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mov hMemoryDC,eax</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke SelectObject,eax,hBitMap</font></tt></b>
<br><b><tt><font color="#66FF99">
mov hOldBmp,eax</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke GetObject,hBitMap,sizeof BITMAP,addr bitmap</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke StretchBlt,hdc,0,0,250,250,\</font></tt></b>
<br><b><tt><font color="#66FF99">
hMemoryDC,0,0,bitmap.bmWidth,bitmap.bmHeight,SRCCOPY</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke SelectObject,hMemoryDC,hOldBmp</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke DeleteDC,hMemoryDC</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke EndPaint,hWnd,addr ps</font></tt></b>
<br><b><tt><font color="#66FF99">
.elseif uMsg==WM_LBUTTONDOWN</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke DestroyWindow,hWnd</font></tt></b>
<br><tt> .else</tt>
<br><tt>
invoke DefWindowProc,hWnd,uMsg,wParam,lParam</tt>
<br><tt>
ret</tt>
<br><tt> .endif</tt>
<br><tt> xor eax,eax</tt>
<br><tt> ret</tt>
<br><tt>WndProc endp</tt>
<p><tt>End DllEntry</tt>
<h3>
<font face="Arial,Helvetica"><font color="#FFCC33">Analysis:</font></font></h3>
<font face="Arial,Helvetica"><font size=-1>We will examine the code in
the main program first.</font></font>
<blockquote><b><tt><font color="#66FF99"> invoke LoadLibrary,addr
Libname</font></tt></b>
<br><b><tt><font color="#66FF99"> .if eax!=NULL</font></tt></b>
<br><b><tt><font color="#66FF99"> invoke FreeLibrary,eax</font></tt></b>
<br><b><tt><font color="#66FF99"> .endif</font></tt></b></blockquote>
<font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>We call
LoadLibrary to load the DLL named "splash.dll". And after that, unload
it from memory with FreeLibrary. LoadLibrary will not return until the
DLL is finished with its initialization.</font></font></font>
<br><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>That's
all the main program does. The interesting part is in the DLL.</font></font></font>
<p><tt> .if reason==DLL_PROCESS_ATTACH ; When the dll
is loaded</tt>
<br><b><tt><font color="#66FF99"> push hInst</font></tt></b>
<br><b><tt><font color="#66FF99"> pop hInstance</font></tt></b>
<br><b><tt><font color="#66FF99"> call ShowBitMap</font></tt></b>
<p><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>When
the DLL is loaded, Windows calls its entrypoint function with DLL_PROCESS_ATTACH
flag. We take this opportunity to display the splash screen. First we store
the instance handle of the DLL for future use. Then call a function named
ShowBitMap to do the real job. ShowBitMap registers a window class, creates
a window and enters the message loop as usual. The interesting part is
in the CreateWindowEx call:</font></font></font>
<p><tt> INVOKE CreateWindowEx,NULL,ADDR
ClassName,NULL,\</tt>
<br><tt> <b><font color="#66FF99">WS_POPUP</font></b>,CW_USEDEFAULT,\</tt>
<br><tt> CW_USEDEFAULT,250,250,NULL,NULL,\</tt>
<br><tt> hInstance,NULL</tt>
<p><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>Note
that the window style is only WS_POPUP which will make the window borderless
and without caption. We also limit the width and height of the window to
250x250 pixels.</font></font></font>
<br><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>Now
when the window is created, in WM_CREATE message handler we move the window
to the center of the screen with the following code.</font></font></font>
<p><b><tt><font color="#66FF99">
invoke GetWindowRect,hWnd,addr DlgRect</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke GetDesktopWindow</font></tt></b>
<br><b><tt><font color="#66FF99">
mov ecx,eax</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke GetWindowRect,ecx,addr DesktopRect</font></tt></b>
<br><b><tt><font color="#66FF99">
push 0</font></tt></b>
<br><b><tt><font color="#66FF99">
mov eax,DlgRect.bottom</font></tt></b>
<br><b><tt><font color="#66FF99">
sub eax,DlgRect.top</font></tt></b>
<br><b><tt><font color="#66FF99">
mov DlgHeight,eax</font></tt></b>
<br><b><tt><font color="#66FF99">
push eax</font></tt></b>
<br><b><tt><font color="#66FF99">
mov eax,DlgRect.right</font></tt></b>
<br><b><tt><font color="#66FF99">
sub eax,DlgRect.left</font></tt></b>
<br><b><tt><font color="#66FF99">
mov DlgWidth,eax</font></tt></b>
<br><b><tt><font color="#66FF99">
push eax</font></tt></b>
<br><b><tt><font color="#66FF99">
mov eax,DesktopRect.bottom</font></tt></b>
<br><b><tt><font color="#66FF99">
