HTML5响应画布：调整浏览器画布大小的大小消失 [英] HTML5 responsive canvas: resizing the browser canvas draw disappear
问题描述
我想制作一个响应的画布使用大小的百分比，一旦用户将调整窗口的大小相对调整画布。
我可以通过使用下面的代码缩放画布，但唯一的问题是我缩放窗口大小的鼠标绘制消失。
I want to make a responsive canvas using size in percentage and once user will resize the window the canvas adjust relatively. I am able to scale the canvas by using below code but the only problem is as i scale the window size the mouse drawing disappear.
<style>
body{margin:0px;padding:0px;background:#a9a9a9;}
#main{
display:block;
width:80%;
padding:50px 10%;
height:300px;
}
canvas{display:block;background:#fff;}
</style>
</head>
<body>
<div id="main" role="main">
<canvas id="paint" width="100" height="100">
< !-- Provide fallback -->
</canvas>
</div>
<script>
var c = document.getElementById('paint');
var ctx = c.getContext('2d');
var x = null;
var y;
c.onmousedown = function(e){
x = e.pageX - c.offsetLeft;
y = e.pageY - c.offsetTop;
ctx.beginPath();
ctx.moveTo(x,y);
}
c.onmouseup = function(e){
x=null;
}
c.onmousemove = function(e){
if(x==null) return;
x = e.pageX - c.offsetLeft;
y = e.pageY - c.offsetTop;
ctx.lineTo(x,y);
ctx.stroke();
}
$(document).ready( function(){
//Get the canvas &
var c = $('#paint');
var container = $(c).parent();
//Run function when browser resizes
$(window).resize( respondCanvas );
function respondCanvas(){
c.attr('width', $(container).width() ); //max width
c.attr('height', $(container).height() ); //max height
//Call a function to redraw other content (texts, images etc)
}
//Initial call
respondCanvas();
});
</script>
谢谢。
推荐答案
调整画布大小时处理内容
如果调整画布大小，则绘制的内容总是被清除。这就是画布的行为。
If you resize the canvas, the drawn content is always erased. That's how canvas behaves.
您可以在调整大小后重新绘制内容，也可以将内容另存为图像数据，并在调整大小后恢复（请参见canvas.toDataURL）。
You can either redraw the content after resizing or you can save the content as image data and restore after resizing (see canvas.toDataURL).
以下是代码和小提琴： http://jsfiddle.net/m1erickson / V6SVz /
Here is code and a Fiddle: http://jsfiddle.net/m1erickson/V6SVz/
<!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; padding:10px; }
canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
// draw some content
ctx.lineWidth=3;
ctx.fillStyle="blue";
ctx.strokeStyle="red";
ctx.rect(50,50,100,50);
ctx.fill();
ctx.stroke();
ctx.font="14px Verdana";
ctx.fillStyle="white";
ctx.fillText("Scale Me",65,75);
function saveResizeAndRedisplay(scaleFactor){
// save the canvas content as imageURL
var data=canvas.toDataURL();
// resize the canvas
canvas.width*=scaleFactor;
canvas.height*=scaleFactor;
// scale and redraw the canvas content
var img=new Image();
img.onload=function(){
ctx.drawImage(img,0,0,img.width,img.height,0,0,canvas.width,canvas.height);
}
img.src=data;
}
$("#resizer").click(function(){ saveResizeAndRedisplay(1.5); });
}); // end $(function(){});
</script>
</head>
<body>
<button id="resizer">Click to resize the canvas</button><br/>
<canvas id="canvas" width=200 height=150></canvas>
</body>
</html>
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