*****************************************************************
* Neveprise Inc. Delphi FAQ					*
*****************************************************************
* Section: DirectX		Topic:   Enum DD devices 	*
* Created: July 27th, 1999	Revised: July 27th, 1999 	*
* Updates: www.neveprise.de	Info:	 support@neveprise.de	*
*****************************************************************

Q: How can I enumerate DirectDraw devices? How to declare the callback?

A: Finding an enumeration function in DirectX is not hard, but the problem
	is how to declare the required callback function and what the
	lpContext param can be used for. What we do is to write one single
	function that retrieves all needed information as TStrings. This
	function contains the call to DirectDrawEnumerate() and in the var
	part our callback.
	The advantage of using TStrings as result is, that we have readable
	(for the user) and internal DirectX values in one object without
	declaring complex custom types. Perhaps you know that a string
	in TStrings can have an additional pointer to TObject (using
	AddObject() etc.) we can combine both information.


//a "pseudo-record" as TObject, it contains information that is needed
//later when we want to initialize a DirectDraw device driver (at least
//the GUID of the graphics card is needed, it should be used in
//DirectDrawCreate() as first parameter instead of nil)

TDisplayDriver_SD = class (TObject)
   Name:          string;
   Desc:          string;
   GUID:          PGUID;
end;

//the function to call from your app, Drivers will contain a list with all
//devices and description

function EnumDisplayDrivers_SD(var Drivers: TStringList): boolean;
    //callback function that fills the list
    function EnumCallBack(const lpGUID: PGUID; lpDeviceDescription: lpcStr;
             lpDeviceName: lpcStr; lpUserArg: Pointer): HResult; stdcall;
    var DisDrv: TDisplayDriver_SD;
    begin
    DisDrv:= TDisplayDriver_SD.Create;
    with DisDrv do begin
         Name:= lpDeviceName; //fill with values
         Desc:= lpDeviceDescription;
         GUID:= lpGUID;
         // .. and assign to stringlist as TObject
         TStringList(lpUserArg).AddObject(Desc, DisDrv);
    end;
    Result:=DDEnumRet_Ok; //enum was okay
    end;
begin
Result:=false;
DXStat:='Enumerate Display Drivers';
if DXCheck(DirectDrawEnumerate(@EnumCallBack, Drivers))=true then Result:=true;
end;

//now you have TStrings, use it this way:

//this fills a combobox (cbVideoDrivers) with all device names

slDrivers:=TStringList.Create;
if EnumDisplayDrivers_SD(slDrivers)=true then cbVideoDrivers.Items:=slDrivers;

//if an item is selected, we can retrieve the GUID this way to pass'em
//to DirectDrawCreate etc.

var DevDD: TDisplayDriver_SD;
TObject(DD):=slDrivers.Objects[cbVideoDrivers.ItemIndex];



	Blazko