I noticed there was a lack of a hue rotation shader, which makes certain things difficult. I took a stab at it, and it … kind of works. Im not certain what I am doing wrong, and frankly, kindof moved on. So I post it here for those who want to give it a shot and repair it:

// http://www.graficaobscura.com/matrix/index.html – Hue rotation Matrix calculations.

This should be pretty straightforward, so I assume im making an assumption I should not be about either the linear RGB colorspace (which, im 99 % sure is what textures are usually handed off as),

Other than that, anyone? Beuller?

best-
parag.

// based on “Hue Rotation while preserving luminance”
// http://www.graficaobscura.com/matrix/index.html
// Paul Haeberli
//
// ported to glsl by vade

uniform float hue;

// define our varying texture coordinates
varying vec2 texcoord0;
// define our rectangular texture samplers
uniform sampler2DRect tex0;

// 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 (void)
{

vec4 inputVec = texture2DRect(tex0, texcoord0);

// 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, inputVec);
float zsx = something.x/something.z;
float zsy = something.x/something.z;
transformMat = shearZMatrix(zsx,zsy) * transformMat;

// rotate hue, make angle input in degrees

float hue_rs = sin(radians(hue));
float hue_rc = cos(radians(hue));
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;

// convert to a vec with proper rgb values from our mat4.

// gl_FragColor = vec4(input0Mat[0][0], input0Mat[1][1],
input0Mat[2][2], input0Mat[3][3] );

gl_FragColor = inputVec;
}

The only parameter is ‘hue’, in degrees.

Thanks again PKM. I noticed your fixes do a bunch of additional matrix multiplies in there. Nice catches. :) This actually is of great help with some other stuff im working on :)

vec4 something = xformpnt(transformMat, inputVec);
float zsx = something.x/something.z;
float zsy = something.x/something.z;
transformMat = shearZMatrix(zsx,zsy) * transformMat;

to:

vec4 something = xformpnt(transformMat, lumcoeff);
float zsx = something.x/something.z;
float zsy = something.y/something.z;
transformMat = shearZMatrix(zsx,zsy) * transformMat;

Though to be honest, it looks more interesting with the typo…

vec4 inputVec = texture2DRect(tex0, texcoord0);

// 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(hue));
float hue_rc = cos(radians(hue));
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;

Ok I’m checking gimp/ps in a second to see what it’s really supposed
to look like…

sorry for the confusion! :)

I just tried loading this shader into a jit.gl.slab, and for some reason everything just passes through completely unaffected. Sending “param hue $1″ doesn’t seem to do anything. Any thoughts as to why this might be the case?

.mmb

I think it misses some part of the codes to make it working… I’m quite beginner in coding shader…

could you send the whole finale version of the shader please?

Thanks