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// Copyright 2015 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef COBALT_CSSOM_TIMING_FUNCTION_H_
#define COBALT_CSSOM_TIMING_FUNCTION_H_
#include <string>
#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/memory/ref_counted.h"
#include "base/stringprintf.h"
#include "cobalt/base/polymorphic_equatable.h"
#include "cobalt/cssom/keyword_names.h"
#include "cobalt/math/cubic_bezier.h"
namespace cobalt {
namespace cssom {
// The TimingFunction class represents a timing function CSS property value
// that transforms time (from 0 to 1) into animation progress (where 0
// means the beginning and 1 means the end). Since CSS provides keywords
// for common timing function parameters, these specific timing functions also
// have getter methods provided here.
// More information on CSS timing functions can be found in the specification:
// https://www.w3.org/TR/css3-transitions/#transition-timing-function-property
class TimingFunction : public base::RefCountedThreadSafe<TimingFunction>,
public base::PolymorphicEquatable {
public:
// Transforms a time value (x) into an animation progress value (the return
// value).
virtual float Evaluate(float x) const = 0;
// Functions to retreive specific timing functions that are named by CSS
// keywords.
static const scoped_refptr<TimingFunction>& GetEase();
static const scoped_refptr<TimingFunction>& GetEaseIn();
static const scoped_refptr<TimingFunction>& GetEaseInOut();
static const scoped_refptr<TimingFunction>& GetEaseOut();
static const scoped_refptr<TimingFunction>& GetLinear();
static const scoped_refptr<TimingFunction>& GetStepEnd();
static const scoped_refptr<TimingFunction>& GetStepStart();
virtual std::string ToString() = 0;
protected:
virtual ~TimingFunction() {}
friend class base::RefCountedThreadSafe<TimingFunction>;
};
// A cubic bezier timing function is parameterized by two 2D control points, one
// at position (0, 0) and the other at position (1, 1).
// Note that this is not a 1D bezier curve, rather it is the function defined by
// drawing a 2D bezier curve to act as the graph of a 1D function. The only
// reason this function maps each x value to a *unique* y value is because of
// restrictions on the input control points. The defined function is NOT a
// polynomial (it contains square-root and cube-root terms).
class CubicBezierTimingFunction : public TimingFunction {
public:
CubicBezierTimingFunction(float p1_x, float p1_y, float p2_x, float p2_y)
: cubic_bezier_(p1_x, p1_y, p2_x, p2_y) {}
float Evaluate(float x) const override;
std::string ToString() override;
bool operator==(const CubicBezierTimingFunction& other) const {
return cubic_bezier_ == other.cubic_bezier_;
}
DEFINE_POLYMORPHIC_EQUATABLE_TYPE(CubicBezierTimingFunction);
protected:
~CubicBezierTimingFunction() override {}
private:
math::CubicBezier cubic_bezier_;
};
// A stepping timing function is a piecewise constant function that progress
// towards the result in discrete steps.
class SteppingTimingFunction : public TimingFunction {
public:
// When should the step in progress occur, at the starts of the step intervals
// or the ends of the step intervals.
enum ValueChangeLocation {
kStart,
kEnd,
};
SteppingTimingFunction(int number_of_steps,
ValueChangeLocation value_change_location)
: number_of_steps_(number_of_steps),
value_change_location_(value_change_location) {
DCHECK_LT(0, number_of_steps_);
}
float Evaluate(float x) const override;
std::string ToString() override;
bool operator==(const SteppingTimingFunction& other) const {
return number_of_steps_ == other.number_of_steps_ &&
value_change_location_ == other.value_change_location_;
}
DEFINE_POLYMORPHIC_EQUATABLE_TYPE(SteppingTimingFunction);
protected:
~SteppingTimingFunction() override{};
private:
int number_of_steps_;
ValueChangeLocation value_change_location_;
};
} // namespace cssom
} // namespace cobalt
#endif // COBALT_CSSOM_TIMING_FUNCTION_H_