hue rotation

hueRotation.FSH

varying highp vec2 textureCoordinate;
uniform sampler2D inputImageTexture;
uniform lowp float hueAdjust;

precision mediump float;
// no need to compute these...
const float sqrt2 = 1.414213562373095;
const float sqrt3 = 1.732050807568877;
const float oneoversqrt2 = 0.707106781186548;
const float oneoversqrt3 = 0.577350269189626;

//const vec4 lumcoeff = vec4(0.299,0.587,0.114, 1.0);
const vec4 lumcoeff = vec4(0.3086,0.6094,0.0820, 1.0);

const float zsx = lumcoeff.x/lumcoeff.z;
const float zsy = lumcoeff.y/lumcoeff.z;

// matrix functions.

mat4 ident = mat4(1.0, 0.0, 0.0, 0.0,
                  0.0, 1.0, 0.0, 0.0,
                  0.0, 0.0, 1.0, 0.0,
                  0.0, 0.0, 0.0, 1.0);

// red
mat4 rotateXMat(float rs, float rc)
{
    return mat4(1.0, 0.0, 0.0, 0.0,
                0.0, rc, rs, 0.0,
                0.0, -rs, rc, 0.0,
                0.0, 0.0, 0.0, 1.0);
}

// green
mat4 rotateYMat(float rs, float rc)
{
    return mat4(rc, 0.0, -rs, 0.0,
                0.0, 1.0, 0.0, 0.0,
                rs, 0.0, rc, 0.0,
                0.0, 0.0, 0.0, 1.0);
}

// blue	
mat4 rotateZMat( float rs, float rc)
{
    return mat4(rc, rs, 0.0, 0.0,
                -rs, rc, 0.0, 0.0,
                0.0, 0.0, 1.0, 0.0,
                0.0, 0.0, 0.0, 1.0);	
}

mat4 shearZMatrix(float dx, float dy)
{
    return mat4(1.0, 0.0, dx, 0.0,
                0.0, 1.0, dy, 0.0,
                0.0, 0.0, 1.0, 0.0,
                0.0, 0.0, 0.0, 1.0);
}

vec4 xformpnt(mat4 matrix, vec4 inputVec)
{
    
    return vec4( inputVec.x*matrix[0][0] + inputVec.y*matrix[1][0] +
                inputVec.z*matrix[2][0] + matrix[3][0],
                inputVec.x*matrix[0][1] + inputVec.y*matrix[1][1] +
                inputVec.z*matrix[2][1] + matrix[3][1],
                inputVec.x*matrix[0][2] + inputVec.y*matrix[1][2] +
                inputVec.z*matrix[2][2] + matrix[3][2], 1.0);
}



void main() {

   
   
   vec4 inputVec = texture2D(inputImageTexture, textureCoordinate);
   
   // setup our transform mat - cant convert a const
   mat4 transformMat = ident;
   
   // rotate grey vector into positive Z
   transformMat = rotateXMat(oneoversqrt2, oneoversqrt2) * transformMat;
   transformMat = rotateYMat(-oneoversqrt3, sqrt2/sqrt3) * transformMat;
   
   // shear to preserve lumanince
   vec4 something = xformpnt(transformMat, lumcoeff);
   float zsx = something.x/something.z;
   float zsy = something.y/something.z;
   transformMat = shearZMatrix(zsx,zsy) * transformMat;
   
   // rotate hue, make angle input in degrees
   
   float hue_rs = sin(radians(30.0));
   float hue_rc = cos(radians(30.0));
   transformMat = rotateZMat(hue_rs, hue_rc) * transformMat;
   
   // unshear to preserve luminance
   transformMat = shearZMatrix(-zsx,-zsy) * transformMat;
   
   // unrotate
   transformMat = rotateYMat(oneoversqrt3, sqrt2/sqrt3 ) * transformMat;
   transformMat = rotateXMat(-oneoversqrt2, oneoversqrt2) * transformMat;
   
   // do the hue transformation on our pixels
   inputVec = transformMat * inputVec;
   
   // convert to a vec with proper rgb values from our mat4.
   
   gl_FragColor = inputVec;
}