使用HTML5的canvas做一个会动的时钟

这次我们的目标是画一个会和时间同步的时钟，不过没有美学感觉，样子丑的厉害。

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。

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）

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();
}