Trouble with Gerstner Waves Normals

OpenGL OpenGL: Advanced Coding
1

Hello all,

I have been implementing Gerstner Waves in my engine and i have encontered a problem that as kept me from moving on :D.
The positions are being computed correctly but the computed normals (using equation 12 in this paper Chapter 1. Effective Water Simulation from Physical Models) do not seem to be correctly interpolating in the fragment shader.
Here is the code:

// Normal
        for(int i = 0; i < nGerstnerWaves; i++)
        {
            float WA = waveFrequency[i] * waveAmplitude[i];

            float waveNormal = waveFrequency[i] * dot(waveDirection[i], totalPosition.xz) + (wavePhaseConstant[i] * timeStep);

            totalNormal.x += waveDirection[i].x * WA * cos(waveNormal);
            totalNormal.y += waveCrest[i] * WA * sin(waveNormal);
            totalNormal.z += waveDirection[i].y * WA * cos(waveNormal);
        }

        totalNormal.x = -totalNormal.x;
        totalNormal.y = 1 - totalNormal.y;
        totalNormal.z = -totalNormal.z;


        totalNormal = normalize(totalNormal);

And the Wave parameters are these (just one wave for now)

{"amplitude": 1.5, "direction": [1.0, 0.0], "steepness": 0.8, "speed": 0.9, "length": 10.0}

And heres two quick videos of the issue:

Thanks in advance,
André

2

I have added a geometry shader in between to draw each normal and each normal per face and this is what i got:

https://youtu.be/sTsA84ZCSlw
As you can see some normals are being negative for a part of a wave cycle which should never happen, any ideas on why this is happening?

Thank you