var xPos = 300;
var yPos = 200;
var step = 1;
var delay = 30;
var height = 0;
var Hoffset = 0;
var Woffset = 0;
var yon = 0;
var xon = 0;
var pause = true;
var interval;
img1.style.top = yPos;
function changePos()
{
width = document.body.clientWidth;
height = document.body.clientHeight;
Hoffset = img1.offsetHeight;
Woffset = img1.offsetWidth;
img1.style.left = xPos + document.body.scrollLeft;
img1.style.top = yPos + document.body.scrollTop;
if (yon)
{yPos = yPos + step;}
else
{yPos = yPos - step;}
if (yPos < 0)
{yon = 1;yPos = 0;}
if (yPos >= (height - Hoffset))
{yon = 0;yPos = (height - Hoffset);}
if (xon)
{xPos = xPos + step;}
else
{xPos = xPos - step;}
if (xPos < 0)
{xon = 1;xPos = 0;}
if (xPos >= (width - Woffset))
{xon = 0;xPos = (width - Woffset); }
}
function start()
{
img1.visibility = "visible";
interval = setInterval('changePos()', delay);
}
function pause_resume()
{
if(pause)
{
clearInterval(interval);
pause = false;}
else
{
interval = setInterval('changePos()',delay);
pause = true;
}
}
start();谁帮忙解释一下
红色字体部分
var yPos = 200;
var step = 1;
var delay = 30;
var height = 0;
var Hoffset = 0;
var Woffset = 0;
var yon = 0;
var xon = 0;
var pause = true;
var interval;
img1.style.top = yPos;
function changePos()
{
width = document.body.clientWidth;
height = document.body.clientHeight;
Hoffset = img1.offsetHeight;
Woffset = img1.offsetWidth;
img1.style.left = xPos + document.body.scrollLeft;
img1.style.top = yPos + document.body.scrollTop;
if (yon)
{yPos = yPos + step;}
else
{yPos = yPos - step;}
if (yPos < 0)
{yon = 1;yPos = 0;}
if (yPos >= (height - Hoffset))
{yon = 0;yPos = (height - Hoffset);}
if (xon)
{xPos = xPos + step;}
else
{xPos = xPos - step;}
if (xPos < 0)
{xon = 1;xPos = 0;}
if (xPos >= (width - Woffset))
{xon = 0;xPos = (width - Woffset); }
}
function start()
{
img1.visibility = "visible";
interval = setInterval('changePos()', delay);
}
function pause_resume()
{
if(pause)
{
clearInterval(interval);
pause = false;}
else
{
interval = setInterval('changePos()',delay);
pause = true;
}
}
start();谁帮忙解释一下
红色字体部分
如果ypos小于0,表示图片已经到了底部,所以设置ytop=0,让程序使img1上升
如果ypos高出最大高度,表示图片已经到了顶部,所以设置ytop=1,让程序使img1下降
xon则是对于横向范围的判断