Flash/Flex学习笔记(20)：运动学原理

先写一个公用的小球类Ball:

package{

import flash.display.Sprite;

//小球 类

public class Ball extends Sprite{

private var radius:Number ;//半径

private var color:uint;//颜色

public function Ball(r:Number=50,c:uint=0xff0000){

this.radius = r;

this.color = c;

init();

}

private function init():void{

graphics.beginFill(color);

graphics.drawCircle(0,0,radius);

graphics.endFill();

}

 
}

}

圆周运行与椭圆运动：

主要依靠三角函数结合椭圆公式计算对象的x,y坐标

var ball:Ball = new Ball(5,0xff0000);

 
var ball2:Ball = new Ball(8,0x0000ff);

 
addChild(ball);

addChild(ball2);

var _radius:uint = 75;

var _angle:Number = 0;

var _centerX = stage.stageWidth/2;

var _centerY = stage.stageHeight/2;

var _radius_X = 100;

var _radius_Y = 175;

addEventListener(Event.ENTER_FRAME,EnterFrameHandler);

graphics.lineStyle(1);

 
graphics.moveTo(_centerX,_centerY);

function EnterFrameHandler(event:Event):void {

ball.x =  _centerX +  _radius * Math.cos(_angle * Math.PI/180);

ball.y = _centerY + _radius * Math.sin(_angle * Math.PI/180);

ball2.x =  _centerX +  _radius_X * Math.cos(_angle * Math.PI/180);

 
ball2.y = _centerY + _radius_Y * Math.sin(_angle * Math.PI/180);

_angle += 1;

if (_angle<=360){        

graphics.moveTo(ball.x,ball.y);

graphics.lineStyle(1,_angle * Math.pow(2,24)/360,1);

 
//graphics.lineStyle(1,Math.random() * 0xffffff,1);

 
graphics.lineTo(ball2.x,ball2.y);

 
}   

 
}

匀加速直线运动：
速度公式：v = v0 + at，物理学上的公式虽然是这样，但是到了Flash中思路得稍微换一下，Flash默认为每秒24帧，而EnterFrame事件在每次进入新一帧时触发，所以可粗略的认为每一帧就是一个“单位时间”，匀加速的重要特征就是每单位时间速度增加固定值，所以在Flash中只要在EnterFrame中将速度增加固定值即可

var ball:Ball;

var vx:Number = 0;

 
var ax:Number = 0;

var vy:Number = 0;

var ay:Number = 0;

 
ball = new Ball  ;

addChild(ball);

ball.x = stage.stageWidth/2;

ball.y = stage.stageHeight/2;

 
ball.scaleX = 0.1;

 
ball.scaleY = 0.1;

addEventListener(Event.ENTER_FRAME,EnterFrameHandler);

stage.addEventListener(KeyboardEvent.KEY_DOWN, KeyDownHandler);

 
stage.addEventListener(KeyboardEvent.KEY_UP, KeyUpHandler);

graphics.lineStyle(1,0,1);

graphics.moveTo((stage.stageWidth/2)-10,stage.stageHeight/2);

 
graphics.lineTo((stage.stageWidth/2)+10,stage.stageHeight/2);

 
graphics.moveTo(stage.stageWidth/2,(stage.stageHeight/2)-10);

 
graphics.lineTo(stage.stageWidth/2,(stage.stageHeight/2)+10); 

function EnterFrameHandler(event:Event):void {

vx += ax; //每次进入该帧时，x轴方向的速度增加指定值（即x轴方向匀加速运行）

ball.x += vx;

vy += ay; //每次进入该帧时，y轴方向的速度增加指定值（即y轴方向匀加速运行）    

ball.y += vy;

if (ball.x>=stage.stageWidth-ball.width/2) {

 
ball.x=stage.stageWidth-ball.width/2;       

vx = 0;

} else if (ball.x <= ball.width/2) {

ball.x = ball.width/2;      

vx = 0;

}   

if (ball.y>=stage.stageHeight-ball.height/2) {

 
ball.y=stage.stageHeight-ball.height/2;     

vy = 0;

} else if (ball.y <= ball.height/2) {

 
ball.y = ball.height/2;     

 
vy = 0;

 
}

 
}

function KeyDownHandler(event:KeyboardEvent):void {

switch(event.keyCode){

case Keyboard.RIGHT:

ax = 0.5;

break;

case Keyboard.LEFT:

ax = -0.5;

break;

 
case Keyboard.DOWN:

 
ay = 0.5;

 
break;

case Keyboard.UP:

ay = -0.5;

default:

 
break;

}

 
}

function KeyUpHandler(event:KeyboardEvent):void {

ax=0;

 
ay=0;

