我能够在 HTML Canvas 上成功绘制图像。但我需要能够在 Canvas 上拖动图像。
我知道这个功能可以通过一些JavaScript库(例如KinectJS)轻松实现。但我想用简单的 JavaScript 来完成它。
window.onload = function(){
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
var destX = 0;
var destY = 0;
var imageObj = new Image();
imageObj.onload = function(){
context.drawImage(imageObj, destX, destY);
};
imageObj.src = "westeros.png";
<canvas id="myCanvas" height=1024 width=360></canvas>
最佳答案
要进行拖动，您需要处理 3 个鼠标事件:
mousedown -- 设置一个标志来指示拖动已经开始。
mouseup -- 清除拖动标志，因为拖动已结束
mousemove -- 如果设置了拖动标志，则清除 Canvas 并在鼠标位置绘制图像
这是一些代码:
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
canvas{border:1px solid red;}
</style>
<script>
$(function(){
var img = new Image();
img.onload = function(){
ctx.drawImage(img, 0,0);
};
img.src = "http://images.christmastimeclipart.com/images/2/1271716593176_1788/img_1271716593176_17881.jpg";
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var canvasOffset=$("#canvas").offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
var canvasWidth=canvas.width;
var canvasHeight=canvas.height;
var isDragging=false;
function handleMouseDown(e){
canMouseX=parseInt(e.clientX-offsetX);
canMouseY=parseInt(e.clientY-offsetY);
// set the drag flag
isDragging=true;
}
function handleMouseUp(e){
canMouseX=parseInt(e.clientX-offsetX);
canMouseY=parseInt(e.clientY-offsetY);
// clear the drag flag
isDragging=false;
}
function handleMouseOut(e){
canMouseX=parseInt(e.clientX-offsetX);
canMouseY=parseInt(e.clientY-offsetY);
// user has left the canvas, so clear the drag flag
//isDragging=false;
}
function handleMouseMove(e){
canMouseX=parseInt(e.clientX-offsetX);
canMouseY=parseInt(e.clientY-offsetY);
// if the drag flag is set, clear the canvas and draw the image
if(isDragging){
ctx.clearRect(0,0,canvasWidth,canvasHeight);
ctx.drawImage(img,canMouseX-128/2,canMouseY-120/2,128,120);
}
}
$("#canvas").mousedown(function(e){handleMouseDown(e);});
$("#canvas").mousemove(function(e){handleMouseMove(e);});
$("#canvas").mouseup(function(e){handleMouseUp(e);});
$("#canvas").mouseout(function(e){handleMouseOut(e);});
}); // end $(function(){});
</script>
</head>
<body>
<canvas id="canvas" width=400 height=300></canvas>
</body>
</html>
关于javascript - 使用 JavaScript 使在 Canvas 上绘制的图像可拖动，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/15036386/