What is _MainTex_ST ?

【What is _MainTex_ST ?】

　　在Unity自带的Unlit/Texture中，有引用到float4 _MainTex_ST，如下：

// Unlit shader. Simplest possible textured shader.
// - no lighting
// - no lightmap support
// - no per-material color

Shader "Unlit/Texture" {
Properties {
    _MainTex ("Base (RGB)", 2D) = "white" {}
}

SubShader {
    Tags { "RenderType"="Opaque" }
    LOD 100
    
    Pass {  
        CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            
            #include "UnityCG.cginc"

            struct appdata_t {
                float4 vertex : POSITION;
                float2 texcoord : TEXCOORD0;
            };

            struct v2f {
                float4 vertex : SV_POSITION;
                half2 texcoord : TEXCOORD0;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            
            v2f vert (appdata_t v)
            {
                v2f o;
                o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
                o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
                return o;
            }
            
            fixed4 frag (v2f i) : SV_Target
            {
                fixed4 col = tex2D(_MainTex, i.texcoord);
                return col;
            }
        ENDCG
    }
}

}

　　TRANSFORM_TEX宏如下：

　　

　　indeed for any texture property, Unity provides value for float4 with "_ST" suffix. The x,y contains texture scale, and z,w contains translation (offset).

　　_ST变量有4个值，xy是texture scale，zw是offset。

　　

　　在Material中可以设置的Tiling就是xy，Offset就是zw。

参考：http://forum.unity3d.com/threads/what-is-_maintex_st.24962/