varying vec2 v_vTexcoord;
varying vec4 v_vColour;

uniform float h_curve[64];
uniform int   h_amount;

uniform float s_curve[64];
uniform int   s_amount;

uniform float v_curve[64];
uniform int   v_amount;

float eval_curve_segment_t(in float _y0, in float ax0, in float ay0, in float bx1, in float by1, in float _y1, in float prog) {
	return _y0 * pow(1. - prog, 3.) + 
		   ay0 * 3. * pow(1. - prog, 2.) * prog + 
		   by1 * 3. * (1. - prog) * pow(prog, 2.) + 
		   _y1 * pow(prog, 3.);
}

float eval_curve_segment_x(in float _y0, in float ax0, in float ay0, in float bx1, in float by1, in float _y1, in float _x) {
	float st = 0.;
	float ed = 1.;
	float _prec = 0.0001;
	
	float _xt = _x;
	int _binRep = 8;
	
	if(_x <= 0.) return _y0;
	if(_x >= 1.) return _y1;
	if(_y0 == ay0 && _y0 == by1 && _y0 == _y1) return _y0;
	
	for(int i = 0; i < _binRep; i++) {
		float _ftx = 3. * pow(1. - _xt, 2.) * _xt * ax0 
			       + 3. * (1. - _xt) * pow(_xt, 2.) * bx1
			       + pow(_xt, 3.);
		
		if(abs(_ftx - _x) < _prec)
			return eval_curve_segment_t(_y0, ax0, ay0, bx1, by1, _y1, _xt);
		
		if(_xt < _x) st = _xt;
		else		 ed = _xt;
		
		_xt = (st + ed) / 2.;
	}
	
	int _newRep = 16;
	
	for(int i = 0; i < _newRep; i++) {
		float slope = (  9. * ax0 - 9. * bx1 + 3.) * _xt * _xt
					+ (-12. * ax0 + 6. * bx1) * _xt
					+    3. * ax0;
		float _ftx = 3. * pow(1. - _xt, 2.) * _xt * ax0 
				   + 3. * (1. - _xt) * pow(_xt, 2.) * bx1
				   + pow(_xt, 3.)
				   - _x;
		
		_xt -= _ftx / slope;
		
		if(abs(_ftx) < _prec)
			break;
	}
	
	_xt = clamp(_xt, 0., 1.);
	return eval_curve_segment_t(_y0, ax0, ay0, bx1, by1, _y1, _xt);
}

float curveEval(in float[64] curve, in int amo, in float _x) {
	
	int   _shf   = amo - int(floor(float(amo) / 6.) * 6.);
	int   _segs  = (amo - _shf) / 6 - 1;
	float _shift = _shf > 0? curve[0] : 0.;
	float _scale = _shf > 1? curve[1] : 1.;
	
	_x = _x / _scale - _shift;
	_x = clamp(_x, 0., 1.);
	
	for( int i = 0; i < _segs; i++ ) {
		int ind = _shf + i * 6;
		float _x0 = curve[ind + 2];
		float _y0 = curve[ind + 3];
	  //float bx0 = _x0 + curve[ind + 0];
	  //float by0 = _y0 + curve[ind + 1];
		float ax0 = _x0 + curve[ind + 4];
		float ay0 = _y0 + curve[ind + 5];
		
		float _x1 = curve[ind + 6 + 2];
		float _y1 = curve[ind + 6 + 3];
		float bx1 = _x1 + curve[ind + 6 + 0];
		float by1 = _y1 + curve[ind + 6 + 1];
	  //float ax1 = _x1 + curve[ind + 6 + 4];
	  //float ay1 = _y1 + curve[ind + 6 + 5];
		
		if(_x < _x0) continue;
		if(_x > _x1) continue;
		
		return eval_curve_segment_x(_y0, ax0, ay0, bx1, by1, _y1, (_x - _x0) / (_x1 - _x0));
	}
	
	return curve[0];
}

#region =========================================== COLORS SPACES ===========================================
	vec3 rgb2hsv(vec3 c) { #region
		vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
	    vec4 p = mix(vec4(c.bg, K.wz), vec4(c.gb, K.xy), step(c.b, c.g));
	    vec4 q = mix(vec4(p.xyw, c.r), vec4(c.r, p.yzx), step(p.x, c.r));
	
	    float d = q.x - min(q.w, q.y);
	    float e = 0.0000000001;
	    return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + e)), d / (q.x + e), q.x);
	 } #endregion
	
	vec3 hsv2rgb(vec3 c) { #region
	    vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
	    vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
	    return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
	} #endregion
	
#endregion =========================================== COLORS SPACES ===========================================

void main() {
	vec4 col = texture2D( gm_BaseTexture, v_vTexcoord );
	vec3 hsv = rgb2hsv(col.rgb);
	
	hsv.r = curveEval(h_curve, h_amount, hsv.r);
	hsv.g = curveEval(s_curve, s_amount, hsv.g);
	hsv.b = curveEval(v_curve, v_amount, hsv.b);
	
	vec3 rgb = hsv2rgb(hsv);
	
    gl_FragColor = vec4(rgb, col.a);
}