source: code/archive/skybox/Media/materials/programs/Ocean2HLSL_Cg.vert @ 11183

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Comments:
        Simple ocean shader with animated bump map and geometric waves
        Based partly on "Effective Water Simulation From Physical Models", GPU Gems

11 Aug 05: heavily modified by Jeff Doyle (nfz) for Ogre

******************************************************************************/

struct a2v {
        float4 Position : POSITION;   // in object space
        float2 TexCoord : TEXCOORD0;
};

struct v2f {
        float4 Position  : POSITION;  // in clip space
        float3 rotMatrix1 : TEXCOORD0; // first row of the 3x3 transform from tangent to obj space
        float3 rotMatrix2 : TEXCOORD1; // second row of the 3x3 transform from tangent to obj space
        float3 rotMatrix3 : TEXCOORD2; // third row of the 3x3 transform from tangent to obj space

        float2 bumpCoord0 : TEXCOORD3;
        float2 bumpCoord1 : TEXCOORD4;
        float2 bumpCoord2 : TEXCOORD5;

        float3 eyeVector  : TEXCOORD6;
};

// wave functions

struct Wave {
  float freq;  // 2*PI / wavelength
  float amp;   // amplitude
  float phase; // speed * 2*PI / wavelength
  float2 dir;
};

v2f main(a2v IN,
                uniform float4x4 WorldViewProj,
                uniform float3 eyePosition,
                uniform float BumpScale,
                uniform float2 textureScale,
                uniform float2 bumpSpeed,
                uniform float time,
                uniform float waveFreq,
                uniform float waveAmp
        )
{
        v2f OUT;

        #define NWAVES 2
        Wave wave[NWAVES] = {
                { 1.0, 1.0, 0.5, float2(-1, 0) },
                { 2.0, 0.5, 1.7, float2(-0.7, 0.7) }
        };

    wave[0].freq = waveFreq;
    wave[0].amp = waveAmp;

    wave[1].freq = waveFreq * 3.0;
    wave[1].amp = waveAmp * 0.33;

    float4 P = IN.Position;

        // sum waves
        float ddx = 0.0, ddy = 0.0;
        float deriv;
        float angle;

        // wave synthesis using two sine waves at different frequencies and phase shift
        for(int i = 0; i<NWAVES; ++i)
        {
                angle = dot(wave[i].dir, P.xz) * wave[i].freq + time * wave[i].phase;
                P.y += wave[i].amp * sin( angle );
                // calculate derivate of wave function
                deriv = wave[i].freq * wave[i].amp * cos(angle);
                ddx -= deriv * wave[i].dir.x;
                ddy -= deriv * wave[i].dir.y;
        }

        // compute the 3x3 tranform from tangent space to object space
        // first rows are the tangent and binormal scaled by the bump scale

        OUT.rotMatrix1.xyz = BumpScale * normalize(float3(1, ddy, 0)); // Binormal
        OUT.rotMatrix2.xyz = BumpScale * normalize(float3(0, ddx, 1)); // Tangent
        OUT.rotMatrix3.xyz = normalize(float3(ddx, 1, ddy)); // Normal

        OUT.Position = mul(WorldViewProj, P);

        // calculate texture coordinates for normal map lookup
        OUT.bumpCoord0.xy = IN.TexCoord*textureScale + time * bumpSpeed;
        OUT.bumpCoord1.xy = IN.TexCoord*textureScale * 2.0 + time * bumpSpeed * 4.0;
        OUT.bumpCoord2.xy = IN.TexCoord*textureScale * 4.0 + time * bumpSpeed * 8.0;

        OUT.eyeVector = P.xyz - eyePosition; // eye position in vertex space
        return OUT;
}