}

自由落体运动:
其实就是匀加速直线运动的特例，把上面的代码稍作修改即可。

function EnterFrameHandler(event:Event):void {

 
vx += ax; 

ball.x += vx;

 
vy += ay;   

vy += 0.45; //这里再强行增加一个值做为重力加速度，所以不做控制的时候，也会自己向下掉

ball.y += vy;

if (ball.x>=stage.stageWidth-ball.width/2) {

ball.x=stage.stageWidth-ball.width/2;       

vx = 0;

} else if (ball.x <= ball.width/2) {

ball.x = ball.width/2;      

vx = 0;

 
}   

if (ball.y>=stage.stageHeight-ball.height/2) {

ball.y=stage.stageHeight-ball.height/2;     

vy *= -0.7; //假设反弹后的反向速度是原来速度的70%

} else if (ball.y <= ball.height/2) {

ball.y = ball.height/2;     

vy = 0;

}

}

反弹：只要将上面的例子稍候修改即可

var ball:Ball;

 
var vx:Number = 0;

 
var ax:Number = 0;

 
var vy:Number = 0;

var ay:Number = 0;

ball = new Ball  ;

addChild(ball);

ball.x = stage.stageWidth/2;

ball.y = stage.stageHeight/2;

 
ball.scaleX = 0.1;

ball.scaleY = 0.1;

addEventListener(Event.ENTER_FRAME,EnterFrameHandler);

stage.addEventListener(KeyboardEvent.KEY_DOWN, KeyDownHandler);

stage.addEventListener(KeyboardEvent.KEY_UP, KeyUpHandler);

graphics.lineStyle(1,0,1);

graphics.moveTo((stage.stageWidth/2)-10,stage.stageHeight/2);

graphics.lineTo((stage.stageWidth/2)+10,stage.stageHeight/2);

graphics.moveTo(stage.stageWidth/2,(stage.stageHeight/2)-10);

graphics.lineTo(stage.stageWidth/2,(stage.stageHeight/2)+10); 

var _bounce:Number = -0.5;//反弹后的速度百分比

function EnterFrameHandler(event:Event):void {

vx += ax; 

ball.x += vx;

vy += ay;   

ball.y += vy;

if (ball.x>=stage.stageWidth-ball.width/2) {

ball.x=stage.stageWidth-ball.width/2;       

vx *= _bounce;

} else if (ball.x <= ball.width/2) {

ball.x = ball.width/2;      

 
vx *= _bounce;

}   

if (ball.y>=stage.stageHeight-ball.height/2) {

ball.y=stage.stageHeight-ball.height/2;     

 
vy *= _bounce; 

} else if (ball.y <= ball.height/2) {

ball.y = ball.height/2;     

vy *= _bounce; 

}

}

function KeyDownHandler(event:KeyboardEvent):void {

switch(event.keyCode){

case Keyboard.RIGHT:

 
ax = 0.5;

 
break;

case Keyboard.LEFT:

ax = -0.5;

break;

case Keyboard.DOWN:

ay = 0.5;

break;

case Keyboard.UP:

ay = -0.5;

default:

break;

 
}   

}

function KeyUpHandler(event:KeyboardEvent):void {

ax=0;

ay=0;

}

往返直线运动：

 
graphics.lineStyle(1,0xff0000,0.5);

graphics.moveTo(0,0);

graphics.lineTo(stage.stageWidth,stage.stageHeight);

 
graphics.lineStyle(1,0x00ff00,0.5);

graphics.moveTo(stage.stageWidth,0);

graphics.lineTo(0,stage.stageHeight);

var ball:Ball=new Ball(10,0xff0000);

ball.x=0;

ball.y=0;

 
var _seedX=-90;

 
var _seedY=0;

var angle:Number = 45* Math.PI/180;

 
addChild(ball);

var ball2:Ball = new Ball(10,0x00ff00);

ball2.x = stage.stageWidth;

 
var speed = 2;

var isDown = true;

addChild(ball2);

addEventListener(Event.ENTER_FRAME,EnterFrameHandler);

function EnterFrameHandler(e:Event):void {  

ball.x = Math.cos(_seedX*Math.PI/180)*stage.stageWidth; 

ball.y = Math.sin(_seedY*Math.PI/180)*stage.stageHeight;

 
_seedX+=1;

 
_seedY+=1;

if (_seedX > 90){

_seedX = -90;

 
}

if (_seedY > 180){

 
_seedY = 0;

 
}   

//向下

if (isDown){

 
ball2.x -= speed;

ball2.y += speed;

if (ball2.x < 0){

isDown = false;

}

 
}

else{//向上

ball2.x -= -speed;

ball2.y += -speed;

if (ball2.x > stage.stageWidth){

isDown = true;

