【笔记】【imooc】canvas(绚丽的时钟效果)

*课程最终成果展示：
CodePen: https://codepen.io/YitingLi/full/jwjgdP/
GitHub: https://github.com/Liyiting/canvas-Gorgeous-clock-effects*

七巧板demo

HTML

html5的一个新的标签。

<canvas id="canvas"></canvas>

不指定长宽时，默认是300px*150px

<canvas id="canvas" width="1024" height="768"></canvas>

这里的宽高没有单位，因为他们也决定了canvas画布内里的精度

Javascript

var canvas = document.getElementById('canvas')
var context = canvas.getContext('2d')
//使用context进行绘制

Canvas

canvas.width
canvas.height
canvas.getContext(‘2d’)

Draw a line 绘制直线

Canvas是基于状态的绘制

context.moveTo(100, 100)//下笔处

context.lineTo(700, 700)//画到哪儿

context.lineWidth = 5 //线条宽度

//空心
context.strokeStyle = "#005588" //线条颜色

context.stroke() //画!

//实心
context.fillStyle = "rgb(2,100,30)"//填充颜色

context.fill()

//路径分开绘制
//closePath的意思不是结束路径，而是闭合当前路径使得所有线段连接。它会试图从当前路径的终点连一条路径到起点，让整个路径闭合起来。（这样才能填色吗不是）但是，这并不意味着它之后的路径就是新路径了，要开启新路径，仍然需要使用beginPath，简单说，closePath和beginPath其实没有任何联系的。
context.beginPath()

context.closePath()

七巧板demo：

<!DOCTYPE html>
<html>
<head>
    <meta charset = "UTF-8">
    <title></title>
</head>
<body>
    <canvas id="canvas" style="border: 1px solid #aaa;display: block; margin: 0 auto;">
        当前浏览器不支持Canvas, 请更换浏览器后再试。
    </canvas>
    <script>
    var tangram = [
        {p:[{x:0, y:0},{x:800, y:0},{x:400, y:400}], color: "#caff67"},
        {p:[{x:0, y:0},{x:400, y:400},{x:0, y:800}], color: "#67becf"},
        {p:[{x:800, y:0},{x:800, y:400},{x:600, y:600},{x:600, y:200}], color: "#ef3d61"},
        {p:[{x:600, y:200},{x:600, y:600},{x:400, y:400}], color: "#f9f51a"},
        {p:[{x:400, y:400},{x:600, y:600},{x:400, y:800},{x:200, y:600}], color: "#a594c0"},
        {p:[{x:200, y:600},{x:400, y:800},{x:0, y:800}], color: "#fa8ecc"},
        {p:[{x:800, y:400},{x:800, y:800},{x:400, y:800}], color: "#f6ca29"}
    ]

        window.onload = function() {
            var canvas = document.getElementById("canvas");

            canvas.width = 800;
            canvas.height = 800;

            var context = canvas.getContext("2d")
            for(var i = 0; i < tangram.length; i++){
                draw(tangram[i], context);
            }
        }

        function draw(piece, cxt){
            cxt.beginPath();
            cxt.moveTo(piece.p[0].x, piece.p[0].y);
            for(var i = 1; i<piece.p.length; i++) {
                cxt.lineTo(piece.p[i].x, piece.p[i].y);
            }
            cxt.closePath();

            cxt.fillStyle = piece.color;
            cxt.fill();

            cxt.strokeStyle = "black";
            cxt.lineWidth = 3;
            cxt.stroke();
        }
    </script>
</body>
</html>

Draw an arc 绘制弧线

context.arc(
    centerx, centery, radius, //圆心坐标及半径
    startingAngle, endingAngle, //起始弧度制
    anticlockwise = false //顺/逆时针
    //对于一个圆来说0pi在右边，顺逆时针角度不变
)

closePath对于fill来说是没有用的，因为调用fill时canvas会自动把没有closePath的路径首尾相连

clearRct(x,y,width, height)//对矩形区域进行一次刷新操作