drawImage
的第4和第5个参数是宽度和高度。下面的例子将占据整个画布。
var URL = window.webkitURL || window.URL;
window.onload = function() {
var input = document.getElementById('input');
input.addEventListener('change', handleFiles, false);
}
function handleFiles(e) {
var ctx = document.getElementById('canvas').getContext('2d');
var url = URL.createObjectURL(e.target.files[0]);
var img = new Image();
img.onload = function() {
ctx.drawImage(img, 0, 0, ctx.canvas.width, ctx.canvas.height);
}
img.src = url;
}
#canvas {
background-color: salmon;
max-width: 50%;
}
<input type="file" id="input" />
<canvas id="canvas" />
如果你想要成比例的图像,我们可以使用
solution
在这里计算
var URL = window.webkitURL || window.URL;
window.onload = function() {
var input = document.getElementById('input');
input.addEventListener('change', handleFiles, false);
}
function handleFiles(e) {
var ctx = document.getElementById('canvas').getContext('2d');
var url = URL.createObjectURL(e.target.files[0]);
var img = new Image();
img.onload = function() {
var newDimen = calculateAspectRatioFit(img.width, img.height, ctx.canvas.width, ctx.canvas.height);
ctx.drawImage(img, 0, 0, newDimen.width, newDimen.height);
}
img.src = url;
}
function calculateAspectRatioFit(srcWidth, srcHeight, maxWidth, maxHeight) {
var ratio = Math.min(maxWidth / srcWidth, maxHeight / srcHeight);
return {
width: srcWidth * ratio,
height: srcHeight * ratio
};
}
#画布{
最大宽度:50%;
}
<输入type=“file”id=“input”/>
<canvas id=“canvas”/>
集中化
图像,您可以:
function handleFiles(e) {
var ctx = document.getElementById('canvas').getContext('2d');
var url = URL.createObjectURL(e.target.files[0]);
var img = new Image();
img.onload = function() {
var newDimen = calculateAspectRatioFit( img.width, img.height, ctx.canvas.width, ctx.canvas.height );
var tSpace = ( ctx.canvas.height - newDimen.height ) / 2;
var lSpace = ( ctx.canvas.width - newDimen.width ) / 2;
ctx.drawImage(img, lSpace, tSpace, newDimen.width, newDimen.height);
}
img.src = url;
}