}

}

}

注：上面演示了二种方法，对于往返匀速直线运动，最简单的办法就是让x,y轴方向速度增加固定值；如果不要求匀速的话，用sin,cos函数也许更简单

飞船键盘控制演示：(来自ActionScript 3.0 Animation中的示例)

飞船类

package {

 
import flash.display.Sprite;

public class Ship extends Sprite {

 
public function Ship() {

 
draw(false);

 
}

 
public function draw(showFlame:Boolean):void {

 
graphics.clear();

 
graphics.lineStyle(1,0xffffff);

graphics.moveTo(10,0);

 
graphics.lineTo(-10,10);

 
graphics.lineTo(-5,0);

 
graphics.lineTo(-10,-10);

 
graphics.lineTo(10,0);

 
if (showFlame) {

 
graphics.moveTo(-7.5,-5);

 
graphics.lineTo(-15,0);

 
graphics.lineTo(-7.5,5);

 
}

 
}

 
}

}

主动画

 
package {

 
import flash.display.Sprite;

 
import flash.events.Event;

import flash.events.KeyboardEvent;

 
import flash.ui.Keyboard;

 
public class ShipSim extends Sprite {

private var ship:Ship;

private var vr:Number=0;

 
private var thrust:Number=0;

 
private var vx:Number=0;

 
private var vy:Number=0;

 
public function ShipSim() {

init();

 
}

private function init():void {

 
ship=new Ship  ;

 
ship.scaleX = ship.scaleY = 1.5;

addChild(ship);

ship.x=stage.stageWidth/2;

 
ship.y=stage.stageHeight/2;

 
addEventListener(Event.ENTER_FRAME,EnterFrameHandler);

 
stage.addEventListener(KeyboardEvent.KEY_DOWN,KeyDownHandler);

 
stage.addEventListener(KeyboardEvent.KEY_UP,KeyUpHandler);

 
}

private function KeyDownHandler(event:KeyboardEvent):void {         

 
switch (event.keyCode) {

 
case Keyboard.LEFT :

vr=-5;

break;

case Keyboard.RIGHT :

 
vr=5;

 
break;

case Keyboard.UP :

 
thrust=0.2;

 
ship.draw(true);

 
break;

 
default :

 
break;

 
}

 
}

 
private function KeyUpHandler(event:KeyboardEvent):void {

 
vr=0;

thrust=0;

ship.draw(false);

 
}

private function EnterFrameHandler(event:Event):void {

ship.rotation+=vr;

var angle:Number=ship.rotation*Math.PI/180;

var ax:Number=Math.cos(angle)*thrust;

 
var ay:Number=Math.sin(angle)*thrust;           

 
vx+=ax;

 
vy+=ay;

 
ship.x+=vx;

 
ship.y+=vy;

if (ship.x < ship.width/2){

 
ship.x = ship.width/2;              

vx = 0;

}

if (ship.x>stage.stageWidth -ship.width/2){

ship.x = stage.stageWidth -ship.width/2;

 
vx = 0;

}

if (ship.y > stage.stageHeight - ship.height/2){

 
ship.y = stage.stageHeight - ship.height/2;

vy=0;

 
}

 
if (ship.y < ship.height/2){

ship.y = ship.height/2;

vy=0;

}

 
}

 
}

 
}

带摩擦力的加速旋转:

 
addEventListener(Event.ENTER_FRAME,EnterFrameHandler);

stage.addEventListener(KeyboardEvent.KEY_DOWN,KeyDownHandler);

 
stage.addEventListener(KeyboardEvent.KEY_UP,KeyUpHandler);

var ar:Number=0;

var vr:Number=0;

var _isStart:Boolean=false;//是否正在加速(或减速)

 
var _isRight:Boolean=true;//是否正在向右顺时针转动

 
function EnterFrameHandler(e:Event):void {

 
vr+=ar;

 
obj.rotation+=vr;//obj是舞台中的箭头实例

 
if (!_isStart) {

 
if (_isRight) {

if (vr<=0) {

vr=0;

ar=0.0;

}

} else {

if (vr>=0) {

vr=0;

ar=0.0;

 
}

}

 
}

 
}

 
function KeyDownHandler(e:KeyboardEvent):void {

 
_isStart=true;

 
if (e.keyCode==Keyboard.RIGHT) {

 
ar=0.2;

 
_isRight=true;

} else if (e.keyCode == Keyboard.LEFT) {

ar=-0.2;

 
_isRight=false;

}

}

function KeyUpHandler(e:KeyboardEvent):void {

if (e.keyCode==Keyboard.RIGHT) {

ar=-0.1;

} else if (e.keyCode == Keyboard.LEFT) {

ar=0.1;

 
}

_isStart=false;

}