Source code

Revision control

Other Tools

1
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
3
/* This Source Code Form is subject to the terms of the Mozilla Public
4
* License, v. 2.0. If a copy of the MPL was not distributed with this
5
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
6
7
#ifndef mozilla_layers_AxisPhysicsModel_h
8
#define mozilla_layers_AxisPhysicsModel_h
9
10
#include <sys/types.h> // for int32_t
11
#include "mozilla/TimeStamp.h" // for TimeDuration
12
13
namespace mozilla {
14
namespace layers {
15
16
/**
17
* AxisPhysicsModel encapsulates a generic 1-dimensional physically-based motion
18
* model.
19
*
20
* It performs frame-rate independent interpolation and RK4 integration for
21
* smooth animation with stable, deterministic behavior.
22
* Implementations are expected to subclass and override the Acceleration()
23
* method.
24
*/
25
class AxisPhysicsModel {
26
public:
27
AxisPhysicsModel(double aInitialPosition, double aInitialVelocity);
28
virtual ~AxisPhysicsModel();
29
30
/**
31
* Advance the physics simulation.
32
* |aDelta| is the time since the last sample.
33
*/
34
void Simulate(const TimeDuration& aDeltaTime);
35
36
/**
37
* Gets the raw velocity of this axis at this moment.
38
*/
39
double GetVelocity() const;
40
41
/**
42
* Sets the raw velocity of this axis at this moment.
43
*/
44
void SetVelocity(double aVelocity);
45
46
/**
47
* Gets the raw position of this axis at this moment.
48
*/
49
double GetPosition() const;
50
51
/**
52
* Sets the raw position of this axis at this moment.
53
*/
54
void SetPosition(double aPosition);
55
56
protected:
57
struct State {
58
State(double ap, double av) : p(ap), v(av){};
59
double p; // Position
60
double v; // Velocity
61
};
62
63
struct Derivative {
64
Derivative() : dp(0.0), dv(0.0){};
65
Derivative(double aDp, double aDv) : dp(aDp), dv(aDv){};
66
double dp; // dp / delta time = Position
67
double dv; // dv / delta time = Velocity
68
};
69
70
/**
71
* Acceleration must be overridden and return the number of
72
* axis-position-units / second that should be added or removed from the
73
* velocity.
74
*/
75
virtual double Acceleration(const State& aState) = 0;
76
77
private:
78
/**
79
* Duration of fixed delta time step (seconds)
80
*/
81
static const double kFixedTimestep;
82
83
/**
84
* 0.0 - 1.0 value indicating progress between current and next simulation
85
* sample. Normalized to units of kFixedTimestep duration.
86
*/
87
double mProgress;
88
89
/**
90
* Sample of simulation state as it existed
91
* (1.0 - mProgress) * kFixedTimestep seconds in the past.
92
*/
93
State mPrevState;
94
95
/**
96
* Sample of simulation state as it will be in mProgress * kFixedTimestep
97
* seconds in the future.
98
*/
99
State mNextState;
100
101
/**
102
* Perform RK4 (Runge-Kutta method) Integration to calculate the next
103
* simulation sample.
104
*/
105
void Integrate(double aDeltaTime);
106
107
/**
108
* Apply delta velocity and position represented by aDerivative over
109
* aDeltaTime seconds, calculate new acceleration, and return new deltas.
110
*/
111
Derivative Evaluate(const State& aInitState, double aDeltaTime,
112
const Derivative& aDerivative);
113
114
/**
115
* Helper function for performing linear interpolation (lerp) of double's
116
*/
117
static double LinearInterpolate(double aV1, double aV2, double aBlend);
118
};
119
120
} // namespace layers
121
} // namespace mozilla
122
123
#endif