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:///...../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。//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 corner if(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 corner if(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();

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。