canva画图 图片居中裁剪_Canvas裁剪图片（截选框可拖拽）
利用Canvas實現圖片裁剪
效果圖
實現思路
打開圖片并將圖片繪制到canvas中；
利用canvas的drawImage()函數來裁剪圖片；
將canvas轉化為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
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
// 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
可伸縮截圖框實現思路：
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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