src/ui/a11y/lib/magnifier/magnifier_util.h

// Copyright 2021 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_UI_A11Y_LIB_MAGNIFIER_MAGNIFIER_UTIL_H_
#define SRC_UI_A11Y_LIB_MAGNIFIER_MAGNIFIER_UTIL_H_

#include <map>

#include "src/ui/a11y/lib/gesture_manager/gesture_util_v2/util.h"

#include <glm/glm.hpp>

namespace a11y {

// Represents a change from the previous GestureContext 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;

  float scale = 1;
};

// Converts a PointF to a vec2.
glm::vec2 ToVec2(::fuchsia::math::PointF point);

// Returns the Delta for two GestureContexts.
//
// * This method expects that |current| and |previous| have the same set of
//   pointers. If not, it will return the "NOOP" Delta with a translation of (0,
//   0) and a scale of 1.
//
// * This method checks if the |previous| distance between each finger and the
//   centroid is less than or equal to |scale_min_finger_distance|. If so, the
//   returned delta will have scale of 1.0.
//
//   This enables callers to filter out accidental scale adjustments that might
//   happen when the user moves fingers while intending to pan. (With a small
//   distance between fingers, even a small absolute change in the distance can
//   cause a large scale adjustment, since the scale is multiplied by
//   |new_distance/old_distance|.)
Delta GetDelta(const a11y::gesture_util_v2::GestureContext& current,
               const a11y::gesture_util_v2::GestureContext& previous,
               float scale_min_finger_radius);

}  // namespace a11y

#endif  // SRC_UI_A11Y_LIB_MAGNIFIER_MAGNIFIER_UTIL_H_