flightgear/Scenery/moon.c

/**************************************************************************
 * moon.c
 * Written by Durk Talsma. Started October 1997, for the flight gear project.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 * $Id$
 * (Log is kept at end of this file)
 **************************************************************************/


#include <math.h>
#include <GL/glut.h>

#include "orbits.h"
#include "moon.h"

#include "../general.h"
#include "../Main/views.h"
#include "../Time/fg_time.h"

struct CelestialCoord moonPos;

float xMoon, yMoon, zMoon;
GLint moon;

/*
static GLfloat vdata[12][3] =
{
   {-X, 0.0, Z }, { X, 0.0, Z }, {-X, 0.0, -Z}, {X, 0.0, -Z },
   { 0.0, Z, X }, { 0.0, Z, -X}, {0.0, -Z, -X}, {0.0, -Z, -X},
   { Z, X, 0.0 }, { -Z, X, 0.0}, {Z, -X, 0.0 }, {-Z, -X, 0.0}
};

static GLuint tindices[20][3] =
{
   {0,4,1}, {0,9,4}, {9,5,4}, {4,5,8}, {4,8,1},
   {8,10,1}, {8,3,10}, {5,3,8}, {5,2,3}, {2,7,3},
   {7,10,3}, {7,6,10}, {7,11,6}, {11,0,6}, {0,1,6},
   {6,1,10}, {9,0,11}, {9,11,2}, {9,2,5}, {7,2,11}
};*/

/* -------------------------------------------------------------
      This section contains the code that generates a yellow
      Icosahedron. It's under development... (of Course)
______________________________________________________________*/
/*
void NormalizeVector(float v[3])
{
   GLfloat d = sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]);
   if (d == 0.0)
   {
      printf("zero length vector\n");
      return;
   }
   v[0] /= d;
   v[1] /= d;
   v[2] /= d;
}

void drawTriangle(float *v1, float *v2, float *v3)
{
   glBegin(GL_POLYGON);
   //glBegin(GL_POINTS);
      glNormal3fv(v1);
      glVertex3fv(v1);
      glNormal3fv(v2);
      glVertex3fv(v2);
      glNormal3fv(v3);
      glVertex3fv(v3);
   glEnd();
}

void subdivide(float *v1, float *v2, float *v3, long depth)
{
   GLfloat v12[3], v23[3], v31[3];
   GLint i;

   if (!depth)
   {
     drawTriangle(v1, v2, v3);
     return;
   }
   for (i = 0; i < 3; i++)
   {
       v12[i] = (v1[i] + v2[i]);
       v23[i] = (v2[i] + v3[i]);
       v31[i] = (v3[i] + v1[i]);
   }
   NormalizeVector(v12);
   NormalizeVector(v23);
   NormalizeVector(v31);
   subdivide(v1, v12, v31, depth - 1);
   subdivide(v2, v23, v12, depth - 1);
   subdivide(v3, v31, v23, depth - 1);
   subdivide(v12, v23, v31,depth - 1);

} */
/*
void display(void)
{
   int i;
   glClear(GL_COLOR_BUFFER_BIT);
   glPushMatrix();
   glRotatef(spin, 0.0, 0.0, 0.0);
   glColor3f(1.0, 1.0, 0.0);
//   glBegin(GL_LINE_LOOP);
   for (i = 0; i < 20; i++)
   {

       //glVertex3fv(&vdata[tindices[i][0]][0]);
       //glVertex3fv(&vdata[tindices[i][1]][0]);
       //glVertex3fv(&vdata[tindices[i][2]][0]);

       subdivide(&vdata[tindices[i][0]][0],
                 &vdata[tindices[i][1]][0],
                 &vdata[tindices[i][2]][0], 3);


   }
//   glEnd();
  // glFlush();
  glPopMatrix();
  glutSwapBuffers();
} */

/* --------------------------------------------------------------

      This section contains the code that calculates the actual
      position of the moon in the night sky.

----------------------------------------------------------------*/

struct CelestialCoord fgCalculateMoon(struct OrbElements params,
                                      struct OrbElements sunParams,
                                      struct fgTIME t)
{
	struct CelestialCoord
          result;

    double
    	  eccAnom, ecl, lonecl, latecl, actTime,
        xv, yv, v, r, xh, yh, zh, xg, yg, zg, xe, ye, ze,
        Ls, Lm, D, F;

    /* calculate the angle between ecliptic and equatorial coordinate system */
    actTime = fgCalcActTime(t);
    ecl = fgDegToRad(23.4393 - 3.563E-7 * actTime);  // in radians of course

    /* calculate the eccentric anomaly */
    eccAnom = fgCalcEccAnom(params.M, params.e);

