ScreenEvent
 
Queries for and retrieves system events.

Syntax

Declare Function ScreenEvent ( ByVal event As Any Ptr = 0 ) As Integer

Usage

result = ScreenEvent( [ event ] )

Parameters

event
Specifies the buffer where the function should store the event data.

Return Value

Returns -1 if there are pending events to be retrieved, 0 otherwise.

Description

This function returns the latest available system event from the internal GfxLib events queue. By "event" we mean any mouse or keyboard activity for example.

The event data (if available) will be copied into the buffer pointed to by the event parameter; this buffer must currently be at least 5 integers long (20 bytes). The first integer will contain the event type ID, while the remaining 4 integers will hold sensitive data to the event type. The fbgfx.bi header file contains a definition of the EVENT user data type, whose memory layout is compatible with the event data returned by this function; this can be used to ease the interpretation of the event data. Here we report the EVENT structure for clarity:
Type EVENT Field = 1
    Type As Integer
    Union
        Type
            scancode As Integer
            ascii As Integer
        End Type
        Type
            x As Integer
            y As Integer
            dx As Integer
            dy As Integer
        End Type
        button As Integer
        z As Integer
    End Union
End Type

Event types
The event type is identified by an ID number returned into the first integer of the event buffer (the .type field in the EVENT structure). Known event type IDs are:

  • EVENT_KEY_PRESS (1) A key was pressed on the keyboard. The .scancode field contains the platform independent scancode value for the key; if the key has an ascii representation, it is held into the .ascii field, which otherwise has a value of 0.
  • EVENT_KEY_RELEASE (2) A key was released on the keyboard. The .scancode and .ascii fields have the same meaning as with the EVENT_KEY_PRESS event.
  • EVENT_KEY_REPEAT (3) A key is being held down repeatedly. The .scancode and .ascii fields have the same meaning as with the EVENT_KEY_PRESS event.
  • EVENT_MOUSE_MOVE (4) The mouse was moved while it was on the program window. The .x and .y fields contain the new mouse position relative to the upper-left corner of the screen, while the .dx and .dy fields contain the motion deltas.
  • EVENT_MOUSE_BUTTON_PRESS (5) One of the mouse buttons was pressed. The .button field has one bit set identifying the button that was pressed; bit 0 identifies the left mouse button, bit 1 the right mouse button and bit 2 the middle mouse button.
  • EVENT_MOUSE_BUTTON_RELEASE (6) One of the mouse buttons was released. The .button field has the same meaning as with the EVENT_MOUSE_BUTTON_PRESS event.
  • EVENT_MOUSE_DOUBLE_CLICK (7) One of the mouse buttons was double clicked. The .button field has the same meaning as with the EVENT_MOUSE_BUTTON_PRESS event.
  • EVENT_MOUSE_WHEEL (8) The mouse wheel was used; the new wheel position is returned into the .z field.
  • EVENT_MOUSE_ENTER (9) The mouse was moved into the program window.
  • EVENT_MOUSE_EXIT (10) The mouse was moved out of the program window.
  • EVENT_WINDOW_GOT_FOCUS (11) The program window has got focus.
  • EVENT_WINDOW_LOST_FOCUS (12) The program window has lost focus.
  • EVENT_WINDOW_CLOSE (13) The user attempted to close the program window.

Querying for events
The function returns -1 if there are pending events to be retrieved, 0 otherwise. If the event parameter is set to 0 (the default if omitted) ScreenEvent will not be able to copy the event data and it will not dequeue it from the internal events queue. Calling the function this way can be useful to check if there are pending events without actually fetching them.

Example

'' include fbgfx.bi for some useful definitions
#include "fbgfx.bi"

Using fb

Dim e As EVENT

ScreenRes 640, 480
Do
    If (ScreenEvent(@e)) Then
        Select Case e.type
        Case EVENT_KEY_PRESS
            If (e.scancode = SC_ESCAPE) Then
                End
            End If
            If (e.ascii > 0) Then
                Print "'" & e.ascii & "'";
            Else
                Print "unknown key";
            End If
            Print " was pressed (scancode " & e.scancode & ")"
        Case EVENT_KEY_RELEASE
            If (e.ascii > 0) Then
                Print "'" & e.ascii & "'";
            Else
                Print "unknown key";
            End If
            Print " was released (scancode " & e.scancode & ")"
        Case EVENT_KEY_REPEAT
            If (e.ascii > 0) Then
                Print "'" & e.ascii & "'";
            Else
                Print "unknown key";
            End If
            Print " is being repeated (scancode " & e.scancode & ")"
        Case EVENT_MOUSE_MOVE
            Print "mouse moved to " & e.x & "," & e.y & " (delta " & e.dx & "," & e.dy & ")"
        Case EVENT_MOUSE_BUTTON_PRESS
            If (e.button = BUTTON_LEFT) Then
                Print "left";
            ElseIf (e.button = BUTTON_RIGHT) Then
                Print "right";
            Else
                Print "middle";
            End If
            Print " button pressed"
        Case EVENT_MOUSE_BUTTON_RELEASE
            If (e.button = BUTTON_LEFT) Then
                Print "left";
            ElseIf (e.button = BUTTON_RIGHT) Then
                Print "right";
            Else
                Print "middle";
            End If
            Print " button released"
        Case EVENT_MOUSE_DOUBLE_CLICK
            If (e.button = BUTTON_LEFT) Then
                Print "left";
            ElseIf (e.button = BUTTON_RIGHT) Then
                Print "right";
            Else
                Print "middle";
            End If
            Print " button double clicked"
        Case EVENT_MOUSE_WHEEL
            Print "mouse wheel moved to position " & e.z
        Case EVENT_MOUSE_ENTER
            Print "mouse moved into program window"
        Case EVENT_MOUSE_EXIT
            Print "mouse moved out of program window"
        Case EVENT_WINDOW_GOT_FOCUS
            Print "program window got focus"
        Case EVENT_WINDOW_LOST_FOCUS
            Print "program window lost focus"
        Case EVENT_WINDOW_CLOSE
            End
        End Select
    End If
Loop


Platform Differences

  • ScreenEvent does not return window related events in the DOS version, but does return input events.

Dialect Differences

  • Not available in the -lang qb dialect.

Differences from QB

  • New to FreeBASIC

See also