Shader "Custom/Convolution"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        [Enum(kerEdgeDetectionA,1,kerEdgeDetectionB,2,kerEdgeDetectionC,3,kerSharpen,4,kerBoxBlur,5)]
        _Kernel("Kernel", Float) = 1
    }
    SubShader
    {
        // No culling or depth
        Cull Off ZWrite Off ZTest Always

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

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

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

            v2f vert(appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv;
                return o;
            }

            sampler2D _MainTex;
            float4 _MainTex_TexelSize;

            float3x3 GetData(int channel, sampler2D tex, float2 uv, float4 size)
            {
                float3x3 mat;
                for (int y = -1; y < 2; y++)
                {
                    for (int x = -1; x < 2; x++)
                    {
                        mat[x + 1][y + 1] = tex2D(tex, uv + float2(x * size.x, y * size.y))[channel];
                    }
                }
                return mat;
            }

            float3x3 GetMean(float3x3 matr, float3x3 matg, float3x3 matb)
            {
                float3x3 mat;
                for (int y = 0; y < 3; y++)
                {
                    for (int x = 0; x < 3; x++)
                    {
                        mat[x][y] = (matr[x][y] + matg[x][y] + matb[x][y]) / 3.0;
                    }
                }
                return mat;
            }

            float Convolve(float3x3 kernel, float3x3 pixels, float denom, float offset)
            {
                float res = 0.0;
                for (int y = 0; y < 3; y++)
                {
                    for (int x = 0; x < 3; x++)
                    {
                        res += kernel[2 - x][2 - y] * pixels[x][y];
                    }
                }

                return res;
            }

            float _Kernel;

            fixed4 frag(v2f i) : SV_Target
            {
                float3x3 kerEdgeDetectionA = float3x3(0.0, 0, -1.0,
                                                      1.0, 0, -1.0,
                                                      0.0, 1.0, 0.0);

                float3x3 kerEdgeDetectionB = float3x3(0.0, 1.0, 0.0,
                                                      1.0, -4.0, 1.0,
                                                      0.0, 1.0, 0.0);

                float3x3 kerEdgeDetectionC = float3x3(-1.0, -1.0, -1.0,
                                                      -1.0, 8.0, -1.0,
                                                      -1.0, -1.0, -1.0);

                float3x3 kerSharpen = float3x3(0.0, -1.0, 0.0,
                                               -1.0, 5.0, -1.0,
                                               0.0, -1.0, 0.0);


                float3x3 kerBoxBlur = (1.0 / 9.0) * float3x3(1.0, 1.0, 1.0,
                                                             1.0, 1.0, 1.0,
                                                             1.0, 1.0, 1.0);


                float3x3 kernelSelection;

                if (_Kernel == 1)
                {
                    kernelSelection = kerEdgeDetectionA;
                }
                else if (_Kernel == 2)
                {
                    kernelSelection = kerEdgeDetectionB;
                }
                else if (_Kernel == 3)
                {
                    kernelSelection = kerEdgeDetectionC;
                }
                else if (_Kernel == 4)
                {
                    kernelSelection = kerSharpen;
                }
                else if (_Kernel == 5)
                {
                    kernelSelection = kerBoxBlur;
                }

                float3x3 matr = GetData(0, _MainTex, i.uv, _MainTex_TexelSize);
                float3x3 matg = GetData(1, _MainTex, i.uv, _MainTex_TexelSize);
                float3x3 matb = GetData(2, _MainTex, i.uv, _MainTex_TexelSize);
                float3x3 mata = GetMean(matr, matg, matb);


                // kernel
                float4 gl_FragColor = float4(Convolve(kernelSelection, matr, 1.0, 0.0),
                                             Convolve(kernelSelection, matg, 1.0, 0.0),
                                             Convolve(kernelSelection, matb, 1.0, 0.0),
                                             1.0);

                return gl_FragColor;
            }
            ENDCG
        }
    }
}