sub eax,DlgHeight</font></tt></b>
<br><b><tt><font color="#66FF99">
shr eax,1</font></tt></b>
<br><b><tt><font color="#66FF99">
push eax</font></tt></b>
<br><b><tt><font color="#66FF99">
mov eax,DesktopRect.right</font></tt></b>
<br><b><tt><font color="#66FF99">
sub eax,DlgWidth</font></tt></b>
<br><b><tt><font color="#66FF99">
shr eax,1</font></tt></b>
<br><b><tt><font color="#66FF99">
push eax</font></tt></b>
<br><b><tt><font color="#66FF99">
push hWnd</font></tt></b>
<br><b><tt><font color="#66FF99">
call MoveWindow</font></tt></b>
<p><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>It
retrieves the dimensions of the desktop and the window then calculates
the appropriate coordinate of the left upper corner of the window to make
it center.</font></font></font>
<p><b><tt><font color="#66FF99">
invoke LoadBitmap,hInstance,addr BitmapName</font></tt></b>
<br><b><tt><font color="#66FF99">
mov hBitMap,eax</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke SetTimer,hWnd,1,2000,NULL</font></tt></b>
<br><b><tt><font color="#66FF99">
mov TimerID,eax</font></tt></b>
<p><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>Next
it loads the bitmap from the resource with LoadBitmap and creates a timer
with the timer ID of 1 and the time interval 2 seconds. The timer will
send WM_TIMER messages to the window every 2 seconds.</font></font></font>
<p><tt> .elseif uMsg==WM_PAINT</tt>
<br><b><tt><font color="#66FF99">
invoke BeginPaint,hWnd,addr ps</font></tt></b>
<br><b><tt><font color="#66FF99">
mov hdc,eax</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke CreateCompatibleDC,hdc</font></tt></b>
<br><b><tt><font color="#66FF99">
mov hMemoryDC,eax</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke SelectObject,eax,hBitMap</font></tt></b>
<br><b><tt><font color="#66FF99">
mov hOldBmp,eax</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke GetObject,hBitMap,sizeof BITMAP,addr bitmap</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke StretchBlt,hdc,0,0,250,250,\</font></tt></b>
<br><b><tt><font color="#66FF99">
hMemoryDC,0,0,bitmap.bmWidth,bitmap.bmHeight,SRCCOPY</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke SelectObject,hMemoryDC,hOldBmp</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke DeleteDC,hMemoryDC</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke EndPaint,hWnd,addr ps</font></tt></b>
<p><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>When
the window receives WM_PAINT message, it creates a memory DC, select the
bitmap into the memory DC, obtain the size of the bitmap with GetObject
and then put the bitmap on the window by calling StretchBlt which performs
like BitBlt but it can stretch or compress the bitmap to the desired dimension.
In this case, we want the bitmap to fit into the window so we use StretchBlt
instead of BitBlt. We delete the memory DC after that.</font></font></font>
<p><b><tt><font color="#66FF99">
.elseif uMsg==WM_LBUTTONDOWN</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke DestroyWindow,hWnd</font></tt></b>
<p><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>It
would be frustrating to the user if he has to wait until the splash screen
to disappear. We can provide the user with a choice. When he clicks on
the splash screen, it will disappear. That's why we need to process WM_LBUTTONDOWN
message in the DLL. Upon receiving this message, the window is destroyed
by DestroyWindow call.</font></font></font>
<p><tt> .elseif uMsg==WM_TIMER</tt>
<br><b><tt><font color="#66FF99">
invoke SendMessage,hWnd,WM_LBUTTONDOWN,NULL,NULL</font></tt></b>
<br><b><tt><font color="#66FF99">
invoke KillTimer,hWnd,TimerID</font></tt></b>
<p><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>If
the user chooses to wait, the splash screen will disappear when the specified
time has elapsed (in our example, it's 2 seconds). We can do this by processing
WM_TIMER message. Upon receiving this message, we closes the window by
sending WM_LBUTTONDOWN message to the window. This is to avoid code duplication.
We don't have further use for the timer so we destroy it with KillTimer.</font></font></font>
<br><font face="Arial,Helvetica"><font color="#FFFFFF"><font size=-1>When
the window is closed, the DLL will return control to the main program.</font></font></font>
<br>
<hr WIDTH="100%">
<center><b>[<a href="http://win32asm.cjb.net">Iczelion's Win32 Assembly
HomePage</a>]</b></center>
</body>
</html>
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