<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。