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DirectX7:
DirectXEvent
By: Jack Hoxley
Written: June 2000
DirectXEvent is used only in
DirectMusic, DirectSound, DirectInput and DirectPlay. It allows you (the programmer)
to recieve information from DirectX. A good example of this is in DirectSound.
When you can use the DirectXEvent to get DirectX to tell you when the sound
buffer has got to a certain point; and then you can act on it.
You could think of it like this;
almost your entire program is you telling directX to do this, to do that - you're
talking to it; but apart from any return values it's not talking to you. Using
the directXEvent you can get it to talk back to you without you directly asking
it to; although you're setting it up to talk to you, it automatically talks
to you after this point - regardless of whether you just asked it to.
DirectXEvent can only be used
in a form object; not in modules or classes. It uses this code:
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'In the declarations
section:
Implements DirectXEvent
'This part will automatically
appear:
Private Sub DirectXEvent_DXCallBack(ByVal eventid as Long)
End Sub
'You can then modify it like so:
Private Sub DirectXEvent_DXCallBack(ByVal eventid as Long)
select case eventid
case 0 'Event 0 has happened
'This code is executed when event 0 happens
case 1 'Event 1 has happened
'Event 1 code is here
case 2 'Event 2 code is here
'Do stuff for Event 2
end select
End Sub
'Events Must be created before they can be used;
Dim EventHandle as long
EventHandle = dx.CreateEvent(Me) 'Creates a general
event
EventHandle = dx.CreateEvent(0) 'Creates a specific
event - you can then use
'the select case method above.
'Events MUST be explicitely destroyed before you're
application terminates; otherwise
'you'll get 'unexpected' results - ie. It'll crash :)
If EventHandle <> 0 Then 'If the EventHandle value
is 0 there is no event there.
dx.DestroyEvent EventHandle 'Destroy the event
represented by the value in the variable.
end if
'NB: destroying events can take several seconds;
bare this in mind when you're application
'takes ten minutes to shut down :)
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DirectSound
-Getting the current playback position in a normal buffer; or detecting when
the end of the sound has been reached.
'The variables that
we need,
Public EventID(1) As Long
Public EVNT(1) As DSBPOSITIONNOTIFY
'Create two Events
EventID(0) = DX.CreateEvent(Me)
EventID(1) = DX.CreateEvent(Me)
'Set up the first event.
EVNT(0).hEventNotify = EventID(0) 'This event
has this ID (0)
EVNT(0).lOffset = 0 'Time from when the start
of the buffer
'to when it is triggered. 0 would therefore mean it is triggered at
the start.
'Set up the second event.
EVNT(1).hEventNotify = EventID(1) 'This event
is represented by event 1
EVNT(1).lOffset = DSBPN_OFFSETSTOP 'A simple constant.
This sets the event
'To be raised when the buffer has finished playback (a natural finish)
or it was halted (by you - buffer.Stop)
'The events have been created; but we now need
them to be linked to the sound buffer.
Buffer.SetNotificationPositions 2, EVNT() 'the
2 specifies that there are 2 entries in the EVNT() member
'Now we can put code behind these events.
Private Sub DirectXEvent_DXCallback(ByVal EventID As Long)
'Check which event was triggered...
Select Case EventID
case EVNT(0).hEventNotify
msgbox "Event 0 occured: Sound should be playing"
Case EVNT(1).hEventNotify
msgbox "Event 1 occured: Sound should have just finished"
End Select
End Sub
'REMEMBER TO DESTROY THE EVENTS - see above. |
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DirectMusic
and DirectInput
-When the music being played gets to a certain point.
-Change in state of the
device: Joystick moved, mouse moved, buttons pressed etc...
Both DirectMusic and DirectInput
can be handled in a similiar way:
dim EventHandle as long
Implements DirectXEvent
EventHandle = Dx.CreateEvent(me)
DiDev.SetEventNotification EventHandle 'For directinput
'-Or-
Perf.SetEventNotificationHandle EventHandle
'For DirectMusic
'Because there is no special way of checking what
the status of these two are; you can just use
'the fact that when the Event is triggered something has changed. In
the case of DirectInput; when
'the event is triggered check the status of whichever device you are
using - as it has just changed
'With DirectMusic; check the position of the performance. |
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DirectPlay
- When a lobby recieves a message.
dim EventHandle as long
Implements DirectXEvent
EventHandle=Dx.CreateEvent(me)
Lobby.SetLobbyMessageEvent(0, EventHandle)
'The first argument is the Application number.
The number is obtained from the "runApplication" method.
'If you are only comunicating with one lobby client; this number must
be 0.
'The event is raised when the lobby hosting the event recieves a message.
The EventHandle is used to create a
'standard event to host this. |
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