html5 乒乓球(碰撞检测)实例二_html5教程技巧

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

复制代码

代码如下:

<头>


<脚本>
var ctx;
var 画布；
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;
varbound_left=box_x ball_radius;
varbound_right=box_x box_width-ball_radius;
varbound_top=box_y ball_radius;
varbound_bottom=box_y box_height-ball_radius;
var 单位=10；
函数相交(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));
如果 (t {
t = 0.0;
}
否则 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 返回 true；
否则
返回 false；
}
函数 move_ball()
{
ball_x=ball_x ball_vx;
ball_y=ball_y ball_vy;
if(ball_x{
ball_x=bound_left;
ball_vx=-ball_vx;
}
if(ball_x>bound_right)
{
ball_x=bound_right;
ball_vx=-ball_vx;
}
if(ball_y{
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;
}
}
函数 move_wall(ev)
{
var keyCode;
if(event==null)
{
keyCode=window.event.keyCode;
window.event.preventDefault();
}
其他
{
keyCode=event.keyCode;
event.preventDefault();
}
开关(keyCode)
{
case 37://left;
wall_x-=单位；
if(wall_xwall_x=bound_left;
休息；
案例 38://up
wall_y-=unit;
if(wall_ywall_y=bound_top;
休息；
案例 39://right
wall_x =unit;
if(wall_x wall_width>bound_right)
wall_x=bound_right-wall_width;
休息；
案例 40://down
wall_y =unit;
if(wall_y wall_height>bound_bottom)
wall_y=bound_bottom-wall_height;
休息；
默认：
中断；
}
}
函数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();//注意
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);
}
函数 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);//注意
}
;

难点

小球和砖块的碰撞检测以及碰撞处理
将砖块重组为4条线段
分别对小球和每条线段进行

小球和线段的碰撞检测在另一篇文章http://www.jb51.net/html5/93997.html中有介绍。