Attack/Follow my player

Question

I want to create a game where you try to avoid objects(circles) that are "attacking" you. The way I did this:

• First calculate the x_and y difference between the object and me (in this code AI_x is the object's x-location (AI_y: y-location) and x, y the player's location)
• Calculate the angle the object has to make in order to go straight towards the player (with Math.Atan(difference between x-axis' / difference between y-axis')) -I then use these angles to calculate the x and y distance it has to move per tick (For Example distancePerTick_x = Math.Cos(angle) * speed)

However it doesn't work when my distanceToPlayer_x (see code) is positive or both distanceToPlayer_x and distanceToPlayer_y are negative so the devided number becomes positive again.

I know why this occurs, but I have tried 2 hours to solve it but can't handle the pain anymore :P.

I hope you guys can help me.

CODE:

namespace AI
{
    public partial class mainClass : Form
    {
        //variables
        int health;
        double startPosition_x, startPosition_y, angle;
        float x, y, speed, AI_x, AI_y, distanceToPlayer_x, distanceToPlayer_y;

        //gameloop
        Timer gameLoop;

        //field
        Bitmap bmp;

        //player color
        Pen playerColor;

        //Random
        Random random_x, random_y;

    //constructor
    public mainClass()
    {
        InitializeComponent();
        Initialization();
    }

    //on startup do this:
    private void Initialization()
    {
        //initializing variables
        health = 100;
        speed = (float) 0.75;

        //startposition
        startPosition_x = pbField.Width / 2;
        startPosition_y = pbField.Height / 2;

        //set x and y value to start position
        x = (float) startPosition_x;
        y = (float)startPosition_y;

        //random
        random_x = new Random();
        random_y = new Random();

        AI_x = 0;//random_x.Next(1, 550);
        AI_y = 0;//random_y.Next(1, 320);
        //player color
        playerColor = new Pen(Color.Red, 5);

        //gameloop
        gameLoop = new Timer();
        gameLoop.Tick += new EventHandler(gameMethode);
        gameLoop.Interval = 5;
        gameLoop.Start();
    }

    //the gameloop
    private void gameMethode(object sender, EventArgs e)
    {
        //field
        bmp = new Bitmap(550, 320);
        pbField.Image = bmp;

        using (Graphics g = Graphics.FromImage(bmp))
        {
            //key manager
            if (InputManager.pressed(Keys.W))
            {
                y -= speed;
            }
            else if (InputManager.pressed(Keys.S))
            {
                y += speed;
            }
            else if (InputManager.pressed(Keys.A))
            {
                x -= speed;
            }
            else if (InputManager.pressed(Keys.D))
            {
                x += speed;
            }

            g.DrawEllipse(playerColor, AI_x, AI_y, 5, 5);
            g.DrawEllipse(playerColor, x, y, 5, 5);

            attackPlayer();
        }
    }

    //attack player method
    private void attackPlayer()
    {
        //the distance to the player
        distanceToPlayer_x = AI_x - x;
        distanceToPlayer_y = AI_y - y;

        angle = Math.Atan(distanceToPlayer_y / distanceToPlayer_x);

        Console.WriteLine("Radiants: " + angle);
        Console.WriteLine("Degrees: "+ angle * (180 / Math.PI));

        AI_x += (float) Math.Cos(angle) * (speed/(float)1.25);
        AI_y += (float) Math.Sin(angle) * (speed/(float)1.25);
    }

    //if keydown
    private void mainClass_KeyDown(object sender, KeyEventArgs e)
    {
        //if escape button is pressed
        if (e.KeyCode == Keys.Escape)
        {
            Application.Exit();
        }

        InputManager.changeState(e.KeyCode, true);
    }

    //if keyup
    private void mainClass_KeyUp(object sender, KeyEventArgs e)
    {
        InputManager.changeState(e.KeyCode, false);
    }

    }
}

Answer 1

When computing the entire range [0..2 * pi] angle, a typical solution involves Atan2 method:

 angle = Math.Atan2(distanceToPlayer_y, distanceToPlayer_x);

see https://msdn.microsoft.com/en-us/library/system.math.atan2(v=vs.110).aspx for details