<!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></title>
</head>
<body>
<canvas id="canvas"></canvas>
<script>
const canvas = document.getElementById('canvas')
const ctx = canvas.getContext('2d')
const W = canvas.width = 900
const H = canvas.height = 700
canvas.style.border = '8px solid #000'
// rp([1, 3]) ==> 1 | 2 | 3
// rp([3, 1], true) ==> 1 - 3 之间随机的小数
const rp = function (arr, uint){
const min = Math.min(...arr)
const max = Math.max(...arr)
const ret = Math.random() * (max - min) + min
return uint ? ret : Math.round(ret)
}
const maxBranch = 3
tree(ctx, W/2, H/2 + 200, 70, -Math.PI/2, 14, 20)
function tree(ctx, startX, startY, branchLen, angle, depth, branchWidth) {
const endX = startX + branchLen * Math.cos(angle)
const endY = startY + branchLen * Math.sin(angle)
const color = (depth--) < maxBranch - 1 ? `rgb(0, ${rp([128, 196])}, 0)` : 'rgb(68, 50, 25)'
ctx.save()
ctx.lineCap = 'round'
ctx.lineWidth = branchWidth
ctx.strokeStyle = color
ctx.beginPath()
ctx.moveTo(startX, startY)
ctx.lineTo(endX, endY)
ctx.stroke()
ctx.restore()
if (!depth) return
const subBranches = rp([1, maxBranch])
for (let i=0; i<subBranches; i++) {
setTimeout(
tree,
0,
ctx,
endX,
endY,
branchLen * rp([0.7, 1], true),
angle + rp([-Math.PI/5, Math.PI/5], true),
depth,
branchWidth * 0.72
)
}
}
</script>
</body>
</html>