Paint.NET CodeLab filter to calculate alpha for Windows tooltip shadow pixels in screenshots

GrayAlpha.cs

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#region UICode
IntSliderControl Amount1 = 0; // [0,100] Slider 1 Description
IntSliderControl Amount2 = 0; // [0,100] Slider 2 Description
IntSliderControl Amount3 = 0; // [0,100] Slider 3 Description
#endregion

const byte TOOLTIP_GRAY = 118;

void Render(Surface dst, Surface src, Rectangle rect)
{
    for (int y = rect.Top; y < rect.Bottom; y++)
    {

        for (int x = rect.Left; x < rect.Right; x++)
        {
            ColorBgra currentPixel = src[x,y];
            float grayDist = (currentPixel.R - TOOLTIP_GRAY) * 256 / (256 - TOOLTIP_GRAY);
            currentPixel.R = currentPixel.G = currentPixel.B = 118;
            currentPixel.A = (byte)(255 - grayDist);
            dst[x,y] = currentPixel;
        }
    }
}