source: code/archive/skybox/Media/materials/programs/Ocean2GLSL.vert @ 11878

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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: converted from HLSL to GLSL by Jeff Doyle (nfz) to work in Ogre

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

uniform vec3 eyePosition;
uniform float BumpScale;
uniform vec2 textureScale;
uniform vec2 bumpSpeed;
uniform float time;
uniform float waveFreq;
uniform float waveAmp;

varying mat3 rotMatrix; //  transform from tangent to obj space
varying vec2 bumpCoord0;
varying vec2 bumpCoord1;
varying vec2 bumpCoord2;
varying vec3 eyeVector;

// wave functions
struct Wave {
  float freq;  // 2*PI / wavelength
  float amp;   // amplitude
  float phase; // speed * 2*PI / wavelength
  vec2 dir;
};


void main(void)
{

        #define NWAVES 2

        Wave wave[NWAVES];

        wave[0] = Wave( waveFreq, waveAmp, 0.5, vec2(-1, 0) );
        wave[1] = Wave( 3.0 * waveFreq, 0.33 * waveAmp, 1.7, vec2(-0.7, 0.7) );


    vec4 P = gl_Vertex;

        // 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
        // compute tangent basis
    vec3 T = normalize(vec3(1.0, ddy, 0.0)) * BumpScale;
    vec3 B = normalize(vec3(0.0, ddx, 1.0)) * BumpScale;
    vec3 N = normalize(vec3(ddx, 1.0, ddy));

        rotMatrix = mat3(T, B, N);

        gl_Position = gl_ModelViewProjectionMatrix * P;

        // calculate texture coordinates for normal map lookup
        bumpCoord0.xy = gl_MultiTexCoord0.xy * textureScale + time * bumpSpeed;
        bumpCoord1.xy = gl_MultiTexCoord0.xy * textureScale * 2.0 + time * bumpSpeed * 4.0;
        bumpCoord2.xy = gl_MultiTexCoord0.xy * textureScale * 4.0 + time * bumpSpeed * 8.0;


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