unique_ptr<Surface> surface);
 
   ~FlutterPlatformViewLayer();
 
   fml::scoped_nsobject<UIView> overlay_view;
+  fml::scoped_nsobject<UIView> overlay_view_wrapper;
   std::unique_ptr<IOSSurface> ios_surface;
   std::unique_ptr<Surface> surface;
 
@@ -198,7 +200,6 @@ class FlutterPlatformViewsController {
   // Mapping a platform view ID to the count of the clipping operations that were applied to the
   // platform view last time it was composited.
   std::map<int64_t, int64_t> clip_count_;
-  std::map<int64_t, std::unique_ptr<FlutterPlatformViewLayer>> overlays_;
   SkISize frame_size_;
 
   // This is the number of frames the task runners will stay

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.mm

@@ -11,10 +11,13 @@
 
 namespace flutter {
 
-FlutterPlatformViewLayer::FlutterPlatformViewLayer(fml::scoped_nsobject<UIView> overlay_view,
-                                                   std::unique_ptr<IOSSurface> ios_surface,
-                                                   std::unique_ptr<Surface> surface)
+FlutterPlatformViewLayer::FlutterPlatformViewLayer(
+    fml::scoped_nsobject<UIView> overlay_view,
+    fml::scoped_nsobject<UIView> overlay_view_wrapper,
+    std::unique_ptr<IOSSurface> ios_surface,
+    std::unique_ptr<Surface> surface)
     : overlay_view(std::move(overlay_view)),
+      overlay_view_wrapper(std::move(overlay_view_wrapper)),
       ios_surface(std::move(ios_surface)),
       surface(std::move(surface)){};