Shader "Unlit/Corner"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
	}
	SubShader
	{
		Tags { "RenderType"="Opaque" }
		LOD 100

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			// make fog work
			#pragma multi_compile_fog
			
			#include "UnityCG.cginc"

			struct appdata{
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
			};

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

			sampler2D _MainTex;
			float4 _MainTex_ST;
			
			v2f vert (appdata v){
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				o.uv = TRANSFORM_TEX(v.uv, _MainTex);
				return o;
			}

			static const float3x3 sobelX = float3x3(
				float3(-1, 0, 1),
				float3(-2, 0, 2),
				float3(-1, 0, 1)
				);

			static const float3x3 sobelY = float3x3(
				float3(-1, -2, -1),
				float3(0, 0, 0),
				float3(1, 2, 1)
				);
			
			float sobelFilter(sampler2D image, float2 uv, float3x3 kernel) {
				float2 textureSize = float2(512, 512);

				float sum = 0.0f;
				for (int y = -1; y <= 1; ++y) {
					for (int x = -1; x <= 1; ++x) {
						sum += tex2D(image, uv + float2((float)x / textureSize.x, (float)y / textureSize.y)).r * kernel[y + 1][x + 1];
					}
				}
				return sum;
			}

			float4 frag (v2f i) : SV_Target{
				float2 textureSize = float2(512,512);
				float2 texelSize = 1.0f / textureSize;

				float Ix = tex2D(_MainTex, i.uv + float2(texelSize.x, 0.0f)).r - tex2D(_MainTex, i.uv).r;
				float Iy = tex2D(_MainTex, i.uv + float2(0.0f, texelSize.y)).r - tex2D(_MainTex, i.uv).r;

				float2x2 jacobi;
				jacobi[0][0] = Ix * Ix;
				jacobi[0][1] = Ix * Iy;
				jacobi[1][0] = Ix * Iy;
				jacobi[1][1] = Iy * Iy;
				
				float jacobian = (Ix * Ix) * (Iy * Iy) - (Ix * Iy) * (Ix * Iy);

				//return tex2D(_MainTex, i.uv).r;
				float sX = sobelFilter(_MainTex, i.uv, sobelX);
				float sY = sobelFilter(_MainTex, i.uv, sobelY);

				//return sX;
				return sY;
				return sX*sX + sY*sY;
				//return jacobian == 0;
				//return abs(float4(Ix, Iy, 0, 1));
			}
			ENDCG
		}
	}
}