html5模拟平抛运动

<html>

<head>

<meta charset=utf-8>

<title>html5炮弹</title>

<script>

//box

var box_x=0;

var box_y=0;

var box_width=300;

var box_height=300;

//ball

var ball_x=10;

var ball_y=10;

var ball_radius=10;

var ball_vx=10;

var ball_vy=0;

//constant

var g=10;//note

var rate=0.9;

//bound

var bound_left=box_x+ball_radius;

var bound_right=box_x+box_width-ball_radius;

var bound_top=box_y+ball_radius;

var bound_bottom=box_y+box_height-ball_radius;

//context

var ctx;

function init()

{

	ctx=document.getElementById('canvas').getContext('2d');

	ctx.lineWidth=ball_radius;

	ctx.fillStyle="rgb(200,0,50)";

	move_ball();

	setInterval(move_ball,100);

}

function move_ball()

{

	ctx.clearRect(box_x,box_y,box_width,box_height);

	move_and_check();

	ctx.beginPath();

	ctx.arc(ball_x,ball_y,ball_radius,0,Math.PI*2,true);

	ctx.fill();

	ctx.strokeRect(box_x,box_y,box_width,box_height);

}

function move_and_check()

{

	var cur_ball_x=ball_x+ball_vx;

                  var temp=ball_vy;

	ball_vy=ball_vy+g;

	var cur_ball_y=ball_y+ball_vy+g/2;

	if(cur_ball_x<bound_left)

	{

		cur_ball_x=bound_left;

		ball_vx=-ball_vx*0.9;

                                     ball_vy=ball_vy*0.9;

	}

	if(cur_ball_x>bound_right)

	{

		cur_ball_x=bound_right;

		ball_vx=-ball_vx*0.9;

                                   ball_vy=ball_vy*0.9;

	}

	if(cur_ball_y<bound_top)

	{

		cur_ball_y=bound_top;

		ball_vy=-ball_vy*0.9;

                                    ball_vx=ball_vx*0.9;

	}

	if(cur_ball_y>bound_bottom)

	{

		cur_ball_y=bound_bottom;

		ball_vy=-ball_vy*0.9;

                                    ball_vx=ball_vx*0.9;

	}

	ball_x=cur_ball_x;

	ball_y=cur_ball_y;

}

</script>

</head>

<body onLoad="init()">

<canvas id="canvas" width="400" height="400"/>

</body>

</html>
html5模拟小球平抛运动过程。