public void update(ref Bitmap bitmap, DateTime time)
{
ImageHandler blend = new ImageHandler(bitmap);
// Lock bitmaps
day.lockBitmap();
night.lockBitmap();
blend.lockBitmap();
// Calculate the Greenwich Sidereal Time
double GST = getGreenwichSiderealTime(time);
// Calculate the solar right ascension and declination
double alpha = getSolarRightAscension(time);
double delta = getSolarDeclination(time);
// Loop over the y-pixels of the night/day images
int i_x;
int i_y;
for (i_x = 0; i_x < this.n_x; i_x++)
{
// Calculate the longitude
double longitude = 180 - (i_x + 0.5) / this.n_x * 360;
// Calculate the solar hour angle
double HA = GST * 360 / 24 - longitude - alpha;
for (i_y = 0; i_y < this.n_y; i_y++)
{
// Calculate the latitude
double latitude = 90 - (i_y + 0.5) / this.n_y * 180;
// Calculate the altitude of the sun
double alt = getAltitude(HA, delta, latitude, longitude);
// Work out the interpolation factor for drawing the pixel
double intFactor;
if (alt > dayAltMin)
{
intFactor = 1;
}
else if (alt < nightAltMax)
{
intFactor = 0;
}
else
{
intFactor = (alt - nightAltMax) / (dayAltMin - nightAltMax);
}
// Get the RGB pixels of the day and night images
int dayRGB = (int)this.day.getPixel(i_x, i_y);
int nightRGB = (int)this.night.getPixel(i_x, i_y);
int dayR = dayRGB >> 16 & 0xFF;
int dayG = dayRGB >> 8 & 0xFF;
int dayB = dayRGB & 0xFF;
int nightR = nightRGB >> 16 & 0xFF;
int nightG = nightRGB >> 8 & 0xFF;
int nightB = nightRGB & 0xFF;
// Calculate the interpolated value of the blended pixel
int blendedRGB = (int)(dayR * intFactor + nightR * (1 - intFactor)) << 16 |
(int)(dayG * intFactor + nightG * (1 - intFactor)) << 8 |
(int)(dayB * intFactor + nightB * (1 - intFactor));
blend.setPixel(i_x, i_y, blendedRGB);
}
}
// Lock bitmaps
day.unlockBitmap();
night.unlockBitmap();
blend.unlockBitmap();
}