canvas操作插件fabric.js使用方法详解 canvas操作插件fabric.js使用方法

fabric.js是一个很好用的 canvas 操作插件，下面整理了一些平时项目中用到的知识点：

//1: 获得画布上的所有对象：var items = canvas.getObjects(); //2: 设置画布上的某个对象为活动对象。canvas.setActiveObject(items[i]); //3：获得画布上的活动对象canvas.getActiveObject()//4：取消画布中的所有对象的选中状态。canvas.discardActiveObject(); //5: 设置画布中的对象的某个属性值，比如第 0 个对象的 idvar items = canvas.getObjects(); tems[0].id ="items_id0" 或 items[0].set("id","items_id0")//6：获得画布中对象的某个属性，比如第0 个对象的 idvar items = canvas.getObjects(); items[0].id; //或items[0].get("id"); //7: 重新渲染一遍画布，当画布中的对象有变更，在最后显示的时候，需要执行一次该操作canvas.renderAll()//8: 清除画布中所有对象：canvas.clear(); //9:清除画布中的活动对象： var t = canvas.getActiveObject(); t && canvas.remove(t); //10: 设置活动对象在画布中的层级var t = canvas.getActiveObject(); canvas.sendBackwards(t) //向下跳一层canvas.sendToBack(t)//向下跳底层：canvas.bringForward(t) //向上跳一层：canvas.bringToFront(t) //向上跳顶层：//或者：t.sendBackwards(); t.sendToBack(); t.bringForward(); t.bringToFront(); //10：加载图片时图片缩放到指定的大小。fabric.Image.fromURL(image_src, function(oImg) {oImg.set({left:tmp_left,top:tmp_top,centeredScaling:true,cornerSize: 7,cornerColor: "#9cb8ee",transparentCorners: false,}); oImg.scaleToWidth(image_width); oImg.scaleToHeight(image_height); canvas.add(oImg).setActiveObject(oImg); }); //11：当选择画布中的对象时，该对象不出现在顶层。canvas.preserveObjectStacking = true; // 12：为画布通过URL方式添加背景图片var bg_url = "http://www.xxxx.com/...../bg.png"fabric.Image.fromURL( bg_url , function(oImg) {oImg.set({width: canvas_obj.width, height: canvas_obj.height,originX: 'left', originY: 'top'}); canvas_obj.setBackgroundImage(oImg, canvas_obj.renderAll.bind(canvas_obj)); }); //13: originx: originy:代表坐标系。

