Underwater Light Rays (Unity)

Shader "SweetRollStudio/Underwater"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
		_WaveStrength("WaveStrength", Float) = 1
		_WaveSpeed("WaveSpeed", Float) = 1
		_Power("Power", Range(0,1)) = 1
	}
	SubShader
	{
		// No culling or depth
		Cull Off ZWrite Off ZTest Always

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag

			#include "UnityCG.cginc"

			struct appdata
			{
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
			};

			struct v2f
			{
				float2 uv : TEXCOORD0;
				float4 vertex : SV_POSITION;
			};

			v2f vert (appdata v)
			{
				v2f o;
				o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
				o.uv = v.uv;
				return o;
			}

			sampler2D _MainTex;
			float _WaveStrength;
			float _WaveSpeed;
			float _Power;

			float rayStrength(float2 raySource, float2 rayRefDirection, float2 coord, float seedA, float seedB, float speed)
			{
				float2 sourceToCoord = coord - raySource;
				float cosAngle = dot(normalize(sourceToCoord), rayRefDirection);

				return clamp(
					(0.45 + 0.15 * sin(cosAngle * seedA + _Time.y * speed)) +
					(0.3 + 0.2 * cos(-cosAngle * seedB + _Time.y * speed)),
					0.0, 1.0) * clamp((_ScreenParams.x - length(sourceToCoord)) / _ScreenParams.x, 0.5, 1.0);
			}

			fixed4 frag (v2f i) : SV_Target
			{
				fixed4 main = tex2D(_MainTex, i.uv);
				if (_Power <= 0) {
					return main;
				}
				fixed4 ret;
				i.vertex.y *= -1;
				float2 uv = i.vertex.xy / _ScreenParams.xy;
				uv.y = 1.0 - uv.y;
				float2 coord = float2(i.vertex.x, _ScreenParams.y - i.vertex.y);

				float2 rayPos1 = float2(_ScreenParams.x * 0.7, _ScreenParams.y * 0.4);
				float2 rayRefDir1 = normalize(float2(1.0, -0.116));
				float raySeedA1 = 36.2214;
				float raySeedB1 = 21.11349;
				float raySpeed1 = 1.5 * _WaveSpeed;

				float2 rayPos2 = float2(_ScreenParams.x * 0.8, _ScreenParams.y * 0.6);
				float2 rayRefDir2 = normalize(float2(1.0, 0.241));
				const float raySeedA2 = 22.39910;
				const float raySeedB2 = 18.0234;
				const float raySpeed2 = 1.1 * _WaveSpeed;

				float4 rays1 = float4(1.0, 1.0, 1.0, 1.0) * rayStrength(rayPos1, rayRefDir1, coord, raySeedA1, raySeedB1, raySpeed1) ;

				float4 rays2 = float4(1.0, 1.0, 1.0, 1.0) * rayStrength(rayPos2, rayRefDir2, coord, raySeedA2, raySeedB2, raySpeed2);

				ret = rays1 * 0.5 + rays2 * 0.4;

				float brightness = (coord.y / _ScreenParams.y);
				ret.x = mul(ret.x, 0.1 + (brightness * 0.8));
				ret.y = mul(ret.x, 0.3 + (brightness * 0.6));
				ret.z = mul(ret.x, 0.5 + (brightness * 0.5));

				ret = main * ret * _WaveStrength;

				ret = lerp(main, ret, _Power);

				return ret;
			}
			ENDCG
		}
	}
}