關于截取部分圖像顯示demo，有興趣可以把玩一下~~
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
*{margin: 0;padding: 0;}
canvas{display: block;border:solid 1px grey;margin: 50px auto;}
</style>
</head>
<body>
<canvas id="canvas"></canvas>
<script>
var canvas = document.getElementById('canvas');
var cxt = canvas.getContext('2d');
var image = new Image();
var image_bak = new Image();
window.onload = function(){
canvas.width = 800;
canvas.height = 400;
image.src = 'kn1.jpg';
image_bak.src = 'kn1.jpg';
image.onload = function(){
cxt.drawImage(image,0,0);
}
clip();
}
function clip(){
canvas.onmousedown = function(event){
event.stopPropagation();
var downX = event.clientX - canvas.getBoundingClientRect().left;
var downY = event.clientY - canvas.getBoundingClientRect().top;
this.onmousemove = function(e){
var curX = e.clientX - canvas.getBoundingClientRect().left;
var curY = e.clientY - canvas.getBoundingClientRect().top;
if(curX-downX<0 && curY-downY<0){
dx = ?downX - curX;
dy = ?downY - curY;
drawImage(cxt,image,curX,curY,dx,dy,500,0,dx,dy);
}else {
drawImage(cxt,image,downX,downY,curX-downX,curY-downY,500,0,curX-downX,curY-downY);
}
drawRect(cxt,downX,downY,curX-downX,curY-downY)
this.onmouseup = function(event){
this.onmousemove = null;
}
}
}
}
function drawImage(cxt,obj,sx,sy,dw,dh,dx,dy,dw,dh){
cxt.clearRect(0,0,canvas.width,canvas.height);
cxt.drawImage(image,0,0);
cxt.drawImage(obj,sx,sy,dw,dh,dx,dy,dw,dh);
}
function drawRect(cxt,x,y,w,h){
cxt.strokeStyle = 'red';
cxt.strokeRect(x,y,w,h);
}
</script>
</body>
</html>
2017-08-11
good