CDE/cde/programs/dtscreen/hsbramp.c

/*
 * CDE - Common Desktop Environment
 *
 * Copyright (c) 1993-2012, The Open Group. All rights reserved.
 *
 * These libraries and programs are free software; you can
 * redistribute them and/or modify them under the terms of the GNU
 * Lesser General Public License as published by the Free Software
 * Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 * These libraries and programs are distributed in the hope that
 * they will be useful, but WITHOUT ANY WARRANTY; without even the
 * implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
 * PURPOSE. See the GNU Lesser General Public License for more
 * details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with these libraries and programs; if not, write
 * to the Free Software Foundation, Inc., 51 Franklin Street, Fifth
 * Floor, Boston, MA 02110-1301 USA
 */
/* $XConsortium: hsbramp.c /main/3 1995/11/02 16:07:23 rswiston $ */
/*
 */
/*                                                                      *
 * (c) Copyright 1993, 1994 Hewlett-Packard Company                     *
 * (c) Copyright 1993, 1994 International Business Machines Corp.       *
 * (c) Copyright 1993, 1994 Sun Microsystems, Inc.                      *
 * (c) Copyright 1993, 1994 Novell, Inc.                                *
 */
/*-
 * hsbramp.c - Create an HSB ramp.
 *
 * Copyright (c) 1991 by Patrick J. Naughton.
 *
 * See dtscreen.c for copying information.
 *
 * Revision History:
 * 29-Jul-90: renamed hsbramp.c from HSBmap.c
 *	      minor optimizations.
 * 01-Sep-88: Written.
 */

#include <sys/types.h>
#include <math.h>

void
hsb2rgb(double H, double S, double B,  u_char *r, u_char *g, u_char *b)
{
    int         i;
    double      f;
    double      bb;
    u_char      p;
    u_char      q;
    u_char      t;

    H -= floor(H);		/* remove anything over 1 */
    H *= 6.0;
    i = floor(H);		/* 0..5 */
    f = H - (float) i;		/* f = fractional part of H */
    bb = 255.0 * B;
    p = (u_char) (bb * (1.0 - S));
    q = (u_char) (bb * (1.0 - (S * f)));
    t = (u_char) (bb * (1.0 - (S * (1.0 - f))));
    switch (i) {
    case 0:
	*r = (u_char) bb;
	*g = t;
	*b = p;
	break;
    case 1:
	*r = q;
	*g = (u_char) bb;
	*b = p;
	break;
    case 2:
	*r = p;
	*g = (u_char) bb;
	*b = t;
	break;
    case 3:
	*r = p;
	*g = q;
	*b = (u_char) bb;
	break;
    case 4:
	*r = t;
	*g = p;
	*b = (u_char) bb;
	break;
    case 5:
	*r = (u_char) bb;
	*g = p;
	*b = q;
	break;
    }
}


/*
 * Input is two points in HSB color space and a count
 * of how many discreet rgb space values the caller wants.
 *
 * Output is that many rgb triples which describe a linear
 * interpolate ramp between the two input colors.
 */

void
hsbramp(double h1, double s1, double b1,
        double h2, double s2, double b2,
        int count,
        u_char *red, u_char *green, u_char *blue)
{
    double      dh;
    double      ds;
    double      db;

    dh = (h2 - h1) / count;
    ds = (s2 - s1) / count;
    db = (b2 - b1) / count;
    while (count--) {
	hsb2rgb(h1, s1, b1, red++, green++, blue++);
	h1 += dh;
	s1 += ds;
	b1 += db;
    }
}