Vermillion Hue Shader

varying vec2 v_vTexcoord;
varying vec4 v_vColour;

uniform float xhueval;
uniform float xsatval;

void main()
{
	vec2 tmp_coord = v_vTexcoord;
    vec4 tmp_col = texture2D( gm_BaseTexture, tmp_coord );

	//rgb to hsl
	float colr = tmp_col.r;
	float colg = tmp_col.g;
	float colb = tmp_col.b;
	float xmin = min(min(colr, colg), colb);
	float xmax = max(max(colr, colg), colb);
	float hslh;
	float hsls;
	float hsll = (xmin+xmax)/2.;
	if (xmin == xmax) {
		hsls = 0.;
		hslh = 0.;
	}
	else {
		if (hsll < 0.5) hsls = (xmax-xmin)/(xmax+xmin);
		else hsls = (xmax-xmin)/(2.-xmax-xmin);
		if (colr == xmax) hslh = (colg-colb)/(xmax-xmin);
		if (colg == xmax) hslh = 2.+(colb-colr)/(xmax-xmin);
		if (colb == xmax) hslh = 4.+(colr-colg)/(xmax-xmin);
		hslh = hslh*60.;
		if (hslh < 0.) hslh += 360.;
	}

	//change hsl values
	hslh += xhueval;
	if (hslh >= 360.) hslh -= 360.;
	if (hslh < 0.) hslh += 360.;
	hsls = xsatval*hsls;

	//hsl to rgb
	if (hsls == 0.) {
		colr = hsll;
		colg = colr;
		colb = colr;
	}
	else {
		float varc = (1.-abs(2.*hsll-1.))*hsls;
		float varx = varc*(1.-abs(mod(hslh/60., 2.) - 1.));
		float varm = hsll - varc/2.;
		if ((hslh >= 0.) && (hslh < 60.)) {
			colr = varc + varm;
			colg = varx + varm;
			colb = varm;
		}
		if ((hslh >= 60.) && (hslh < 120.)) {
			colr = varx + varm;
			colg = varc + varm;
			colb = varm;
		}
		if ((hslh >= 120.) && (hslh < 180.)) {
			colr = varm;
			colg = varc + varm;
			colb = varx + varm;
		}
		if ((hslh >= 180.) && (hslh < 240.)) {
			colr = varm;
			colg = varx + varm;
			colb = varc + varm;
		}
		if ((hslh >= 240.) && (hslh < 300.)) {
			colr = varx + varm;
			colg = varm;
			colb = varc + varm;
		}
		if ((hslh >= 300.) && (hslh < 360.)) {
			colr = varc + varm;
			colg = varm;
			colb = varx + varm;
		}
	}

	//change rgb values
	tmp_col.r = colr;
	tmp_col.g = colg;
	tmp_col.b = colb;

	gl_FragColor = tmp_col * v_vColour;
}