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函数:
function drawNum(x, y, num, ctx){
for (var i = 0; i < digit[num].length; i++){
for(var j = 0; j < digit[num][i].length; j++){
if( digit[num][i][j] == 1){
ctx.beginPath();
ctx.fillStyle = "rgb(0, 102, 153)";
ctx.arc(x+(RADIUS+1)*2*j+(RADIUS+1), y+(RADIUS+1)*2*i+(RADIUS+1), RADIUS, 0, Math.PI*2);
ctx.fill();
ctx.closePath();
}
}
}
}
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
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:
甚至我们还可以这样子: