How to fluctuate between values in a shader

Questions & Answers
1

I need to change _GlowPower value within the range of 1 to 6 in runtime.
I’ve tried this:

	float _GlowPower;
	float _UpDown = 0;
	float _TimeElapsed = 0;
	void surf(Input IN, inout SurfaceOutput o) {
		if (_UpDown == 0) {
			_GlowPower += _Time.z - _TimeElapsed;
		}
		if (_UpDown == 1) {
			_GlowPower -= _Time.z - _TimeElapsed;
		}
		if (_GlowPower <=  1) {
			_UpDown = 0;
		}
		if (_GlowPower >=  6) {
			_UpDown = 1;
		}
		_TimeElapsed = _Time.z;
		IN.color = _ColorTint;
		o.Albedo = tex2D(_MainTex, IN.uv_MainTex).rgb * IN.color;
		half rim = 1.0 - saturate(dot(normalize(IN.viewDir), o.Normal));
		o.Emission = _GlowColor.rgb * pow(rim, _GlowPower);
	}

_GlowPower always goes up, never down.
How could achieve this inside the shader?
I know I can do this by script, but I need to keep this clean.
Thanks in advice.

2

Get the SIN function of the time. This will make it into a number that fluctuates between -1 and +1. You can then scale this to 1 though 6.

The sin of the time is available as a builtin shader variable: _SinTime