Create your own Flip Task Bar with live thumbnails using Vista Desktop Window Manager DWM

Article
05/06/2007

The sample below uses Desktop Window Manager under Windows Vista with Aero to get dynamic live thumbnails of running applications. If a movie is playing in Windows Media Player, it will play in the thumbnail too!

EnumChildWindows or EnumWindows is used to enumerate all running windows created by the various processes on your machine.

I extracted code from: How does EventHandler work? IConnectionPoint! to make the CAsmLib class to generate assembly code. The sample below uses the class to generate ASM code that gets called by EnumChildWindows and calls _VFP.DoCmd method to insert the Window handles found into a cursor.

On both XP and Vista, the code will generate a cursor with Window Handles and their titles.

A SQL statement executed in a timer routine determines if any new processes were added and if so, to refresh the display.

SELECT hWnd,Title FROM NewTopLevel WHERE hWnd NOT in (SELECT hWnd FROM TopLevel) UNION ;

SELECT hWnd,Title FROM TopLevel WHERE hWnd NOT in (SELECT hWnd FROM NewTopLevel) ;

INTO CURSOR temp

If you’re running on Vista and DwmIsCompositionEnabled, the code will then create a form and an array of live thumbnails on it. The form uses an array of invisible commandbuttons for each thumbnail. Using an Image control without an image displays a cross. All we’re doing is providing an hWnd and a rect for DWM to draw the thumbnail.

(Vista Aero can have DwmIsCompositionEnabled enabled or disabled. See Control Panel->System and Maintenance->System->Advanced System Settings->Advanced->Performance->Settings->Visual Effects->Enable desktop composition)

GetWindowThreadProcessId is called to get the Process Id of the window handle.

Play a movie: make it repeat if it’s short, do things in other windows, and you’ll see the thumbnails update on the form. Hit Alt-Tab (or Alt-Ctrl-Tab to keep the flip display on, or even WindowsKey-Tab), and you’ll see the thumbnail still live. Use the slider to changes the size of the thumbnails. You can even make the thumbs larger than the source application!

Click on a thumbnail to make it the foreground application. Resize the thumbnail form. Modify source windows by editing text, etc. Hit WindowKey->M to minimize all windows.

CLEAR ALL

CLEAR

MODIFY COMMAND PROGRAM() NOWAIT

SET SAFETY OFF

PUBLIC oForm

oForm=CREATEOBJECT("CThumbForm")

#define WS_VISIBLE 0x10000000

#define WS_BORDER 0x00800000

DEFINE CLASS CThumbForm as Form

ShowWindow=2 && Top Level

width=SYSMETRIC(1) && entire width of display

height=100

MinButton=.f. && don't allow minimize for us

nThumbs=0 && number of thumbs currently on form

fDWM = .f. && are we running under Vista Desktop Window Management?

nThumbWidth=400 && size of thumb to draw

nThumbHeight=this.nThumbWidth * SYSMETRIC(2)/SYSMETRIC(1) && same aspect ratio as desktop

ADD OBJECT cmdQuit as CommandButton WITH Caption="\<Quit",cancel=.t.

ADD OBJECT cmdRefresh as CommandButton WITH Caption="\<Refresh",left=120

ADD OBJECT oSlider as cSlider WITH left=250

ADD OBJECT oTimer as Timer WITH interval=2000 && millisecs

PROCEDURE oTimer.Timer

thisform.GetHWnds("NewTopLevel")

SELECT hWnd,Title FROM NewTopLevel WHERE hWnd NOT in (SELECT hWnd FROM TopLevel) UNION ;

SELECT hWnd,Title FROM TopLevel WHERE hWnd NOT in (SELECT hWnd FROM NewTopLevel) ;

INTO CURSOR temp

IF _Tally>0 && a new window was created or destroyed

thisform.GetThumbNails() && ToDo: optimize for only the change

ENDIF

PROCEDURE cmdRefresh.Click

thisform.GetThumbNails()

PROCEDURE cmdQuit.Click

thisform.release

PROCEDURE Init

SET TALK OFF

IF VAL(OS(3))>=6 && runnning under Vista. Check for Desktop Compostion enabled

DECLARE integer DwmIsCompositionEnabled IN dwmapi integer @ dwEnabled

dwEnabled=0

IF DwmIsCompositionEnabled(@dwEnabled) = 0 AND dwEnabled>0

this.fDWM = .t.

