/*
 * C code used to produce images appearing in:
 *
 * "Texturing and Modeling: A Procedural Approach," by David S. Ebert, ed.,
 * F. Kenton Musgrave, Darwyn Peachey, Ken Perlin, and Steven Worley.
 * Academic Press, 1998.  ISBN 0-12-228730-4.
 *
 * Note that this is the original C texture code, on which the Larry Gritz's
 * RenderMan shaders that appear in the text were based.
 *
 * Copyright 1998 F. Kenton Musgrave
 * All rights reserved.
 */


/*
 * "Earth" planet texture, as re-developed to illustrate process
 *
 * Called as:
 * texture  earth earth_map 0.25 2. -.48 11. 0. 0.45 300. 2.6 0.7 20 0.75 220 170 20 0.6 4.0
 * 1.125 1.2 -0.085 1 0.3 0
 * (colormap "earth_map" lives in ../Colormaps)
 */
void Earth(	Vector texture, Vector intersect, Vector *normal,
		Colour *colour, Colour *cmap, 
		double spectral_exp, double lacunarity, double octaves, 
		double bump_scale, 
		int multifractal, 
		double dist_scale, double offset, double sea_level, 
		double mtn_scale, double lat_scale, double nonlinear, 
		double purt_scale, double map_exp, double ice_caps, 
		double depth_scale, double depth_max, double mottle_limit, 
		double mottle_scale, double mottle_dim, double mottle_mag )
{
	Vector	bump, distort, point;
	double	chaos, latitude, purt;
	Colour	color;
	int	index;

	/*
	 * Choose between fractal bump functions: 
	 * "ordinary" or multifractal fBm.
 	 */
	if ( !multifractal )	/* use a "standard" fBm bump function */
		bump = VecfBm(texture, spectral_exp, lacunarity, octaves );
	else {			/* use "multifractal" fBm bump function */
			/* get "distortion" vector, as used with clouds */
		distort = VecNoise( texture );
			/* scale distortion vector */
		SCALE( dist_scale, distort );
			/* insert distortion vector */
		texture = VEC_ADD( distort, texture );
			/* compute bump vector using displaced point */
			/* (using vector-valued multifractal) */
		bump = MVfBm(texture, spectral_exp, lacunarity, octaves );
	}

		/* get the "height" of the bump, displacing by offset */
	chaos = -DOT(bump, *normal) + offset;
		/* set bump for land masses (areas above "sea level") */
	if ( chaos > sea_level ) {
		chaos *= mtn_scale;
		sea_level *= mtn_scale;
		normal->x += bump_scale * bump.x;
		normal->y += bump_scale * bump.y;
		normal->z += bump_scale * bump.z;
		Unit(normal);
	}

		/* if there's a colormap assoc. with the texture, use it */
	if( cmap ) {
			/* use a scaled "z" value for offset in color map */
		latitude = intersect.z;
			/* make climate symmetric about equator */
		if ( latitude < 0. ) latitude = -latitude;
			/* fractally purturb color map offset using "chaos" */
			/*  "nonlinear" scales purturbation-by-z */
			/*  "purt_scale" scales overall purturbation */
		latitude += chaos*(nonlinear*(1.-latitude) + purt_scale);
		if ( map_exp )
			latitude = lat_scale*pow(latitude,map_exp);
		else	latitude *= lat_scale;
		if ( chaos > sea_level )
			index = 1 + (int)(latitude);
		else	index = 0;	/* ocean color is in map entry 0 */
			/* do oceans, adjusted for polar caps */
		if ( ice_caps && latitude>ice_caps && index==0 )
			index = 255;
			/* clamp color map offset to bounds */
		if ( index > 255 ) index = 255;
		if ( index < 0 ) index = 0;
			/* set surface color to calculated color map entry */
		color = cmap[index];

			/* darken the "deep waters" */
		if ( index == 0 )	{
			chaos -= sea_level;
			chaos *= depth_scale;
			chaos = MAX( chaos, -depth_max );
			color.red += chaos * color.red;
			color.green += chaos * color.green;
			color.blue += chaos * color.blue;
		}
			/* else mottle the color some */
			/* ("mottle_limit" ensures the poles stay white) */
		else if ( index < mottle_limit ) {
			point = texture;
			SMULT(mottle_scale, point);
			purt = fBm( point, mottle_dim, 2., 8. );
			color.red += color.red * 0.5*mottle_mag*purt;
			color.green += color.green * 0.175*mottle_mag*purt;
			color.blue += color.green * 0.5*mottle_mag*purt;

			if ( color.red < 0. )	color.red = 0.;
			if ( color.green < 0. )	color.green = 0.;
			if ( color.blue < 0. )	color.blue = 0.;
			if ( color.red > 1. )	color.red = 1.;
			if ( color.green > 1. )	color.green = 1.;
			if ( color.blue > 1. )	color.blue = 1.;
		}
		*colour = color;
	}
} /* Earth() */