com.google.gwt.touch.client.Momentum Maven / Gradle / Ivy
/*
* Copyright 2011 Google Inc.
*
* 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.
*/
package com.google.gwt.touch.client;
/**
* Describes the momentum of a gesture after the gesture has been completed. You
* can use it to control the speed of scrolling for scrollable widgets affected
* by {@link TouchScroller}.
*/
public interface Momentum {
/**
* A snapshot of the current state.
*/
public static class State {
private int cumulativeElapsedMillis = 0;
private int elapsedMillis = 0;
private final Point initialPosition;
private final Point initialVelocity;
private Point position;
private Point velocity;
/**
* Construct a new {@link State}.
*
* @param initialPosition the initial position, which is also set to the
* current position
* @param initialVelocity the initial velocity in pixels per millisecond,
* which is also set to the current velocity
*/
public State(Point initialPosition, Point initialVelocity) {
this.initialPosition = initialPosition;
this.initialVelocity = initialVelocity;
this.position = new Point(initialPosition);
this.velocity = new Point(initialVelocity);
}
/**
* Get the cumulative elapsed time in milliseconds since momentum took over.
*
* @return the elapsed time in milliseconds
*/
public int getCumulativeElapsedMillis() {
return cumulativeElapsedMillis;
}
/**
* Get the elapsed time in milliseconds since the last time the state was
* updated.
*
* @return the elapsed time in milliseconds
*/
public int getElapsedMillis() {
return elapsedMillis;
}
/**
* Get the initial position when the momentum took over.
*
* @return the initial position
*/
public Point getInitialPosition() {
return initialPosition;
}
/**
* Get the initial velocity in pixels per millisecond when the momentum took
* over.
*
* @return the initial velocity
*/
public Point getInitialVelocity() {
return initialVelocity;
}
/**
* Get the current position.
*
* @return the current position
*/
public Point getPosition() {
return position;
}
/**
* Get the current velocity in pixels per millisecond.
*
* @return the current velocity
*/
public Point getVelocity() {
return velocity;
}
/**
* Set the current position.
*
* @param position set the current position
*/
public void setPosition(Point position) {
this.position = position;
}
/**
* Get the current velocity in pixels per millisecond.
*
* @param velocity set the current velocity
*/
public void setVelocity(Point velocity) {
this.velocity = velocity;
}
/**
* Set the cumulative elapsed time in milliseconds since momentum took over.
*
* @return the elapsed time in milliseconds
*/
void setCumulativeElapsedMillis(int cumulativeElapsedMillis) {
this.cumulativeElapsedMillis = cumulativeElapsedMillis;
}
/**
* Set the elapsed time in milliseconds since the last time the state was
* updated.
*
* @return the elapsed time
*/
void setElapsedMillis(int elapsedMillis) {
this.elapsedMillis = elapsedMillis;
}
}
/**
* Create a {@link State} instance. The {@link State} instance will be passed
* to {@link Momentum#updateState(State)} until the momentum is depleted.
*
* @param initialPosition the initial position
* @param initialVelocity the initial velocity in pixels per millisecond
*/
State createState(Point initialPosition, Point initialVelocity);
/**
*
* Update the state based on the specified {@link State}. When no more
* momentum remains, this method should return false to stop future calls.
*
*
* The {@link State} instance is created by a call to
* {@link #createState(Point, Point)}, and the same instance if used for the
* duration of the momentum. This method should modify the existing state by
* calling {@link State#setPosition(Point)} and/or
* {@link State#setVelocity(Point)}.
*
*
* @param state the current state
* @return true to continue momentum, false if no momentum remains
*/
boolean updateState(State state);
}