c++ - Vector2D math not giving me the right results - c++

Question

I'm trying to create a vector2D class for my game but I think I'm getting the math wrong.
When I create a new vector2d object it automatically sets its x and y to 1, 1 in the constructor.
Vector2D vec;
std::cout << " x: " << vec.GetX() << " y: " << vec.GetY() << " angle rad: " << vec.GetAngleRad() << " magnitude: " << vec.GetMagnitude() << std::endl;
system("pause");
return 0;
and it outputs:
x: 1
y: 1
angle in rad: 0.785398
magnitude: 1.41421
(which is exactly what i expect)
but the problem is when I parse anything to the setAngle funciton, I get some wired results.
For example:
Vector2D vec;
vec.SetAngleRad(3);
std::cout << " x: " << vec.GetX() << " y: " << vec.GetY() << " angle rad: " << vec.GetAngleRad() << " magnitude: " << vec.GetMagnitude() << std::endl;
system("pause");
return 0;
I would expect it to output angle in rad: 3
but instead I get
angle in rad: 0.141593.
This is the vector2D class (I've tried to comment my code so you can see my what I was thinking when I wrote it):
#include "Vector2D.h"
Vector2D::Vector2D():
_x(1.0f),
_y(1.0f)
{
}
Vector2D::~Vector2D()
{
}
void Vector2D::SetX(float x)
{
_x = x;
}
float Vector2D::GetX()
{
return _x;
}
void Vector2D::SetY(float y)
{
_y = y;
}
float Vector2D::GetY()
{
return _y;
}
void Vector2D::SetAngleRad(float angle)
{
float hypotenuse = GetMagnitude();
SetX( cos(angle) * hypotenuse); // cos of angle = x / hypotenuse
// so x = cos of angle * hypotenuse
SetY( sin(angle) * hypotenuse); //sin of angle = y / hypotenuse
// so y = sin of angle * hypotenuse
}
float Vector2D::GetAngleRad()
{
float hypotenuse = GetMagnitude();
return asin( _y / hypotenuse ); // if sin of angle A = y / hypotenuse
// then asin of y / hypotenuse = angle
}
void Vector2D::SetMagnitude(float magnitude)
{
float angle = GetAngleRad();
float hypotenuse = GetMagnitude();
SetX( (cos(angle) * hypotenuse) * magnitude ); // cos of angle = x / hypotenuse
// so cos of angle * hypotenuse = x
// multiplied by the new magnitude
SetY( (sin(angle) * hypotenuse) * magnitude); //sin of angle = y / hypotenuse
// so sin of angle * hypotenuse = y
// multipied by the new magnitude
}
float Vector2D::GetMagnitude()
{
return sqrt( (_x * _x) + (_y * _y) ); // a^2 + b^2 = c^2
//so c = sqrt( a^2 + b^2 )
}
So I'd really appreciate it if someone could explain to me what I'm doing wrong here :)

Answer 1

To get angle in full circle range, you have to use both y and x components with atan2 function
return atan2( _y, _x );
Note result range -Pi..Pi and correct negative one by +2*Pi if you need range 0..2*Pi
Another issue: :SetMagnitude method really multiplies current magnitude by magnitude multiplier, while name assumes that method should set it (so vector length 2 after applying SetMagnitude(2) will have magnitude 4)).
So it would better to remove *hypotenuse multiplication (or change method name)