# canvas 2d 入门
canvas的坐标是右下坐标
绘制步骤
- 向HTML5页面添加canvas元素
- 通过js获取canvas对象，并创建contex对象
- 指定绘路径以及样式
- 开始绘制
html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
<canvas id="can" height="500" width="500"></canvas>
<script src="./line.js"></script>
</body>
</html>
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- 定义好canvas2d画布
# 线
var canvas = document.getElementById('can');
var ctx = canvas.getContext('2d');
ctx.moveTo(100, 100);
ctx.lineTo(300, 300);
ctx.lineTo(100, 200);
ctx.stroke();
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# 圆
var canvas = document.getElementById('can');
var ctx = canvas.getContext('2d');
ctx.fillStyle = "#ff0";
ctx.beginPath();
ctx.arc(200, 200, 100, 0 * Math.PI, 2 * Math.PI);
ctx.closePath();
ctx.stroke(); // 描边
ctx.fill(); // 填充颜色
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- arc的参数: x坐标，y坐标，圆半径，起始角度，终点角度
# 渐变矩形
var canvas = document.getElementById('can');
var ctx = canvas.getContext('2d');
var grd = ctx.createLinearGradient(0, 0, 500, 500);
grd.addColorStop(0, 'red');
grd.addColorStop(0.5, 'blue');
grd.addColorStop(1, 'yellow');
ctx.fillStyle = grd;
ctx.fillRect(0, 0, 500, 500);
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- 定义渐变色 grd
# 字
var canvas = document.getElementById('can');
var ctx = canvas.getContext('2d');
ctx.font = '30px Arial';
ctx.fillText('yideng', 10, 50);
ctx.strokeText('xuetang', 10 ,200);
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# 图片
var canvas = document.getElementById('can');
var ctx = canvas.getContext('2d');
var img = document.getElementById('images');
img.onload = function() {
ctx.drawImage(img, 10, 10);
}
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