2: #include <petscsys.h>              /*I "petscsys.h" I*/

  4: /*
  5:     Set up a color map, using uniform separation in hue space.
  6:     Map entries are Red, Green, Blue.
  7:     Values are "gamma" corrected.
  8:  */

 10: /*  
 11:    Gamma is a monitor dependent value.  The value here is an 
 12:    approximate that gives somewhat better results than Gamma = 1.
 13:  */
 14: static PetscReal Gamma = 2.0;

 18: PetscErrorCode  PetscDrawUtilitySetGamma(PetscReal g)
 19: {
 21:   Gamma = g;
 22:   return(0);
 23: }


 26: /*
 27:  * This algorithm is from Foley and van Dam, page 616
 28:  * given
 29:  *   (0:359, 0:100, 0:100).
 30:  *      h       l      s
 31:  * set
 32:  *   (0:255, 0:255, 0:255)
 33:  *      r       g      b
 34:  */
 37: static PetscErrorCode PetscDrawUtilityHlsHelper(int h,int n1,int n2)
 38: {
 40:   while (h > 360) h = h - 360;
 41:   while (h < 0)   h = h + 360;
 42:   if (h < 60)  PetscFunctionReturn(n1 + (n2-n1)*h/60);
 43:   if (h < 180) PetscFunctionReturn(n2);
 44:   if (h < 240) PetscFunctionReturn(n1 + (n2-n1)*(240-h)/60);
 45:   PetscFunctionReturn(n1);
 46: }

 50: static PetscErrorCode PetscDrawUtilityHlsToRgb(int h,int l,int s,unsigned char *r,unsigned char *g,unsigned char *b)
 51: {
 52:   int m1,m2;         /* in 0 to 100 */

 55:   if (l <= 50) m2 = l * (100 + s) / 100 ;           /* not sure of "/100" */
 56:   else         m2 = l + s - l*s/100;

 58:   m1  = 2*l - m2;
 59:   if (!s) {
 60:     /* ignore h */
 61:     *r  = 255 * l / 100;
 62:     *g  = 255 * l / 100;
 63:     *b  = 255 * l / 100;
 64:   } else {
 65:     *r  = (255 * PetscDrawUtilityHlsHelper(h+120,m1,m2)) / 100;
 66:     *g  = (255 * PetscDrawUtilityHlsHelper(h,m1,m2))     / 100;
 67:     *b  = (255 * PetscDrawUtilityHlsHelper(h-120,m1,m2)) / 100;
 68:   }
 69:   return(0);
 70: }

 74: PetscErrorCode  PetscDrawUtilitySetCmapHue(unsigned char *red,unsigned char *green,unsigned char * blue,int mapsize)
 75: {
 77:   int        i,hue,lightness,saturation;
 78:   PetscReal  igamma = 1.0 / Gamma;

 81:   red[0]      = 0;
 82:   green[0]    = 0;
 83:   blue[0]     = 0;
 84:   hue         = 0;        /* in 0:359 */
 85:   lightness   = 50;       /* in 0:100 */
 86:   saturation  = 100;      /* in 0:100 */
 87:   for (i = 0; i < mapsize; i++) {
 88:     PetscDrawUtilityHlsToRgb(hue,lightness,saturation,red + i,green + i,blue + i);
 89:     red[i]   = (int)floor(255.999 * pow(((PetscReal) red[i])/(PetscReal)255.0,igamma));
 90:     blue[i]  = (int)floor(255.999 * pow(((PetscReal)blue[i])/(PetscReal)255.0,igamma));
 91:     green[i] = (int)floor(255.999 * pow(((PetscReal)green[i])/(PetscReal)255.0,igamma));
 92:     hue     += (359/(mapsize-2));
 93:   }
 94:   return(0);
 95: }