Rotating particles using particleVelocity

ParticleRotation.shader

Shader "Custom/ParticleRotation" {
    Properties {
        _MainTex ("Particle Texture", 2D) = "white" {}
        _TintColor ("Tint Color", Color) = (1, 1, 1, 1)
    }

    SubShader {
        Tags {"Queue"="Transparent" "RenderType"="Transparent"}
        LOD 100

        CGPROGRAM
        #pragma surface surf Lambert vertex:vert

        sampler2D _MainTex;
        float4 _TintColor;

        struct Input {
            float2 uv_MainTex;
            float3 particleVelocity;
        };

        void vert (inout appdata_full v, out Input o) {
            UNITY_INITIALIZE_OUTPUT(Input, o);
            o.particleVelocity = v.vertex.y * v.tangent.xyz;
            v.vertex.y = 0;
        }

        void surf (Input IN, inout SurfaceOutput o) {
            float4 c = tex2D(_MainTex, IN.uv_MainTex) * _TintColor;
            o.Albedo = c.rgb;
            o.Alpha = c.a;
            o.Normal = float3(IN.particleVelocity.xy, 0);
        }
        ENDCG
    }
    FallBack "Diffuse"
}