SaturnImage.cpp

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/*
 * SaturnImage.cpp
 *
 * Part of Fly! Legacy project
 *
 * Copyright 2003 Chris Wallace
 *
 * Fly! Legacy 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.
 *
 * Fly! Legacy 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 Fly! Legacy; if not, write to the Free Software
 *    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */

#include "../Include/Sky.h"
#include "../Include/Utility.h"

//
// Pre-draw callback
//
static int saturn_predraw (ssgEntity *e)
{
  ssgLeaf *f = (ssgLeaf*)e;
  if (f->hasState()) f->getState()->apply();

  glPushAttrib (GL_DEPTH_BUFFER_BIT | GL_FOG_BIT | GL_POINT_BIT);
  glDisable (GL_DEPTH_TEST);
  glDisable (GL_FOG);
  glEnable (GL_POINT_SMOOTH);
  glPointSize (2.0);

  return true;
}


//
// Post-draw callback
//
static int saturn_postdraw (ssgEntity *e)
{
  glPopAttrib ();

  return true;
}


CSaturnImage::CSaturnImage (void)
{
  // Instantiate SSG entities
  top = new ssgTransform;
  top->setName ("Saturn");

  // Create simple SSG state
  ssgSimpleState *state = new ssgSimpleState ();
  state->setShadeModel (GL_SMOOTH);
  state->disable (GL_LIGHTING);
  state->disable (GL_CULL_FACE);
  state->disable (GL_TEXTURE_2D);
  state->enable (GL_COLOR_MATERIAL);
  state->enable (GL_BLEND);
  state->enable (GL_ALPHA_TEST);
  state->setColourMaterial (GL_AMBIENT_AND_DIFFUSE);
  state->setMaterial (GL_EMISSION, 0, 0, 0, 1);
  state->setMaterial (GL_SPECULAR, 0, 0, 0, 1);

  // Default colour is pale yellow
  rgba = new ssgColourArray (1);
  sgVec4 default_colour;
  sgSetVec4 (default_colour, 1.0, 0.99, 0.90, 1.0);
  rgba->add (default_colour);

  // Create as single point at the origin
  va = new ssgVertexArray (1);
  sgVec3 v;
  sgSetVec3 (v, 0, 0, 0);
  va->add (v);

  // Construct the leaf object
  ssgLeaf *leaf = new ssgVtxTable (GL_POINTS, va, NULL, NULL, rgba);
  leaf->setState (state);
  leaf->setCallback (SSG_CALLBACK_PREDRAW, saturn_predraw);
  leaf->setCallback (SSG_CALLBACK_POSTDRAW, saturn_postdraw);
  top->addKid (leaf);
}


ssgEntity* CSaturnImage::GetSSGEntity (void)
{
  return top;
}


//
// Repaint the appearance of the image
//
void CSaturnImage::Repaint (float mv, float limit, float factor)
{
  float nmag, alpha;
  if (mv < limit) {
    // This star is brighter than the limiting magnitude
    nmag = (limit - mv) / limit;    // Scale brightness to 0.0..1.0
    alpha = (nmag * 0.85);        // Scale alpha to 0.0..0.85
    alpha += 0.25;            // Bias +25%
    alpha *= factor;          // Adjust alpha for ambient light
  } else {
    // Star is dimmer than the limiting magnitude
    alpha = 0.0;
  }

  // Clamp alpha to 0.0..1.0
  if (alpha > 1.0) { alpha = 1.0; }
  if (alpha < 0.0) { alpha = 0.0; }

  float* colour = rgba->get (0);
  colour[3] = alpha;
}


//
// Reposition the image in the sky
//
// Arguments:
//  pos     3D position of the eye (cartesian coordinates??)
//  lst     Local Sidereal Time, in degrees
//  ra      Right Ascension, in radians
//  dec     Declination, in radians
//  distance  Distance from the eye in world units
//
void CSaturnImage::Reposition (sgVec3 pos, double lst, double lat,
                 double ra, double dec, double distance)
{
  sgMat4 LST, LAT, RA, DEC, D;
  sgVec3 axis;
  sgVec3 v;

  // Rotation matrix for latitude
  sgSetVec3 (axis, -1, 0, 0);
  sgMakeRotMat4 (LAT, 90-lat, axis);

  // Rotation matrix for local sidereal time, converted from h to deg
  sgSetVec3 (axis, 0, 0, -1);
  sgMakeRotMat4 (LST, (lst * 15), axis);

  // Rotation matrix for right ascension
  sgSetVec3 (axis, 0, 0, 1);
  sgMakeRotMat4 (RA, RadToDeg (ra), axis);

  // Rotation matrix for declination
  sgSetVec3 (axis, 1, 0, 0);
  sgMakeRotMat4 (DEC, 90 - RadToDeg (dec), axis);

  // Translate sun distance
  sgSetVec3 (v, 0, 0, distance);
  sgMakeTransMat4 (D, v);

  // Combine all transforms
  sgMat4 T;
  sgMakeIdentMat4 (T);
  sgPreMultMat4 (T, LAT);
  sgPreMultMat4 (T, LST);
  sgPreMultMat4 (T, RA);
  sgPreMultMat4 (T, DEC);
  sgPreMultMat4 (T, D);
  
  top->setTransform (T);
}

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