Shader "Custom/SpriteWithGroundClip"
{
    // 带地面裁剪的Sprite Shader
    // 当Sprite的世界Y坐标低于地面高度时，会被裁剪掉
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _GroundHeight ("地面高度 (Y坐标)", Float) = 0.0
        [MaterialToggle] _EnableClip ("启用裁剪", Float) = 1.0
        _ClipSoftness ("裁剪边缘柔和度", Range(0, 0.5)) = 0.05
        
        // 颜色
        _Color ("颜色", Color) = (1, 1, 1, 1)
    }
    SubShader
    {
        Tags
        {
            "RenderPipeline" = "UniversalPipeline"
            "Queue" = "Transparent"
            "RenderType" = "Transparent"
        }
        
        Blend SrcAlpha OneMinusSrcAlpha
        ZWrite Off
        Cull Off

        Pass
        {
            Name "SpriteWithGroundClip"
            
            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_instancing

            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

            struct Attributes
            {
                float4 positionOS : POSITION;
                float2 uv : TEXCOORD0;
                float4 color : COLOR;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct Varyings
            {
                float4 positionCS : SV_POSITION;
                float2 uv : TEXCOORD0;
                float4 color : COLOR;
                float3 worldPos : TEXCOORD1;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            CBUFFER_START(UnityPerMaterial)
                float4 _MainTex_ST;
                float4 _Color;
                float _GroundHeight;
                float _EnableClip;
                float _ClipSoftness;
            CBUFFER_END

            TEXTURE2D(_MainTex);
            SAMPLER(sampler_MainTex);

            Varyings vert(Attributes input)
            {
                Varyings output;
                UNITY_SETUP_INSTANCE_ID(input);
                UNITY_TRANSFER_INSTANCE_ID(input, output);

                output.positionCS = TransformObjectToHClip(input.positionOS.xyz);
                output.uv = TRANSFORM_TEX(input.uv, _MainTex);
                output.color = input.color;
                output.worldPos = TransformObjectToWorld(input.positionOS.xyz);
                return output;
            }

            half4 frag(Varyings input) : SV_Target
            {
                UNITY_SETUP_INSTANCE_ID(input);

                // 采样纹理
                half4 texColor = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, input.uv);
                half4 color = texColor * input.color * _Color;

                // 地面裁剪逻辑
                if (_EnableClip > 0.5)
                {
                    float worldY = input.worldPos.y;
                    float distanceToGround = worldY - _GroundHeight;
                    
                    // 如果在地面以下，裁剪掉
                    if (distanceToGround < 0)
                    {
                        // 使用柔和边缘
                        float alpha = smoothstep(0, _ClipSoftness, distanceToGround);
                        color.a *= alpha;
                        
                        // 如果Alpha太小，直接丢弃
                        if (color.a < 0.01)
                        {
                            discard;
                        }
                    }
                }

                return color;
            }
            ENDHLSL
        }
    }
    FallBack "Sprites/Default"
}