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Canvas初识 什么是Canvas？HTML5 的 canvas 元素使用 JavaScript 在网页上绘制图像。 创建Canvas元素向 HTML5 页面添加 canvas 元素。 <canvas id="myCanvas" width="200" height="100"></canvas> Canvas坐标系[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-axGxgAIc-1612178234725)(images/location.jpg)] 通过JavaScript来绘制 /*获取元素*/var myCanvas = document.querySelector('#myCanvas');/*获取绘图工具*/var context = myCanvas.getContext('2d');/*设置绘图的起始位置*/context.moveTo(100,100);/*绘制路径*/context.lineTo(200,200);/*描边*/context.stroke(); 完整代码 <!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;/*不建议在 css样式设置尺寸 这里只是样式多大 是对画布的拉伸 实际画布还是初始值那么大*//*width: 600px;
height: 400px;*/}</style></head><body><!--1.准备画布--><!--1.1 画布是白色的 而且默认300*150--><!--1.2 设置画布的大小 width="600" height="400" --><canvas width="600" height="400" ></canvas><!--2.准备绘制工具--><!--3.利用工具绘图--><script>/*1.获取元素*/var myCanvas = document.querySelector('canvas');/*2.获取上下文 绘制工具箱 *//*是否有3d 暂时没有*/var ctx = myCanvas.getContext('2d'); /*web gl 绘制3d效果的网页技术*//*3.移动画笔*/ctx.moveTo(100,100);/*4.绘制直线 (轨迹，绘制路径)*/ctx.lineTo(200,100);/*5.描边*/ctx.stroke();</script></body></html> Canvas的基本使用图形绘制需要理解些概念：
设置样式
画笔实例练习渐变色绘制<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}</style></head><body><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');/*线是由点构成的*/ctx.lineWidth = 30;for (var i = 0; i < 255; i++) {ctx.beginPath();ctx.moveTo(100+i-1,100);ctx.lineTo(100+i,100);ctx.strokeStyle = 'rgb('+i+',0,0)';ctx.stroke();}</script></body></html> 镂空的房子<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}</style></head><body><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');/*1.绘制两个正方形 一大200一小100 套在一起*/ctx.moveTo(100,100);ctx.lineTo(300,100);ctx.lineTo(300,300);ctx.lineTo(100,300);ctx.closePath();ctx.moveTo(150,150);ctx.lineTo(150,250);ctx.lineTo(250,250);ctx.lineTo(250,150);ctx.closePath();/*2.去填充*///ctx.stroke();ctx.fillStyle = 'red';ctx.fill();/*在填充的时候会遵循非零环绕规则*/</script></body></html> 绘制坐标网格<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}</style></head><body><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');/*1.绘制网格*//*2.网格的大小*/var gridSize = 10;var canvasHeight = ctx.canvas.height;var canvasWidth = ctx.canvas.width;/*3.画多少条X轴方向的线 横线的条数 画布高度/小格大小 */var xLineTotal = Math.floor(canvasHeight / gridSize);for (var i = 0; i <= xLineTotal; i++) {ctx.beginPath();ctx.moveTo(0, i * gridSize - 0.5 );ctx.lineTo(canvasWidth, i * gridSize - 0.5);ctx.strokeStyle = '#eee';ctx.stroke();}/*4.画多少条Y轴方向的线*/var yLineTotal = Math.floor(canvasWidth / gridSize);for (var i = 0; i <= yLineTotal; i++) {ctx.beginPath();ctx.moveTo(i*gridSize - 0.5 ,0);ctx.lineTo(i*gridSize - 0.5 ,canvasHeight);ctx.strokeStyle = '#eee';ctx.stroke();}</script></body></html> 绘制坐标系<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}</style></head><body><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');/*1.绘制坐标系*//*2.确定原点*//*3.