// Copyright (c) .NET Foundation and Contributors (https://dotnetfoundation.org/ & https://stride3d.net) and Silicon Studio Corp. (https://www.siliconstudio.co.jp)
// Distributed under the MIT license. See the LICENSE.md file in the project root for more information.
shader ComputeColorDarken3ds : ComputeColor
{
    compose ComputeColor color1;
    compose ComputeColor color2;

    override float4 Compute()
    {
        float4 backColor = color1.Compute();
        float4 frontColor = color2.Compute();

        // From http://msdn.microsoft.com/en-us/library/windows/desktop/hh706313(v=vs.85).aspx
        //
        //  b = background, f = foreground, c = color, a = alpha, r = result color obtained with the specific blend formula
        //
        //  Darken:
        //      color = min((1 - fa) * ba * bc + (fa * fc), (1 - ba) * fa * fc + (ba * bc))
        //      alpha = fa * (1-ba) + ba

        return float4(min(lerp(backColor.a * backColor.rgb, frontColor.rgb, frontColor.a), lerp(frontColor.a * frontColor.rgb, backColor.rgb, backColor.a)),
                      BlendUtils.BasicAlphaBlend(backColor.a, frontColor.a));
    }
};
