Canvas入门－利用Canvas绘制好玩的电子时钟

2016-07-21 00:23:00

在这之前

你需要了解一下方法的使用：

beginPath()
closePath()
moveTo()
lineTo()
fill()
stroke()
fillRect()
clearRect()

这些我在前面的文章介绍过，可以看：

canvas入门－利用 canvas 制作一个七巧板

画个圆

arc()方法
arc(x, y, radius, startAngle, endAngle, anticlockwise)
= > 画一个以（x,y）为圆心的以radius为半径的圆弧（圆），从startAngle开始到endAngle结束，按照anticlockwise给定的方向（默认为顺时针）来生成。
该方法有五个参数：x,y为绘制圆弧所在圆上的圆心坐标。radius为半径。startAngle以及endAngle参数用弧度定义了开始以及结束的弧度。这些都是以x轴为基准。参数anticlockwise 为一个布尔值。为true时，是逆时针方向，否则顺时针方向。

注意：arc()函数中的角度单位是弧度，不是度数。角度与弧度的js表达式:radians=(Math.PI/180)*degrees。

//画一个带边框的实心圆
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
canvas.width = 600;
canvas.height = 600;
ctx.beginPath();
var x = 200, // x 坐标值
y = 200, // y 坐标值
radius = 50, //半径
startAngle = 0 ; //开始点
endAngle = Math.PI * 2; //结束点
anticlockwise = true; //逆时针
ctx.arc(x, y, radius, startAngle, endAngle, anticlockwise);
ctx.lineWidth = 10;
ctx.fillStyle = "# 1208ff";
ctx.strokeStyle = "# 333";
ctx.stroke();
ctx.fill();
实现的效果图如下：

准备工作

会画个圆之后呢，就要开始绘制我们的电子时钟。开始之前，我们需要理清思路。首先，我们要创建个二维数组放置我们从0-9的点阵图形，当元素的值为1的时候，就要将其绘制出来。以下是二维数组的片段：

[
[0,0,1,1,1,0,0],
[0,1,1,0,1,1,0],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[0,1,1,0,1,1,0],
[0,0,1,1,1,0,0]
]//0
我们要做的就是将 0 － 9 个数字用二维数组表示出来。

绘制电子时钟的数字

首先，我们要遍历我们的二维数组，如果元素的值为 1 ，则我们就将他绘制成圆形，那如何确定每个元素的圆心呢，看下面这张图：

接着我们写这样一个绘制数字的数字：

function drawNum(x, y, num, ctx){
for (var i = 0; i
然后，调用该函数来绘制我们的数字：

var RADIUS = 4; // 圆的半径
drawNum(0, 0, 1, ctx);
绘制的效果如下：

绘制简单的电子时钟

我们需要定义一个函数draw()来绘制我们的电子时钟。

function draw(ctx){
var curDate = new Date();
var hour = curDate.getHours();
var minute = curDate.getMinutes();
var seconds = curDate.getSeconds();
drawNum(Margin_X, Margin_Y, parseInt(hour/10), ctx);
drawNum(Margin_X + (RADIUS+1)15, Margin_Y, parseInt(hour%10), ctx);
drawNum(Margin_X + (RADIUS+1)30, Margin_Y, 10, ctx);
drawNum(Margin_X + (RADIUS+1)45, Margin_Y, parseInt(minute/10), ctx);
drawNum(Margin_X + (RADIUS+1)60, Margin_Y, parseInt(minute%10), ctx);
drawNum(Margin_X + (RADIUS+1)75, Margin_Y, 10, ctx);
drawNum(Margin_X + (RADIUS+1)90, Margin_Y, parseInt(seconds/10), ctx);
drawNum(Margin_X + (RADIUS+1)*105, Margin_Y, parseInt(seconds%10), ctx);
}
为了让每个数字之间有些间隔，不重叠在一起，定义了两个变量 Margin_X和Margin_Y来控制它距画布左边和顶部的距离。初始值都是30；

var Margin_X = 30; // 离 canvas 原点的坐标值 x
var Margin_Y = 30; // 离 canvas 原点的坐标值 y

让电子时钟动起来

setInterval()方法
setInterval(function,time)
= > 该方法会循环执行一个函数，时间间隔为 time（ms）

我们利用 setInterval方法让我们的电子时钟动起来。

setInterval(function(){
draw(ctx);
}, 500);
相应的，我们需要在重复绘制前，清楚我们的画布，不然会导致数字重叠在一起。这里用到了clearRect()清楚我们的画布。

ctx.clearRect(0,0,1024,786);
附上完整的代码：

canvas    当前浏览器不支持canvas

//电子时钟

var RADIUS = 4; // 圆的半径
var Margin_X = 30; // 离 canvas 原点的坐标值 x
var Margin_Y = 30; // 离 canvas 原点的坐标值 y

window.onload = function(){
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
setInterval(function(){
draw(ctx);
}, 500);
}