ENDIF

IF this.fDWM

DECLARE integer DwmRegisterThumbnail IN dwmapi integer hwndDest, integer hwndSrc, integer @ nThumbnailId

DECLARE integer DwmUnregisterThumbnail IN dwmapi integer nThumbnailId

DECLARE integer DwmQueryThumbnailSourceSize IN dwmapi integer nThumbnailId, string @pSize

DECLARE integer DwmUpdateThumbnailProperties IN dwmapi integer hThumbnailId, string @ ptnProperties

DECLARE integer SetForegroundWindow IN WIN32API integer

DECLARE integer GetWindowPlacement IN WIN32API integer hWnd, string @ pPlacement

DECLARE integer SetWindowPlacement IN WIN32API integer hWnd, string @ pPlacement

this.Visible=1

* this.GetThumbNails() && Resize will call GetThumbNails

ELSE

NEWOBJECT("CEnumWindows") && call the class that creates the cursor of hWnds

LOCATE && go to the top of the cursor

BROWSE LAST NOWAIT

RETURN .f. && don't create form

ENDIF

PROCEDURE Resize

this.GetThumbNails()

PROCEDURE GetHWnds(DestCursor as string)

NEWOBJECT("CEnumWindows") && call the class that creates the cursor of hWnds

SELECT * FROM hwnds WHERE BITAND(style,WS_VISIBLE+WS_BORDER) = WS_VISIBLE+WS_BORDER AND ;

hWnd != thisform.HWnd ;

INTO CURSOR (DestCursor) && Only those hWnds which are visible and have a border

RETURN _tally

PROCEDURE GetThumbNails

LOCAL cStr,oLbl,cName,x,y,oi

thisform.LockScreen= .T.

FOR indx = 1 TO thisform.nThumbs

cName="im"+PADL(indx,3,"0") && im001, im002...

thisform.RemoveObject(cName)

IF TYPE("thisForm."+cName+"lbl")="O"

thisform.RemoveObject(cName+"lbl")

ENDIF

ENDFOR

thisform.nThumbs=this.GetHWnds("TopLevel")

INDEX on hwnd TAG hwnd

nRatio = thisform.oSlider.Value/thisform.oSlider.max

x = 0

y = 20

indx=1

SCAN

cName="im"+PADL(indx,3,"0") && im001, im002...

thisform.AddObject(cName,"CThumb")

cStr="Thisform."+cName

oi = EVALUATE(cStr)

oi.Height = this.nThumbHeight * nRatio

oi.Width = this.nThumbWidth * nRatio

oi.Left = x

oi.Top = y

oi.visible=1

oi.RegThumb(hWnd,ALLTRIM(title))

indx=indx+1

x = x + this.nThumbWidth* nRatio

IF x + this.nThumbWidth* nRatio > thisform.Width

x=0

y = y + this.nThumbHeight* nRatio+20

ENDIF

ENDSCAN

thisform.LockScreen= .f.

ENDDEFINE

DEFINE CLASS cSlider AS Olecontrol

OleClass="mscomctllib.slider.2"

PROCEDURE Init

this.min=1

this.max=100

this.value=INT(this.max/5)

this.SmallChange=INT(this.max/50)

this.LargeChange=INT(this.max/5)

PROCEDURE Change && when the slider value changes

thisform.GetThumbNails()

ENDDEFINE

#define GWL_STYLE 0xfffffff0

#define WS_MINIMIZE 0x20000000

#define SW_RESTORE 9

#define DWM_TNP_RECTDESTINATION 1

#define DWM_TNP_RECTSOURCE 2

#define DWM_TNP_OPACITY 4

#define DWM_TNP_VISIBLE 8

#define DWM_TNP_SOURCECLIENTAREAONLY 0x10

DEFINE CLASS CThumb as CommandButton

nThumbId = 0

style=1 && invisible

enabled=.t.

hWnd=0

PROCEDURE click && user clicked on thumbnail: let's activate it

IF BITAND(GetWindowLong(this.hWnd,GWL_STYLE), WS_MINIMIZE) > 0 && if window is minimized

pPlacement=BINTOC(11*4,"4rs") + SPACE(10*4) && 11 4 byte words

IF GetWindowPlacement(this.hWnd, @pPlacement) > 0

pPlacement = LEFT(pPlacement,2*4) + BINTOC(SW_RESTORE,"4rs")+SUBSTR(pPlacement,13) && Restore it

