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最近有网友问到了，HTML5 Canvas的缩放图片功能。我这里整理一下关于Canvas的相关图片操作写了一个实例，希望对大家能有所帮助！
<!DOCTYPE html>
<html>
<head>
<title>CANVAS touch测试</title>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"/>
<meta name="viewport" content="width=device-width,initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no">
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="Cache-Control" content="no-cache">
<meta http-equiv="Expires" content="0">
<meta name="apple-mobile-web-app-capable" content="yes">
<meta name="apple-mobile-web-app-status-bar-style" content="black">
<meta name="format-detection" content="telephone=no">
<meta name="apple-mobile-web-app-title" content="">
<style type="text/css">
*{ margin:0px; padding:0px; -webkit-tap-highlight-color:rgba(0,0,0,0); box-sizing:border-box;}
html{ min-width:320px; max-width:640px; margin:0 auto;}
body{ font-family:"PingFangSC-Regular","sans-serif","STHeitiSC-Light","微软雅黑","Microsoft YaHei"; color:; font-size:16px;
-webkit-user-select:none;/* 禁用长触选择文字等功能 */
user-select:none;
-webkit-touch-callout:none; /* 禁用长触弹出的下载图片菜单 */
touch-callout:none;
}
li{ list-style:none;}
i{ font-style:normal;}
a:link , a:visited , a:hover ,a:active{ text-decoration:none; color:;}
.cle:after{ content:""; display:block; height:0; clear:both;}
button ,
input ,
select ,
textarea{
outline:none; border-radius:0; font-size:16px; font-family:"PingFangSC-Regular","sans-serif","STHeitiSC-Light","微软雅黑","Microsoft YaHei";
-webkit-appearance:none; -moz-appearance:none; -ms-appearance:none; -o-appearance:none; appearance:none;
}
img{ vertical-align:middle;}
.f_right{ float:right;}
html,body{ display:block; width:100%; height:100%; position:relative;}
.hide{ display:none;}
.page1 , .page2{ width:100%; height:100%; line-height:1rem; position:absolute; left:0; top:0;}
.page1{ padding-top:2rem;}
.page1 > div{ margin-bottom:.5rem;}
.page1_left , .page1_right{ min-height:1rem; float:left;}
.page1_left{ width:30%; padding-right:.3rem; text-align:right;}
.page1_right{ width:70%;}
input , textarea{ width:80%; border:#e1e1e1 solid 1px; background:none; resize:none;}
input{ height:1rem;}
textarea{ height:2rem; line-height:.6rem;}
.show_img{ text-align:center;}
.show_img img{ height:2rem;}
.filebtn{ display:block; width:4rem; height:1rem; text-align:center; border-radius:.2rem; background-color:#ddd; cursor:pointer;}
.setbtn , .resetbtn{ width:5rem; height:1rem; margin:0 auto .5rem auto; border-radius:2px; border:#e1e1e1 solid 1px; background-color:#eee; text-align:center; cursor:pointer;}
.page2{}
canvas{ width:100%; height:auto; margin:0; padding:0;}
.roat_img{ display:block; width:2rem; height:2rem; line-height:2rem; text-align:center; border-radius:50%; background-color:#ddd; cursor:pointer; position:fixed; right:.5rem; top:50%;}
.show_end_img{ display:block; width:5rem; height:1rem; border-radius:2px; border:#e1e1e1 solid 1px; background-color:#eee; text-align:center; cursor:pointer; position:fixed; left:50%; margin-left:-2.5rem; bottom:2rem;}
