canva画图 图片居中裁剪_Canvas裁剪图片（截选框可拖拽）
利用Canvas實現(xiàn)圖片裁剪
效果圖
實現(xiàn)思路
打開圖片并將圖片繪制到canvas中；
利用canvas的drawImage()函數(shù)來裁剪圖片；
將canvas轉(zhuǎn)化為Image即可。
HTML代碼：
截圖
確認截圖
打開
CSS代碼
CSS代碼基本通過javaScript添加
body {
background-color: black;
}
重點JavaScript代碼
變量定義、添加各事件按鈕、容器等：
let originWidth; // 圖片原始寬度
let originHeight; // 圖片原始高度
let container = document.getElementById('container');
let imgDiv = document.getElementById('imgDiv'); // 存放mycanvas
let btnDiv = document.getElementById('btnDiv');
let clipImgDiv = document.getElementById('clipImgDiv'); // 顯示裁剪所獲的圖片
let btn1 = document.getElementById('btn1'); // 截圖按鈕
let btn2 = document.getElementById('btn2'); // 確認截圖按鈕
let btn3 = document.getElementById('btn3'); // 打開文件按鈕
var oRelDiv = document.createElement("div"); // 截圖框
var scaleX = 1;// 圖片寬度縮放比例(當前實際/原始)
var scaleY = 1; // 圖片高度縮放比例(當前實際/原始)
//拖拽與拉伸方法
//拖拽拉伸所需參數(shù)
let params = {
left: 0,
top: 0,
width: 0,
height: 0,
currentX: 0,
currentY: 0,
flag: false,
kind: "drag"
};
// CSS樣式修改
container.style.display = 'flex';
container.style.flexDirection = 'column';
btnDiv.style.marginBottom = '20px';
btnDiv.style.height = '30px';
imgDiv.style.marginBottom = '20px';
// 創(chuàng)建canvas，用于顯示被裁剪圖片
var myCanvas = document.createElement('canvas');
myCanvas.setAttribute('id', 'myCanvas');
myCanvas.style.display = 'block';
/*myCanvas.style.position = 'absolute';*/
myCanvas.width = 600;
myCanvas.height = 600;
myCanvas.style.border = "1px solid #d3d3d3";
myCanvas.innerText = '您的瀏覽器不支持 HTML5 canvas 標簽。';
myCanvas.style.zIndex = 'auto';
var ctx = myCanvas.getContext('2d');
// 被裁剪圖片
var img = new Image();
img.src = './images/IMG_1550.jpg';
img.setAttribute('id', 'img');
img.width = 600;
img.height = 600;
img.onload = function () {
console.log('onload()執(zhí)行...');
ctx.drawImage(img, 0, 0, 600, 600);
originWidth = img.naturalWidth;
originHeight = img.naturalHeight;
console.log('圖片原始寬度=', originWidth);
console.log('圖片原始高度=', originHeight);
};
// 裁剪得到的圖片
let clipImg = new Image();
clipImg.src = '';
clipImg.style.height = '100px';
clipImg.style.width = '100px';
clipImg.alt = '裁剪獲得圖片...';
// input用于打開文件
let fileInput = document.createElement('input');
fileInput.setAttribute('multiple', 'multiple');
fileInput.setAttribute('type', 'file');
fileInput.setAttribute('id', 'fileInput');
/*btnDiv.appendChild(fileInput);*/
imgDiv.appendChild(myCanvas);
/*clipImgDiv.appendChild(clipImg);*/
一些簡單的功能函數(shù)
// 生成本地圖片URL地址
let getObjectURL = function (file) {
let url = null;
if (window.createObjectURL !== undefined) { // basic
url = window.createObjectURL(file);
} else if (window.webkitURL !== undefined) { // webkit or chrome
url = window.webkitURL.createObjectURL(file);
} else if (window.URL !== undefined) { // mozilla(firefox)
url = window.URL.createObjectURL(file);
}
return url;
};
// 獲取指定元素DOM
const ID = function (id) {
return document.getElementById(id);
};
//獲取相關(guān)CSS屬性方法
let getCss = function (o, key) {
return o.currentStyle ? o.currentStyle[key] : document.defaultView.getComputedStyle(o, false)[key];
};
打開本地圖片
可伸縮截圖框?qū)崿F(xiàn)思路：
截圖框由8各控制截圖框大小、位置小div組成，鼠標在選中截圖框后在拖動鼠標的過程中會根據(jù)鼠標位置對截圖框進行實時繪制
// 打開本地圖片
fileInput.addEventListener('change', function () {
console.log('change()執(zhí)行...');
img.src = getObjectURL(this.files[0]);
});
btn3.addEventListener("click", function () {
fileInput.click();
});
截圖選框的繪制、拖動、大小調(diào)整
btn1.addEventListener("click", function () {
var clickFlag = false;
