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Best of PC Windows Shareware 1.0 - Wayzata Technology (7111) (1993).iso
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FOGDECK.C
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C/C++ Source or Header
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1992-04-28
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3KB
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121 lines
/*
* fogdeck.c
*
* Copyright (C) 1989, 1991, Craig E. Kolb
* All rights reserved.
*
* This software may be freely copied, modified, and redistributed
* provided that this copyright notice is preserved on all copies.
*
* You may not distribute this software, in whole or in part, as part of
* any commercial product without the express consent of the authors.
*
* There is no warranty or other guarantee of fitness of this software
* for any purpose. It is provided solely "as is".
*
* $Id: fogdeck.c,v 4.0 91/07/17 14:40:28 kolb Exp Locker: kolb $
*
* $Log: fogdeck.c,v $
* Revision 4.0 91/07/17 14:40:28 kolb
* Initial version.
*
*/
#include "atmosphere.h"
#include "fogdeck.h"
Fogdeck *
FogdeckCreate(alt, offset, scale, chaoscale, octaves, color, trans)
Float alt, offset, chaoscale;
Vector *scale;
int octaves;
Color *color, *trans;
{
Fogdeck *fogdeck;
static void ComputeFogdeck();
fogdeck = (Fogdeck *)RayMalloc(sizeof(Fogdeck));
fogdeck->alt = alt;
fogdeck->octaves = octaves;
fogdeck->scale = *scale;
fogdeck->chaoscale = chaoscale;
fogdeck->offset = offset;
if (color == (Color *)NULL)
fogdeck->color.r = fogdeck->color.g = fogdeck->color.b = 0.;
else
fogdeck->color = *color;
if (trans == (Color *)NULL)
fogdeck->trans.r = fogdeck->trans.g = fogdeck->trans.b =
FAR_AWAY;
else {
fogdeck->trans = *trans;
}
return fogdeck;
}
/*
* Add fogdeck to the given color.
*/
void
FogdeckApply(fogdeck, ray, pos, dist, color)
Fogdeck *fogdeck;
Ray *ray;
Vector *pos;
Float dist;
Color *color;
{
Float atten, hitdist, density;
Color trans;
Vector endp;
extern Float ExpAtten(), PAChaos();
/*
* Find distance from origin at which ray strikes
* z = fogdeck->alt plane
*/
if (abs(ray->dir.z) < EPSILON)
return;
hitdist = (fogdeck->alt - ray->pos.z) / ray->dir.z;
if (hitdist < EPSILON || hitdist > dist)
return;
/*
* Compute ray endpoint
*/
VecAddScaled(ray->pos, hitdist, ray->dir, &endp);
/*
* Modify transmissivity based on point of
* intersection.
*/
endp.x *= fogdeck->scale.x;
endp.y *= fogdeck->scale.y;
endp.z *= fogdeck->scale.z;
density = fogdeck->offset +
fogdeck->chaoscale * PAChaos(&endp, fogdeck->octaves);
if (density < EPSILON)
density = HUGE;
else
density = 1. / density;
trans = fogdeck->trans;
ColorScale(density, trans, &trans);
dist -= hitdist;
atten = ExpAtten(dist, trans.r);
if (trans.r == trans.g &&
trans.r == trans.b) {
ColorBlend(color, &fogdeck->color, atten, 1. - atten);
return;
}
color->r = atten*color->r + (1. - atten) * fogdeck->color.r;
atten = ExpAtten(dist, trans.g);
color->g = atten*color->g + (1. - atten) * fogdeck->color.g;
atten = ExpAtten(dist, trans.b);
color->b = atten*color->b + (1. - atten) * fogdeck->color.b;
}