.page3{ width:100%; height:100%; text-align:center; background-color:rgba(0,0,0,.6); position:fixed; left:50%; top:50%; -webkit-transform:translate(-50%,-50%); transform:translate(-50%,-50%);}
.page3 img{ display:inline-block; width:90%;}
.page3:after{ content:""; display:inline-block; width:0; height:100%; vertical-align:middle;}
</style>
</head>
<body>
<section class="page1">
<div class="cle">
<div class="page1_left">第一句话</div>
<div class="page1_right"><input type="text" id="uptitle" name="uptitle" value="" maxlength="10" /></div>
</div>
<div class="cle">
<div class="page1_left">第二句话</div>
<div class="page1_right"><textarea id="upcontent" name="upcontent"></textarea></div>
</div>
<div class="show_img hide"><img src="" /></div>
<div class="cle">
<div class="page1_left">上传照片</div>
<div class="page1_right"><span class="filebtn">选择图片</span><input class="hide" type="file" id="upfile" name="upfile" value="" accept="image/*" /></div>
</div>
<div class="setbtn">生成预览</div>
<div class="resetbtn">重置</div>
</section>
<section class="page2 hide">
<canvas id="canvas_img"></canvas>
<span class="roat_img">旋转</span>
<span class="show_end_img">生成图片</span>
</section>
<section class="page3 hide"><img src=""/></section>
<script type="text/javascript" src="http://code.jquery.com/jquery-2.0.0.min.js"></script>
<script type="text/javascript">
function initHtmlFontSize(){
var _width = document.body.clientWidth;
_width = _width>640?640:_width;
var _fs = _width/16;
document.getElementsByTagName("html")[0].style.fontSize = _fs+"px";
}
initHtmlFontSize();
function getObjectURL(file) {
var url = null ;
if (window.createObjectURL!=undefined) { // basic
url = window.createObjectURL(file) ;
} else if (window.URL!=undefined) { // mozilla(firefox)
url = window.URL.createObjectURL(file) ;
} else if (window.webkitURL!=undefined) { // webkit or chrome
url = window.webkitURL.createObjectURL(file) ;
}
return url ;
}
$(function(){
var img , imgurl;
var canvas_img = document.getElementById("canvas_img");
var ctx_2d = canvas_img.getContext("2d");
//上传图片
$('.filebtn').on('click',function(){
$('#upfile').trigger('click');
});
$('#upfile').on('change', function(){
imgurl = getObjectURL(this.files[0]);
img = new Image();
img.src = imgurl;
img.onload = function(){
ctxmsg.imgoldw = img.width ,
ctxmsg.imgoldh = img.height;
};
$(this).val('');
$('.show_img img').attr('src', imgurl);
$('.show_img').show();
});
//重置
$('.resetbtn').on('click',function(){
$('#uptitle').val('');
$('#upcontent').val('');
$('#upfile').val('');
$('.show_img').hide();
$('.show_img img').attr('src', '');
});
//生成图片
$('.show_end_img').on('click',function(){
var new_img_src = canvas_img.toDataURL("image/jpg");
$('.page3 img').attr('src', new_img_src);
$('.page3').show();
})
//旋转canvas中的图片
var roate_num = 0;
var create_cvs = document.createElement('canvas');
var create_cvs_2d = create_cvs.getContext('2d');
var ifroate = false;
$('.roat_img').on('click',function(){
console.log('上次宽：' + ctxmsg.imgw + ' 上次高：' + ctxmsg.imgh);
