Help with moving object according to rotation

[Rdevs]

I would like some help with moving an entity in proportion to it's rotation, For example if it is rotated 30 degrees clockwise, I would like it to move in that line from 30 degrees. I know this seems a fairly basic task/problem, but I don't quite know how to do it exactly. I have read a bit on radians and similar, but my code below doesn't seem to work correctly. This is the closest I have got to it working, but I want it to move in the same linear direction, and when you rotate it, it works correctly.

//convert the angle of the object to radians
radians = 3.1415926536 / 360*object.getRotation();

//x and y
x = 0.5f*cos(radians);
y = 0.5f*-sin(radians);
//rotate accordingly
object.move(x, y);

 

[Arcade]

//convert the angle of the object to radians
radians = 3.1415926536 / 360*object.getRotation();
 

This isn't the right formula for converting degrees to radians (assuming object.getRotation() is returning degrees). It either needs to be ((2 * pi / 360) * degrees) or ((pi/180) * degrees)

[Rdevs]

I see, ok so I changed it to 180, but unfortunately it is not working as it should. I think the rotation of it isn't working properly. When the object is moved linearly, the rotation goes incorrectly. I want the angle to be the rotation around the same point (the center of the object) if you see what I mean.

[Arcade]

I can't understand exactly what you are trying to do and what the problem is. Can you first explain what you want your program to do and then explain what exactly is going wrong? The code snippet you provided doesn't show much and I don't really understand when you say "When the object is moved linearly, the rotation goes incorrectly". Do you just mean that your object isn't moving at the angle you expect? Can you provide an example of the angle you are setting and the resulting incorrect behavior? It would also help if you can show a complete (but stripped-down and minimal) version of the code you currently have so we can help you debug it.

[Rdevs]

To explain a bit more, what I would like is to replicate the controls of the object you control in the 2d game asteroids, please can someone tell me what I need to do in order to achieve this? 

Update: @Arcade, As above basically I would like the controls to be like the game Asteroids. it doesn't go in the direction I expected when the object is rotated.

[eXpl0it3r]

This is quite a common problem as such you'll find a lot of answers on the internet (e.g. here) or even this forum (e.g. here or here ).

[Hapax]

I normally see:

x = sin
y = -cos

not

x = cos
y = -sin

Could you describe a little more about what you mean by "not working", "not as it should" and "the direction I expected"?

[Rdevs]

It's hard to describe. In best words, it's point that it rotates around doesn't seem to be consistent. For example, when rotated 30 degrees, it moves in that direction as it should, but then when you change the rotation of the object to, say 60 degrees, it goes in a random direction that is not proportional to it's original direction.

        if (sf::Keyboard::isKeyPressed(sf::Keyboard::Left)){
                object.rotate(0.5);
        }
        if (sf::Keyboard::isKeyPressed(sf::Keyboard::Right)){
                object.rotate(-0.5);
        }

        X = speed*sin(object.getRotation());
        Y = speed*cos(object.getRotation());
       

        if (sf::Keyboard::isKeyPressed(sf::Keyboard::Down)){
                object.move(X, Y);
        }
       
 

[eXpl0it3r]

SFML works with degrees. C++ trigonometry functions work with Radian. So you need to convert between degrees and Radians and ther other way around.

Also keep in mind that rotate() rotates relative to the previous rotation, while set/getRotation() work with the absolute rotation.

[SpeCter]

Why not use vector math for that?
Just construct a unit vector pointing in the initial direction, apply the rotation with a Transform object multiply that with your speed and you are good.

[Hapax]

   X = speed*sin(object.getRotation());
   Y = speed*cos(object.getRotation());

I normally see:

x = sin
y = -cos