InvalidateRect/UpdateWindow fails but RedrawWindow work fine, why? - winapi

Question

I'm new to windows programming and started working on a text game a few months ago. I decided to rewrite the WM_PAINT section of my code, I normally had the entire client area continually redrawn but thought I'd try redrawing specific regions instead to reduce flicker. I noticed in one specific section of my code, InvalidateRect/UpdateWindow doesn't seem to want to work, but if I replace the 2 functions with RedrawWindow, it displays perfectly. Should there be an instance where InvalidateRect/UpdateWindow fails to work but RedrawWindow works fine in it's place?
Would there be any drawbacks to just replace all InvalidateRect/UpdateWindow calls in my code with RedrawWindow?
Thanks for an info!
.if uMsg==WM_PAINT
invoke BeginPaint,hWnd,ADDR ps
mov hdc,eax
.if (PAINT_DMGMSG>0) ;contains ->to a char's DMGMSG
invoke CreateFont,16,12,0,0,400,0,0,0,OEM_CHARSET,OUT_DEFAULT_PRECIS,CLIP_DEFAULT_PRECIS,DEFAULT_QUALITY,DEFAULT_PITCH,NULL
invoke SelectObject,hdc,eax
mov hfont,eax
invoke SetTextColor,hdc,COLOR_SNOWWHITE
mov esi,TS_MSG2
mov edi,TS_MSG1
mov ecx,len(TS_MSG2)
rep movsb
mov BYTE ptr [edi],0
mov esi,TS_MSG3
mov edi,TS_MSG2
mov ecx,len(TS_MSG3)
rep movsb
mov BYTE ptr [edi],0
mov esi,PAINT_DMGMSG
mov edi,TS_MSG3
mov ecx,len(esi)
rep movsb
mov BYTE ptr [edi],0
invoke TextOut,hdc,0,500,TS_MSG1,len(TS_MSG1)
invoke TextOut,hdc,0,518,TS_MSG2,len(TS_MSG2)
invoke TextOut,hdc,0,536,TS_MSG3,len(TS_MSG3)
mov PAINT_DMGMSG,0
.endif
invoke EndPaint,hWnd,ADDR ps
.elseif uMsg==WM_CHAR ;used to handle keyboard input
push wParam
pop char
.if(SDWORD ptr [ebx+OFFSET_ALLEGIANCE]<0)&&(DWORD ptr [ebx+OFFSET_STATUS]!=STAT_DEAD)
invoke Combat,[esi+12],ebx
mov ebx,[edi+4]
mov eax,[human.color]
mov [ebx+OFFSET_CHARCOLOR],eax
mov ebx,pChar
mov ebx,[ebx+OFFSET_MOBMEM]
.if (DWORD ptr [ebx+OFFSET_MOBMEM_DMGMSG]>0)
mov ebx,[ebx+OFFSET_MOBMEM_DMGMSG]
mov XYrc.left,0
mov XYrc.top,500
push wWin
pop XYrc.right
mov XYrc.bottom,560 ;+font height
mov PAINT_DMGMSG,ebx
; invoke InvalidateRect,hWnd,ADDR XYrc,TRUE
; invoke UpdateWindow,hWnd
invoke RedrawWindow,hWnd,ADDR XYrc,NULL,NULL ;<- WORKS FINE!
.endif
.endif

Answer 1

Assuming you use 0 as the last argument for the RedrawWindow() (as you do), there indeed is one important difference:
UpdateWindow() sends WM_PAINT immediately, before the function returns.
RedrawWindow() (unless flag RDW_UPDATENOW is used) just places WM_PAINT into the message queue so the painting actually happens later.
This can make difference, if you invalidate the rectangle, but change the window state then after. In case (1), the control is painted using the "old" data, but (2) "works".
If your issue is caused by this difference, you may try to use InvalidateRect() only (do not call UpdateWindow(), nor RedrawWindow(). The rect invalidation will cause then WM_PAINT will come when the queue has no other event in it. (Originally UpdateWindow() prevented that as the immediate WM_PAINT validates the window as a side effect of the painting).