ifroate = true;
roate_num += 90;
roate_num = roate_num % 360;
var w = img.width;
var h = img.height;
var x = w/-2;
var y = h/-2;
if(roate_num % 180 != 0){
create_cvs.width = h;
create_cvs.height = w;
if(w > h){
console.log(1);
ctxmsg.imgw = ctxmsg.w;
ctxmsg.imgh = ctxmsg.w / h * w;
}else{
console.log(2);
ctxmsg.imgh = ctxmsg.h;
ctxmsg.imgw = ctxmsg.h / w * h;
}
}else{
create_cvs.width = w;
create_cvs.height = h;
if(w > h){
console.log(3);
ctxmsg.imgh = ctxmsg.h;
ctxmsg.imgw = ctxmsg.h / h * w;
}else{
console.log(4);
ctxmsg.imgw = ctxmsg.w;
ctxmsg.imgh = ctxmsg.w / w * h;
}
}
create_cvs_2d.translate(create_cvs.width/2, create_cvs.height/2);
create_cvs_2d.rotate(roate_num * Math.PI/180);
create_cvs_2d.drawImage(img, x, y);
//防止旋转图片后，指定画图区留白（图片小于画图区）
if(ctxmsg.imgw < ctxmsg.w){
ctxmsg.imgh = ctxmsg.w / ctxmsg.imgw * ctxmsg.imgh;
ctxmsg.imgw = ctxmsg.w;
}
if(ctxmsg.imgh < ctxmsg.h){
ctxmsg.imgw = ctxmsg.h / ctxmsg.imgh * ctxmsg.imgw;
ctxmsg.imgh = ctxmsg.h;
}
ctxmsg.imgx = ctxmsg.x;
ctxmsg.imgy = ctxmsg.y;
drawNewImg();
console.log('本次宽：' + ctxmsg.imgw + ' 本次高：' + ctxmsg.imgh);
});
//预览（首次生成CANVAS图片）
$('.setbtn').on('click',function(){
var title = $.trim($('#uptitle').val());
var content = $.trim($('#upcontent').val());
if(!$.trim(title)){
alert('请填写你的表白对象哦');
return;
}
if(!$.trim(content)){
alert('请填写你想说的话哦');
return;
}
if(!imgurl){
alert('请上传图片');
return;
}
setcanvas(title,content,imgurl);
});
function setcanvas(title,content,imgurl){
bgimg = new Image();
//底图图片 640 的宽度，所有距离长度 相对此宽度 设置的
bgimg.src = "bg.jpg";//跨域问题，只能相对路径的图片生成图片时不会出错
bgimg.onload = function() {
var iw = bgimg.width;
var ih = bgimg.height;
canvas_img.width = iw;
canvas_img.height = ih;
ctx_2d.drawImage(bgimg,0,0,iw,ih,0,0,iw,ih);
drawNewImg();
ctx_2d.font = 'bold 24px "PingFangSC-Regular","sans-serif","STHeitiSC-Light","微软雅黑","Microsoft YaHei"';
ctx_2d.fillStyle = '#E86B59';
ctx_2d.textBaseline="top";
ctx_2d.textAlign="left";
ctx_2d.fillText(title, 182, 543);
ctx_2d.fillStyle = '#A14FB1';
writeTextOnCanvas(ctx_2d,40,24,content,182,615);
$('.page1').hide();
$('.page2').show();
}
}
var touchs = {
startx:0,starty:0,endx:0,endy:0,
startx2:0,starty2:0,endx2:0,endy2:0,
};
canvas_img.addEventListener("touchstart", canvasTouchStart, false);
canvas_img.addEventListener("touchmove", canvasTouchMove, false);
canvas_img.addEventListener("touchend", canvasTouchEnd, false);
function canvasTouchEnd(e){
}
function canvasTouchStart(e){
e.preventDefault();
touchs.startx = e.touches[0].pageX;
touchs.starty = e.touches[0].pageY;
if(e.touches.length == 1){
ctxmsg.imgoldx = ctxmsg.imgx;
ctxmsg.imgoldy = ctxmsg.imgy;
}else if(e.touches.length == 2){
touchs.startx2 = e.touches[1].pageX;
touchs.starty2 = e.touches[1].pageY;
ctxmsg.imgoldw = ctxmsg.imgw;
ctxmsg.imgoldh = ctxmsg.imgh;
}
}
function canvasTouchMove(e){
e.preventDefault();
touchs.endx = e.touches[0].pageX;
touchs.endy = e.touches[0].pageY;
if(e.touches.length == 1){
ctxmsg.imgx = ctxmsg.imgoldx + touchs.endx - touchs.startx;
ctxmsg.imgy = ctxmsg.imgoldy + touchs.endy - touchs.starty;
