unity shader序列帧动画代码，顺便吐槽一下unity shader系统

Shader "HELLOHUAN/Hello_Sequence" {
Properties {
    _Color ("Main Color", Color) = (1,1,1,1)
    _MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
    _SizeX ("列数", Float) = 4
    _SizeY ("行数", Float) = 4
    _Speed ("播放速度", Float) = 200
}

SubShader {
    Tags { "RenderType"="Opaque"}
    LOD 200

CGPROGRAM
#pragma surface surf Lambert alpha

sampler2D _MainTex;
fixed4 _Color;

uniform fixed _SizeX;
uniform fixed _SizeY;
uniform fixed _Speed;

struct Input {
    float2 uv_MainTex;
};

void surf (Input IN, inout SurfaceOutput o) {
    
    int index = floor(_Time .x * _Speed);
    int indexY = index/_SizeX;
    int indexX = index - indexY*_SizeX;
    float2 testUV = float2(IN.uv_MainTex.x /_SizeX, IN.uv_MainTex.y /_SizeY);
    
    testUV.x += indexX/_SizeX;
    testUV.y += indexY/_SizeY;
    
    fixed4 c = tex2D(_MainTex, testUV) * _Color;
    o.Albedo = c.rgb;
    
    o.Alpha = c.a;
    //o.Albedo = float3( floor(_Time .x * _Speed) , 1.0, 1.0);
}
ENDCG
}

Fallback "Transparent/VertexLit"
}