确定距离画布旁边的距离*//*4.确定坐标轴的长度*//*5.确定箭头的大小 是个等腰三角形 10 *//*6.绘制箭头填充*/// 坐标轴与底部的间隔var space = 20;// 箭头大小var arrowSize = 10; /*计算原点 x0 y0*/var canvasWidth = ctx.canvas.width;var canvasHeight = ctx.canvas.height;var x0 = space;var y0 = canvasHeight - space;/*绘制x轴*/ctx.beginPath();ctx.moveTo(x0, y0);ctx.lineTo(canvasWidth - space, y0);/*箭头*/ctx.lineTo(canvasWidth - space - arrowSize, y0 + arrowSize / 2);ctx.lineTo(canvasWidth - space - arrowSize, y0 - arrowSize / 2);ctx.lineTo(canvasWidth - space, y0);ctx.fill();ctx.stroke();/*绘制y轴*/ctx.beginPath();ctx.moveTo(x0, y0);ctx.lineTo(space, space);/*箭头*/ctx.lineTo(space + arrowSize / 2, space + arrowSize);ctx.lineTo(space - arrowSize / 2, space + arrowSize);ctx.lineTo(space, space);ctx.fill();ctx.stroke();</script></body></html> 绘制坐标点<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}</style></head><body><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');/*1.绘制点*//*2.点的尺寸*//*3.以坐标中心绘制点*//*点坐标*/var coordinate = {x:100,y:100}/*点尺寸*/var dottedSize = 10;ctx.moveTo(coordinate.x - dottedSize / 2,coordinate.y - dottedSize / 2);ctx.lineTo(coordinate.x + dottedSize / 2,coordinate.y - dottedSize / 2);ctx.lineTo(coordinate.x + dottedSize / 2,coordinate.y + dottedSize / 2);ctx.lineTo(coordinate.x - dottedSize / 2,coordinate.y + dottedSize / 2);ctx.closePath();ctx.fill();</script></body></html> 绘制折线图<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>折线图</title><style>canvas {border: 1px solid #ccc;}</style></head><body><canvas width="600" height="400"></canvas><script>/*1.构造函数*/var LineChart = function (ctx) {/*获取绘图工具*/this.ctx = ctx || document.querySelector('canvas').getContext('2d');/*画布的大小*/this.canvasWidth = this.ctx.canvas.width;this.canvasHeight = this.ctx.canvas.height;/*网格的大小*/this.gridSize = 10;/*坐标系的间距*/this.space = 20;/*坐标原点*/this.x0 = this.space;this.y0 = this.canvasHeight - this.space;/*箭头的大小*/this.arrowSize = 10;/*绘制点*/this.dottedSize = 6;/*点的坐标 和数据有关系 数据可视化*/}/*2.行为方法*/LineChart.prototype.init = function (data) {this.drawGrid();this.drawAxis();this.drawDotted(data);};/*绘制网格*/LineChart.prototype.drawGrid = function () {/*x方向的线*/var xLineTotal = Math.floor(this.canvasHeight / this.gridSize);this.ctx.strokeStyle = '#eee';for (var i = 0; i <= xLineTotal; i++) {this.ctx.beginPath();this.ctx.moveTo(0, i * this.gridSize - 0.5);this.ctx.lineTo(this.canvasWidth, i * this.gridSize - 0.5);this.ctx.stroke();}/*y方向的线*/var yLineTotal = Math.floor(this.canvasWidth / this.gridSize);for (var i = 0; i <= yLineTotal; i++) {this.ctx.beginPath();this.ctx.moveTo(i * this.gridSize - 0.5, 0);this.ctx.lineTo(i * this.gridSize - 0.5, this.canvasHeight);this.ctx.stroke();}};/*绘制坐标系*/LineChart.prototype.drawAxis = function () {/*X轴*/this.ctx.beginPath();this.ctx.strokeStyle = '#000';this.ctx.moveTo(this.x0, this.y0);this.ctx.lineTo(this.canvasWidth - this.space, this.y0);this.ctx.lineTo(this.canvasWidth - this.space - this.arrowSize, this.y0 + this.arrowSize / 2);this.ctx.lineTo(this.canvasWidth - this.space - this.arrowSize, this.y0 - this.arrowSize / 2);this.ctx.lineTo(this.canvasWidth - this.space, this.y0);this.ctx.stroke();this.ctx.fill();/*Y轴*/this.ctx.beginPath();this.ctx.strokeStyle = '#000';this.ctx.moveTo(this.x0, this.y0);this.ctx.lineTo(this.space, this.space);this.ctx.lineTo(this.space + this.arrowSize / 2, this.space + this.arrowSize);this.ctx.lineTo(this.space - this.arrowSize / 2, this.space + this.arrowSize);this.ctx.lineTo(this.space, this.space);this.ctx.stroke();this.ctx.fill();};/*绘制所有点*/LineChart.prototype.drawDotted = function (data) {/*1.数据的坐标 需要转换 canvas坐标*//*2.再进行点的绘制*//*3.把线连起来*/var that = this;/*记录当前坐标*/var prevCanvasX = 0;var prevCanvasY = 0;data.forEach(function (item, i) {/* x = 原点的坐标 + 数据的坐标 *//* y = 原点的坐标 - 数据的坐标 */console.log("item =");console.log(item);console.log( "i="+i);var canvasX = that.x0 + item.x;var canvasY = that.y0 - item.y;/*绘制点*/that.ctx.beginPath();that.ctx.moveTo(canvasX - that.dottedSize / 2, canvasY - that.dottedSize / 2);that.ctx.lineTo(canvasX + that.dottedSize / 2, canvasY - that.dottedSize / 2);that.ctx.lineTo(canvasX + that.dottedSize / 2, canvasY + that.dottedSize / 2);that.ctx.lineTo(canvasX - that.dottedSize / 2, canvasY + that.dottedSize / 2);that.ctx.closePath();that.ctx.fill();/*点的连线*//*当时第一个点的时候 起点是 x0 y0*//*当时不是第一个点的时候 起点是 上一个点*/if(i == 0){that.ctx.beginPath();that.ctx.moveTo(that.x0,that.y0);that.ctx.lineTo(canvasX,canvasY);that.ctx.stroke();}else{/*上一个点*/that.ctx.beginPath();that.ctx.moveTo(prevCanvasX,prevCanvasY);that.ctx.lineTo(canvasX,canvasY);that.ctx.stroke();}/*记录当前的坐标，下一次要用*/prevCanvasX = canvasX;prevCanvasY = canvasY;});};/*3.初始化*/var data = [{x: 100,y: 300},{x: 200,y: 160},{x: 300,y: 240},{x: 400,y: 120},{x: 500,y: 80}];var lineChart = new LineChart();lineChart.init(data);</script></body></html> 参考文档
Canvas图形绘制矩形绘制
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}</style></head><body><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');/*绘制矩形路径 不是独立路径*/ctx.rect(100,100,100,100);ctx.fillStyle = 'green';ctx.stroke();ctx.fill();/*绘制矩形 有自己的独立路径*/ctx.fillStyle = 'red';ctx.strokeRect(200,200,100,100);
ctx.fillStyle = 'skyblue';ctx.fillRect(300,300,100,100);/*清除矩形的内容*/// ctx.clearRect(0,0,ctx.canvas.width,ctx.canvas.height);</script></body></html> createLinearGradient()方法绘制渐变颜色矩形 <!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}/* .linearGradient{
width: 400px;
height: 100px;
background-image: linear-gradient(to right,pink,blue);
}*/</style></head><body><div class="linearGradient"></div><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');/*fillStyle 'pink' '#000' 'rgb()' 'rgba()' *//*也可以使用一个渐变的方案了填充矩形*//*创建一个渐变的方案*//*渐变是由长度的*//*x0y0 起始点 x1y1 结束点 确定长度和方向*/var linearGradient = ctx.createLinearGradient(100,100,500,400);linearGradient.addColorStop(0,'pink');//linearGradient.addColorStop(0.5,'red');linearGradient.addColorStop(1,'blue');ctx.fillStyle = linearGradient;ctx.fillRect(100,100,400,100);/*pink---->blue*//*回想线性渐变---->要素 方向 起始颜色 结束颜色 *//*通过两个点的坐标可以控制 渐变方向*/</script></body></html> 圆弧绘制弧度概念这就和数学中的概念知识是一样的。
