Shader "MyShader/ScrollingBackground"
{
	Properties
	{
        _MainTex("Base Layer (RGB)",2D) = "white"{}
        _DetailTex("2nd Layer (RGB)",2D) = "white"{}
        _ScrollX("Base layer Scroll Speed",Float) = 1.0
        _Scroll2X("2nd layer Scroll Speed",Float) = 1.0
        _Multiplier("layer Multiplier",Float) = 1
	}

	SubShader
	{
        Tags{"RenderType" = "Opaque" "Queue" = "Geometry"}

		Pass
		{
            Tags{"LightMode" = "ForwardBase"}

			CGPROGRAM

			#pragma vertex vert
			#pragma fragment frag
			
			#include "UnityCG.cginc"

            sampler2D _MainTex;
            sampler2D _DetailTex;
            float4 _MainTex_ST;
            float4 _DetailTex_ST;
            float _ScrollX;
            float _Scroll2X;
            float _Multiplier;

            struct a2v 
            {
                float4 vertex : POSITION;
                float4 texcoord : TEXCOORD0;
            };

            struct v2f 
            {
                float4 pos : SV_POSITION;
                float4 uv : TEXCOORD0;
            };

            v2f vert(a2v v) 
            {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                o.uv.xy = TRANSFORM_TEX(v.texcoord, _MainTex) + frac(float2(_ScrollX, 0.0) * _Time.y);
                o.uv.zw = TRANSFORM_TEX(v.texcoord, _DetailTex) + frac(float2(_Scroll2X, 0.0) * _Time.y);
                return o;
            }

            fixed4 frag(v2f i) : SV_Target
            {
                fixed4 firstLayer = tex2D(_MainTex, i.uv.xy);
                fixed4 secondLayer = tex2D(_DetailTex, i.uv.zw);

                fixed4 c = lerp(firstLayer, secondLayer, secondLayer.a);
                c.rgb *= _Multiplier;

                return c;
            }

			ENDCG
		}
	}
    Fallback "Transparent/VertexLit"
}

参考 我买的 unity shader 入门精要