How to rotate a vector?

Question

If I have [1, 0], and I rotate it 90 degrees = 1/2PI radians, I must receive [0, -1]. How to achieve this?

I looked at this page and implemented this:

var rotateVector = function(vec, ang)
{
    // not right!
    return new PVector(
        vec.x * cos(ang) - vec.y * sin(ang),
        vec.x * sin(ang) + vec.y * cos(ang)
    );
};

But that does not work.

It does not matter degrees or radians, because the geometry remains unchanged. I'm using radians right now.

Answer 1

Your formulas are correct, but you need to use the angle in radians instead of degrees:

radians = degrees * (Math.PI/180)

And if you want to rotate it clockwise, note that your angle is -90 degrees instead of 90. Or, consider its 90, but change the formula to:

radians = -degrees * (Math.PI/180)

Edit:

, , :

[6.123233995736766e-17, -1]

, "" . , , , 0. .

:.

var rotateVector = function(vec, ang)
{
    ang = -ang * (Math.PI/180);
    var cos = Math.cos(ang);
    var sin = Math.sin(ang);
    return new Array(Math.round(10000*(vec[0] * cos - vec[1] * sin))/10000, Math.round(10000*(vec[0] * sin + vec[1] * cos))/10000);
};

, :

rotateVector([1,0], 90)

:

[0, -1]

Answer 2

, PVector : rotate(angle)