SetWindowPlacement(this.hWnd, @pPlacement)

ENDIF

SetForegroundWindow(this.hWnd)

PROCEDURE RegThumb(hWnd as Integer,cTitle as String)

LOCAL cStr,oLbl,cName

nResult=0

this.hWnd=hWnd

IF DwmRegisterThumbnail(thisform.hWnd, m.hWnd, @nResult ) = 0 AND nResult > 0

this.nThumbId = nResult

cName=this.Name+"lbl" && iml001002lbl

cStr="thisform."+cName

thisform.AddObject(cName,"Label")

oLbl=EVALUATE(cStr)

WITH oLbl as Label

.Top=this.Top+this.Height

.Left = this.Left

.Width = MAX(this.Width-10,0)

.Height = 20

.Caption=cTitle

.Visible=1

ENDWITH

* @this.Left,this.top+this.Height say cTitle

cStr=SPACE(8)

*!* ?"TSize",DwmQueryThumbnailSourceSize(nResult, @cStr) && gets the size of the Source window

*!* ?CTOBIN(LEFT(cStr,4),"4rs"),CTOBIN(RIGHT(cStr,4),"4rs")

dwFlags= DWM_TNP_RECTDESTINATION + DWM_TNP_OPACITY + DWM_TNP_VISIBLE

nOpacity = 255 && can make the thumbnails glass

fVisible= 1 && make the thumb visible?

fSourceClientAreaOnly = 0 && just client area of source thumbnail?

rDest= ;

BINTOC(this.Left,"4rs") + ;

BINTOC(this.Top,"4rs") + ;

BINTOC(this.Left + this.Width,"4rs") + ;

BINTOC(this.Top+this.Height,"4rs") && where to render the thumbnail

rSrc= ;

BINTOC(0,"4rs") + ;

BINTOC(0,"4rs") && rSrc: region of thumbnail to render. We'll use the whole src image

cProps = ;

BINTOC(dwFlags,"4rs") + ;

rDest + ;

rSrc + ;

CHR(nOpacity) + ;

BINTOC(fVisible,"4rs") + ;

BINTOC(fSourceClientAreaOnly,"4rs")

hr =DwmUpdateThumbnailProperties(nResult, @ cProps)

ENDIF

PROCEDURE destroy

IF this.nThumbId > 0

DwmUnregisterThumbnail(this.nThumbId)

ENDIF

ENDDEFINE

DEFINE CLASS CEnumWindows AS CAsmLib

PROCEDURE Init

DODEFAULT() && call parent class Init

DECLARE integer GetWindowText IN WIN32API integer, string @, integer

DECLARE integer GetWindowLong IN WIN32API integer, integer

DECLARE integer GetWindowThreadProcessId IN WIN32API integer hWnd, integer @ pid

CREATE cursor HWnds (hWnd i, title c(100), style i,pid n)

this.CreateEnumWindowCode("INSERT INTO HWnds (hWnd) VALUES (%d)") && use this cmd to insert a record into the cursor

SELECT hWnds && Now scan through the cursor and get the window titles and styles

SCAN

cText=SPACE(100)

nLen=GetWindowText(hWnd,@cText,LEN(cText)) && Get the title of the window

mPid=0

GetWindowThreadProcessId(hWnd,@mpid) && Get the window's ProcessID

REPLACE title WITH LEFT(cText,nLen) ,style WITH GetWindowLong(hWnd,GWL_STYLE),pid WITH mPid

ENDSCAN

PROTECTED PROCEDURE CreateEnumWindowCode(cCmd as String)

*This simple code doesn't need jumps, but included anyway for general usefulness for branching code

CREATE CURSOR jumps (cLabel c(20),cFlag c(1),sCodePos i) && cFlag="D" defined, "R", reference

INDEX on cLabel+cFlag TAG cLabel

nLocals=0x60 && enough space for local vars

sCode=""

sCode = sCode + CHR(0x55) && push ebp

sCode = sCode + CHR(0x8b) + CHR(0xec) && mov ebp, esp

sCode = sCode + CHR(0x81) + CHR(0xec)+BINTOC(nLocals * 4, "4rs") && sub esp, nLocals

