| /* |
| * 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); |
| |
| /** |
| * <p> |
| * Update the state based on the specified {@link State}. When no more |
| * momentum remains, this method should return false to stop future calls. |
| * </p> |
| * <p> |
| * 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)}. |
| * </p> |
| * |
| * @param state the current state |
| * @return true to continue momentum, false if no momentum remains |
| */ |
| boolean updateState(State state); |
| } |