/*
Created by jiadong chen
https://jiadong-chen.medium.com/
*/

// Atlas VAT shader.
// 支持 1 张大图存多个 clip,clip 段沿 Y 轴堆叠。
// 通过 MaterialPropertyBlock 设置 _AnimYStart / _AnimYSpan / _AnimLen / _AnimTimeOffset 可切换 clip,
// 无需切换 material → 不破坏 SRP Batcher / GPU Instancing。
// 单 clip 模式向后兼容: _AnimYStart=0, _AnimYSpan=1, 行为与原 shader 一致。
Shader "chenjd/BuiltIn/AnimMapShader"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
		_AnimMap ("AnimMap", 2D) ="white" {}
		_AnimLen("Anim Length", Float) = 1
		_AnimYStart("Anim Y Start [0,1]", Float) = 0
		_AnimYSpan ("Anim Y Span [0,1]", Float) = 1
		_AnimTimeOffset("Anim Time Offset", Float) = 0
		[Toggle] _AnimLoop("Loop Anim", Float) = 1
	}
	
    SubShader
    {
        Tags { "RenderType" = "Opaque" }
        Cull off
		LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            //开启gpu instancing
            #pragma multi_compile_instancing

            #include "UnityCG.cginc"

            struct appdata
            {
                float2 uv : TEXCOORD0;
                float4 pos : POSITION;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;

            sampler2D _AnimMap;
            float4 _AnimMap_TexelSize; // x == 1/width, y == 1/height

            // Per-instance friendly props (set via MaterialPropertyBlock to keep SRP Batcher / instancing)
            UNITY_INSTANCING_BUFFER_START(Props)
                UNITY_DEFINE_INSTANCED_PROP(float, _AnimLen)
                UNITY_DEFINE_INSTANCED_PROP(float, _AnimYStart)
                UNITY_DEFINE_INSTANCED_PROP(float, _AnimYSpan)
                UNITY_DEFINE_INSTANCED_PROP(float, _AnimTimeOffset)
                UNITY_DEFINE_INSTANCED_PROP(float, _AnimLoop)
            UNITY_INSTANCING_BUFFER_END(Props)

            v2f vert (appdata v, uint vid : SV_VertexID)
            {
                UNITY_SETUP_INSTANCE_ID(v);

                float animLen   = UNITY_ACCESS_INSTANCED_PROP(Props, _AnimLen);
                float yStart    = UNITY_ACCESS_INSTANCED_PROP(Props, _AnimYStart);
                float ySpan     = UNITY_ACCESS_INSTANCED_PROP(Props, _AnimYSpan);
                float timeOff   = UNITY_ACCESS_INSTANCED_PROP(Props, _AnimTimeOffset);
                float loopFlag  = UNITY_ACCESS_INSTANCED_PROP(Props, _AnimLoop);

                // 时间 → 段内归一化 t [0,1]
                float playTime = _Time.y - timeOff;
                float t = playTime / max(animLen, 0.0001);
                // 循环 or 停在最后一帧
                t = lerp(saturate(t), frac(t), step(0.5, loopFlag));

                float animMap_x = (vid + 0.5) * _AnimMap_TexelSize.x;
                float animMap_y = yStart + t * ySpan;

                float4 pos = tex2Dlod(_AnimMap, float4(animMap_x, animMap_y, 0, 0));

                v2f o;
                o.vertex = UnityObjectToClipPos(pos);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                return o;
            }
            
            fixed4 frag (v2f i) : SV_Target
            {
                fixed4 col = tex2D(_MainTex, i.uv);
                return col;
            }
            ENDCG
        }
	}
}