[游戏开发]UE4滤镜：桑园滤镜 Paint Filter

shader

?Global

    return 1;
}

float4 GetKernelMeanAndVariance(float2 UV, float4 Range, float2x2 RotationMatrix)
{
    float2 TexelSize = View.BufferSizeAndInvSize.zw;
    float3 Mean = float3(0, 0, 0);
    float3 Variance = float3(0, 0, 0);
    float Samples = 0;
    
    for (int x = Range.x; x <= Range.y; x++)
    {
        for (int y = Range.z; y <= Range.w; y++)
        {
            float2 Offset = mul(float2(x, y) * TexelSize, RotationMatrix);
            float3 PixelColor = SceneTextureLookup(UV + Offset, 14, false).rgb;
            Mean += PixelColor;
            Variance += PixelColor * PixelColor;
            Samples++;
        }
    }
    
    Mean /= Samples;
    Variance = Variance / Samples - Mean * Mean;
    float TotalVariance = Variance.r + Variance.g + Variance.b;
    return float4(Mean.r, Mean.g, Mean.b, TotalVariance);
}

float GetPixelAngle(float2 UV)
{
    float2 TexelSize = View.BufferSizeAndInvSize.zw;
    float GradientX = 0;
    float GradientY = 0;
    float SobelX[9] = {-1, -2, -1, 0, 0, 0, 1, 2, 1};
    float SobelY[9] = {-1, 0, 1, -2, 0, 2, -1, 0, 1};
    int i = 0;
    
    for (int x = -1; x <= 1; x++)
    {
        for (int y = -1; y <= 1; y++)
        {
            // 1
            float2 Offset = float2(x, y) * TexelSize;
            float3 PixelColor = SceneTextureLookup(UV + Offset, 14, false).rgb;
            float PixelValue = dot(PixelColor, float3(0.3,0.59,0.11));
            
            // 2
            GradientX += PixelValue * SobelX[i];
            GradientY += PixelValue * SobelY[i];
            i++;
        }
    }
    
    return atan(GradientY / GradientX);

KuWhara

float2 UV = GetDefaultSceneTextureUV(Parameters, 14);
float4 MeanAndVariance[4];
float4 Range;
float Angle = GetPixelAngle(UV);
float2x2 RotationMatrix = float2x2(cos(Angle), -sin(Angle), sin(Angle), cos(Angle));

Range = float4(-XRadius, 0, -YRadius, 0);
MeanAndVariance[0] = GetKernelMeanAndVariance(UV, Range, RotationMatrix);

Range = float4(0, XRadius, -YRadius, 0);
MeanAndVariance[1] = GetKernelMeanAndVariance(UV, Range, RotationMatrix);

Range = float4(-XRadius, 0, 0, YRadius);
MeanAndVariance[2] = GetKernelMeanAndVariance(UV, Range, RotationMatrix);

Range = float4(0, XRadius, 0, YRadius);
MeanAndVariance[3] = GetKernelMeanAndVariance(UV, Range, RotationMatrix);

// 1
float3 FinalColor = MeanAndVariance[0].rgb;
float MinimumVariance = MeanAndVariance[0].a;

// 2
for (int i = 1; i < 4; i++)
{
    if (MeanAndVariance[i].a < MinimumVariance)
    {
        FinalColor = MeanAndVariance[i].rgb;
        MinimumVariance = MeanAndVariance[i].a;
    }
}
return FinalColor;

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