// This shader is mostly an adaptation of the shader found at
//  http://www.bonzaisoftware.com/water_tut.html and its glsl conversion
//  available at http://forum.bonzaisoftware.com/viewthread.php?tid=10
//  © Michael Horsch - 2005
//  Major update and revisions - 2011-10-07
//  © Emilian Huminiuc and Vivian Meazza

#version 120

varying vec4 waterTex1;
varying vec4 waterTex2;
varying vec4 waterTex4;
varying vec4 ecPosition;

varying vec3 viewerdir;
varying vec3 lightdir;
varying vec3 normal;

uniform float osg_SimulationTime;
uniform float WindE, WindN;

/////// functions /////////

void rotationmatrix(in float angle, out mat4 rotmat)
{
    rotmat = mat4( cos( angle ), -sin( angle ), 0.0, 0.0,
        sin( angle ),  cos( angle ), 0.0, 0.0,
        0.0         ,  0.0         , 1.0, 0.0,
        0.0         ,  0.0         , 0.0, 1.0 );
}

void main(void)
{
    mat4 RotationMatrix;
    vec3 N = normalize(gl_Normal);
    normal = N;

    ecPosition = gl_ModelViewMatrix * gl_Vertex;

    viewerdir = vec3(gl_ModelViewMatrixInverse[3]) - vec3(gl_Vertex);
    lightdir = normalize(vec3(gl_ModelViewMatrixInverse * gl_LightSource[0].position));

    waterTex4 = vec4( ecPosition.xzy, 0.0 );

    vec4 t1 = vec4(0.0, osg_SimulationTime * 0.005217, 0.0, 0.0);
    vec4 t2 = vec4(0.0, osg_SimulationTime * -0.0012, 0.0, 0.0);

    float windFactor = sqrt(pow(abs(WindE),2)+pow(abs(WindN),2)) * 0.01;
    float Angle = atan(-WindN + 0.001, WindE + 0.001) - atan(1.0);

    rotationmatrix(Angle, RotationMatrix);
    waterTex1 = gl_MultiTexCoord0 * RotationMatrix - t1 * windFactor;

    rotationmatrix(Angle, RotationMatrix);
    waterTex2 = gl_MultiTexCoord0 * RotationMatrix - t2 * windFactor;

    gl_Position = ftransform();
}