如何使用 javascript 更改 canvas 的颜色？

Question

我知道如何在 CSS 中轻松地做到这一点，但我想知道如何使用 Javascript 将默认的白色 canvas 变为黑色。我在背景上得到了我想要的圆圈总数，但我每次尝试更改背景颜色都会摆脱我的圆圈。

<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title>Loops Homework</title>
</head>
<body>
<canvas id="myCanvas" width="800" height="600"></canvas>
<script src="js/main.js"></script>
</body>
</html>

Javascript:

var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext('2d');



for(var i = 0; i < 10; i++) {

ctx.fillStyle="rgba(255,0,0,0.8)";


fillCircle(200,200,i*2);

fillCircle(150,200,i*2);

fillCircle(100,200,i*2);

fillCircle(0,200,i*2);

fillCircle(50,200,i*2);

fillCircle(250,200,i*2);

fillCircle(300,200,i*2);

fillCircle(350,200,i*2);

fillCircle(400,200,i*2);

fillCircle(450,200,i*2);
}


var width = window.innerWidth;
var height = 100;


function fillCircle(x, y, radius) {
ctx.beginPath();
ctx.arc(x, y, radius, 0, Math.PI * 2);
ctx.closePath();
ctx.fill();
}

Answer 1

在开始画圆圈之前，使用 fillRect:

用黑色填充整个 canvas

var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext('2d');

// fill the entire canvas with black before drawing the circles
ctx.fillStyle='black';
ctx.fillRect(0,0,canvas.width,canvas.height);

for(var i = 0; i < 10; i++) {

...

如何使用 javascript 更改 canvas 的颜色？

How to change the color of a canvas using javascript?

javascript

html

loops

canvas

background-color