javascript:上传图片文件并将其绘制到画布中 [英] javascript: upload image file and draw it into a canvas
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问题描述
我在一个Web应用程序中工作,用于绘制图像。我使用CANVAS元素和javascript来绘制它,但我有一个问题:如何从用户的PC加载图像,并将其绘制在画布上?我不想将它保存在服务器上,只保存在网页上!
I work at a web application for painting images. I use a CANVAS element and javascript to draw on it, but I have a problem: how can I load an image from the pc of the user and draw it on the canvas? I don't want to save it on the server, only on the webpage!
这是代码的缩写版本(完整代码太长):
Here is a shortened version of the code (the full code would be too long):
HTML:
Open file: <input type="file" id="fileUpload" accept="image/*" /><br />
<canvas id="canvas" onmousemove="keepLine()" onmouseup="drawLine()" onmousedown="startLine()" width="900" height="600" style="background-color:#ffffff;cursor:default;">
Please open this website on a browser with javascript and html5 support.
</canvas>
javascript:
javascript:
var x = 0;
var y = 0;
var clicked = false;
var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");
context.strokeStyle = "black";
context.lineCap = "round";
canvas.addEventListener('mousemove', function(e) { getMousePos(canvas, e); }, false);
takePicture.onchange = function (event) {
var files = event.target.files,
file;
if (files && files.length > 0) {
file = files[0];
processImage(file);
}
};
function processImage(file) {
var reader = new FileReader();
reader.readAsDataUrl(file)
reader.onload = function(e) {
var img = new Image();
img.onload = function() {
context.drawImage(img, 100,100)
}
img.src = e.target.result;
}
}
// functions for drawing (works perfectly well)
function getMousePos(canvas, e) {
var rect = canvas.getBoundingClientRect();
x = evt.clientX - rect.left;
y = evt.clientY - rect.top;
}
function startLine() {
context.moveTo(x,y);
context.beginPath();
clicked = true;
}
function keepLine() {
if(clicked) {
context.lineTo(x,y);
context.stroke();
context.moveTo(x,y);
}
}
function drawLine() {
context.lineTo(x,y);
context.stroke();
clicked = false;
}
没有版权
推荐答案
function el(id){return document.getElementById(id);} // Get elem by ID
var canvas = el("canvas");
var context = canvas.getContext("2d");
function readImage() {
if ( this.files && this.files[0] ) {
var FR= new FileReader();
FR.onload = function(e) {
var img = new Image();
img.onload = function() {
context.drawImage(img, 0, 0);
};
img.src = e.target.result;
};
FR.readAsDataURL( this.files[0] );
}
}
el("fileUpload").addEventListener("change", readImage, false);
<input type='file' id="fileUpload" />
<canvas id="canvas" width="900" height="600"></canvas>
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