WindowEvent()

Syntax

Event = WindowEvent()

Checks if an event has occurred on any of the opened windows.

Parameters

None.

Return value

The next event from the event queue and or zero if there are no more events. Unlike WaitWindowEvent() it doesn't wait for the next event - it always returns immediately.

This makes it useful for window event loops, where other processing needs to be done without waiting for an event to happen (e.g. Network transactions) and therefore WaitWindowEvent() can't be used.

It must be handled with care though if used on a continuing basis, because unlike WaitWindowEvent(), it will not give CPU time to other programs while waiting for an event and therefore consume all CPU power. In this case, either Delay() should be used somewhere in the loop or WaitWindowEvent() with a small timeout value.

To get the window number in which the event occurred, use the EventWindow() function.

Possible Events are :

  #PB_Event_Menu            : a menu has been selected
  #PB_Event_Gadget          : a gadget has been pushed
  #PB_Event_SysTray         : an icon in the systray zone was clicked
  #PB_Event_Timer           : a timer has reached its timeout
  #PB_Event_CloseWindow     : the window close gadget has been pushed
  #PB_Event_Repaint         : the window content has been destroyed and must be repainted (useful for 2D graphics operations)
  #PB_Event_SizeWindow      : the window has been resized
  #PB_Event_MoveWindow      : the window has been moved
  #PB_Event_MinimizeWindow  : the window has been minimized
  #PB_Event_MaximizeWindow  : the window has been maximized
  #PB_Event_RestoreWindow   : the window has been restored to normal size (either from a minimum or maximum size)
  #PB_Event_ActivateWindow  : the window has been activated (got the focus)
  #PB_Event_DeactivateWindow: the window has been deactivated (lost the focus)
  #PB_Event_WindowDrop      : a Drag & Drop operation was finished on a window
  #PB_Event_GadgetDrop      : a Drag & Drop operation was finished on a gadget 
  #PB_Event_RightClick      : a right mouse button click has occurred on the window. This can be useful to display a popup menu
  #PB_Event_LeftClick       : a left mouse button click has occurred on the window
  #PB_Event_LeftDoubleClick : a left mouse button double-click has occurred on the window
  

A basic example for event handling can be found in the WaitWindowEvent() description.

Remarks

After a #PB_Event_WindowDrop or #PB_Event_GadgetDrop Event, the event functions of the Drag & Drop library can be used to examine and read the dropped data.

Important: The window event loop should not be processed in a thread, as there is some limitation on OS X and Linux. A debugger error will be raised.

Correct way to handle an infinite WindowEvent() loop:

  Repeat 
    Event = WindowEvent()

    If Event    ; An event was in the queue so process it 
      .... 
    Else  
      Delay(1)  ; No event, let the others apps get some CPU time too ! 
    EndIf 
  Until Event = #PB_Event_CloseWindow

Important: The 'Delay' shouldn't be put after each event, because when lot of events will come (like refresh, gadgets updates etc..) the app will wait between each event. So the delay need to be put when no events are received. Other (recommened) ways is to use WaitWindowEvent() with a small timeout value, or setup a timer with AddWindowTimer().
Important: If you use a FlipBuffers() somewhere in your code, so the 'Delay(1)' is not necessary.

Example: n°1 With Gadget

    If OpenWindow(0, 0, 0, 600, 100, "Position of the mouse on the window: ", #PB_Window_SystemMenu | #PB_Window_ScreenCentered)
    TextGadget(0, 10, 6, 200, 20, "")
    
    Repeat
      Event = WindowEvent()
      
      If Event <> 0 ; All events are treated, so we can display the coordinates of the mouse
        SetWindowTitle(0, "Position of the mouse on the window: " + Str(WindowMouseX(0)) + "," + Str(WindowMouseX(0))) 
      Else
      
      Delay(1) ; Without a FlipBuffers(), Delay() frees the CPU for the multitasking
      EndIf
    Until Event = #PB_Event_CloseWindow
  EndIf

Example: n°2 With Gadget

  If OpenWindow(0, 0, 0, 300, 30, "Position of the mouse on the desktop", #PB_Window_SystemMenu | #PB_Window_ScreenCentered)
    TextGadget(0, 10, 6, 200, 20, "")
    
    Repeat
      Event = WindowEvent()
      
      If Event = 0 ; No more events in the queue, so we can display the coordinates of the mouse
        SetGadgetText(0, "Coordinates: "+Str(DesktopMouseX())+","+Str(DesktopMouseY()))
      EndIf
      
      Delay(20) ;  Without a FlipBuffers(), Delay() frees the CPU for the multitasking
      
    Until Event = #PB_Event_CloseWindow
  EndIf

Example: Without Gadgets (General case)

  ;Few variables
  BallX = 400
  BallY = 200
  BallSpeedY.f = 5
  Gravitation.f = 2

  ;Initialization 
  If InitSprite()
    InitKeyboard()
    InitMouse()
  EndIf

  ;Window
  OpenWindow(0, 0, 0, 800, 600, "WindowEvent", #PB_Window_SystemMenu|#PB_Window_ScreenCentered)
  OpenWindowedScreen(WindowID(0), 0, 0, 800, 600)

  ;Ground
  Ground = CreateSprite(#PB_Any, 800, 30)
  StartDrawing(SpriteOutput(Ground))
  Box(0,0,800,30,RGB(128, 0, 0))
  StopDrawing()

  ;Ball
  Ball = CreateSprite(#PB_Any, 16, 16)
  StartDrawing(SpriteOutput(Ball))
  Box(0,0,16,16,RGB(135, 206, 235))
  Circle(8,8,8,RGB(255, 255, 0))
  StopDrawing()

  ;Gauge
  Image = CreateImage(#PB_Any, 8, 8, 24, RGB(255, 255, 255))
  *Buffer=EncodeImage(Image ,#PB_ImagePlugin_BMP)
  Gauge = CatchSprite(#PB_Any, *Buffer)

  
  ;Main Loop
  Repeat 
  
    Repeat
    ;Window events
    ;====================================
    ;Try all possibilities but only one at a time
    Event = WindowEvent()    ; Animation
    ;Event = WaitWindowEvent()  ; Blocking animation
    ;Event = WaitWindowEvent(1) ; Animation but a 1ms unnecessary delay and furthermore it's a 
                                ; bad way to program events because the queue is not empty

    Select Event   
      Case #PB_Event_CloseWindow
      End
    EndSelect 
    Until Event=0
    
    FlipBuffers() ; ==> With WindowEvent(), FlipBuffers() frees the CPU for the multitasking so Delay(1) is not necessary 
    ClearScreen(RGB(135, 206, 235))
    
    ExamineKeyboard() ;Keyboard
     
    DisplaySprite(Gauge, 50, 570-BallY) ;Display the gauge
    ZoomSprite(Gauge,  20, 570)
     
    DisplaySprite(Ground, 0, 570) ;Display the ground
    
    DisplaySprite(Ball, BallX, BallY) ;Display the ball
    
    ;Ball Movement 
    BallSpeedY = BallSpeedY + Gravitation 
    BallY = BallY + BallSpeedY
    
    ;Management of the collision of the ball with the ground
    If SpriteCollision(Ball, BallX, BallY+16, Ground, 0, 570)
    BallY= 554
    BallSpeedY = -BallSpeedY
    EndIf
    
  Until KeyboardPushed(#PB_Key_Escape)

See Also

WaitWindowEvent(), EventWindow(), EventGadget(), EventMenu(), EventTimer(), EventData(), EventType(), PostEvent(), BindEvent(), UnbindEvent()

Supported OS

All