Fire bullet in the direction of travel

Question

I have trouble trying to work out how to shoot a bullet in 1 of 8 directions.

The player can only point in compass directions 0, 45, 90, 135, 180, etc.

So what I need is a formula that I can use in spawnEntity to send the bullet in the direction the player is facing at a constant speed.

I've tried this;

    sinAngle = Math.cos(90) * 1000;
    cosAngle = Math.sin(90) * 1000;

    bulletX = (this.pos.x);
    bulletY = (this.pos.y);
    return { x: bulletX, y: bulletY, sin: sinAngle, cos: cosAngle };

The call is like this then;

   trajectory = this.calculateAngle();
   ig.game.spawnEntity(EntityBullet, trajectory.x, trajectory.y, { vel: { x: trajectory.sin, y: -trajectory.cos } });

But everything is in radians and I'd like it to be in compass degrees.

Answer 1

If all you want to do is convert degrees to radians, then you simply use: d * (π/180) where d is degrees.

If you also want to be able to say the compass direction (as in North, South, East, West), create an enum and convert these to degrees and use a degrees-to-radians function.

Answer 2

It's been awhile since I've done any game programming, but you can use MathHelper.ToDegrees to convert your radians to degrees.