Reacting on multiple arrow keys simultanously

Question

Hello everyone,

I have a little problem with a small Jump 'n' Run game I am currently developing involving keyboard input.

To better illustrate my problem, I've created a small example program (see below). In order to react accordingly to the user input, I want to keep track of the keys currently being pressed. This is achieved by setting a corresponding variable to 1 once the key is being pressed and back to 0 after it got released. As long as only one key is pressed at a time, the source code below works perfectly fine.

GraphicsWindow.Width = 400
GraphicsWindow.Height = 200
GraphicsWindow.Title = "Multiple keys test"
GraphicsWindow.CanResize = "false"
GraphicsWindow.KeyDown =  KeyPressed
GraphicsWindow.KeyUp = KeyReleased
GraphicsWindow.Show()

leftDown = 0
rightDown = 0
upDown = 0

While 1 = 1
  GraphicsWindow.Clear()
  GraphicsWindow.DrawText(50,50, "Left down: " + leftDown)
  GraphicsWindow.DrawText(50,75, "Right down: " + rightDown)
  GraphicsWindow.DrawText(50,100, "Up down: " + upDown)

  Program.Delay(30)
endwhile

Sub KeyPressed
  key = GraphicsWindow.LastKey
  If key = "Left" And leftDown = 0 Then
    leftDown = 1
  EndIf
  If key = "Right" And rightDown = 0 Then
    rightDown = 1
  Endif
  If key = "Up" And upDown = 0 Then
    upDown = 1
  EndIf
EndSub
  
Sub KeyReleased
  If key = "Left" Then
    leftDown = 0
  EndIf
  If key = "Right" Then
    rightDown = 0
  endif
  if key = "Up" Then
   upDown = 0 
  EndIf
EndSub

The problem arises if for instance the following sequence of key actions is executed:

• Press "Right" key
• Press "Up" key
• Release "Up" key
• Release "Right" key

One would expect the program to show all keys as released after this procedure. However, this is not my observed result. For me the "Right" arrow key will still be displayed as pressed, despite it being already released of course. In the context of my Jump 'n' Run game that would mean, that the protagonist keeps running to the right with no keys being pressed.

Evidently my goal will be to implement a system, which allows to correctly identify the state of each arrow key, while simultaniously allowing more than one key to be pressed at a time, hence eliminating the problem stated above.

Thanks for reading this so far! If anyone could help me with this problem, I would greatly appreciate it.

galgtonold

Answer 1

Hi galgtonold

This situation is because the variable "key" is equal to the last key pressed as set in the KeyPressed Subroutine only.

So

• Press "Right" key  = 1st key pressed
• Press "Up" key   =  last  key pressed
• Release "Up" key  --->  key  is still set as "Up"
• Release "Right" key  ---->  key isn't set

Copy this line "key = GraphicsWindow.LastKey"  into the  Key Released Subroutine and the problem is fixed.

Answer 2

Here's a sample for the above: FTW338

Answer 3

A flickerless version:  (^_^)

SBR991

'************************************************************'
' Multiple Keys Test (v2.03)
' by  galgtonold (2013/Oct)
' mod GoToLoop

' SBR991

' http://social.msdn.microsoft.com/Forums/en-US/
' fea3b8a2-ee28-45dc-a06b-0dd0c4754e24/
' reacting-on-multiple-arrow-keys-simultanously
'************************************************************'

'---------------------------------------------------------------------------'
GW = 150
GH = 150

isUp = "False"
isDown = "False"
isLeft = "False"
isRight = "False"

isWaitingKey = "True"
'---------------------------------------------------------------------------'
GraphicsWindow.Title = "Mult Keys"
GraphicsWindow.CanResize = "False"
GraphicsWindow.BackgroundColor = "MidnightBlue"

GraphicsWindow.Width  = GW
GraphicsWindow.Height = GH

CreateLabels()

GraphicsWindow.KeyDown =  KeyPressed
GraphicsWindow.KeyUp = KeyReleased
'---------------------------------------------------------------------------'
Loop:

While isWaitingKey
  Program.Delay(10)
EndWhile

isWaitingKey = "True"
UpdateLabels()

Goto Loop
'---------------------------------------------------------------------------'
Sub KeyPressed
  
  k = GraphicsWindow.LastKey
  
  If k = "Up" Then
    isUp = "True"
    
  ElseIf k = "Down" Then
    isDown = "True"
    
  ElseIf k = "Left" Then
    isLeft = "True"
    
  ElseIf k = "Right" Then
    isRight = "True"
    
  ElseIf k = "Escape" Then
    Sound.PlayChimeAndWait()
    Program.End()
  EndIf
  
  isWaitingKey = "False"
  
EndSub
'---------------------------------------------------------------------------'
Sub KeyReleased
  
  kk = GraphicsWindow.LastKey
  
  If kk = "Up" Then
    isUp = "False"
    
  ElseIf kk = "Down" Then
    isDown = "False"
    
  ElseIf kk = "Left" Then
    isLeft = "False"
    
  ElseIf kk = "Right" Then
    isRight = "False"
  EndIf
  
  isWaitingKey = "False"
  
EndSub
'---------------------------------------------------------------------------'
Sub CreateLabels
  
  GraphicsWindow.BrushColor = "Gold"
  
  up = Shapes.AddText("Up: False")
  down = Shapes.AddText("Down: False")
  left = Shapes.AddText("Left: False")
  right = Shapes.AddText("Right: False")
  
  Shapes.Move(up  40, 25)
  Shapes.Move(down  40, 50)
  Shapes.Move(left  40, 75)
  Shapes.Move(right  40, 100)
  
EndSub
'---------------------------------------------------------------------------'
Sub UpdateLabels
  
  Shapes.SetText(up  "Up: " + isUp)
  Shapes.SetText(down  "Down: " + isDown)
  Shapes.SetText(left  "Left: " + isLeft)
  Shapes.SetText(right  "Right: " + isRight)
  
EndSub
'---------------------------------------------------------------------------'

---

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Answer 4

Thank you everyone for your quick responses, you allowed me to solve my problem. Although it makes me feel quite stupid unfortunately...

I am just too used to working with programming languages where that last key would be provided as a paramter.

Thanks again also for the flickerless version, I already was aware of how to implement it, I just implemented the other version, as it was shorter to write. ;)