*!* sCode = sCode + CHR(0x6a) + CHR(0x00) && push 0

*!* sCode = sCode + this.CallDllFunction("MessageBeep", "user32") && MessageBeep(0)

* sCode = sCode + CHR(0xcc) && int 3 DebugBreak() to attach a debugger

*swprintf(ebp-a0h, 0x30,cCmd,hWnd) && replace the "%d" with the hWnd: "INSERT INTO HWnds (hWnd) VALUES (%d)"

sCode = sCode + CHR(0x8b) + CHR(0x45) + CHR(0x08) && mov eax, [ebp+8] && get the hWnd

sCode = sCode + CHR(0x50) && push eax

sCode = sCode + CHR(0xb8) + BINTOC(this.MakeStr(cCmd,.t.),"4rs") && mov eax, str (Unicode)

sCode = sCode + CHR(0x50) && push eax

sCode = sCode + CHR(0x8d) + CHR(0x45)+CHR(0xa0) && lea eax, [ebp-a0h] && addr to put swprintf result

sCode = sCode + CHR(0x50) && push eax

sCode = sCode + this.CallDllFunction("swprintf", "msvcrt") && swprintf(ebp-a0h, 0x30,cCmd,hWnd)

sCode = sCode + CHR(0x83)+ CHR(0xc4)+ CHR(0xc) && add esp, 0ch pop 3*4 _cdecl args

*SysAllocString() This string for each window,so it must be freed with SysFreeString below

sCode = sCode + CHR(0x8d) + CHR(0x45)+CHR(0xa0) && lea eax, [ebp-a0h] && addr of swprintf result

sCode = sCode + CHR(0x50) && push eax

sCode = sCode + this.CallDllFunction("SysAllocString", "oleaut32") && SysAllocString

*_vfp.DoCmd()

sCode = sCode + CHR(0x89) + CHR(0x45) + CHR(0xf0) && mov [ebp-10h], eax ; save the bstr so we can free it

sCode = sCode + CHR(0x50) && push eax

sCode = sCode + CHR(0xb8) + BINTOC(SYS(3095,_vfp),"4rs") && mov eax, the IDispatch for _VFP

sCode = sCode + CHR(0x50) && push eax && the THIS pointer(_vfp)

sCode = sCode + CHR(0x8b) + CHR(0) && mov eax, [eax] && get the vTable

sCode = sCode + CHR(0x05) + BINTOC(0x84,"4rs") && add eax, 84h the function at 84h in the vTable, which is DoCmd

sCode = sCode + CHR(0xff) + CHR(0x10)&& call [eax] && call indirect

sCode = sCode + CHR(0x83) + CHR(0xf8) + CHR(0x00) && cmp eax, 0 && if hr = SUCCESS

* jne FailedDoCmd

sCode = sCode + CHR(0x75)+CHR(0x00) && jne nBytes && nBytes calc'd below. je= 0x74, Jump if Equal, jne = 0x75

INSERT INTO jumps values ("FailedDoCmd","R",LEN(sCode)) && refer to a label to jump to at this pos

*else { //FailedDoCmd

INSERT INTO jumps values ("FailedDoCmd","D",LEN(sCode)) && define a label at this pos

* now free the bstr

sCode = sCode + CHR(0x8b) + CHR(0x45) + CHR(0xf0) && mov eax, [ebp-10h]

sCode = sCode + CHR(0x50) && push eax

sCode = sCode + this.CallDllFunction("SysFreeString", "oleaut32") && vswprintf(ebp-a0h, 0x30,cCmd,hWnd)

sCode = sCode + CHR(0xb8) + BINTOC(1,"4rs") && mov eax, 1 && return 1 so Enum continues

* sCode = sCode + CHR(0x33) + CHR(0xc0) && xor eax,eax && make return value 0 so won't enum any more windows

sCode = sCode + CHR(0x8b) + CHR(0xe5) && mov esp, ebp

sCode = sCode + CHR(0x5d) && pop ebp

sCode = sCode + CHR(0xc2)+CHR(0x08)+CHR(0x00) && ret 8 && EnumChildProc has 2 parms: pop 2 args=8 bytes

