OpenGL：围绕3D空间中的点旋转

Question

I've been doing some hunting through similar questions and haven't been able to find exactly what I'm looking for.

I'm attempting to rotate an object around (0, 0, 0), regardless of its x, y, and z offset.

To give an example of this, consider the following relevant situation:

I have a moon that is rotating around a planet centred at (0, 0, 0). The moon has an initial offset of (1, 1, 1). I want to rotate the moon, and other moons, around the planet each frame.

To accomplish this, I've started off with the following code:

    for (GMoon moon : moonList)
    {
        Point offset = moon.getOffset();

        float newRot = moon.getRotation() + moon.getRotSpeed();
        moon.setRotation(newRot);

        // Return to the identity matrix
        gl.glLoadIdentity();

        // Translate and rotate the planet
        gl.glTranslatef(0.0f, 0.0f, OBJECT_DISTANCE);
        gl.glRotatef(newRot, 0, 0, 1);
        gl.glTranslatef(offset.getX(), offset.getY(), offset.getZ());

        // Draw the moon
        moon.draw(gl);
    }

(OBJECT_DISTANCE is equal to -10 for viewing purposes).

Instead of rotating in front of the planet, it simply rotates around it.

Am I doing something obviously wrong?

Thank you very much for your time.

---

EDIT: I'm under the assumption that I need to rotate each axis by a certain component based on the offset of the moon. I'm not quite sure how such a component should be calculated.

Answer 1

I am assuming you would like to rotate the moon around the planet as well as around it's center point. To reach this:

• Apply rotation to moon first (this will rotate around it's center point)

• Translate the moon with the (moon - planet) distance

• Rotate the moon again, this rotation will become the moon's rotation around the planet.

• Translate the moon with the planet's coordinates. You can find the formula for calculating the planet's location: https://en.wikipedia.org/wiki/Spherical_coordinate_system#Cartesian_coordinates

And there is also a similar question to this I think: Rotating an object around a fixed point in opengl