function draw(ctx){
ctx.clearRect(0,0,1024,786);
var curDate = new Date();
var hour = curDate.getHours();
var minute = curDate.getMinutes();
var seconds = curDate.getSeconds();
drawNum(Margin_X, Margin_Y, parseInt(hour/10), ctx);
drawNum(Margin_X + (RADIUS+1)15, Margin_Y, parseInt(hour%10), ctx);
drawNum(Margin_X + (RADIUS+1)30, Margin_Y, 10, ctx);
drawNum(Margin_X + (RADIUS+1)45, Margin_Y, parseInt(minute/10), ctx);
drawNum(Margin_X + (RADIUS+1)60, Margin_Y, parseInt(minute%10), ctx);
drawNum(Margin_X + (RADIUS+1)75, Margin_Y, 10, ctx);
drawNum(Margin_X + (RADIUS+1)90, Margin_Y, parseInt(seconds/10), ctx);
drawNum(Margin_X + (RADIUS+1)*105, Margin_Y, parseInt(seconds%10), ctx);
}

function drawNum(x, y, num, ctx){
for (var i = 0; i

digit.js

digit =
[
[
[0,0,1,1,1,0,0],
[0,1,1,0,1,1,0],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[0,1,1,0,1,1,0],
[0,0,1,1,1,0,0]
],//0
[
[0,0,0,1,1,0,0],
[0,1,1,1,1,0,0],
[0,0,0,1,1,0,0],
[0,0,0,1,1,0,0],
[0,0,0,1,1,0,0],
[0,0,0,1,1,0,0],
[0,0,0,1,1,0,0],
[0,0,0,1,1,0,0],
[0,0,0,1,1,0,0],
[1,1,1,1,1,1,1]
],//1
[
[0,1,1,1,1,1,0],
[1,1,0,0,0,1,1],
[0,0,0,0,0,1,1],
[0,0,0,0,1,1,0],
[0,0,0,1,1,0,0],
[0,0,1,1,0,0,0],
[0,1,1,0,0,0,0],
[1,1,0,0,0,0,0],
[1,1,0,0,0,1,1],
[1,1,1,1,1,1,1]
],//2
[
[1,1,1,1,1,1,1],
[0,0,0,0,0,1,1],
[0,0,0,0,1,1,0],
[0,0,0,1,1,0,0],
[0,0,1,1,1,0,0],
[0,0,0,0,1,1,0],
[0,0,0,0,0,1,1],
[0,0,0,0,0,1,1],
[1,1,0,0,0,1,1],
[0,1,1,1,1,1,0]
],//3
[
[0,0,0,0,1,1,0],
[0,0,0,1,1,1,0],
[0,0,1,1,1,1,0],
[0,1,1,0,1,1,0],
[1,1,0,0,1,1,0],
[1,1,1,1,1,1,1],
[0,0,0,0,1,1,0],
[0,0,0,0,1,1,0],
[0,0,0,0,1,1,0],
[0,0,0,1,1,1,1]
],//4
[
[1,1,1,1,1,1,1],
[1,1,0,0,0,0,0],
[1,1,0,0,0,0,0],
[1,1,1,1,1,1,0],
[0,0,0,0,0,1,1],
[0,0,0,0,0,1,1],
[0,0,0,0,0,1,1],
[0,0,0,0,0,1,1],
[1,1,0,0,0,1,1],
[0,1,1,1,1,1,0]
],//5
[
[0,0,0,0,1,1,0],
[0,0,1,1,0,0,0],
[0,1,1,0,0,0,0],
[1,1,0,0,0,0,0],
[1,1,0,1,1,1,0],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[0,1,1,1,1,1,0]
],//6
[
[1,1,1,1,1,1,1],
[1,1,0,0,0,1,1],
[0,0,0,0,1,1,0],
[0,0,0,0,1,1,0],
[0,0,0,1,1,0,0],
[0,0,0,1,1,0,0],
[0,0,1,1,0,0,0],
[0,0,1,1,0,0,0],
[0,0,1,1,0,0,0],
[0,0,1,1,0,0,0]
],//7
[
[0,1,1,1,1,1,0],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[0,1,1,1,1,1,0],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[0,1,1,1,1,1,0]
],//8
[
[0,1,1,1,1,1,0],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[1,1,0,0,0,1,1],
[0,1,1,1,0,1,1],
[0,0,0,0,0,1,1],
[0,0,0,0,0,1,1],
[0,0,0,0,1,1,0],
[0,0,0,1,1,0,0],
[0,1,1,0,0,0,0]
],//9
[
[0,0,0,0],
[0,0,0,0],
[0,1,1,0],
[0,1,1,0],
[0,0,0,0],
[0,0,0,0],
[0,1,1,0],
[0,1,1,0],
[0,0,0,0],
[0,0,0,0]
]//:
];
实现的效果图如下：