Shader "Hidden/HizCull"
{
    SubShader
    {
        ZTest Off
        ZWrite Off
        
        Pass
        {
            HLSLPROGRAM
            #pragma vertex Vertex
            #pragma fragment CullFrag
            #pragma enable_d3d11_debug_symbols
            #pragma target 5.0

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

            struct Attributes
            {
                float4 positionOS : POSITION;
                float2 texcoord : TEXCOORD0;
            };

            struct Varyings
            {
                float2 uv : TEXCOORD0;
                float4 positionCS : SV_POSITION;
            };

            Varyings Vertex(Attributes input)
            {
                Varyings output = (Varyings)0;
                output.positionCS = TransformObjectToHClip(input.positionOS.xyz);
                output.uv = input.texcoord;
                return output;
            }

            TEXTURE2D(_ObjectAABBTexture0);
            SAMPLER(sampler_ObjectAABBTexture0);
            TEXTURE2D(_ObjectAABBTexture1);
            SAMPLER(sampler_ObjectAABBTexture1);


            TEXTURE2D(_DepthPyramidTexture);
            SAMPLER(sampler_DepthPyramidTexture);
            float4x4 _GPUCullingVP;
            float2 _MipmapLevelMinMaxIndex;
            float2 _Mip0Size;
            float4 _MipOffsetAndSize[16];

            static const float3 aggressiveExtentArray[8] =
            {
                float3(1, 1, 1),
                float3(1, 1, -1),
                float3(1, -1, 1),
                float3(1, -1, -1),
                float3(-1, 1, 1),
                float3(-1, 1, -1),
                float3(-1, -1, 1),
                float3(-1, -1, -1)
            };
         float3 TransferNDC(float3 pos) 
            {
                float4 ndc = mul(_GPUCullingVP, float4(pos, 1.0));
                ndc.xyz /= ndc.w;
                ndc.xy = ndc.xy * 0.5f + 0.5f;
                ndc.y = 1 - ndc.y;
                return ndc.xyz;
            }

            half CullFrag(Varyings input) : SV_Target
            {
                float2 uv = input.uv;
                float4 aabbCenter = SAMPLE_TEXTURE2D_LOD(_ObjectAABBTexture0, sampler_ObjectAABBTexture0, uv, 0.0);
                float4 aabbSize = SAMPLE_TEXTURE2D_LOD(_ObjectAABBTexture1, sampler_ObjectAABBTexture1, uv, 0.0);
                float3 aabbExtent = aabbSize.xyz;
                UNITY_BRANCH
                if (aabbCenter.a == 0.0)
                {
                    return 1;
                }
                
                #ifdef UNITY_REVERSED_Z
                float minZ = 0;
                #else
                float minZ = 1;
                #endif
                
                float2 maxXY = 0;
                float2 minXY = 1;
                for (uint i = 0; i < 8; ++i)
                {
                    float3 boxCorner = aabbCenter + aabbExtent * aggressiveExtentArray[i];
                    float4 clipPos = mul(_GPUCullingVP, float4(boxCorner, 1));
                    clipPos /= clipPos.w;
                    clipPos.xy = clipPos.xy * 0.5f + 0.5f;
                    #if UNITY_UV_STARTS_AT_TOP
                    clipPos.y = 1 - clipPos.y;
                    #endif
                    
                    minXY = min(clipPos.xy, minXY);
                    maxXY = max(clipPos.xy, maxXY);
                    #ifdef UNITY_REVERSED_Z
                    minZ = max(minZ, clipPos.z);
                    #else
                    minZ = min(minZ, clipPos.z);
                    #endif
                }
                
                float4 boxUVs = float4(minXY, maxXY);
                
                // if( boxUVs.x < 0 || boxUVs.y < 0 || boxUVs.x > 1 || boxUVs.y > 1 || boxUVs.z >1 || boxUVs.z<0)
                // {
                //     return 1;
                // }
                
                float2 size = (boxUVs.zw - boxUVs.xy) * _Mip0Size.xy;
                float mip = (log2(max(size.x, size.y)));
                
                mip = ceil(mip);
                mip = clamp(mip, _MipmapLevelMinMaxIndex.x, _MipmapLevelMinMaxIndex.y);
                
                // float  level_lower = max(mip - 1, 0);
                // float2 scale = exp2(-level_lower) / _Mip0Size.xy;
                // float2 a = floor(boxUVs.xy*scale);
                // float2 b = ceil(boxUVs.zw*scale);
                // float2 dims = b - a;
                //
                // // Use the lower level if we only touch <= 2 texels in both dimensions
                // if (dims.x <= 2 && dims.y <= 2)
                //     mip = level_lower;

                float4 offsetAndSize = _MipOffsetAndSize[mip];
                int4 pxMinMax = boxUVs * offsetAndSize.zwzw + offsetAndSize.xyxy;
                float4 depth = float4(LOAD_TEXTURE2D_LOD(_DepthPyramidTexture, pxMinMax.xy, 0).r,
                      LOAD_TEXTURE2D_LOD(_DepthPyramidTexture, pxMinMax.zy, 0).r,
                      LOAD_TEXTURE2D_LOD(_DepthPyramidTexture, pxMinMax.xw, 0).r,
                      LOAD_TEXTURE2D_LOD(_DepthPyramidTexture, pxMinMax.zw, 0).r
                );
                
                #ifdef UNITY_REVERSED_Z
                depth.xy = min(depth.xy, depth.zw);
                depth.x = min(depth.x, depth.y);
                return minZ > depth.x ? 0 : 1;
                #else
                depth.xy = max(depth.xy, depth.zw);
                depth.x = max(depth.x, depth.y);
                return minZ < depth.x ? 1 : 0;
                #endif
            }
            ENDHLSL
        }

    }
}