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html5 乒乓球(碰撞检测)实例二

2013-07-25 17:21 537 查看


演示地址
http://koking.8u.hanmandarin.com/html5/1.html

简单介绍

小球可以在方框内部自由运动
可以通过方向键控制黑色砖块上下左右移动去与小球发生碰撞

代码实现 

<!-- 
To change this template, choose Tools | Templates 
and open the template in the editor. 
--> 
<!DOCTYPE html> 
<html> 
<head> 
<title>乒乓球游戏</title> 
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 
<script> 
var ctx; 
var canvas; 
var ball_x=10; 
var ball_y=10; 
var ball_radius=10; 
var ball_vx=10; 
var ball_vy=8; 
var wall_x=30; 
var wall_y=40; 
var wall_width=30; 
var wall_height=60; 
var box_x=0; 
var box_y=0; 
var box_width=300; 
var box_height=300; 
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; 
var unit=10; 
function intersect(sx, sy, fx, fy, cx, cy, rad) 
{ 
var dx; 
var dy; 
var t; 
var rt; 
dx = fx - sx; 
dy = fy - sy; 
t = 0.0 - (((sx - cx) * dx + (sy - cy) * dy) / (dx * dx + dy * dy)); 
if (t < 0.0) 
{ 
t = 0.0; 
} 
else if (t > 1.0) 
t = 1.0; 
var dx1 = (sx + t * dx) - cx; 
var dy1 = (sy + t * dy) - cy; 
var rt = dx1 * dx1 + dy1 * dy1; 
if (rt < rad * rad) 
return true; 
else 
return false; 
} 
function move_ball() 
{ 
ball_x=ball_x+ball_vx; 
ball_y=ball_y+ball_vy; 
if(ball_x<bound_left) 
{ 
ball_x=bound_left; 
ball_vx=-ball_vx; 
} 
if(ball_x>bound_right) 
{ 
ball_x=bound_right; 
ball_vx=-ball_vx; 
} 
if(ball_y<bound_top) 
{ 
ball_y=bound_top; 
ball_vy=-ball_vy; 
} 
if(ball_y>bound_bottom) 
{ 
ball_y=bound_bottom; 
ball_vy=-ball_vy; 
} 
//撞到上边 
if(intersect(wall_x,wall_y,wall_x+wall_width,wall_y+wall_height,ball_x,ball_y,ball_radius)) 
{ 
ball_y=wall_y-ball_radius; 
ball_vy=-ball_vy; 
} 
//撞到左边 
if(intersect(wall_x,wall_y,wall_x,wall_y+wall_height,ball_x,ball_y,ball_radius)) 
{ 
ball_x=wall_x-ball_radius; 
ball_vx=-ball_vx; 
} 
//撞到右边 
if(intersect(wall_x+wall_width,wall_y,wall_x+wall_width,wall_y+wall_height,ball_x,ball_y,ball_radius)) 
{ 
ball_x=wall_x+wall_width+ball_radius; 
ball_vx=-ball_vx; 
} 
//撞到下边 
if(intersect(wall_x,wall_y+wall_height,wall_x+wall_width,wall_y+wall_height,ball_x,ball_y,ball_radius)) 
{ 
ball_y=wall_y+wall_height+ball_radius; 
ball_vy=-ball_vy; 
} 
} 
function move_wall(ev) 
{ 
var keyCode; 
if(event==null) 
{ 
keyCode=window.event.keyCode; 
window.event.preventDefault(); 
} 
else 
{ 
keyCode=event.keyCode; 
event.preventDefault(); 
} 
switch(keyCode) 
{ 
case 37://left; 
wall_x-=unit; 
if(wall_x<bound_left) 
wall_x=bound_left; 
break; 
case 38://up 
wall_y-=unit; 
if(wall_y<bound_top) 
wall_y=bound_top; 
break; 
case 39://right 
wall_x+=unit; 
if(wall_x+wall_width>bound_right) 
wall_x=bound_right-wall_width; 
break; 
case 40://down 
wall_y+=unit; 
if(wall_y+wall_height>bound_bottom) 
wall_y=bound_bottom-wall_height; 
break; 
default: 
break; 
} 
} 
function draw_all() 
{ 
ctx.beginPath(); 
ctx.clearRect(box_x,box_y,box_width,box_height); 
ctx.fillStyle="rgb(255,0,0)"; 
//ctx.lineWidth=ball_radius; 
ctx.arc(ball_x,ball_y,ball_radius,0,Math.PI*2,true); 
ctx.fill();//note 
ctx.fillStyle="rgb(0,0,0)"; 
ctx.fillRect(wall_x,wall_y,wall_width,wall_height); 
ctx.strokeRect(box_x,box_y,box_width,box_height); 
} 
function init() 
{ 
canvas=document.getElementById('canvas'); 
ctx=canvas.getContext('2d'); 
draw_all(); 
setInterval(draw_all,100); 
setInterval(move_ball,50); 
window.addEventListener('keydown',move_wall,false);//note 
} 
</script> 
</head> 
<body onLoad="init();"> 
<canvas id="canvas" width="300" height="300"></canvas> 
</body> 
</html>

难点

小球和砖块的碰撞检测以及碰撞处理
将砖块分解为4条线段
分别对小球和每条线段进行碰撞检测。

小球和线段的碰撞检测在另一篇文章/article/1295225.html中有介绍。
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