how to get velocity x and y from angle and speed?

Question

I have found several answers to this, but none of them have worked for me. The go something like this:

velocityX = (int) (velocity*Math.cos(angle));
velocityY = (int) (velocity*Math.sin(angle));
        
posX += velocityX;
posY += velocityY;

This does not work for me, the angle 0 moves it directly right, every 90 degrees more in the angle changes the angle of the object 45 degrees counter-clockwise. Could it be because the center of my screen is 0, 0 and not the usual top left is 0, 0? Or is there something else I am doing wrong?

Answer 1

In Java, trigonometric functions such as Math.sin and Math.cos accept the argument in radians.

If the input angle is measured in degrees, it can be converted into radians using Math.toRadians helper function:

velocityX = (int) (velocity*Math.cos(Math.toRadians(angle)));
velocityY = (int) (velocity*Math.sin(Math.toRadians(angle)));

It is also possible to define a constant and use it to convert degrees to radians:

public static final double TO_RAD = Math.PI / 180;

//...

velocityX = (int) (velocity*Math.cos(angle * TO_RAD));
velocityY = (int) (velocity*Math.sin(angle * TO_RAD));