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;
}
?