名词：
最终的结论：一个角度等于多少弧度 π/180 用三角函数体验曲线的绘制<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}</style></head><body><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');/*1.体验曲线的绘制*//*2.线是由点构成的*//*3.曲线可以由数学公式得来*//*公式：y = x/2 *//*公式：y = (x + 2) ^2 *//*公式：y = sin(x) */for(var i = 1 ; i < 600 ; i ++){var x = i;//var y = x/2;//var y = Math.pow(x/10-30,2);var y = 50*Math.sin(x/10) + 100;ctx.lineTo(x,y);}ctx.stroke();</script></body></html> arc() 方法画圆弧arc(x,y,r,startAngle,endAngle,anticlockwise) 参数：
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}</style></head><body><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');/*绘制圆弧*//*确定圆心 坐标 x y*//*确定圆半径 r *//*确定起始绘制的位置和结束绘制的位置 确定弧的长度和位置 startAngle endAngle 弧度*//*取得绘制的方向 direction 默认是顺时针 false 逆时针 true *//*在中心位置画一个半径150px的圆弧左下角*/var w = ctx.canvas.width;var h = ctx.canvas.height;ctx.arc(w/2,h/2,150,Math.PI/2,Math.PI,true);ctx.stroke();</script></body></html> 圆实例练习绘制六种颜色等分的圆<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}</style></head><body><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');var w = ctx.canvas.width;var h = ctx.canvas.height;/*分成几等分*/var num = 360;/*一份多少弧度*/var angle = Math.PI * 2 / num;/*原点坐标*/var x0 = w / 2;var y0 = h / 2;/*获取随机颜色*/var getRandomColor = function () {var r = Math.floor(Math.random() * 256);var g = Math.floor(Math.random() * 256);var b = Math.floor(Math.random() * 256);return 'rgb(' + r + ',' + g + ',' + b + ')';}/*上一次绘制的结束弧度等于当前次的起始弧度*///var startAngle = 0;for (var i = 0; i < num; i++) {var startAngle = i * angle;var endAngle = (i + 1) * angle;ctx.beginPath();ctx.moveTo(x0, y0);ctx.arc(x0, y0, 150, startAngle, endAngle);/*随机颜色*/ctx.fillStyle = getRandomColor();ctx.fill();}</script></body></html> 绘制扇形<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}</style></head><body><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');/*在中心位置画一个半径150px的圆弧右上角 扇形 边 填充 */var w = ctx.canvas.width;var h = ctx.canvas.height;/*把起点放到圆心位置*/ctx.moveTo(w/2,h/2);ctx.arc(w/2,h/2,150,0,-Math.PI/2,true);/*闭合路径*///ctx.closePath();ctx.fill();</script></body></html> 绘制数据饼图
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}</style></head><body><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');/*1.根据37期的年龄分布绘制饼图*//*2.准备统计的数据*//*15-20岁 6个*//*20-25岁 30个*//*25-30岁 10个*//*30-35岁 8个*/var data = [6, 30, 10, 8];/*3.在饼图表示出来*//*4.需要把数据转出弧度*/var angleList = [];var total = 0;data.forEach(function (item, i) {total += item;});console.log(total);/*第二是转换成弧度的时候就可以去绘制扇形 减少一次遍历*/data.forEach(function (item, i) {var angle = Math.PI * 2 * (item/total);angleList.push(angle);});console.log(angleList);/*5.