pursuing object

[Marcus]

A question, if I have two objects and one is the player who can move with the keys and the other is the enemy who is stationary in one place on the screen.

The question would be how can I make it so that when the player is close to the enemy he starts chasing the player and if the player moves away the enemy stops chasing him and returns to the starting position.

Here is a small example:

Code:

set window "Chasing enemy", 640, 480, false
set redraw off

' Player.
visible player = [x: 100, y: 100, w: 32, h: 32]
' Move with arrow keys.
player.Update = function()
    if keydown(KEY_LEFT)  this.x = this.x - 4
    if keydown(KEY_RIGHT)  this.x = this.x + 4
    if keydown(KEY_UP)  this.y = this.y - 4
    if keydown(KEY_DOWN)  this.y = this.y + 4
endfunc
player.Draw = function()
    set color 255, 255, 0
    draw rect this.x, this.y, this.w, this.h, true
endfunc

' Enemy.
enemy = [baseX: 400, baseY: 100, x: 400, y: 100, w: 32, h: 32, chasing: false, home: true, speed: 2]
enemy.Update = function()
    ' Calculate distance to player.
    dx = player.x - this.x
    dy = player.y - this.y
    d = sqr(dx*dx + dy*dy)
  
    ' Toggle chasing based on distance.
    if this.chasing
        ' Stop chasing if distance is larger than 150.
        if d > 150
            this.chasing = false
            this.home = false
        endif
    else
        ' Start chasing if distance is less than 100.
        if d < 100
            this.chasing = true
        endif
    endif
  
    ' Chasing?
    if this.chasing
        ' Move towards player.
        if d > 0
            k = this.speed/d
            this.x = this.x + dx*k
            this.y = this.y + dy*k
        endif
    ' Not chasing, return to base position if not already there.
    elseif not this.home
        ' Calculate distance to base position.
        dx = this.baseX - this.x
        dy = this.baseY - this.y
        d = sqr(dx*dx + dy*dy)
        ' Home?
        if d < this.speed
            this.x = this.baseX
            this.y = this.baseY
            this.home = true
        ' Move towards home.
        else
            k = this.speed/d
            this.x = this.x + dx*k
            this.y = this.y + dy*k
        endif
    endif
  
endfunc
enemy.Draw = function()
    ' Draw base position just for testing.
    set color 64, 64, 64
    draw rect this.baseX, this.baseY, this.w, this.h
    ' Different color when chasing.
    if this.chasing  set color 255, 0, 0
    else  set color 128, 128, 128
    draw rect this.x, this.y, this.w, this.h, true
endfunc

while not keydown(KEY_ESCAPE, true)
    player.Update()
    enemy.Update()

    set color 0, 0, 0
    cls
    player.Draw()
    enemy.Draw()
  
    redraw
    fwait 60
wend

Hope it helps! If there's something you don't understand, please ask