USE jumps AGAIN IN 0 ORDER 1 ALIAS jumpdefs

SCAN FOR cFlag="R" && look for all references

=SEEK(jumps.cLabel+"D","jumpdefs")

sCode=LEFT(sCode,jumps.sCodePos-1)+CHR(jumpdefs.sCodePos - jumps.sCodePos) + SUBSTR(sCode,jumps.sCodePos+1) && now fix up the jump location to jump to the definition

ENDSCAN

AdrCode=this.memAlloc(LEN(sCode),sCode) && allocate memory for the code

EnumChildWindows(0,AdrCode,0) && EnumChildWindows needs a callback function. We'll give it our code.Added benefit: Win32 Exception handling of Declare dll

USE IN jumpdefs

USE IN jumps

ENDDEFINE

DEFINE CLASS CAsmLib as Custom && utility to help generate ASM code

hProcHeap =0

PROCEDURE Init

SET ASSERTS ON

DECLARE integer LoadLibrary IN WIN32API string

DECLARE integer FreeLibrary IN WIN32API integer

DECLARE integer GetProcAddress IN WIN32API integer hModule, string procname

DECLARE integer GetProcessHeap IN WIN32API

DECLARE integer HeapAlloc IN WIN32API integer hHeap, integer dwFlags, integer dwBytes

DECLARE integer HeapFree IN WIN32API integer hHeap, integer dwFlags, integer lpMem

DECLARE integer CLSIDFromString IN ole32 string lpszProgID, string @ strClSID

DECLARE integer SysAllocString IN oleaut32 string wstr

DECLARE integer SysFreeString IN oleaut32 integer bstr

DECLARE integer EnumChildWindows IN WIN32API integer hWnd, integer lpEnumProc, integer lParam

CREATE CURSOR memAllocs (memPtr i, AllocType c(1)) && track mem allocs that need to be freed: H=Heap,B=BSTR,L=Library

this.hProcHeap = GetProcessHeap()

PROCEDURE MemAlloc(nSize as Integer, cStr as String) as Integer

LOCAL nAddr

nAddr = HeapAlloc(this.hProcHeap, 0, nSize) && allocate memory

ASSERT nAddr != 0 MESSAGE "Out of memory"

INSERT INTO memAllocs VALUES (nAddr,"H") && track them for freeing later

SYS(2600,nAddr, LEN(cStr),cStr) && copy the string into the mem

RETURN nAddr

PROCEDURE CallDllFunction(strExport as String, strDllName as String) as String

*Create a string of machine code that calls a function in a DLL. Parms should already be pushed

LOCAL nAddr as Integer, hModule as Integer

hModule = LoadLibrary(strDllName)

INSERT INTO memAllocs VALUES (hModule,"L") && track loads for freeing later

nAddr=GetProcAddress(hModule,strExport)

ASSERT nAddr != 0 MESSAGE "Error: Export not found "+ strExport+" "+ strDllName

RETURN CHR(0xb8)+BINTOC(nAddr,"4rs") + CHR(0xff) + CHR(0xd0) && mov eax, addr; call eax

PROCEDURE MakeStr(str as String, fConvertToUnicode as Logical, fMakeBstr as Logical) as Integer

* converts a string into a memory allocation and returns a pointer

LOCAL nRetval as Integer

IF fConvertToUnicode

str=STRCONV(str+CHR(0),5)

ELSE

str = str + CHR(0) && null terminate

ENDIF

IF fMakeBstr

nRetval= SysAllocString(str)

ASSERT nRetval != 0 MESSAGE "Out of memory"

INSERT INTO memAllocs VALUES (nRetval,"B") && track them for freeing later

ELSE

nRetval= this.MemAlloc(LEN(str),str)

ENDIF

RETURN nRetval

PROCEDURE Destroy

LOCAL i,nSel

nSel=SELECT()

SELECT memAllocs

SCAN

DO CASE

CASE AllocType="B" && BSTR

SysFreeString(memPtr)

CASE AllocType="H" && Heap

HeapFree(this.hProcHeap,0,memPtr)

CASE AllocType="L" && LoadLibrary

FreeLibrary(memPtr)

ENDCASE

ENDSCAN

USE

SELECT (nSel)

ENDDEFINE

End Of Code

Create your own Flip Task Bar with live thumbnails using Vista Desktop Window Manager DWM

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