根据弧度绘制扇形*/var w = ctx.canvas.width;var h = ctx.canvas.height;var x0 = w/2;var y0 = h/2;/*获取随机颜色*/var getRandomColor = function () {var r = Math.floor(Math.random() * 256);var g = Math.floor(Math.random() * 256);var b = Math.floor(Math.random() * 256);return 'rgb(' + r + ',' + g + ',' + b + ')';}var startAngle = 0;angleList.forEach(function (item,i) {/*上一次绘制的结束弧度等于当前次的起始弧度*/var endAngle = startAngle + item;ctx.beginPath();ctx.moveTo(x0,y0);ctx.arc(x0,y0,150,startAngle,endAngle);ctx.fillStyle = getRandomColor();ctx.fill();/*记录当前的结束位置作为下一次的起始位置*/startAngle = endAngle;});</script></body></html> 绘制文本
案例：画布中心绘制文字
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;display: block;margin: 100px auto;}</style></head><body><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');/*1.在画布的中心绘制一段文字*//*2.申明一段文字*/var str = '您吃饭中饭了吗';/*3.确定画布的中心*/var w = ctx.canvas.width;var h = ctx.canvas.height;/*4.画一个十字架在画布的中心*/ctx.beginPath();ctx.moveTo(0, h / 2 - 0.5);ctx.lineTo(w, h / 2 - 0.5);ctx.moveTo(w / 2 - 0.5, 0);ctx.lineTo(w / 2 - 0.5, h);ctx.strokeStyle = '#eee';ctx.stroke();/*5.绘制文本*/ctx.beginPath();ctx.strokeStyle = '#000';var x0 = w/2;var y0 = h/2;/*注意：起点位置在文字的左下角*//*有文本的属性 尺寸 字体 左右对齐方式 垂直对齐的方式*/ctx.font = '40px Microsoft YaHei';/*左右对齐方式 (center left right start end) 基准起始坐标*/ctx.textAlign = 'center';/*垂直对齐的方式 基线 baseline(top,bottom,middle) 基准起始坐标*/ctx.textBaseline = 'middle';//ctx.direction = 'rtl';//ctx.strokeText(str,x0,y0);ctx.fillText(str,x0,y0);/*6.画一个下划线和文字一样长*/ctx.beginPath();/*获取文本的宽度*/console.log(ctx.measureText(str));var width = ctx.measureText(str).width;ctx.moveTo(x0-width/2,y0 + 20);ctx.lineTo(x0+width/2,y0 + 20);ctx.stroke();</script></body></html> 圆与文本综合案例：数据饼状图
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;display: block;margin: 100px auto;}</style></head><body><canvas width="600" height="400"></canvas><script>/*var myCanvas = document.querySelector('canvas');
var ctx = myCanvas.getContext('2d');*//*1.绘制饼状态图*//*1.1 根据数据绘制一个饼图*//*1.2 绘制标题 从扇形的弧中心伸出一条线在画一条横线在横线的上面写上文字标题*//*1.3 在画布的左上角 绘制说明 一个和扇形一样颜色的矩形 旁边就是文字说明*/var PieChart = function (ctx) {/*绘制工具*/this.ctx = ctx || document.querySelector('canvas').getContext('2d');/*绘制饼图的中心*/this.w = this.ctx.canvas.width;this.h = this.ctx.canvas.height;/*圆心*/this.x0 = this.w / 2 + 60;this.y0 = this.h / 2;/*半径*/this.radius = 150;/*伸出去的线的长度*/this.outLine = 20;/*说明的矩形大小*/this.rectW = 30;this.rectH = 16;this.space = 20;}PieChart.prototype.init = function (data) {/*1.准备数据*/this.drawPie(data);};PieChart.prototype.drawPie = function (data) {var that = this;/*1.转化弧度*/var angleList = this.transformAngle(data);/*2.绘制饼图*/var startAngle = 0;angleList.forEach(function (item, i) {/*当前的结束弧度要等于下一次的起始弧度*/var endAngle = startAngle + item.angle;that.ctx.beginPath();that.ctx.moveTo(that.x0, that.y0);that.ctx.arc(that.x0, that.y0, that.radius, startAngle, endAngle);var color = that.ctx.fillStyle = that.getRandomColor();that.ctx.fill();/*下一次要使用当前的这一次的结束角度*//*绘制标题*/that.drawTitle(startAngle, item.angle, color , item.title);/*绘制说明*/that.drawDesc(i,item.title);startAngle = endAngle;});};PieChart.prototype.drawTitle = function (startAngle, angle ,color , title) {/*1.