09-canvas绘制坐标系
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>09-Canvas绘制坐标系</title>
<style>
*{
margin: 0;
padding: 0;
}
canvas{
display: block;
margin: 0 auto;
background: red;
}
</style>
</head>
<body>
<canvas width="500" height="400"></canvas>
<script>
// 1.拿到canvas
let oCanvas = document.querySelector("canvas");
// 2.从canvas中拿到绘图工具
let oCtx = oCanvas.getContext("2d");
// 3.定义变量保存小方格的尺寸
let gridSize = 50;
// 4.拿到canvas的宽高
let canvasWidth = oCtx.canvas.width;
let canvasHeight = oCtx.canvas.height;
// 5.计算在垂直方向和水平方向可以绘制多少条横线
let row = Math.floor(canvasHeight / gridSize);
let col = Math.floor(canvasWidth / gridSize);
// 6.绘制垂直方向的横线
for(let i = 0; i < row; i++){
oCtx.beginPath();
oCtx.moveTo(0, i * gridSize - 0.5);
oCtx.lineTo(canvasWidth, i * gridSize - 0.5);
oCtx.strokeStyle = "#ccc";
oCtx.stroke();
}
// 7.绘制水平方向的横线
for(let i = 0; i < col; i++){
oCtx.beginPath();
oCtx.moveTo(i * gridSize - 0.5, 0);
oCtx.lineTo(i * gridSize - 0.5, canvasHeight);
oCtx.strokeStyle = "#ccc";
oCtx.stroke();
}
// 1.计算坐标系原点的位置
let originX = gridSize;
let originY = canvasHeight - gridSize;
// 2.计算X轴终点的位置
let endX = canvasWidth - gridSize;
// 3.绘制X轴
oCtx.beginPath();
oCtx.moveTo(originX, originY);
oCtx.lineTo(endX, originY);
oCtx.strokeStyle = "#000";
oCtx.stroke();
// 4.绘制X轴的箭头
oCtx.lineTo(endX - 10, originY + 5);
oCtx.lineTo(endX - 10, originY - 5);
oCtx.lineTo(endX, originY);
oCtx.fill();
// 5.计算Y轴终点的位置
let endY = gridSize;
// 3.绘制Y轴
oCtx.beginPath();
oCtx.moveTo(originX, originY);
oCtx.lineTo(originX, endY);
oCtx.strokeStyle = "#000";
oCtx.stroke();
// 4.绘制X轴的箭头
oCtx.lineTo(originX - 5, endY + 10);
oCtx.lineTo(originX + 5, endY + 10);
oCtx.lineTo(originX, endY);
oCtx.fill();
</script>
</body>
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