Automatic Window Scrolling

[redskull]

My current experiment is to have a window with some random text/lines painted to it, and automatically scroll it around (without scroll bars).  I started off having a timer that posts a WM_VSCROLL message, and then the window procedure uses ScrollWindowEx to shift the window.  What i'm having trouble with is repainting the window correctly;  it doesn't seem to want to send paint messages at all after ScrollWindowEx even though I have UpdateWindow right after it, and whenever it does repaint the window, it always starts over at the top-most, left-most origin.  I'm guessing theres an API call for this, but seraching has yet to yield any results...I tried OffsetViewportOrgEx with no success.  Any design suggestions are always welcome

alan

[Human]

create window get DC from gdi,create bitmap with text and scroll it, or just draw to bitmap,and refresh, you do with InvalidateRect, where you define ractangle to redraw or RedrawWindow

   cmp eax,WM_PAINT
   jne nopaint
   call BeginPaint,[hWnd],o ps
   call BitBlt,eax,0,75,640,256,[hBackDC],0,shit,SRCCOPY
   call EndPaint,[hWnd],o ps
nopaint:
   cmp eax,WM_VSCROLL
   je _wmvscroll
   cmp eax,WM_MOUSEWHEEL
   je _wmmousewheel
   cmp eax,WM_DESTROY
   je _wmdestroy
   cmp eax,WM_CLOSE
   je _wmdestroy
   cmp eax,WM_COMMAND
   je _wmcommand
   cmp eax,WM_LBUTTONDOWN
   jne unknown
   call SendMessage,[hWnd],WM_NCLBUTTONDOWN,HTCAPTION,0
unknown:
   xor eax,eax
   ret

_wmvscroll:
   mov eax,[wparam]
   mov ebx,[scinfo.nPos]
   cmp ax,SB_THUMBTRACK
   jne maybe_sb_linedown
   mov ebx,eax
   shr ebx,16

maybe_sb_linedown:
   cmp ax,SB_LINEDOWN
   jne maybe_sb_lineup
   add ebx,8

maybe_sb_lineup:
   cmp ax,SB_LINEUP
   jne maybe_sb_pagedown
   sub ebx,8

maybe_sb_pagedown:
   cmp ax,SB_PAGEDOWN
   jne maybe_sb_pageup
   add ebx,256

maybe_sb_pageup:
   cmp ax,SB_PAGEUP
   jne _setscrollinfo
   sub ebx,256

_setscrollinfo:
   or ebx,ebx
   jnl scroll_min_ok
   xor ebx,ebx
scroll_min_ok:
   cmp ebx,ScrollBar
   jng scroll_max_ok
   mov ebx,ScrollBar
scroll_max_ok:
   mov [scinfo.nPos],ebx
   mov shit,ebx
   call SetScrollInfo,hScroll,SB_CTL,o scinfo,1
   call RedrawWindow,[hWnd],o DrawRect,0,1
   ret

_wmmousewheel:
   mov eax,[wparam]
   mov ebx,SB_PAGEUP
   test eax,80000000h
   je wheel_up
   mov ebx,SB_PAGEDOWN
wheel_up:
   call SendMessage,[hWnd],WM_VSCROLL,ebx,0
   ret

[tenkey]

The tricky part is, in the general case, you don't know when a WM_PAINT message will be sent. When the WM_PAINT message is sent, its routine will do its painting job on top of any other painting you've done. One specific case, an InvalidateWindow followed by an UpdateWindow will immediately trigger a WM_PAINT message.

One way to manage your graphics is to structure code to generate all graphics when you get WM_PAINT. This means "caching" information needed to create the display, and using the cached information during WM_PAINT.

Another way is to use a back buffer to hold the image you want to display, and bitblit it when WM_PAINT is sent. You make all your "immediate" changes to the back buffer.

There may be other ways as well.