src/embedder/mouse_delegate.h

// Copyright 2022 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef SRC_EMBEDDER_MOUSE_DELEGATE_H_
#define SRC_EMBEDDER_MOUSE_DELEGATE_H_

#include <fuchsia/ui/pointer/cpp/fidl.h>

#include <functional>
#include <optional>
#include <unordered_map>
#include <unordered_set>
#include <vector>

#include "src/embedder/engine/embedder.h"
#include "src/embedder/logging.h"

namespace embedder {

/// Channel processor for fuchsia.ui.pointer.MouseSource protocol
/// protocol. It manages the channel state, collects mouse events, and
/// converts them to generic FlutterPointerEvent types before
/// returning them to the embedder's main function, which
/// dispatches them to the flutter engine using the embedder API
class MouseDelegate {
 public:
  /// Initializes the MouseDelegate. Does NOT start watching for events.
  /// |mouse_source| - the FIDL handle for mouse input events
  MouseDelegate(fuchsia::ui::pointer::MouseSourceHandle mouse_source);

  /// This function collects Fuchsia's ui::pointer::MouseEvent's and
  /// transforms them into FlutterPointerEvent structs. It then calls
  /// the supplied callback with a vector of FlutterPointerEvent, which
  /// uses the embedder API to forward these to the flutter engine
  void WatchLoop(std::function<void(std::vector<FlutterPointerEvent>)> callback);

 private:
  /// Channel for mouse events from Scenic.
  fuchsia::ui::pointer::MouseSourcePtr mouse_source_;

  /// Receive mouse events from Scenic. Must be copyable as the FIDL protocol
  /// accepting this callback will take this by value.
  std::function<void(std::vector<fuchsia::ui::pointer::MouseEvent>)> mouse_responder_;

  /// The set of mouse devices that are currently interacting with the UI.
  /// A mouse is considered flutter::PointerData::Change::kDown if any button is
  /// pressed. This set is used to correctly set the phase in
  /// flutter::PointerData.change, with this high-level algorithm:
  ///   if !mouse_down[id] && !button then: change = kHover
  ///   if !mouse_down[id] &&  button then: change = kDown; mouse_down.add(id)
  ///   if  mouse_down[id] &&  button then: change = kMove
  ///   if  mouse_down[id] && !button then: change = kUp; mouse_down.remove(id)
  std::unordered_set</*mouse device ID*/ uint32_t> mouse_down_;

  /// For each mouse device, its device-specific information, such as mouse
  /// button priority order.
  std::unordered_map</*mouse device ID*/ uint32_t, fuchsia::ui::pointer::MouseDeviceInfo>
      mouse_device_info_;

  /// The fuchsia.ui.pointer.MouseSource protocol issues channel-global view
  /// parameters on connection and on change. Events must apply these view
  /// parameters to correctly map to logical view coordinates. The "nullopt"
  /// state represents the absence of view parameters, early in the protocol
  /// lifecycle.
  std::optional<fuchsia::ui::pointer::ViewParameters> mouse_view_parameters_;
};

}  // namespace embedder

#endif  // SRC_EMBEDDER_MOUSE_DELEGATE_H_