help with solar system

i have managed to rotate my planets aorund the sun but wat i want to do is rotate the planet about its on axis any help from people out there?

[Relic]

RedBook example 3.6 planet.c explains transformation hierarchies.
Add another rotation which only affects the planet and put all other transfomrations around that inner.

[nexusone]

Here is a simple example, we use push/pop matrix to store our past matrix:

// Start Solar system
glPushMatrix();
glTranslate(....) // location of the center of the system
glRotate(...) // Rotation of the system
// Draw Sun
glPushMatrix(); // Save matrix so spinning sun on axis will not spin other planets
glRotate(...) // Spin sun on axis
DrawSun();
glPopMatrix() // Restore matrix to before sun was rotated.

// repeat next for each planets
glPushMatrix();
glRotate(....); // Orbit location
glTranslate(....); // Distance from center of system(Sun)
glRotate(....); // spin planet on axis
DrawPlanet();

// if planet has a moon, it here and repeat code for each moon
glPushMatrix();
glRotate(); // Moon's orbit
glTranslate(); // Moon distance from planet
glRotate(); // Moon's spin on axis
DrawMoon();
glPopMatrix();
// end moon

glPopMatrix();
// end planet

glPopMatrix();
//end solar system

[cg-hci_novice]

I am working on the same thing. I was wondering if someone could explain in more detail about the rotations (feel free to refer to Ex. 3-6)? I am a little confused since I am using GLUT not aux as the example uses.

Thank you.

[cutting_crew]

if anyone would like the executable, i can send someone the solar system executable i did, all the planets and the moon for the earth. its on linux but could easily port to windows with just a few changes. thanks!

[cg-hci_novice]

Does it make sense to have a push/pop within a for loop that loops through a data stucture containing planets, etc.?

For example (some pseudocode):

for (...) //loop through data struct
{
glPushMatrix()

if planet1 found in data stuct
then:
glPushMatrix()
draw_planet1
glPopMatrix()

if planet2 found in data struct
then:
glPushMatrix()
draw_planet2
glPopMatrix()

glPopMatrix()

} // end for loop


I am trying to follow the logic posted by Nexusone (at least to some extent) however, I am having a difficult time with putting the constructs of looping through a data struct together with what is suggested.

Appreciate any feedback. Thanks.

[nexusone]

Maybe you need to look at a diffrent aproach to how you load your planets.

You need to create a structure in which to load you planet data.

typedef struct PLANETS
{
int x, y, z; // Location of planet
int rx, ry, rz; // Rotation of Planet
int ox, oy, oz; // Orbit of planet
int size;
};

PLANETS Planet[10]; // Create space to store data on 10 planets.



// Draw planets in Display routine

for(i = 0; i < Max_planets; i++)
{

DrawPlanet( i ); // Where "i" tell's what planet to draw
}

// End planet draw

void DrawPlanet( int p )
{

glPushMatrix();
glTranslatef(Planet[p].x, Planet[p].y, Planet[p].z); // Location of planet, sun would be 0,0,0
glRotatef(Planet[p].rx, 1, 0, 0); Rotate planet
glRotatef(Planet[p].ry, 0, 1, 0);
glRotatef(Planet[p].rz, 0, 0, 1);
glTranslatef(Planet[p].ox, 0, 0); // Set orbit from center of system
// here set planet texture to apply to sphere
Draw_sphere(Planet[p].size);

glPopMatrix();
// End planet routine
}

Reading data structure should be done before drawing.

int get_planets( void ) // We return a int to tell if we did load planet data.
{

OpenFile(......);
do {

read_data();
Max_planets++; //Global variable tracks how many planets where loaded
while( !EOF )

return (error)
}

[nexusone]

I wanted to add that really did not take moom's into acount on that.

typedef struct PLANETS
{
int x, y, z; // Location of planet
int rx, ry, rz; // Rotation of Planet
int ox, oy, oz; // Orbit of planet
int size;
int moons; // How many moons to draw for this planet.
};

void DrawPlanet( int p )
{

glPushMatrix();
glTranslatef(Planet[p].x, Planet[p].y, Planet[p].z); // Location of planet, sun would be 0,0,0
glRotatef(Planet[p].rx, 1, 0, 0); Rotate planet
glRotatef(Planet[p].ry, 0, 1, 0);
glRotatef(Planet[p].rz, 0, 0, 1);
glTranslatef(Planet[p].ox, 0, 0); // Set orbit from center of system
// here set planet texture to apply to sphere
Draw_sphere(Planet[p].size);

// Add moons
for (t=0; t < Planet[p].moons; t++)
{
Draw_Moons( t );
}

glPopMatrix();
// End planet routine
}


Note code is not complete just an example

[cg-hci_novice]

Figured this out - didn't do exactly as suggested due to not having time to redesign the data structure but works ok.

Thanks all.