    /* calculate the moon's distance (d) and  true anomaly (v) */
	 xv = params.a * ( cos(eccAnom) - params.e);
    yv = params.a * ( sqrt(1.0 - params.e*params.e) * sin(eccAnom));
    v =atan2(yv, xv);
    r = sqrt(xv*xv + yv*yv);

    /* estimate the geocentric rectangular coordinates here */
    xh = r * (cos(params.N) * cos(v + params.w) - sin(params.N) * sin(v + params.w) * cos(params.i));
    yh = r * (sin(params.N) * cos(v + params.w) + cos(params.N) * sin(v + params.w) * cos(params.i));
    zh = r * (sin(v + params.w) * sin(params.i));

    /* calculate the ecliptic latitude and longitude here */
    lonecl = atan2( yh, xh);
    latecl = atan2( zh, sqrt( xh*xh + yh*yh));

    /* calculate a number of perturbations */
    Ls = sunParams.M + sunParams.w;
    Lm =    params.M +    params.w + params.N;
    D = Lm - Ls;
    F = Lm - params.N;

    lonecl += fgDegToRad(
    			    - 1.274 * sin (params.M - 2*D)    			// the Evection
                + 0.658 * sin (2 * D)							// the Variation
                - 0.186 * sin (sunParams.M)					// the yearly variation
                - 0.059 * sin (2*params.M - 2*D)
                - 0.057 * sin (params.M - 2*D + sunParams.M)
                + 0.053 * sin (params.M + 2*D)
                + 0.046 * sin (2*D - sunParams.M)
                + 0.041 * sin (params.M - sunParams.M)
                - 0.035 * sin (D)                             // the Parallactic Equation
                - 0.031 * sin (params.M + sunParams.M)
                - 0.015 * sin (2*F - 2*D)
                + 0.011 * sin (params.M - 4*D)
              ); /* Pheeuuwwww */
    latecl += fgDegToRad(
                - 0.173 * sin (F - 2*D)
                - 0.055 * sin (params.M - F - 2*D)
                - 0.046 * sin (params.M + F - 2*D)
                + 0.033 * sin (F + 2*D)
                + 0.017 * sin (2 * params.M + F)
              );  /* Yep */

    r += (
    		     - 0.58 * cos(params.M - 2*D)
              - 0.46 * cos(2*D)
          ); /* Ok! */

    xg = r * cos(lonecl) * cos(latecl);
    yg = r * sin(lonecl) * cos(latecl);
    zg = r *               sin(latecl);

    xe  = xg;
    ye = yg * cos(ecl) - zg * sin(ecl);
    ze = yg * sin(ecl) + zg * cos(ecl);

	 result.RightAscension = atan2(ye, xe);
    result.Declination = atan2(ze, sqrt(xe*xe + ye*ye));
    return result;
}


void fgMoonInit() {
    struct fgLIGHT *l;
    static GLfloat moon_color[4] = { 1.0, 1.0, 1.0, 1.0 };
//   int i;

    l = &cur_light_params;

    moon = glGenLists(1);
    glNewList(moon, GL_COMPILE );

    /* glMaterialfv(GL_FRONT, GL_AMBIENT, l->scene_clear);
    glMaterialfv(GL_FRONT, GL_DIFFUSE, moon_color); */

    fgSolarSystemUpdate(&(pltOrbElements[1]), cur_time_params);
    moonPos = fgCalculateMoon(pltOrbElements[1], pltOrbElements[0], 
			      cur_time_params);
#ifdef DEBUG
    printf("Moon found at %f (ra), %f (dec)\n", moonPos.RightAscension, 
	   moonPos.Declination);
#endif

    /* xMoon = 90000.0 * cos(moonPos.RightAscension) * cos(moonPos.Declination);
       yMoon = 90000.0 * sin(moonPos.RightAscension) * cos(moonPos.Declination);
       zMoon = 90000.0 * sin(moonPos.Declination); */

    xMoon = 60000.0 * cos(moonPos.RightAscension) * cos(moonPos.Declination);
    yMoon = 60000.0 * sin(moonPos.RightAscension) * cos(moonPos.Declination);
    zMoon = 60000.0 * sin(moonPos.Declination);

    glutSolidSphere(1.0, 10, 10);

    glEndList();
}


/* Draw the moon */
void fgMoonRender() {
    struct fgLIGHT *l;
    GLfloat moon_color[4] = { 1.0, 1.0, 1.0, 1.0 };

    l = &cur_light_params;

    /* set lighting parameters */
    glLightfv(GL_LIGHT0, GL_AMBIENT, l->scene_clear );
    glLightfv(GL_LIGHT0, GL_DIFFUSE, moon_color );

    glPushMatrix();
    glTranslatef(xMoon, yMoon, zMoon);
    glScalef(1400, 1400, 1400);

    /* glColor3fv(color); */
    /* glutSolidSphere(1.0, 25, 25); */
    glCallList(moon);

    glPopMatrix();
}