// 獲取canvas中圖片實際大小
var iCurWidth = img.width;
var iCurHeight = img.height;
console.log('圖片當前實際寬度=', iCurWidth);
console.log('圖片當前實際高度=', iCurHeight);
// 可調(diào)整截圖框
oRelDiv.innerHTML = '';
oRelDiv.style.position = "absolute";
oRelDiv.style.width = iCurWidth + "px";
oRelDiv.style.height = iCurHeight + "px";
oRelDiv.style.top = myCanvas.offsetTop + 'px';
console.log('oRelDiv.style.top = ', oRelDiv.style.top);
oRelDiv.id = "cropContainer";
var iOrigWidth = originWidth;
var iOrigHeight = originHeight;
scaleX = iCurWidth / iOrigWidth; // 圖片寬度縮放比例(當前實際/原始)
scaleY = iCurHeight / iOrigHeight; // 圖片高度縮放比例(當前實際/原始)
console.log('圖片橫向(寬度)縮放比=', scaleX);
console.log('圖片縱向(高度)縮放比=', scaleY);
// 將oRelDiv插入到myCanvas前
myCanvas.parentNode.insertBefore(oRelDiv, myCanvas);
//初始化坐標與剪裁高寬
var cropW = 80; //截圖框默認寬度
var cropH = 80; //截圖框默認高度
/*console.log('myCanvas.offsetLeft=', myCanvas.offsetLeft);
console.log('myCanvas.offsetTop=', myCanvas.offsetTop);*/
var posX = myCanvas.width / 2 - cropW / 2; // 截圖框左上角x坐標
var posY = myCanvas.height / 2 - cropH / 2; // 截圖框左上角y坐標
/*console.log('posX=',posX);
console.log('posY=',posY);*/
oRelDiv.innerHTML = '
' +'
'
'
'
'
'
'
'
'
'
' +'' +
'' +
'' +
'';
var startDrag = function (point, target, kind) {
//point是拉伸點，target是被拉伸的目標，其高度及位置會發(fā)生改變
//此處的target與上面拖拽的target是同一目標，故其params.left,params.top可以共用，也必須共用
//初始化寬高
params.width = getCss(target, "width");
params.height = getCss(target, "height");
//初始化坐標
if (getCss(target, "left") !== "auto") {
params.left = getCss(target, "left");
}
if (getCss(target, "top") !== "auto") {
params.top = getCss(target, "top");
}
//target是移動對象
point.onmousedown = function (event) {
params.kind = kind;
params.flag = true;
clickFlag = true;
if (!event) {
event = window.event;
}
var e = event;
params.currentX = e.clientX; //鼠標按下時坐標x軸
params.currentY = e.clientY; //鼠標按下時坐標y軸
/*console.log('params.currentX=', params.currentX);
console.log('params.currentY=', params.currentY);*/
//防止IE文字選中，有助于拖拽平滑
point.onselectstart = function () {
return false;
};
document.onmousemove = function (event) {
let e = event ? event : window.event;
clickFlag = false;
if (params.flag) {
var nowX = e.clientX; // 鼠標移動時x坐標
var nowY = e.clientY; // 鼠標移動時y坐標
var disX = nowX - params.currentX; // 鼠標x方向移動距離
var disY = nowY - params.currentY; // 鼠標y方向移動距離
if (params.kind === "n") {
//上拉伸
//高度增加或減小，位置上下移動
target.style.top = parseInt(params.top) + disY + "px";
target.style.height = parseInt(params.height) - disY + "px";
} else if (params.kind === "w") { //左拉伸
target.style.left = parseInt(params.left) + disX + "px";
target.style.width = parseInt(params.width) - disX + "px";
} else if (params.kind === "e") { //右拉伸
target.style.width = parseInt(params.width) + disX + "px";
} else if (params.kind === "s") { //下拉伸
target.style.height = parseInt(params.height) + disY + "px";
} else if (params.kind === "nw") { //左上拉伸
target.style.left = parseInt(params.left) + disX + "px";
target.style.width = parseInt(params.width) - disX + "px";
target.style.top = parseInt(params.top) + disY + "px";
target.style.height = parseInt(params.height) - disY + "px";
} else if (params.kind === "ne") { //右上拉伸
target.style.top = parseInt(params.top) + disY + "px";
target.style.height = parseInt(params.height) - disY + "px";
target.style.width = parseInt(params.width) + disX + "px";
} else if (params.kind === "sw") { //左下拉伸
target.style.left = parseInt(params.left) + disX + "px";
