RGB 彩虹函数

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这个函数用于彩虹RGB生成 [0-255, 0-255, 0-255]

原理参照这个图片:

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/*reference page http://academe.co.uk/2012/04/arduino-cycling-through-colours-of-the-rainbow/*/

function rainbow(num){
	var num = num || 12;
	var step = 1 / (num/3);
	var colors = [];

	for(var i =0; i<num; i++){
		var r = channelColor(i*step*2 + 2);
		var g = channelColor(i*step*2);
		var b = channelColor(i*step*2 + 4);
		colors.push([r*255, g*255, b*255]);
	}

	function channelColor(num) {//0-1 inclement; 1-3 keep top, 3-4 declement, 4-6 keep bot;
		/*outPut 0-1*/
		while(num >= 6){
			num = num-6
		}
		if(num >=0 && num <1)
			return num;
		if(num >=1 && num <=3)
			return 1;
		if(num >3 && num <4)
			return 1-(num%1);
		if(num >=4 && num <6)
			return 0;
	}

	return colors;
}