2020-06-22-Canvas笔记02-矩形绘制

矩形的绘制

Canvas的API 提供了3个方法，分别用于矩形的清除、描边及填充

• clearRect(double x, double y, double w, double h)

• strokeRect(double x, double y, double w, double h)

• fillRect(double x, double y, double w, double h)

• 绘制一个最简单的矩形，起始位置（10,10），宽度100，高度100

const canvas = document.getElementById('canvas');
const context = canvas.getContext('2d');

context.strokeRect(10, 10, 100, 100);

绘制矩形.png

• 给矩形填充颜色

const canvas = document.getElementById('canvas');
const context = canvas.getContext('2d');

context.strokeRect(10, 10, 100, 100);

context.fillStyle = 'orange';
context.fillRect(20, 20, 100, 100);

填充矩形.png

• 清除矩形
  清除矩形的操作有点类似橡皮擦的效果。

const canvas = document.getElementById('canvas');
const context = canvas.getContext('2d');

context.strokeRect(10, 10, 100, 100);

context.fillStyle = 'orange';
context.fillRect(20, 20, 100, 100);

context.canvas.onmousedown = function(e) {
  context.clearRect(0, 0, 100, 100);
}

清除矩形.png

• 设置绘制矩形的线宽

const canvas = document.getElementById('canvas');
const context = canvas.getContext('2d');
context.lineWidth = 30;
context.strokeRect(50, 50, 400, 200);

设置lineWidth.png

• 设置绘制矩形的lineJoin
  lineJoin的取值有3个：
  • bevel 斜角
  • round 圆角
  • miter 斜切

const canvas = document.getElementById('canvas');
const context = canvas.getContext('2d');
context.lineJoin = 'round';
context.lineWidth = 30;
context.strokeRect(50, 50, 400, 200);

绘制矩形的lineJoin-bevel.png 绘制矩形的lineJoin-round.png 绘制矩形的lineJoin-miter.png