<!DOCTYPE HTML>
<
html
>
<
head
>
<
meta
charset
=
"UTF-8"
>
<
title
>中国标准国旗</
title
>
</
head
>
<
body
>
<
canvas
id
=
"canvas"
width
=
"600"
height
=
"400"
></
canvas
>
<
script
type
=
"text/javascript"
>
// 使用HTML5绘制标准五星红旗
var canvas = document.getElementById("canvas");
var context = canvas.getContext('2d');
var width = canvas.width;
var height = width * 2 / 3;
var w = width / 30;//小网格的宽
context.fillStyle = "red";
context.fillRect(0, 0, width, height);
var maxR = 0.15, minR = 0.05;//
var maxX = 0.25, maxY = 0.25;//大五星的位置
var minX = [0.50, 0.60, 0.60, 0.50];
var minY = [0.10, 0.20, 0.35, 0.45];
// 画大 ☆
var ox = height * maxX, oy = height * maxY;
create5star(context, ox, oy, height * maxR, "#ff0", 0);//绘制五角星
// 画小 ★
for (var idx = 0; idx <
4
; idx++) {
var
sx
=
minX
[idx] * height,
sy
=
minY
[idx] * height;
var
theta
=
Math
.atan((oy - sy) / (ox - sx));
create5star(context, sx, sy, height * minR, "#ff0", -Math.PI / 2 + theta);
}
//辅助线
context.moveTo(0, height / 2)
context.lineTo(width, height / 2);
context.stroke();
context.moveTo(width / 2, 0);
context.lineTo(width / 2, height);
context.stroke();
//画网格,竖线
for (var
j
=
0
; j < 15; j++) {
context.moveTo(j * w, 0);
context.lineTo(j * w, height / 2);
context.stroke();
}
//画网格,横线
for (var
j
=
0
; j < 10; j++) {
context.moveTo(0, j * w);
context.lineTo(width / 2, j * w);
context.stroke();
}
//画大圆
context.beginPath();
context.arc(ox, oy, maxR * height, 0, Math.PI * 2, false);
context.closePath();
context.stroke();
// 画小圆
for (var
idx
=
0
; idx < 4; idx++) {
context.beginPath();
var
sx
=
minX
[idx] * height,
sy
=
minY
[idx] * height;
context.arc(sx, sy, height * minR, 0, Math.PI * 2, false);
context.closePath();
context.stroke();
}
//大圆中心与小圆中心连接线
for (var
idx
=
0
; idx < 4; idx++) {
context.moveTo(ox, oy);
var
sx
=
minX
[idx] * height,
sy
=
minY
[idx] * height;
context.lineTo(sx, sy);
context.stroke();
}
//绘制五角星
/**
* 创建一个五角星形状. 该五角星的中心坐标为(sx,sy),中心到顶点的距离为radius,
rotate
=
0
时一个顶点在对称轴上
* rotate:绕对称轴旋转rotate弧度
*/
function create5star(context, sx, sy, radius, color, rotato){
context.save();
context.fillStyle
=
color
;
context.translate(sx, sy);//移动坐标原点
context.rotate(Math.PI + rotato);//旋转
context.beginPath();//创建路径
var
x
=
Math
.sin(0);
var
y
=
Math
.cos(0);
var
dig
=
Math
.PI / 5 * 4;
for (var
i
=
0
; i < 5; i++) {//画五角星的五条边
var
x
=
Math
.sin(i * dig);
var
y
=
Math
.cos(i * dig);
context.lineTo(x * radius, y * radius);
}
context.closePath();
context.stroke();
context.fill();
context.restore();
}
</script>
</
body
>
</
html
>