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HTML5支持canvas了，我们可以直接在页面上绘图了，我看了下canvas和GDI+的接口差不多，所以我们先了解些基本的概念和方式，然后来做一个应用吧。
我们做所有的画之情需要一个画布，html的canvas标签就是帮我们声明了一个画布。
<canvas id="mycanvas"> </canvas>
这个默认的画布的大小是300*150，接下来的工作大多就是javaScript来做了。首先要实例化这个画布$( function () { var canvas = document.getElementById("mycanvas"); $.log(canvas.width); $.log(canvas.height); var context = canvas.getContext("2d"); $.log(context.canvas); $.log(context.fillStyle); //要填充的区域的颜色 $.log(context.strokeStyle); //要绘制的线条的颜色 $.log(context.lineCap); //笔帽样式 $.log(context.lineJoin); //两条连续线段的连接样式 $.log(context.lineWidth); //线段的宽度 $.log(context.miterLimit); //斜联接 $.log(context.shadowColor); //阴影的颜色，默认为#000000， $.log(context.shadowOffsetX); //阴影在x方向上的偏移量，默认为0，不受坐标转换的影响。 $.log(context.shadowOffsetY); //阴影在y方向上的偏移量，默认为0，不受坐标转换的影响。 $.log(context.shadowBlur); //阴影的模糊度，默认为0，负数值将会被忽略 } );
上面的结果你可以得到一个大致的想法，就是content可以认为是我们将来作画用的画笔（估计有专业人士对强烈抗议，我直接忽略），canvas就是我们的画布。我们现在的画笔是2D的画笔，换句话说就是画平面几何的画笔。接下来，就是我们利用这个画笔来学习怎么画了
各种线$( function () { var canvas = document.getElementById("mycanvas"); var context = canvas.getContext("2d"); context.strokeStyle = "rgb(255, 0, 0)"; context.beginPath(); context.lineCap = "butt"; //默认 context.lineWidth = 10; context.moveTo(10, 10); context.lineTo(100, 10); //简单的一条线 context.stroke(); //该方法真正在画布上绘制该线段 context.beginPath(); context.lineCap = "round"; //圆形线头 context.moveTo(10, 30); context.lineTo(100, 30); context.stroke(); //该方法真正在画布上绘制该线段 context.beginPath(); context.lineCap = "square"; //方形线头 context.moveTo(10, 50); context.lineTo(100, 50); context.stroke(); //该方法真正在画布上绘制该线段 } );
各种阴影$( function () { var canvas = document.getElementById("mycanvas"); var context = canvas.getContext("2d"); context.strokeStyle = "rgb(255, 0, 0)"; context.lineWidth = 10; context.shadowColor = "#0000FF"; context.beginPath(); context.lineCap = "round"; context.moveTo(10, 10); context.lineTo(100, 10); context.shadowOffsetX = 10; context.shadowBlur = 10; context.stroke(); context.beginPath(); context.lineCap = "round"; context.moveTo(10, 30); context.lineTo(100, 30); context.shadowOffsetY = 10; context.shadowBlur = 10; context.stroke(); } );
各种线∠连接$( function () { var canvas = document.getElementById("mycanvas"); var context = canvas.getContext("2d"); context.strokeStyle = "rgb(255, 0, 0)"; context.lineWidth = 10; context.shadowColor = "#0000FF"; context.beginPath(); context.lineJoin = "miter"; //两条线段的外边缘一直扩展到它们相交 context.moveTo(10, 70); context.lineTo(50, 10); context.lineTo(80, 70); context.stroke(); context.lineJoin = "bevel"; //以一个斜边进行连接 context.moveTo(100, 70); context.lineTo(140, 10); context.lineTo(180, 70); context.stroke(); context.lineJoin = "round"; //:以一个圆弧边进行连接 context.beginPath(); context.moveTo(200, 70); context.lineTo(240, 10); context.lineTo(280, 70); context.stroke(); context.closePath(); //关闭path } );
mitre的限定$( function () { var canvas = document.getElementById("mycanvas"); var context = canvas.getContext("2d"); context.strokeStyle = "rgb(255, 0, 0)"; context.lineWidth = 10; context.shadowColor = "#0000FF"; context.beginPath(); context.miterLimit = 1; //miterLimit 属性为斜面的长度设置一个上限。 //只对线条使用设置为 "miter" 的 lineJoin 属性绘制并且两条线段以锐角相交的时候有效 context.lineJoin = "miter"; //两条线段的外边缘一直扩展到它们相交 context.moveTo(10, 70); context.lineTo(50, 10); context.lineTo(80, 70); context.stroke(); } );
各种几何图形$( function () { var canvas = document.getElementById("mycanvas"); canvas.height = 500; //改变默认高度 canvas.width = 500; var context = canvas.getContext("2d"); context.strokeStyle = "rgb(255, 0, 0)"; context.fillStyle = "#AABBCC"; context.lineWidth = 2; context.shadowColor = "#0000FF"; //矩形 context.beginPath(); context.fillRect(10, 10, 50, 50); //实体矩形:x,y,width,height context.strokeRect(70, 10, 50, 50)//空心矩形:x,y,width,height //context.move(10,100); //圆弧:x, y, radius, startAngle, endAngle, anticlockwise context.beginPath(); context.arc(35, 110, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false); context.stroke(); //context.closePath(); context.beginPath(); context.arc(85, 110, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 180, false); context.stroke(); //context.closePath(); context.beginPath(); context.arc(135, 110, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 180, true); context.stroke(); //context.closePath(); context.beginPath(); context.arc(185, 110, 25, (Math.PI / 180) * 180, (Math.PI / 180) * 360, true); context.stroke(); //context.closePath(); context.beginPath(); context.arc(235, 110, 25, (Math.PI / 180) * 90, (Math.PI / 180) * 0, false); context.fillStyle = "blue"; context.fill(); //context.stroke(); //context.closePath(); context.beginPath(); context.arc(285, 110, 25, (Math.PI / 180) * 180, (Math.PI / 180) * 45, false); context.closePath(); context.stroke(); context.beginPath(); context.arc(335, 110, 25, (Math.PI / 180) * 180, (Math.PI / 180) * 45, false); context.closePath(); context.fillStyle = "blue"; context.fill(); context.stroke(); //曲线 context.beginPath(); context.moveTo(10, 160); //二次贝塞尔曲线的起始点 //controlX, controlY, endX, endY context.quadraticCurveTo(70, 280, 235, 140); context.stroke(); context.closePath(); context.beginPath(); context.moveTo(10, 300); //三次贝塞尔曲线的起始点 //controlX1, controlY1, controlX2, controlY2, endX, endY context.bezierCurveTo(70, 280, 50, 400, 235, 190); context.stroke(); context.closePath(); } );
各种变换记得CSS3中的transform不？canvas肯定也有啊平移$( function () { var canvas = document.getElementById("mycanvas"); canvas.height = 500; //改变默认高度 canvas.width = 500; var context = canvas.getContext("2d"); context.strokeStyle = "rgb(255, 0, 0)"; context.fillStyle = "#AABBCC"; context.lineWidth = 2; context.shadowColor = "#0000FF"; context.moveTo(10, 10); //context.beginPath(); //context.beginPath(); context.fillRect(10, 10, 50, 50); //实体矩形:x,y,width,height //context.stroke(); $(canvas).on( "click", { "context",: context }, function(e) { $.log(e.data.context); var ctx = e.data.context; ctx.translate(10, 10); //再最后的路径点上偏移10*10的位置 context.fillRect(10, 10, 50, 50); context.stroke(); } ); } );缩放$( function () { var canvas = document.getElementById("mycanvas"); canvas.height = 500; //改变默认高度 canvas.width = 500; var context = canvas.getContext("2d"); context.strokeStyle = "rgb(255, 0, 0)"; context.fillStyle = "#AABBCC"; context.lineWidth = 2; context.shadowColor = "#0000FF"; context.moveTo(10, 10); //context.beginPath(); //context.beginPath(); context.fillRect(10, 10, 50, 50); //实体矩形:x,y,width,height //context.stroke(); $(canvas).on( "click", { "context": context }, function(e) { $.log(e.data.context); var ctx = e.data.context; ctx.scale(1.1, 1.1); //在最后的大小基础上缩放倍数 必须是正数 context.fillRect(10, 10, 50, 50); context.stroke(); } ); } );旋转$( function () { var canvas = document.getElementById("mycanvas"); canvas.height = 500; //改变默认高度 canvas.width = 500; var context = canvas.getContext("2d"); context.strokeStyle = "rgb(255, 0, 0)"; context.fillStyle = "#AABBCC"; context.lineWidth = 2; context.shadowColor = "#0000FF"; context.moveTo(10, 10); //context.beginPath(); //context.beginPath(); context.fillRect(10, 10, 50, 50); //实体矩形:x,y,width,height //context.stroke(); $(canvas).on( "click", { "context": context }, function(e) { $.log(e.data.context); var ctx = e.data.context; ctx.rotate((Math.PI / 180) * 10); //旋转的角度，旋转的中心是canvas坐标原点 context.fillRect(10, 10, 50, 50); context.stroke(); } ); } );
