1 /*
2 * sky.c
3 *
4 * Copyright (C) 1989, 1991, Craig E. Kolb
5 * All rights reserved.
6 *
7 * This software may be freely copied, modified, and redistributed
8 * provided that this copyright notice is preserved on all copies.
9 *
10 * You may not distribute this software, in whole or in part, as part of
11 * any commercial product without the express consent of the authors.
12 *
13 * There is no warranty or other guarantee of fitness of this software
14 * for any purpose. It is provided solely "as is".
15 *
16 * $Id: sky.c,v 4.0 91/07/17 14:43:43 kolb Exp Locker: kolb $
17 *
18 * $Log: sky.c,v $
19 * Revision 4.0 91/07/17 14:43:43 kolb
20 * Initial version.
21 *
22 */
23 #include "texture.h"
24 #include "sky.h"
25
26 Sky *
SkyCreate(scale,h,lambda,octaves,cthresh,lthresh)27 SkyCreate(scale, h, lambda, octaves, cthresh, lthresh)
28 Float h, lambda, scale, cthresh, lthresh;
29 int octaves;
30 {
31 Sky *sky;
32
33 sky = (Sky *)Malloc(sizeof(Sky));
34 sky->beta = 1. + 2 * h;
35 sky->omega = pow(lambda, -0.5 * sky->beta);
36 sky->lambda = lambda;
37 sky->scale = scale;
38 sky->cthresh = cthresh;
39 sky->lthresh = lthresh;
40 sky->octaves = octaves;
41 return sky;
42 }
43
44 void
SkyApply(sky,prim,ray,pos,norm,gnorm,surf)45 SkyApply(sky, prim, ray, pos, norm, gnorm, surf)
46 Sky *sky;
47 Geom *prim;
48 Ray *ray;
49 Vector *pos, *norm, *gnorm;
50 Surface *surf;
51 {
52 Float It, maxval;
53
54 It = fBm(pos, sky->omega, sky->lambda, sky->octaves);
55 maxval = 1. / (1. - sky->omega);
56 /*
57 * Map from [-maxval,maxval] to [0,1]
58 */
59 It = (maxval + It) * 0.5/maxval;
60
61 It = (It - sky->lthresh) / (sky->cthresh - sky->lthresh);
62 if (It < 0.)
63 It = 0;
64 else if (It > 1.)
65 It = 1;
66
67 if (sky->scale != 0.)
68 It = pow(It, sky->scale);
69
70 surf->transp = 1. - It;
71
72 ColorScale(It, surf->diff, &surf->diff);
73 ColorScale(It, surf->amb, &surf->amb);
74 }
75