/** 管理绘图的工具 */ define(function() { var history = []; //用来保存历史绘制记录的数组，里面存储的是直线类、矩形类或者圆形类的对象 function drawLine(context, line) { line.drawMe(context); } function drawRect(context, rect) { rect.drawMe(context); } function drawArc(context, arc) { arc.drawMe(context); } /** 添加一条绘制轨迹 */ function addHistory(item) { history.push(item); } /** 画出历史轨迹 */ function drawHistory(context) { for(var i = 0; i < history.length; i++) { var obj = history[i]; obj.drawMe(context); } } /** 清除历史轨迹 */ function clearHistory() { history = []; } return { drawLine: drawLine, drawRect: drawRect, drawArc: drawArc, addHistory: addHistory, drawHistory: drawHistory, clearHistory: clearHistory }; })
三、编写界面代码，处理鼠标事件
上面已经将本次简易绘图程序的模块都定义完了，在绘制图形时用到的也就是上面几个模块，下面要开始编写主界面的代码了，主界面里包含四个按钮，还有一块大的画布用于绘图，下面直接上index.html文件的代码：
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>简易绘图程序</title> <style type="text/css"> canvas { background-color: #ECECEC; cursor: default; /** 鼠标设置成默认的指针 */ } .tool-bar { margin-bottom: 10px; } </style> </head> <body> <div> <button>画直线</button> <button>画矩形</button> <button>画圆形</button> <button>清空画布</button> <span>当前操作：画直线</span> </div> <canvas></canvas> <script type="text/javascript" src="https://www.jb51.net/js/require.min.js" data-main="js/main"></script> <script type="text/javascript"> require(['app/point', 'app/line', 'app/rect', 'app/arc', 'app/utils'], function(Point, Line, Rect, Arc, Utils) { var canvas = document.getElementById("canvas"); var context = canvas.getContext('2d'); var canvasRect = canvas.getBoundingClientRect(); //得到canvas所在的矩形 canvas.addEventListener('mousedown', handleMouseDown); canvas.addEventListener('mousemove', handleMouseMove); canvas.addEventListener('mouseup', handleMouseUp); bindClick('btn-clear', menuBtnClicked); bindClick('btn-line', menuBtnClicked); bindClick('btn-rect', menuBtnClicked); bindClick('btn-oval', menuBtnClicked); var mouseDown = false; var selection = 1; // 0, 1, 2分别代表画直线、画矩形、画圆 var downPoint = new Point(0, 0), movePoint = new Point(0, 0), upPoint = new Point(0, 0); var line; var rect; var arc; /** 处理鼠标按下的事件 */ function handleMouseDown(event) { downPoint.x = event.clientX - canvasRect.left; downPoint.y = event.clientY - canvasRect.top; if(selection === 0) { line = new Line(downPoint, downPoint); line.startPoint = downPoint; } else if(selection === 1) { rect = new Rect(new Point(downPoint.x, downPoint.y), 0, 0); } else if(selection === 2) { arc = new Arc(new Point(downPoint.x, downPoint.y), 0); } mouseDown = true; } /** 处理鼠标移动的事件 */ function handleMouseMove(event) { movePoint.x = event.clientX - canvasRect.left; movePoint.y = event.clientY - canvasRect.top; if(movePoint.x == downPoint.x && movePoint.y == downPoint.y) { return ; } if(movePoint.x == upPoint.x && movePoint.y == upPoint.y) { return ; } if(mouseDown) { clearCanvas(); if(selection == 0) { line.endPoint = movePoint; Utils.drawLine(context, line); } else if(selection == 1) { rect.width = movePoint.x - downPoint.x; rect.height = movePoint.y - downPoint.y; Utils.drawRect(context, rect); } else if(selection == 2) { var x = movePoint.x - downPoint.x; var y = movePoint.y - downPoint.y; arc.radius = x > y ? (y / 2) : (x / 2); if(arc.radius < 0) { arc.radius = -arc.radius; } arc.startPoint.x = downPoint.x + arc.radius; arc.startPoint.y = downPoint.y + arc.radius; Utils.drawArc(context, arc); } Utils.drawHistory(context); } } /** 处理鼠标抬起的事件 */ function handleMouseUp(event) { upPoint.x = event.clientX - canvasRect.left; upPoint.y = event.clientY - canvasRect.top; if(mouseDown) { mouseDown = false; if(selection == 0) { line.endPoint = upPoint; if(!downPoint.equals(upPoint)) { Utils.addHistory(new Line(new Point(downPoint.x, downPoint.y), new Point(upPoint.x, upPoint.y))); } } else if(selection == 1) { rect.width = upPoint.x - downPoint.x; rect.height = upPoint.y - downPoint.y; Utils.addHistory(new Rect(new Point(downPoint.x, downPoint.y), rect.width, rect.height)); } else if(selection == 2) { Utils.addHistory(new Arc(new Point(arc.startPoint.x, arc.startPoint.y), arc.radius)); } clearCanvas(); Utils.drawHistory(context); } } /** 清空画布 */ function clearCanvas() { context.clearRect(0, 0, canvas.width, canvas.height); } /** 菜单按钮的点击事件处理 */ function menuBtnClicked(event) { var domID = event.srcElement.id; if(domID === 'btn-clear') { clearCanvas(); Utils.clearHistory(); } else if(domID == 'btn-line') { selection = 0; showHint('当前操作：画直线'); } else if(domID == 'btn-rect') { selection = 1; showHint('当前操作：画矩形'); } else if(domID == 'btn-oval') { selection = 2; showHint('当前操作：画圆形'); } } function showHint(msg) { document.getElementById('hint').innerHTML = msg; } /** 给对应id的dom元素绑定点击事件 */ function bindClick(domID, handler) { document.getElementById(domID).addEventListener('click', handler); } }); </script> </body> </html>