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authorMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
committerMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
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tree10027f336435511475e392454359edea8e25895d /gfx/layers/AxisPhysicsModel.h
parent49ee0794b5d912db1f95dce6eb52d781dc210db5 (diff)
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Add m-esr52 at 52.6.0
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set sw=2 ts=8 et tw=80 : */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_layers_AxisPhysicsModel_h
+#define mozilla_layers_AxisPhysicsModel_h
+
+#include "AxisPhysicsModel.h"
+#include <sys/types.h> // for int32_t
+#include "mozilla/TimeStamp.h" // for TimeDuration
+
+namespace mozilla {
+namespace layers {
+
+
+/**
+ * AxisPhysicsModel encapsulates a generic 1-dimensional physically-based motion
+ * model.
+ *
+ * It performs frame-rate independent interpolation and RK4 integration for
+ * smooth animation with stable, deterministic behavior.
+ * Implementations are expected to subclass and override the Acceleration()
+ * method.
+ */
+class AxisPhysicsModel {
+public:
+ AxisPhysicsModel(double aInitialPosition, double aInitialVelocity);
+ ~AxisPhysicsModel();
+
+ /**
+ * Advance the physics simulation.
+ * |aDelta| is the time since the last sample.
+ */
+ void Simulate(const TimeDuration& aDeltaTime);
+
+ /**
+ * Gets the raw velocity of this axis at this moment.
+ */
+ double GetVelocity();
+
+ /**
+ * Sets the raw velocity of this axis at this moment.
+ */
+ void SetVelocity(double aVelocity);
+
+ /**
+ * Gets the raw position of this axis at this moment.
+ */
+ double GetPosition();
+
+ /**
+ * Sets the raw position of this axis at this moment.
+ */
+ void SetPosition(double aPosition);
+
+protected:
+
+ struct State
+ {
+ State(double ap, double av) : p(ap), v(av) {};
+ double p; // Position
+ double v; // Velocity
+ };
+
+ struct Derivative
+ {
+ Derivative() : dp(0.0), dv(0.0) {};
+ Derivative(double aDp, double aDv) : dp(aDp), dv(aDv) {};
+ double dp; // dp / delta time = Position
+ double dv; // dv / delta time = Velocity
+ };
+
+ /**
+ * Acceleration must be overridden and return the number of
+ * axis-position-units / second that should be added or removed from the
+ * velocity.
+ */
+ virtual double Acceleration(const State &aState) = 0;
+
+private:
+
+ /**
+ * Duration of fixed delta time step (seconds)
+ */
+ static const double kFixedTimestep;
+
+ /**
+ * 0.0 - 1.0 value indicating progress between current and next simulation
+ * sample. Normalized to units of kFixedTimestep duration.
+ */
+ double mProgress;
+
+ /**
+ * Sample of simulation state as it existed
+ * (1.0 - mProgress) * kFixedTimestep seconds in the past.
+ */
+ State mPrevState;
+
+ /**
+ * Sample of simulation state as it will be in mProgress * kFixedTimestep
+ * seconds in the future.
+ */
+ State mNextState;
+
+ /**
+ * Perform RK4 (Runge-Kutta method) Integration to calculate the next
+ * simulation sample.
+ */
+ void Integrate(double aDeltaTime);
+
+ /**
+ * Apply delta velocity and position represented by aDerivative over
+ * aDeltaTime seconds, calculate new acceleration, and return new deltas.
+ */
+ Derivative Evaluate(const State &aInitState, double aDeltaTime,
+ const Derivative &aDerivative);
+
+ /**
+ * Helper function for performing linear interpolation (lerp) of double's
+ */
+ static double LinearInterpolate(double aV1, double aV2, double aBlend);
+
+};
+
+
+} // namespace layers
+} // namespace mozilla
+
+#endif