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// Copyright 2022 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef ASH_AMBIENT_UI_JITTER_CALCULATOR_H_
#define ASH_AMBIENT_UI_JITTER_CALCULATOR_H_
#include "ash/ash_export.h"
#include "ash/public/cpp/ambient/ambient_ui_model.h"
#include "base/functional/callback.h"
#include "ui/gfx/geometry/vector2d.h"
namespace ash {
// Calculates jitter to apply to a UI with the ultimate goal of preventing
// screen burn. The methodology is:
// * Each time jitter is calculated, move by a fixed "step size" (in pixels) in
// both x and y directions. Possible incremental offsets are -step_size, 0,
// and step_size. This is decided randomly.
// * There are limits to the total amount that the jitter can displace the UI
// from its original unshifted position.
// The caller is responsible for calling Calculate() at the desired frequency.
// The recommendation is approximately every 1-2 minutes, but this is specific
// to each use case.
class ASH_EXPORT JitterCalculator {
public:
// Must return either 0 or 1.
using RandomBinaryGenerator = base::RepeatingCallback<int()>;
explicit JitterCalculator(AmbientJitterConfig config);
// Constructor exposed for testing purposes to allow injecting a custom
// random number generator.
JitterCalculator(AmbientJitterConfig config,
RandomBinaryGenerator random_binary_generator);
JitterCalculator(const JitterCalculator& other) = delete;
JitterCalculator& operator=(const JitterCalculator& other) = delete;
~JitterCalculator();
// Returns the new total translation to apply from the UI's original unshifted
// position (0, 0).
gfx::Vector2d Calculate();
const AmbientJitterConfig& config() { return config_; }
private:
void AssertCurrentTranslationWithinBounds() const;
const AmbientJitterConfig config_;
const RandomBinaryGenerator random_binary_generator_;
// Current total translation from the original unshifted position.
gfx::Vector2d current_translation_;
// The direction to translate for the x/y coordinates. `1` means positive
// translate, `-1` negative. Initial values are arbitrary as they are
// continuously updated as the jitter is calculated.
int translate_x_direction = 1;
int translate_y_direction = -1;
};
} // namespace ash
#endif // ASH_AMBIENT_UI_JITTER_CALCULATOR_H_
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