motion.java.svn-base

j2me设计的界面包

/*
 * Copyright 2008 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */
package com.sun.lwuit.animations;

/**
 * Abstracts the notion of physical motion over time from a numeric location to
 * another. This class can be subclassed to implement any motion equation for
 * appropriate physics effects.
 * <p>This class relies on the System.currentTimeMillis() method to provide
 * transitions between coordinates. The motion can be subclassed to provide every
 * type of motion feel from parabolic motion to spline and linear motion. The default
 * implementation provides a simple algorithm giving the feel of acceleration and
 * deceleration.
 *
 * @author Shai Almog
 */
public class Motion {

    public static final int LINEAR = 0;
    public static final int SPLINE = 1;
    public static final int FRICTION = 2;
    
    private int motionType;
    private int sourceValue;
    private int destinationValue;
    private int duration;
    private long startTime;
    private float initVelocity,  friction;
    
    private Motion(int sourceValue, int destinationValue, int duration) {
        this.sourceValue = sourceValue;
        this.destinationValue = destinationValue;
        this.duration = duration;
    }

    private Motion(int sourceValue, float initVelocity, float friction) {
        this.sourceValue = sourceValue;
        this.initVelocity = initVelocity;
        this.friction = friction;
        duration = (int) ((Math.abs(initVelocity)) / friction);
    }


    /**
     * Creates a linear motion starting from source value all the way to destination value
     * 
     * @param sourceValue the number from which we are starting (usually indicating animation start position)
     * @param destinationValue the number to which we are heading (usually indicating animation destination)
     * @param duration the length in milliseconds of the motion (time it takes to get from sourceValue to
     * destinationValue)
     */
    public static Motion createLinearMotion(int sourceValue, int destinationValue, int duration) {
        Motion l = new Motion(sourceValue, destinationValue, duration);
        l.motionType = LINEAR;
        return l;
    }
    
    /**
     * Creates a spline motion starting from source value all the way to destination value
     * 
     * @param sourceValue the number from which we are starting (usually indicating animation start position)
     * @param destinationValue the number to which we are heading (usually indicating animation destination)
     * @param duration the length in milliseconds of the motion (time it takes to get from sourceValue to
     * destinationValue)
     */
    public static Motion createSplineMotion(int sourceValue, int destinationValue, int duration) {
        Motion spline = new Motion(sourceValue, destinationValue, duration);
        spline.motionType = SPLINE;
        return spline;
    }

    /**
     * Creates a friction motion starting from source with initial speed and the friction
     * 
     * @param sourceValue the number from which we are starting (usually indicating animation start position)
     * @param initVelocity the starting velocity
     * @param friction the motion friction
     */
    public static Motion createFrictionMotion(int sourceValue, float initVelocity, float friction) {
        Motion frictionMotion = new Motion(sourceValue, initVelocity, friction);
        frictionMotion.motionType = FRICTION;
        return frictionMotion;
    }
    
    /**
     * Sets the start time to the current time
     */
    public void start() {
        startTime = System.currentTimeMillis();
    }

    /**
     * Returns true if the motion has run its course and has finished meaning the current
     * time is greater than startTime + duration.
     * 
     * @return true if System.currentTimeMillis() > duration + startTime
     */
    public boolean isFinished() {
        return System.currentTimeMillis() > duration + startTime;
    }

    private int getSplineValue() {
        //make sure we reach the destination value.
        if(isFinished()){
            return destinationValue;
        }
        float totalTime = duration;
        float currentTime = (int) (System.currentTimeMillis() - startTime);
        currentTime = Math.min(currentTime, totalTime);
        int p = Math.abs(destinationValue - sourceValue);
        float centerTime = totalTime / 2;
        float l = p / (centerTime * centerTime);
        int x;
        if (sourceValue < destinationValue) {
            if (currentTime > centerTime) {
                x = sourceValue + (int) (l * (-centerTime * centerTime + 2 * centerTime * currentTime -
                        currentTime * currentTime / 2));
            } else {
                x = sourceValue + (int) (l * currentTime * currentTime / 2);
            }
        } else {
            currentTime = totalTime - currentTime;
            if (currentTime > centerTime) {
                x = destinationValue + (int) (l * (-centerTime * centerTime + 2 * centerTime * currentTime -
                        currentTime * currentTime / 2));
            } else {
                x = destinationValue + (int) (l * currentTime * currentTime / 2);
            }
        }
        return x;
    }

    
    /**
     * Returns the value for the motion for the current clock time. 
     * The value is dependent on the Motion type.
     * 
     * @return a value that is relative to the source value
     */
    public int getValue() {
        if (motionType == SPLINE) {
            return getSplineValue();
        }else if(motionType == FRICTION){
            return getFriction();
        }else{
            return getLinear();
        }

    }

    private int getLinear() {
        //make sure we reach the destination value.
        if(isFinished()){
            return destinationValue;
        }
        float totalTime = duration;
        float currentTime = (int) (System.currentTimeMillis() - startTime);
        int dis = destinationValue - sourceValue;
        int val = (int)(sourceValue + (currentTime / totalTime * dis));
        
        if(destinationValue < sourceValue) {
            return Math.max(destinationValue, val);
        } else {
            return Math.min(destinationValue, val);
        }
    }
    
    private int getFriction() {
        int time = (int) (System.currentTimeMillis() - startTime);
        int retVal = 0;

        retVal = (int)((Math.abs(initVelocity) * time) - (friction * (((float)time * time) / 2)));
        if (initVelocity < 0) {
            retVal *= -1;
        }
        retVal += (int) sourceValue;
        return retVal;
    }

    /**
     * The number from which we are starting (usually indicating animation start position)
     */
    public int getSourceValue() {
        return sourceValue;
    }

    /**
     * The number from which we are starting (usually indicating animation start position)
     */
    public void setSourceValue(int sourceValue) {
        this.sourceValue = sourceValue;
    }

    /**
     * The value of System.currentTimemillis() when motion was started
     */
    protected long getStartTime() {
        return startTime;
    }
}