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[akademiks]

Hi,

I implemented an orbital rotation code for my ship sprite around a given planet but i don't remember how to update its rotation so its always perpendicular to its trajectory...

Any tips?

[Netsu]

Something like this should help (assuming your rotation is in radians and you're using a velocity vector):

Code:

rotaton = atan(vel.y, vel.x);

[Polly]

The solution Netsu posted works .. but depending on your game / requirements you might be able to "plug" the variable that drives your orbit directly into the sprite rotation. Check out the following example ( source + exe )

http://bayfiles.com/file/1jDX/bPD4TR/Orbit.zip

[akademiks]

Thanks guys,

Hey Polly is it possible to provide me the source without the bayfiles.com overhead?

Thx

[akademiks]

Finally i found the solution to my problem...

I was not getting the fact that when my sprite has 0 rotation, it means that it has 90 degree of rotation when looking at the horizontal axe
This is because my sprite is a ship, pointing to the top of the screen by default.

Code:

- (void) orbit: (float) dt
{
    float radianToDegree = 180.0f / M_PI;
    float degreeToRadian = M_PI / 180.0f;
    
    float dir = -1.0f;
    float angularSpeed =  120.0f * degreeToRadian * dt;
    
    currentOrbitalRotation += angularSpeed * dir;
    
    if (currentOrbitalRotation > 2 * M_PI) {
        currentOrbitalRotation -= 2 * M_PI;
    }
    else if(currentOrbitalRotation < 0.0f)
    {
        currentOrbitalRotation += 2 * M_PI;
    }
    
    CGPoint newPos = CGPointMake([planet position].x + [planet planetRadius] * cosf(currentOrbitalRotation),
                                 [planet position].y + [planet planetRadius] * sinf(currentOrbitalRotation));
    
    // Multiply by -1.0f because the rotation is the inverse of the orbitation angle
    // + 180.0f because the direction is upside down (clockwise) (cocos2d's rotation goes from 0 -> 180 & -180 -> 0)
    [self setRotation:currentOrbitalRotation * -1.0f * radianToDegree + 180.0f];
    [self setPosition:newPos];
}