}else if(e.touches.length == 2){
touchs.endx2 = e.touches[1].pageX;
touchs.endy2 = e.touches[1].pageY;
//var xdiff = x2 - x1;
//var ydiff = y2 - y1;
var xdiff1 = touchs.startx2 - touchs.startx;
var ydiff1 = touchs.starty2 - touchs.starty;
var line1 = Math.sqrt(Math.pow(xdiff1 , 2) + Math.pow(ydiff1 , 2));
var xdiff2 = touchs.endx2 - touchs.endx;
var ydiff2 = touchs.endy2 - touchs.endy;
var line2 = Math.sqrt(Math.pow(xdiff2, 2) + Math.pow(ydiff2, 2));
img_new_w = ctxmsg.imgw + (line2 - line1) / 20;
img_new_h = img_new_w / ctxmsg.imgw * ctxmsg.imgh;
//固定区域内缩放，画图区域不留白
if(img_new_w <= ctxmsg.w || img_new_h <= ctxmsg.h){
return;
}
ctxmsg.imgx -= img_new_w - ctxmsg.imgw;
ctxmsg.imgy -= img_new_h - ctxmsg.imgh;
ctxmsg.imgw = img_new_w;
ctxmsg.imgh = img_new_h;
}
//固定区域内移动，画图区域不留白
if(ctxmsg.imgw <= ctxmsg.w || ctxmsg.imgx > ctxmsg.x){
ctxmsg.imgx = ctxmsg.x;
}else if(ctxmsg.imgw > ctxmsg.w && ctxmsg.imgx <= ctxmsg.x - (ctxmsg.imgw - ctxmsg.w)){
ctxmsg.imgx = ctxmsg.x - (ctxmsg.imgw - ctxmsg.w);
}
if(ctxmsg.imgh <= ctxmsg.h || ctxmsg.imgy > ctxmsg.y){
ctxmsg.imgy = ctxmsg.y;
}else if(ctxmsg.imgh > ctxmsg.h && ctxmsg.imgy <= ctxmsg.y - (ctxmsg.imgh - ctxmsg.h)){
ctxmsg.imgy = ctxmsg.y - (ctxmsg.imgh - ctxmsg.h);
}
drawNewImg();
}
var ctxmsg = {
x:155,y:77,w:334,h:293,
imgx:155,imgy:77,imgw:0,imgh:0,
imgoldx:0,imgoldy:0,imgoldw:0,imgoldh:0
};
function drawNewImg(cvs){
ctx_2d.clearRect(ctxmsg.x,ctxmsg.y,ctxmsg.w,ctxmsg.h);
ctx_2d.rect(ctxmsg.x,ctxmsg.y,ctxmsg.w,ctxmsg.h);
ctx_2d.save();
ctx_2d.clip();
//ctxmsg.imgoldw = img.width ,
//ctxmsg.imgoldh = img.height;
if(!ctxmsg.imgw){
//设置画入画布内的图片宽、高（等比例铺满指定盒子，溢出被剪切掉）
if(ctxmsg.imgoldw/ctxmsg.imgoldh > ctxmsg.w/ctxmsg.h){
ctxmsg.imgh = ctxmsg.h;
ctxmsg.imgw = ctxmsg.h / ctxmsg.imgoldh * ctxmsg.imgoldw;
}else{
ctxmsg.imgw = ctxmsg.w;
ctxmsg.imgh = ctxmsg.w / ctxmsg.imgoldw * ctxmsg.imgoldh;
}
}
if(ifroate){
ctx_2d.drawImage(create_cvs , ctxmsg.imgx , ctxmsg.imgy , ctxmsg.imgw , ctxmsg.imgh);
}else{
ctx_2d.drawImage(img , ctxmsg.imgx , ctxmsg.imgy , ctxmsg.imgw , ctxmsg.imgh);
}
ctx_2d.restore();
}
function writeTextOnCanvas(ctx_2d, lineheight, bytelength, text ,startleft, starttop){
function getTrueLength(str){//获取字符串的真实长度（字节长度）
var len = str.length, truelen = 0;
for(var x = 0; x < len; x++){
if(str.charCodeAt(x) > 128){
truelen += 2;
}else{
truelen += 1;
}
}
return truelen;
}
function cutString(str, leng){//按字节长度截取字符串，返回substr截取位置
var len = str.length, tlen = len, nlen = 0;
for(var x = 0; x < len; x++){
if(str.charCodeAt(x) > 128){
if(nlen + 2 < leng){
nlen += 2;
}else{
tlen = x;
break;
}
}else{
if(nlen + 1 < leng){
nlen += 1;
}else{
tlen = x;
break;
}
}
}
return tlen;
}
for(var i = 1; getTrueLength(text) > 0; i++){
var tl = cutString(text, bytelength);
ctx_2d.fillText(text.substr(0, tl).replace(/^\s+|\s+$/, ""), startleft, (i-1) * lineheight + starttop);
text = text.substr(tl);
}
}
});
</script>
</body>
</html>
用到的背景图片
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本文原文出处：业余草： » 详解HTML5 canvas移动、缩放、旋转插入的图片