shader with world-space air dust for light shafts etc

Shader "Custom/AdditiveScreenTexture"{
Properties {
    _TintColor ("Tint Color", Color) = (1,1,1,1)
    _EmissionGain ("Emission Gain", Range(0, 1)) = 0.1
    _Mul ("Cloudy", Range (0, 4)) = 1
    _Params ("Size (Min Max) Wind (Min Max)", Vector) = (32, 48, 1, .5)
    _ParamsB ("Windangle (Min Max)", Vector) = (4.05, 5.77, 0, 0)
    _Wind ("Wind speed", Range (0, 2)) = 0.18
    _Rotation ("Rotation", Range (0, 1)) = 0
    _Samples ("Samples", Range (1, 10)) = 2
    _MainTex ("Texture", 2D) = "white" {}

}

Category {
    Tags { "Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent" }
    Blend SrcAlpha One
    ZWrite Off

    SubShader {
        Pass {

            CGPROGRAM
// Upgrade NOTE: excluded shader from DX11; has structs without semantics (struct v2f members worldPos)
#pragma exclude_renderers d3d11
            #pragma vertex vert
            #pragma fragment frag

            fixed4 _TintColor;
            float _EmissionGain;
            half _Mul;
            half _Rotation;
            half _Wind;
            half4 _Params;
            half4 _ParamsB;
            int _Samples;
            sampler2D _MainTex;
            float4 _MainTex_ST;

            struct appdata_t {
                float4 vertex : POSITION;
                fixed4 color : COLOR;
            };

            struct v2f {
                float4 vertex : SV_POSITION;
                fixed4 color : COLOR;
                float2 worldPosition: TEXCOORD0;
            };


            v2f vert (appdata_t v)
            {
                v2f o;
                o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
                o.color = v.color ;
                o.worldPosition = mul(unity_ObjectToWorld, v.vertex);
                return o;
            }

            float pingpong(float value, float freq){
                return sin( (value*3.1415926536) * freq);
            }

            float semiRandom(float2 uv){
                return frac(sin(dot(uv, float2(12.9898, 78.233))) * 43758.5453);
            }

            fixed noise(v2f i, float size, float2 speed){
                float2 uv = speed * _Time.x + i.worldPosition.xy * size;
                return tex2D(_MainTex, uv).x;
            }

            // rotated 45 degrees
            fixed noise45(v2f i, float size, float2 speed){
                float2 uv = speed * _Time.x + i.worldPosition.xy * size;

                float y = uv.y * 0.7071067812;
                float x = uv.x * 0.7071067812;
                uv = half2(x+y,-x+y);

                return tex2D(_MainTex, uv).x;
            }

            float2 rotate(float2 original, float angle ){
                float sinX = sin ( angle );
                float cosX = cos ( angle );
                float sinY = sin ( angle );
                float2x2 rotationMatrix = float2x2( cosX, -sinX, sinY, cosX);
                return mul(original, rotationMatrix );
            }

            fixed4 frag (v2f i) : SV_Target
            {
                float clouds = 1;

                for(int s=0;s<_Samples;s++){
                    float s01 = s/(float)(_Samples-1);
                    float2 direction = rotate(float2(_Wind,0), lerp(_ParamsB.x, _ParamsB.y, s01)  );
                    clouds *= .3+( noise45(i, 1/lerp(_Params.x, _Params.y, s01), direction * (lerp(_Params.z, _Params.w, s01))) + .5);
                }

                float4 shaftColor = i.color*i.color;

                return lerp(shaftColor, shaftColor*clouds, _Mul) * _TintColor * (exp(_EmissionGain * 5));
            }

            ENDCG
        }
    }
}
}