确定伸出去的线 通过圆心点 通过伸出去的点 确定这个线*//*2.确定伸出去的点 需要确定伸出去的线的长度*//*3.固定伸出去的线的长度*//*4.计算这个点的坐标*//*5.需要根据角度和斜边的长度*//*5.1 使用弧度 当前扇形的起始弧度 + 对应的弧度的一半 *//*5.2 半径+伸出去的长度 *//*5.3 outX = x0 + cos(angle) * ( r + outLine)*//*5.3 outY = y0 + sin(angle) * ( r + outLine)*//*斜边*/var edge = this.radius + this.outLine;/*x轴方向的直角边*/var edgeX = Math.cos(startAngle + angle / 2) * edge;/*y轴方向的直角边*/var edgeY = Math.sin(startAngle + angle / 2) * edge;/*计算出去的点坐标*/var outX = this.x0 + edgeX;var outY = this.y0 + edgeY;this.ctx.beginPath();this.ctx.moveTo(this.x0, this.y0);this.ctx.lineTo(outX, outY);this.ctx.strokeStyle = color;/*画文字和下划线*//*线的方向怎么判断 伸出去的点在X0的左边 线的方向就是左边*//*线的方向怎么判断 伸出去的点在X0的右边 线的方向就是右边*//*结束的点坐标 和文字大小*/this.ctx.font = '14px Microsoft YaHei';var textWidth = this.ctx.measureText(title).width ;if(outX > this.x0){/*右*/this.ctx.lineTo(outX + textWidth,outY);this.ctx.textAlign = 'left';}else{/*左*/this.ctx.lineTo(outX - textWidth,outY);this.ctx.textAlign = 'right';}this.ctx.stroke();this.ctx.textBaseline = 'bottom';this.ctx.fillText(title,outX,outY);};PieChart.prototype.drawDesc = function (index,title) {/*绘制说明*//*矩形的大小*//*距离上和左边的间距*//*矩形之间的间距*/this.ctx.fillRect(this.space,this.space + index * (this.rectH + 10),this.rectW,this.rectH);/*绘制文字*/this.ctx.beginPath();this.ctx.textAlign = 'left';this.ctx.textBaseline = 'top';this.ctx.font = '12px Microsoft YaHei';this.ctx.fillText(title,this.space + this.rectW + 10 , this.space + index * (this.rectH + 10));};PieChart.prototype.transformAngle = function (data) {/*返回的数据内容包含弧度的*/var total = 0;data.forEach(function (item, i) {total += item.num;});/*计算弧度 并且追加到当前的对象内容*/data.forEach(function (item, i) {var angle = item.num / total * Math.PI * 2;item.angle = angle;});return data;};PieChart.prototype.getRandomColor = function () {var r = Math.floor(Math.random() * 256);var g = Math.floor(Math.random() * 256);var b = Math.floor(Math.random() * 256);return 'rgb(' + r + ',' + g + ',' + b + ')';};var data = [{title: '15-20岁',num: 6},{title: '20-25岁',num: 30},{title: '25-30岁',num: 10},{title: '30以上',num: 8}];var pieChart = new PieChart();pieChart.init(data);</script></body></html> 做动画绘制图片drawImage()参数：
代码示例： <!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}</style></head><body><!--<img src="image/01.jpg" alt="">--><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');/*1.加载图片到内存即可*//*var img = document.createElement('img');
