gecko/gfx/layers/ipc/Axis.h

/* -*- 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_Axis_h
#define mozilla_layers_Axis_h

#include <sys/types.h>                  // for int32_t
#include "Units.h"                      // for CSSRect, CSSPoint
#include "mozilla/TimeStamp.h"          // for TimeDuration
#include "nsTArray.h"                   // for nsTArray

namespace mozilla {
namespace layers {

const float EPSILON = 0.0001f;

class AsyncPanZoomController;

/**
 * Helper class to maintain each axis of movement (X,Y) for panning and zooming.
 * Note that everything here is specific to one axis; that is, the X axis knows
 * nothing about the Y axis and vice versa.
 */
class Axis {
public:
  Axis(AsyncPanZoomController* aAsyncPanZoomController);

  enum Overscroll {
    // Overscroll is not happening at all.
    OVERSCROLL_NONE = 0,
    // Overscroll is happening in the negative direction. This means either to
    // the left or to the top depending on the axis.
    OVERSCROLL_MINUS,
    // Overscroll is happening in the positive direction. This means either to
    // the right or to the bottom depending on the axis.
    OVERSCROLL_PLUS,
    // Overscroll is happening both ways. This only means something when the
    // page is scaled out to a smaller size than the viewport.
    OVERSCROLL_BOTH
  };

  /**
   * Notify this Axis that a new touch has been received, including a time delta
   * indicating how long it has been since the previous one. This triggers a
   * recalculation of velocity.
   */
  void UpdateWithTouchAtDevicePoint(int32_t aPos, const TimeDuration& aTimeDelta);

  /**
   * Notify this Axis that a touch has begun, i.e. the user has put their finger
   * on the screen but has not yet tried to pan.
   */
  void StartTouch(int32_t aPos);

  /**
   * Notify this Axis that a touch has ended gracefully. This may perform
   * recalculations of the axis velocity.
   */
  void EndTouch();

  /**
   * Notify this Axis that a touch has ended forcefully. Useful for stopping
   * flings when a user puts their finger down in the middle of one (i.e. to
   * stop a previous touch including its fling so that a new one can take its
   * place).
   */
  void CancelTouch();

  /**
   * Takes a requested displacement to the position of this axis, and adjusts
   * it to account for acceleration (which might increase the displacement),
   * overscroll (which might decrease the displacement; this is to prevent the
   * viewport from overscrolling the page rect), and axis locking (which might
   * prevent any displacement from happening). If overscroll ocurred, its amount
   * is written to |aOverscrollAmountOut|.
   * The adjusted displacement is returned.
   *
   * aScrollingDisabled is used to indicate that no scrolling should happen
   * in this axis. This is used to implement overflow: hidden;
   */
  float AdjustDisplacement(float aDisplacement, float& aOverscrollAmountOut,
                           bool aScrollingDisabled);

  /**
   * Gets the distance between the starting position of the touch supplied in
   * startTouch() and the current touch from the last
   * updateWithTouchAtDevicePoint().
   */
  float PanDistance();

  /**
   * Gets the distance between the starting position of the touch supplied in
   * startTouch() and the supplied position.
   */
  float PanDistance(float aPos);

  /**
   * Applies friction during a fling, or cancels the fling if the velocity is
   * too low. Returns true if the fling should continue to another frame, or
   * false if it should end. |aDelta| is the amount of time that has passed
   * since the last time friction was applied.
   */
  bool FlingApplyFrictionOrCancel(const TimeDuration& aDelta);

  /*
   * Returns true if the page is zoomed in to some degree along this axis such that scrolling is
   * possible and this axis has not been scroll locked while panning. Otherwise, returns false.
   */
  bool Scrollable();

  void SetAxisLocked(bool aAxisLocked) { mAxisLocked = aAxisLocked; }

  /**
   * Gets the overscroll state of the axis in its current position.
   */
  Overscroll GetOverscroll();

  /**
   * If there is overscroll, returns the amount. Sign depends on in what
   * direction it is overscrolling. Positive excess means that it is
   * overscrolling in the positive direction, whereas negative excess means
   * that it is overscrolling in the negative direction. If there is overscroll
   * in both directions, this returns 0; it assumes that you check
   * GetOverscroll() first.
   */
  float GetExcess();

  /**
   * Gets the factor of acceleration applied to the velocity, based on the
   * amount of flings that have been done successively.
   */
  float GetAccelerationFactor();

  /**
   * Gets the raw velocity of this axis at this moment.
   */
  float GetVelocity();

  /**
   * Gets the overscroll state of the axis given an additional displacement.
   * That is to say, if the given displacement is applied, this will tell you
   * whether or not it will overscroll, and in what direction.
   */
  Overscroll DisplacementWillOverscroll(float aDisplacement);

  /**
   * If a displacement will overscroll the axis, this returns the amount and in
   * what direction. Similar to GetExcess() but takes a displacement to apply.
   */
  float DisplacementWillOverscrollAmount(float aDisplacement);

  /**
   * If a scale will overscroll the axis, this returns the amount and in what
   * direction. Similar to GetExcess() but takes a displacement to apply.
   *
   * |aFocus| is the point at which the scale is focused at. We will offset the
   * scroll offset in such a way that it remains in the same place on the page
   * relative.
   */
  float ScaleWillOverscrollAmount(float aScale, float aFocus);

  /**
   * Checks if an axis will overscroll in both directions by computing the
   * content rect and checking that its height/width (depending on the axis)
   * does not overextend past the viewport.
   *
   * This gets called by ScaleWillOverscroll().
   */
  bool ScaleWillOverscrollBothSides(float aScale);

  float GetOrigin();
  float GetCompositionLength();
  float GetPageStart();
  float GetPageLength();
  float GetCompositionEnd();
  float GetPageEnd();

  int32_t GetPos() const { return mPos; }

  virtual float GetPointOffset(const CSSPoint& aPoint) = 0;
  virtual float GetRectLength(const CSSRect& aRect) = 0;
  virtual float GetRectOffset(const CSSRect& aRect) = 0;

protected:
  int32_t mPos;
  int32_t mStartPos;
  float mVelocity;
  // Acceleration is represented by an int, which is the power we raise a
  // constant to and then multiply the velocity by whenever it is sampled. We do
  // this only when we detect that the user wants to do a fast fling; that is,
  // they are flinging multiple times in a row very quickly, probably trying to
  // reach one of the extremes of the page.
  int32_t mAcceleration;
  bool mAxisLocked;     // Whether movement on this axis is locked.
  AsyncPanZoomController* mAsyncPanZoomController;
  nsTArray<float> mVelocityQueue;
};

class AxisX : public Axis {
public:
  AxisX(AsyncPanZoomController* mAsyncPanZoomController);
  virtual float GetPointOffset(const CSSPoint& aPoint);
  virtual float GetRectLength(const CSSRect& aRect);
  virtual float GetRectOffset(const CSSRect& aRect);
};

class AxisY : public Axis {
public:
  AxisY(AsyncPanZoomController* mAsyncPanZoomController);
  virtual float GetPointOffset(const CSSPoint& aPoint);
  virtual float GetRectLength(const CSSRect& aRect);
  virtual float GetRectOffset(const CSSRect& aRect);
};

}
}

#endif