Make hsv_to_rgb map the hue periodically to [0, 360] if the input hue is negative, rather than returning undefined rgb.

include/igl/hsv_to_rgb.cpp

@@ -25,7 +25,8 @@ IGL_INLINE void igl::hsv_to_rgb(
   // From medit
   double f,p,q,t,hh;
   int    i;
-  hh = ((int)h % 360) / 60.;
+  // shift the hue to the range [0, 360] before performing calculations
+  hh = ((360 + ((int)h % 360)) % 360) / 60.;
   i = (int)std::floor(hh);    /* largest int <= h     */
   f = hh - i;                    /* fractional part of h */
   p = v * (1.0 - s);

include/igl/hsv_to_rgb.h

@@ -14,7 +14,7 @@ namespace igl
   // Convert RGB to HSV
   //
   // Inputs:
-  //   h  hue value (degrees: [0,360])
+  //   h  hue value (degrees: [0,360]. Values outside this range will be mapped periodically to [0,360].)
   //   s  saturation value ([0,1])
   //   v  value value ([0,1])
   // Outputs: