
#include <grass/gis.h>

/****************************************************************************
 * HIS_to_RGB() returns the R/G/B values for the proper HIS color associated
 *   with the following values:
 *    HUE:
 *       R:      red value 0 - 255
 *       G:      grn value 0 - 255
 *       B:      blu value 0 - 255
 *    INTENSITY:
 *       I    intensity value:  0 (black) to 255 (full color)
 *    SATURATION:
 *       S     saturation val:  0 (gray) to 255 (full color)
 *
 * make_gray_scale() generates a gray-scale color lookup table 
 ****************************************************************************/

int HIS_to_RGB (
    int R,     /* red percent. for hue: value 0 - 255 */
    int G,     /* grn percent. for hue: value 0 - 255 */
    int B,     /* blu percent. for hue: value 0 - 255 */
    int I,     /* intensity value: 0 (black) to 255 (white)     */
    int S,     /* saturation val:  0 (gray) to 255 (full color) */
    CELL *red, /* resulting red value */
    CELL *grn, /* resulting green value */
    CELL *blu  /* resulting blue value */
)
{
	/* modify according to intensity */
	if (I != 255)
	{
		R = R * I / 255;
		G = G * I / 255;
		B = B * I / 255;
	}

	/* modify according to saturation (actually "haze factor") */
	if (S != 255)
	{
		R = 127 + (R - 127) * S / 255 ;
		G = 127 + (G - 127) * S / 255 ;
		B = 127 + (B - 127) * S / 255 ;
	}

	/* make sure final values are within range */
	if (R < 0) R = 0 ;
	if (G < 0) G = 0 ;
	if (B < 0) B = 0 ;

	if (R > 255) R = 255 ;
	if (G > 255) G = 255 ;
	if (B > 255) B = 255 ;

	*red = R;
	*grn = G;
	*blu = B;
}

int make_gray_scale (struct Colors *gray)
{
	int i ;

	G_init_colors(gray) ;

	for (i = 0; i < 256; i++)
		G_set_color((CELL) i, i, i, i, gray) ;

	return 0;
}

