Flat curve editor widget, HSV tool modified to use it.

Usage :
 - click & drag a control point to move it in X&Y direction
 - click & drag a vertical line to move it in horizontal or vertical direction (the very first move will be used to determine the motion direction)
 - click & drag the yellow or blue square handle to modify the tangent of the same color

rtengine/utils.cc

@@ -17,9 +17,16 @@
  *  along with RawTherapee.  If not, see <http://www.gnu.org/licenses/>.
  */
 #include <utils.h>
+#include <math.h>
 #include <string.h>
 #include <stdio.h>
 
+#undef MAX
+#undef MIN
+
+#define MAX(a,b) ((a)<(b)?(b):(a))
+#define MIN(a,b) ((a)>(b)?(b):(a))
+
 namespace rtengine {
 
 void bilinearInterp (const unsigned char* src, int sw, int sh, unsigned char* dst, int dw, int dh) {
@@ -139,6 +146,77 @@ void vflip (unsigned char* img, int w, int h) {
     delete [] flipped;
 }
 
+void rgb2hsv (int r, int g, int b, float &h, float &s, float &v) {
+
+	double var_R = r / 65535.0;
+	double var_G = g / 65535.0;
+	double var_B = b / 65535.0;
+
+	double var_Min = MIN(MIN(var_R,var_G),var_B);
+	double var_Max = MAX(MAX(var_R,var_G),var_B);
+	double del_Max = var_Max - var_Min;
+	v = var_Max;
+	if (fabs(del_Max)<0.00001) {
+		h = 0;
+		s = 0;
+	}
+	else {
+		s = del_Max/var_Max;
+
+		if      ( var_R == var_Max ) h = (var_G - var_B)/del_Max;
+		else if ( var_G == var_Max ) h = 2.0 + (var_B - var_R)/del_Max;
+		else if ( var_B == var_Max ) h = 4.0 + (var_R - var_G)/del_Max;
+		h /= 6.0;
+
+		if ( h < 0 )  h += 1;
+		if ( h > 1 )  h -= 1;
+	}
+}
+
+void hsv2rgb (float h, float s, float v, int &r, int &g, int &b) {
+
+	float h1 = h*6; // sector 0 to 5
+	int i = floor( h1 );
+	float f = h1 - i; // fractional part of h
+
+	float p = v * ( 1 - s );
+	float q = v * ( 1 - s * f );
+	float t = v * ( 1 - s * ( 1 - f ) );
+
+	float r1,g1,b1;
+
+	if (i==0) {r1 = v;  g1 = t;  b1 = p;}
+	if (i==1) {r1 = q;  g1 = v;  b1 = p;}
+	if (i==2) {r1 = p;  g1 = v;  b1 = t;}
+	if (i==3) {r1 = p;  g1 = q;  b1 = v;}
+	if (i==4) {r1 = t;  g1 = p;  b1 = v;}
+	if (i==5) {r1 = v;  g1 = p;  b1 = q;}
+
+	r = (int)((r1)*65535);
+	g = (int)((g1)*65535);
+	b = (int)((b1)*65535);
+}
+
+// The same function but set float values intead if int
+// Function copied for speed concerns
+void hsv2rgb (float h, float s, float v, float &r, float &g, float &b) {
+
+	float h1 = h*6; // sector 0 to 5
+	int i = floor( h1 );
+	float f = h1 - i; // fractional part of h
+
+	float p = v * ( 1 - s );
+	float q = v * ( 1 - s * f );
+	float t = v * ( 1 - s * ( 1 - f ) );
+
+	if (i==0) {r = v;  g = t;  b = p;}
+	if (i==1) {r = q;  g = v;  b = p;}
+	if (i==2) {r = p;  g = v;  b = t;}
+	if (i==3) {r = p;  g = q;  b = v;}
+	if (i==4) {r = t;  g = p;  b = v;}
+	if (i==5) {r = v;  g = p;  b = q;}
+}
+
 }