Generally, when processing image upload, the usual logic is to upload the source image to the server side, and then the server side language performs the operation of scaling.
This mode can generally meet most needs, but when the image we need is just a thumbnail of the source image of a specified size, using this mode will be a way to waste server resources and bandwidth. Therefore, we consider generating small images on the browser and then uploading them.
//The following is the source code
The code copy is as follows:
function drawCanvasImage(obj,width, callback){
var $canvas = $('<canvas></canvas>'),
canvas = $canvas[0],
context = canvas.getContext('2d');
var img = new Image();
img.onload = function(){
if(width){
if(width > img.width){
var target_w = img.width;
var target_h = img.height;
}else{
var target_w = width;
var target_h = parseInt(target_w/img.width*img.height);
}
}else{
var target_w = img.width;
var target_h = img.height;
}
$canvas[0].width = target_w;
$canvas[0].height = target_h;
context.drawImage(img,0,0,target_w,target_h);
_canvas = canvas.toDataURL();
/*console.log(_canvas);*/
callback(obj,_canvas);
}
img.src = getFullPath(obj);
}
function getFullPath(obj)
{
if(obj)
{
//ie
if (window.navigator.userAgent.indexOf("MSIE")>=1)
{
obj.select();
return document.selection.createRange().text;
}
//firefox
else if(window.navigator.userAgent.indexOf("Firefox")>=1 || $.browser.opera || $.browser.mozilla)
{
if(obj.files && window.URL.createObjectURL)
{
return window.URL.createObjectURL(obj.files[0]);
}
return obj.value;
}else if($.browser.safari){
if(window.webkitURL.createObjectURL && obj.files){
return window.webkitURL.createObjectURL(obj.files[0]);
}
return obj.value;
}
return obj.value;
}
}
The function getFullPath is to get the address of the selected image.
_canvas gets the base64-encoded image encoding, and just transfer it to the backend to write to the file.