src/lib/ui/input/gesture.h

// Copyright 2018 The Fuchsia 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_LIB_UI_INPUT_GESTURE_H_
#define SRC_LIB_UI_INPUT_GESTURE_H_

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

#include <map>

#include "src/ui/lib/glm_workaround/glm_workaround.h"

namespace input {

// Tracks an individual gesture, defined as an ensemble of time-overlapping touch points in an
// interaction with a particular input device. Changes are transformed into a |Gesture::Delta| with
// aggregate 2D relative translation, rotation, and scale as suggested by touch point updates.

//
// This class does not handle tapping or threshold-based classification of gestures, which can be
// handled by the caller. |GestureDetector| is an implementation of such a higher level facility.
class Gesture {
 public:
  using PointerId = decltype(fuchsia::ui::input::PointerEvent::pointer_id);

  // Represents a change from the previous |UpdatePointer| state.
  struct Delta {
    Delta& operator+=(const Delta& other);
    bool operator==(const Delta& other) const;

    // Delta translation is expressed in the coordinate system determined by the input source. For
    // most use cases, this is the view space, which is x-right y-down and scaled according to view
    // properties.
    glm::vec2 translation;
    // Delta rotation is expressed in radians about the right-hand z of the coordinate system of the
    // input source. For most use cases, this is clockwise.
    float rotation = 0;
    float scale = 1;
  };

  bool has_pointers() const { return !pointers_.empty(); }
  size_t pointer_count() const { return pointers_.size(); }
  const glm::vec2& centroid() const { return centroid_; }

  void AddPointer(PointerId pointer_id, const glm::vec2& position);
  Delta UpdatePointer(PointerId pointer_id, const glm::vec2& position);
  void RemovePointer(PointerId pointer_id);

 private:
  struct PointerInfo {
    glm::vec2 absolute;  // input coordinates
    glm::vec2 relative;  // centroid coordinates
    float distance;      // centroid-relative
  };

  void UpdateCentroid();
  void UpdateRelative();

  glm::vec2 centroid_;
  std::map<PointerId, PointerInfo> pointers_;
};

}  // namespace input

#endif  // SRC_LIB_UI_INPUT_GESTURE_H_