target.style.width = parseInt(params.width) - disX + "px";
target.style.height = parseInt(params.height) + disY + "px";
} else if (params.kind === "se") { //右下拉伸
target.style.width = parseInt(params.width) + disX + "px";
target.style.height = parseInt(params.height) + disY + "px";
} else { //移動
target.style.left = parseInt(params.left) + disX + "px";
target.style.top = parseInt(params.top) + disY + "px";
}
}
document.onmouseup = function () {
params.flag = false;
if (getCss(target, "left") !== "auto") {
params.left = getCss(target, "left");
}
if (getCss(target, "top") !== "auto") {
params.top = getCss(target, "top");
}
params.width = getCss(target, "width");
params.height = getCss(target, "height");
/*console.log('params.width=', params.width);
console.log('params.height', params.width);*/
//給隱藏文本框賦值
posX = parseInt(target.style.left);
posY = parseInt(target.style.top);
cropW = parseInt(target.style.width);
cropH = parseInt(target.style.height);
if (posX < 0) {
posX = 0;
}
if (posY < 0) {
posY = 0;
}
if ((posX + cropW) > iCurWidth) {
cropW = iCurWidth - posX;
}
if ((posY + cropH) > iCurHeight) {
cropH = iCurHeight - posY;
}
//賦值
ID("cropPosX").value = posX;
ID("cropPosY").value = posY;
ID("cropImageWidth").value = parseInt(ID("zxxCropBox").style.width);
ID("cropImageHeight").value = parseInt(ID("zxxCropBox").style.height);
/*console.log('posX=',posX);
console.log('posY=',posY);*/
};
}
};
};
//綁定拖拽
startDrag(ID("zxxDragBg"), ID("zxxCropBox"), "drag");
//綁定拉伸
startDrag(ID("dragLeftTop"), ID("zxxCropBox"), "nw");
startDrag(ID("dragLeftBot"), ID("zxxCropBox"), "sw");
startDrag(ID("dragRightTop"), ID("zxxCropBox"), "ne");
startDrag(ID("dragRightBot"), ID("zxxCropBox"), "se");
startDrag(ID("dragTopCenter"), ID("zxxCropBox"), "n");
startDrag(ID("dragBotCenter"), ID("zxxCropBox"), "s");
startDrag(ID("dragRightCenter"), ID("zxxCropBox"), "e");
startDrag(ID("dragLeftCenter"), ID("zxxCropBox"), "w");
//圖片不能被選中，目的在于使拖拽順滑
ID("myCanvas").onselectstart = function () {
return false;
};
img.onselectstart = function () {
return false;
};
});
所獲截圖繪制
function cropImage(img, cropPosX, cropPosY, width, height) {
/*var cropContainer = ID("cropContainer");
cropContainer.parentNode.removeChild(cropContainer);*/
/*ctx.clearRect(0, 0, myCanvas.width, myCanvas.height);*/
//sx,sy 是相對于圖片的坐標。巨坑
var newCanvas = document.createElement('canvas');
newCanvas.setAttribute('id', 'newCanvas');
newCanvas.width = width * scaleX;
newCanvas.height = height * scaleY;
newCanvas.style.border = "1px solid #d3d3d3";
var newCtx = newCanvas.getContext('2d');
clipImgDiv.appendChild(newCanvas);
newCtx.drawImage(img, cropPosX, cropPosY, width, height, 0, 0, width * scaleX, height * scaleY);
// canvas轉(zhuǎn)化為圖片
var newImage = new Image();
newImage.src = newCanvas.toDataURL("image/png");
newImage.style.marginLeft = '5px';
clipImgDiv.appendChild(newImage);
oRelDiv.innerHTML = '';
}
確認截圖
// 確認截圖
btn2.addEventListener("click", function () {
console.log("clipend......");
var x = document.getElementById("cropPosX").value;
var y = document.getElementById("cropPosY").value;
var w = document.getElementById("cropImageWidth").value;
var h = document.getElementById("cropImageHeight").value;
console.log('cropImage(img,', x, ',', y, ',', parseInt(w), ',', parseInt(h), ')');
cropImage(img, x / scaleX, y / scaleY, parseInt(w) / scaleX, parseInt(h) / scaleY);
});
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