圣诞将至：js加html5教你写出动态旋转圣诞树。

	<canvas id="c" height="356" width="446">
		<script>
			var collapsed = true;
			function toggle() {
				var fs = top.document.getElementsByTagName('frameset')[0];
				var f = fs.getElementsByTagName('frame');
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					fs.noResize = false;

					f[0].noResize = false;

					f[1].noResize = false;

				}

				else {

					fs.rows = '30px,*';

					fs.noResize = true;

					f[0].noResize = true;

					f[1].noResize = true;

				}

				collapsed = !collapsed;

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		<script>

			var b = document.body;

			var c = document.getElementsByTagName('canvas')[0];

			var a = c.getContext('2d');

			document.body.clientWidth;

		</script>

		<script>

			M = Math;

			Q = M.random; J = [];

			U = 16;

			T = M.sin;

			E = M.sqrt;

			for (O = k = 0; x = z = j = i = k < 200;)

				with (M[k] = k ? c.cloneNode(0) : c) {

					width = height = k ? 32 : W = 446;

					with (getContext('2d'))

					if (k > 10 | !k)

						for (

							font = '60px Impact',

							V = 'rgba('; I = i * U, fillStyle = k ? k == 13 ? V + '205,205,215,.15)' :

								V + (147 + I) + ',' + (k % 2 ? 128 + I : 0) + ',' + I + ',.5)' : '#cca', i < 7;)

							beginPath(fill(arc(U - i / 3, 24 - i / 2, k == 13 ? 4 - (i++) / 2 : 8 - i++, 0, M.PI * 2, 1)));

					else for (;

						x = T(i),

						y = Q() * 2 - 1,

						D = x * x + y * y,

						B = E(D - x / .9 - 1.5 * y + 1),

						R = 67 * (B + 1) * (L = k / 9 + .8) >> 1,

						i++ < W;

					)

						if (D < 1)

							beginPath(strokeStyle = V + R + ',' + (R + B * L >> 0) + ',40,.1)'),

								moveTo(U + x * 8, U + y * 8),

								lineTo(U + x * U, U + y * U),

								stroke();

					for (

						y = H = k + E(k++) * 25,

						R = Q() * W;

						P = 3, j < H;)

						J[O++] = [

							x += T(R) * P + Q() * 6 - 3, y += Q() * U - 8,

							z += T(R - 11) * P + Q() * 6 - 3,

							j / H * 20 + ((j += U) > H & Q() > .8 ? Q(P = 9) * 4 : 0) >> 1]

				}

			setInterval(function G(m, l) {

				A = T(D - 11);

				if (l)

					return (

						m[2] - l[2]) * A + (l[0] - m[0]) * T(D);

				a.clearRect(0, 0, W, W);

				J.sort(G);

				for (

					i = 0;

					L = J[i++];

					a.drawImage(M[L[3] + 1], 207 + L[0] * A + L[2] * T(D) >> 0, L[1] >> 1)) {

					if (i == 2e3)

						a.fillText

							('Happy Christmas!', U, 345);

					if (!(i % 7))

						a.drawImage(M[13],

							((157 * (i * i) + T(D * 5 + i * i) * 5) % W) >> 0,

							((113 * i + (D * i) / 60) % (290 + i / 99)) >> 0);

				}

				D += .02

			}, 1)

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