Aurora Effect Vert Shader

/*
Aurora Effect Vert Shader

by Eddie Lee (twitter: @eddietree)
http://illogictree.com
Jan 30, 2012
*/

#version 110

varying vec2 uv;

uniform vec4 v0;
uniform vec4 v1;
uniform vec4 tan0;
uniform vec4 tan1;

vec3 hermite( vec3 p0, vec3 t0, vec3 p1, vec3 t1, float alpha )
{
    float t = alpha;
    float t_sqr = alpha*alpha;
    float t_cubed = alpha*alpha*alpha;


    float h1 =  2.0*t_cubed - 3.0*t_sqr + 1.0;          // calculate basis function 1
    float h2 = -2.0*t_cubed + 3.0*t_sqr;              // calculate basis function 2
    float h3 =  t_cubed - 2.0*t_sqr + t;         // calculate basis function 3
    float h4 =  t_cubed -  t_sqr;              // calculate basis function 4

    return h1*p0 + h2*p1 + h3*t0 + h4*t1;
}

void main()
{
    // interpolate on x (assume verts are normalized in x,y )
    float splineAlpha = gl_Vertex.x;

    vec3 pos = hermite( v0.xyz, tan0.xyz, v1.xyz, tan1.xyz, splineAlpha);
    pos.y += gl_Vertex.y * 600.0;
    gl_Position = gl_ModelViewProjectionMatrix * vec4(pos.xy,0.0,1.0);
    uv = gl_Vertex.xy;
}