transform，transform的参数比较多，也比较难理解，简单的说transform是最自由的变形方式，下面给出些参考//以下两段代码结果一致 context.transform(1, 0, 0, 1, 10, 10) context.translate(10, 10); //以下两段代码结果一致 context.transform(10, 0, 0, 10, 0, 0); context.scale(10, 10); //以下三段代码结果一致 context.transform(Math.cos((Math.PI / 180) * 10), Math.sin((Math.PI / 180) * 10), -Math.sin((Math.PI / 180) * 10), Math.cos((Math.PI / 180)) * 10, 0, 0); context.transform(-Math.sin((Math.PI/180)*10),Math.cos((Math.PI/180)*10),Math.cos((Math.PI/180)*10)，Math.sin((Math.PI/180)*10), 0,0); context.rotate(10);组合$( function () { var canvas = document.getElementById("mycanvas"); canvas.height = 100; canvas.width = 100; var context = canvas.getContext("2d"); context.fillStyle = "#AABBCC"; context.fillRect(10, 10, 50, 50); //默认 新图形会覆盖在原有内容之上 context.globalCompositeOperation = "source-over"; context.fillStyle = "blue"; context.arc(70, 30, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false); context.fill(); $("span").html(context.globalCompositeOperation); $(canvas).toggle( function() { canvas.width = 100; // 原有内容之下绘制新图形 context.clearRect(0, 0, 500, 500); context.beginPath(); context = canvas.getContext("2d"); context.fillStyle = "#AABBCC"; context.fillRect(10, 10, 50, 50); context.globalCompositeOperation = "destination-over"; context.fillStyle = "blue"; context.arc(70, 30, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false); context.fill(); $("span").html(context.globalCompositeOperation); }, function() { canvas.width = 100; //新图形会仅仅出现与原有内容重叠的部分。其它区域都变成透明的 context.clearRect(0, 0, 500, 500); context.beginPath(); context.fillStyle = "#AABBCC"; context.fillRect(10, 10, 50, 50); context.globalCompositeOperation = "source-in"; context.fillStyle = "blue"; context.arc(70, 30, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false); context.fill(); $("span").html(context.globalCompositeOperation); }, function() { canvas.width = 100; //原有内容中与新图形重叠的部分会被保留，其它区域都变成透明的destination-in context.clearRect(0, 0, 500, 500); context.beginPath(); context = canvas.getContext("2d"); context.fillStyle = "#AABBCC"; context.fillRect(10, 10, 50, 50); context.globalCompositeOperation = "destination-in"; context.fillStyle = "blue"; context.arc(70, 30, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false); context.fill(); $("span").html(context.globalCompositeOperation); }, function() { canvas.width = 100; //只有新图形中与原有内容不重叠的部分会被绘制出来source-out context.clearRect(0, 0, 500, 500); context.beginPath(); context = canvas.getContext("2d"); context.fillStyle = "#AABBCC"; context.fillRect(10, 10, 50, 50); context.globalCompositeOperation = "source-out"; context.fillStyle = "blue"; context.arc(70, 30, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false); context.fill(); $("span").html(context.globalCompositeOperation); }, function() { canvas.width = 100; //原有内容中与新图形不重叠的部分会被保留 context.clearRect(0, 0, 500, 500); context.beginPath(); context = canvas.getContext("2d"); context.fillStyle = "#AABBCC"; context.fillRect(10, 10, 50, 50); context.globalCompositeOperation = "destination-out"; context.fillStyle = "blue"; context.arc(70, 30, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false); context.fill(); $("span").html(context.globalCompositeOperation); }, function() { canvas.width = 100; //新图形中与原有内容重叠的部分会被绘制，并覆盖于原有内容之上 context.clearRect(0, 0, 500, 500); context.beginPath(); context = canvas.getContext("2d"); context.fillStyle = "#AABBCC"; context.fillRect(10, 10, 50, 50); context.globalCompositeOperation = "source-atop"; context.fillStyle = "blue"; context.arc(70, 30, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false); context.fill(); $("span").html(context.globalCompositeOperation); }, function() { canvas.width = 100; //原有内容中与新内容重叠的部分会被保留，并会在原有内容之下绘制新图形 context.clearRect(0, 0, 500, 500); context.beginPath(); context = canvas.getContext("2d"); context.fillStyle = "#AABBCC"; context.fillRect(10, 10, 50, 50); context.globalCompositeOperation = "destination-atop"; context.fillStyle = "blue"; context.arc(70, 30, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false); context.fill(); $("span").html(context.globalCompositeOperation); }, function() { canvas.width = 100; //两图形中重叠部分作加色处理 context.clearRect(0, 0, 500, 500); context.beginPath(); context = canvas.getContext("2d"); context.fillStyle = "#AABBCC"; context.fillRect(10, 10, 50, 50); context.globalCompositeOperation = "lighter"; context.fillStyle = "blue"; context.arc(70, 30, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false); context.fill(); $("span").html(context.globalCompositeOperation); }, function() { canvas.width = 100; //两图形中重叠的部分作减色处理darker context.clearRect(0, 0, 500, 500); context.beginPath(); context = canvas.getContext("2d"); context.fillStyle = "#AABBCC"; context.fillRect(10, 10, 50, 50); context.globalCompositeOperation = "darker"; context.fillStyle = "blue"; context.arc(70, 30, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false); context.fill(); $("span").html(context.globalCompositeOperation); }, function() { canvas.width = 100; //重叠的部分会变成透明 context.clearRect(0, 0, 500, 500); context.beginPath(); context = canvas.getContext("2d"); context.fillStyle = "#AABBCC"; context.fillRect(10, 10, 50, 50); context.globalCompositeOperation = "xor"; context.fillStyle = "blue"; context.arc(70, 30, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false); context.fill(); $("span").html(context.globalCompositeOperation); }, function() { canvas.width = 100; //只有新图形会被保留，其它都被清除掉 context.clearRect(0, 0, 500, 500); context.beginPath(); context = canvas.getContext("2d"); context.fillStyle = "#AABBCC"; context.fillRect(10, 10, 50, 50); context.globalCompositeOperation = "copy"; context.fillStyle = "blue"; context.arc(70, 30, 25, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false); context.fill(); $("span").html(context.globalCompositeOperation); alert("演示结束"); } ); } );
字体（看文档说canvas的字体支持CSS样式的描写，但是，我不知道怎么样让canvas的font支持CSS3的在线字体）<script src="js/jquery-1.7.1.min.js" type="text/javascript"></script> <link rel="stylesheet" type="text/css" href="http://fonts.googleapis.com/css?family=Tangerine"> <script type="text/javascript"> $.log = function(msg) { console.log(msg); } $( function() { var canvas = document.getElementById("mycanvas"); canvas.height = 200; canvas.width = 200; var context = canvas.getContext("2d"); context.font = "20px 新宋体"; context.fillText("这是实心新宋体", 10, 30); context.strokeText("这是空心新宋体", 10, 60); context.font = "20px Tangerine serif"; context.fillText("Hello HTML5", 10, 100); context.strokeText("Hello HTML5", 10, 150); } ); </script>