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//14: 画布对象居中设置：var t = canvas.getActiveObject(); t.center(); //全部居中t.centerH(); //水平居中t.centerV(); //垂直居中t.setCoords(); //注：必须设coords以上设置才会有效。//15: 当对象移动时限制对象的不超出画布// canvas moving limit function objectMoving(e){var obj = e.target; if(obj.currentHeight > obj.canvas.height || obj.currentWidth > obj.canvas.width){return; }obj.setCoords(); // top-left cornerif(obj.getBoundingRect().top < 0 || obj.getBoundingRect().left < 0){obj.top = Math.max(obj.top, obj.top-obj.getBoundingRect().top); obj.left = Math.max(obj.left, obj.left-obj.getBoundingRect().left); }// bot-right cornerif(obj.getBoundingRect().top+obj.getBoundingRect().height > obj.canvas.height || obj.getBoundingRect().left+obj.getBoundingRect().width > obj.canvas.width){obj.top = Math.min(obj.top, obj.canvas.height-obj.getBoundingRect().height+obj.top-obj.getBoundingRect().top); obj.left = Math.min(obj.left, obj.canvas.width-obj.getBoundingRect().width+obj.left-obj.getBoundingRect().left); }}//16：当画布对象放大时限制其操出边界：//注意当创建对象到画布上时必须先加上： obj.saveState(); //在对象修改时方法里就可以调用了。 function objectModified (e) {let obj = e.target; let boundingRect = obj.getBoundingRect(true); if (boundingRect.left < 0|| boundingRect.top < 0|| boundingRect.left + boundingRect.width > obj.canvas.getWidth()|| boundingRect.top + boundingRect.height > obj.canvas.getHeight()) {obj.top = obj._stateProperties.top; obj.left = obj._stateProperties.left; obj.angle = obj._stateProperties.angle; obj.scaleX = obj._stateProperties.scaleX; obj.scaleY = obj._stateProperties.scaleY; obj.setCoords(); obj.saveState(); }else{obj.saveState(); }}//17:当生成json对象时，背景图片显示出来。fabric.Image.fromURL( bgImg, function(oImg) {oImg.set({width: 400,height:400,left:0,top:0,originX: 'left',originY: 'top',opacity:0}); //当toObject方法时显示背景图片。oImg.toObject = (function(toObject) {return function() {return fabric.util.object.extend(toObject.call(this), {opacity:1}); }; })(oImg.toObject); canvas_obj.setBackgroundImage(oImg, canvas_obj.renderAll.bind(canvas_obj)); }, { crossOrigin: 'Anonymous' }); //18：创建蒙版层//获取蒙版位置属性（非必要）：var maskLayerTop= parseInt($(this).attr("data-top")); var maskLayerLeft= parseInt($(this).attr("data-left")); var maskLayerWidth = parseInt($(this).attr("data-width")); var maskLayerHeight = parseInt($(this).attr("data-height")); //创建蒙版var clipMask = new fabric.Rect({originX: 'left',originY: 'top',left: maskLayerLeft,top: maskLayerTop,width: maskLayerWidth,height: maskLayerHeight,fill: 'rgba(0,0,0,0)', strokeWidth:0,selectable: false}); clipMask.set({clipFor: 'pug'}); canvas_obj.add(clipMask); function degToRad(degrees) {return degrees * (Math.PI / 180); }function findByClipName(name){return _(canvas_obj.getObjects()).where({clipFor: name}).first()}canvas_obj.clipByName = function(ctx) {this.setCoords(); var clipObj = findByClipName(this.clipName); var scaleXTo1 = (1 / this.scaleX); var scaleYTo1 = (1 / this.scaleY); var skewXReverse = - this.skewX; var skewYReverse = - this.skewY; ctx.save(); var ctxLeft = -( this.width / 2 ) + clipObj.strokeWidth; var ctxTop = -( this.height / 2 ) + clipObj.strokeWidth; var ctxWidth = clipObj.width - clipObj.strokeWidth; var ctxHeight = clipObj.height - clipObj.strokeWidth; ctx.translate( ctxLeft, ctxTop ); ctx.scale(scaleXTo1, scaleYTo1); ctx.transform(1, skewXReverse, skewYReverse, 1, 0, 0); ctx.rotate(degToRad(this.angle * -1)); ctx.beginPath(); ctx.rect(clipObj.left - this.oCoords.tl.x,clipObj.top - this.oCoords.tl.y,clipObj.width,clipObj.height); ctx.closePath(); ctx.restore(); } //调用的地方：//文字层设置蒙版 var t = new fabric.Text("Your Text", {id: first_level+"-text-input"+unique_id,cornerSize: 7,cornerColor: "#9cb8ee",transparentCorners: false,textAlign:"center",clipName: 'pug',clipTo: function(ctx) { return _.bind(tmp_canvas_obj.clipByName, t)(ctx) }}); // 图片层设置蒙版：// add the forntimage to the canvasfabric.Image.fromURL(image_src, function(oImg) {oImg.set({id:first_level+"-image-input"+unique_id,left:tmp_left,top:tmp_top,centeredScaling:true,cornerSize: 7,cornerColor: "#9cb8ee",transparentCorners: false,clipName: 'pug',clipTo: function(ctx) { return _.bind(tmp_canvas_obj.clipByName, oImg)(ctx) }}); //19：生成的图片缩放到指定的尺寸。oImg.scaleToWidth(image_width); oImg.scaleToHeight(image_height); //20：to object 时添加 id属性。oImg.toObject = (function(toObject) {return function() {return fabric.util.object.extend(toObject.call(this), {id: this.id,}); }; })(oImg.toObject); oImg.id = first_level+"-image-input"+unique_id; oImg.saveState(); tmp_canvas_obj.add(oImg).setActiveObject(oImg); }, { crossOrigin: 'Anonymous' }); tmp_canvas_obj.renderAll();

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