img.src = 'image/01.jpg';*//*创建对象*/var image = new Image();/*绑定加载完成事件*/image.onload = function () {/*实现图片绘制*/console.log(image);/*绘制图片的三种方式*//*3参数*//*图片对象*//*绘制在画布上的坐标 x y*///ctx.drawImage(image,100,100);/*5个参数*//*图片对象*//*绘制在画布上的坐标 x y*//*是图片的大小 不是裁剪 是缩放*///ctx.drawImage(image,100,100,100,100);/*9个参数*//*图片对象*//*图片上定位的坐标 x y *//*在图片上截取多大的区域 w h*//*绘制在画布上的坐标 x y*//*是图片的大小 不是裁剪 是缩放*/ctx.drawImage(image,400,400,400,400,200,200,100,100);};/*设置图片路径*/image.src = 'image/02.jpg';</script></body></html> 序列帧动画方向键控制行走的小人动图中小人的移动是靠键盘的方向键 <!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}</style></head><body><canvas width="600" height="400"></canvas><script>var Person = function (ctx) {/*绘制工具*/this.ctx = ctx || document.querySelector('canvas').getContext('2d');/*图片路径*/this.src = 'image/03.png';/*画布的大小*/this.canvasWidth = this.ctx.canvas.width;this.canvasHeight = this.ctx.canvas.height;/*行走相关参数*/this.stepSzie = 20;/* 0 前 1 左 2 右 3 后 和图片的行数包含的图片对应上*/this.direction = 0;/*x轴方向的偏移步数*/this.stepX = 0;/*y轴方向的偏移步数*/this.stepY = 0;/*初始化方法*/this.init();};Person.prototype.init = function () {var that = this;/*1.加载图片*/this.loadImage(function (image) {/*图片的大小*/that.imageWidth = image.width;that.imageHeight = image.height;/*人物的大小*/that.personWidth = that.imageWidth / 4;that.personHeight = that.imageHeight / 4;/*绘制图片的起点*/that.x0 = that.canvasWidth / 2 - that.personWidth / 2;that.y0 = that.canvasHeight / 2 - that.personHeight / 2;/*2.默认绘制在中心位置正面朝外*/that.ctx.drawImage(image,0,0,that.personWidth,that.personHeight,that.x0,that.y0,that.personWidth,that.personHeight);/*3.能通过方向键去控制人物行走*/that.index = 0;document.onkeydown = function (e) {if(e.keyCode == 40){that.direction = 0;that.stepY ++;that.drawImage(image);/*前*/}else if(e.keyCode == 37){that.direction = 1;that.stepX --;that.drawImage(image);/*左*/}else if(e.keyCode == 39){that.direction = 2;that.stepX ++;that.drawImage(image);/*右*/}else if(e.keyCode == 38){that.direction = 3;that.stepY --;that.drawImage(image);/*后*/}}});}/*加载图片*/Person.prototype.loadImage = function (callback) {var image = new Image();image.onload = function () {callback && callback(image);};image.src = this.src;};/*绘制图片*/Person.prototype.drawImage = function (image) {this.index ++;/*清除画布*/this.ctx.clearRect(0,0,this.canvasWidth,this.canvasHeight);/*绘图*//*在精灵图上的定位 x 索引*//*在精灵图上的定位 y 方向*/this.ctx.drawImage(image,this.index * this.personWidth,this.direction * this.personHeight,this.personWidth,this.personHeight,this.x0 + this.stepX * this.stepSzie ,this.y0 + this.stepY * this.stepSzie,this.personWidth,this.personHeight);/*如果索引超出了 变成0*/if(this.index >= 3){this.index = 0;}};new Person();</script></body></html> 坐标变换
案例：旋转的方块
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><style>canvas {border: 1px solid #ccc;}</style></head><body><canvas width="600" height="400"></canvas><script>var myCanvas = document.querySelector('canvas');var ctx = myCanvas.getContext('2d');//ctx.translate(100,100);//ctx.scale(0.5,1);//ctx.rotate(Math.PI/6);var startAngle = 0;ctx.translate(150,150);setInterval(function () {startAngle += Math.PI/180;ctx.rotate(startAngle);ctx.strokeRect(-50,-50,100,100);},500);</script></body></html> |
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