我们尝试写一圈旋转的文字，吧上面的知识点合起来看看效果$( function () { var canvas = document.getElementById("mycanvas"); canvas.height = 500; canvas.width = 500; var context = canvas.getContext("2d"); context.translate(150, 150); context.scale(0.7, 0.7); context.font = "12px Tahoma"; for (var i = 0; i < 12; i++) { context.fillText((i + 3) % 12 == 0 ? 12 : (i + 3) % 12, 150, 10); context.rotate((Math.PI / 6)); } } );
在具体绘制的时候，定位总是让我这样没有空间感的人感觉痛苦，所以我现在canvas上画上很多格子，帮助我进行布局$( function () { var canvas = document.getElementById("mycanvas"); canvas.height = 500; canvas.width = 500; var context = canvas.getContext("2d"); context.lineWidth = 1; context.strokeStyle = "rgb(211,211,211)"; for (var i = 0; i < 50; i++) { $.log(i); context.moveTo(i * 10, 0); context.lineTo(i * 10, 500); context.stroke(); } for (var i = 0; i < 50; i++) { $.log(i); context.moveTo(0, i * 10); context.lineTo(500, i * 10); context.stroke(); } } );
前面的准备工作都完成了，现在我们来综合下，完成一个具有时分秒的会动的钟$( function () { clock(); setInterval(clock, 1000); } ); function clock() { var canvas = document.getElementById("mycanvas"); canvas.height = 500; canvas.width = 500; var context = canvas.getContext("2d"); context.beginPath(); context.lineWidth = 1; context.strokeStyle = "rgb(211,211,211)"; for (var i = 0; i < 50; i++) { $.log(i); context.moveTo(i * 10, 0); context.lineTo(i * 10, 500); context.stroke(); } for (var i = 0; i < 50; i++) { $.log(i); context.moveTo(0, i * 10); context.lineTo(500, i * 10); context.stroke(); } context.beginPath(); context.strokeStyle = "rgb(255,0,0)"; context.arc(250, 250, 200, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false); context.stroke(); context.save(); //存储当前画布坐标系状态 context.beginPath(); context.font = "14px Tahoma" context.translate(255, 255); //将坐标系坐标原点移至图中间 context.strokeStyle = "#FFFFFF"; for (var i = 0; i < 12; i++) { context.fillText((i + 3) % 12 == 0 ? 12 : (i + 3) % 12, 180, 0); context.rotate((Math.PI / 6)); } context.restore(); context.save(); context.beginPath(); context.lineWidth = 5; context.translate(255, 255); //将坐标系坐标原点移至图中间 for (i = 0; i < 60; i++) { if (i % 5 != 0) { context.beginPath(); context.moveTo(180, 0); context.lineTo(190, 0); context.stroke(); } context.rotate(Math.PI / 30); } context.restore(); var now = new Date(); var sec = now.getSeconds(); var min = now.getMinutes(); var hr = now.getHours() >= 12 ? now.getHours() - 12 : now.getHours(); context.save(); context.translate(255, 255); //将坐标系坐标原点移至图中间 // - (Math.PI / 6) * 3 是因为0度在3点这里 context.rotate(hr * (Math.PI / 6) + (Math.PI / 360) * min + (Math.PI / 21600) * sec - (Math.PI / 6) * 3); context.lineWidth = 14; context.beginPath(); context.moveTo(-20, 0); context.lineTo(150, 0); context.stroke(); context.restore(); context.save(); context.translate(255, 255); //将坐标系坐标原点移至图中间 context.rotate(min * (Math.PI / 30) + (Math.PI / 1800) * sec - (Math.PI / 6) * 3) context.lineWidth = 10; context.beginPath(); context.moveTo(-28, 0); context.lineTo(160, 0); context.stroke(); context.restore(); context.save(); context.translate(255, 255); //将坐标系坐标原点移至图中间 context.lineWidth = 1; context.rotate(sec * (Math.PI / 30) + (Math.PI / 1800) * sec - (Math.PI / 6) * 3) context.lineWidth = 10; context.beginPath(); context.moveTo(-28, 0); context.lineTo(160, 0); context.stroke(); context.restore(); }
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