我正在创建一个可以在Android上运行的HTML5游戏。我经历了一些文章，但还没有得到解决方案。我有一个图像，我通过JavaScript生成，我想使用touchmove移动此图像，以便我可以在我的Android设备中运行它。这是代码：
gameCanvas.addEventListener("touchmove", touchXY, true);
function touchXY(e) {
if (!e)
var e = event;
e.preventDefault();
avatarX = e.targetTouches[0].pageX - gameCanvas.offsetLeft;
avatarY = e.targetTouches[0].pageY - gameCanvas.offsetTop;
}
这是我的画布：
<canvas id="gameCanvas" onclick="setUpGame();" width="400" height="300"></canvas>
这是我的形象：
avatarImage.src = "img/avatar.png";
gameCanvas.getContext("2d").drawImage(avatarImage, Math.random() * 100, Math.random() * 100);
我只是想在画布内移动图像。
我写了一个完整的例子，希望它不是太冗长。
<!DOCTYPE html>
<html>
<head>
<meta charset='UTF-8'>
</head>
<body>
<canvas id='canvas' width='512' height='512'></canvas>
<script>
var c=document.getElementById('canvas'),
ctx=c.getContext('2d'),
activeBox='none',
//populate the map with objects
box=[
{
x:256,
y:128,
width:32,
height:64
},
{
x:128,
y:64,
width:64,
height:64
},
{
x:32,
y:32,
width:32,
height:32
},
];
function draw(){
//clear the screen, draw population
ctx.clearRect(0,0,c.width,c.height);
for(var i=0;i<box.length;i++){
ctx.fillRect(box[i].x,box[i].y,box[i].width,box[i].height);
}
//repeat at 60fps if possible, pause if window looses focus
requestAnimationFrame(draw);
}
function startTouch(e){
//this makes it easier to write control flow later and keeps XY relative to canvas
var xTouch=e.touches[0].pageX-c.offsetLeft,
yTouch=e.touches[0].pageY-c.offsetTop;
//its best to go through this loop in touchstart, because it only happens once per touch
for(var i=0;i<box.length;i++){
if(xTouch>box[i].x&&xTouch<box[i].x+box[i].width){
if(yTouch>box[i].y&&yTouch<box[i].y+box[i].height){
activeBox=i;
}
}
}
}
function moveTouch(e){
//grab a box by the center
if(activeBox!='none'){
box[activeBox].x=e.changedTouches[0].pageX-box[activeBox].width/2;
box[activeBox].y=e.changedTouches[0].pageY-box[activeBox].height/2;
}
}
function endTouch(){
//clear active so that dragging empty space wont move the last active box
activeBox='none';
}
canvas.addEventListener('touchstart',startTouch);
canvas.addEventListener('touchmove',moveTouch);
canvas.addEventListener('touchend',endTouch);
window.addEventListener('load',draw);
</script>
</body>
</html>
我使用fillRect来简化，但是如果你想用drawImage替换它，你需要为每个创建一个新元素，并将一个源属性添加到box对象数组中。这是一个局部的例子。
//you need a new one of these for every image
var img=new Image();
img.src='http://www.w3schools.com/images/w3logotest2.png';
var box={
source:img,
x:Math.floor((Math.random()*256)+1),
y:Math.floor((Math.random()*256)+1)
};
//make sure the image doesnt load before the script
window.onload=function(){
ctx.drawImage(img,box.x,box.y);
}