Clear CWnd Child with png
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From: Manuel Hoeger on 1 Mar 2010 08:16 Hi, I want to overdraw an Image on a CWnd Object with a second Image including transparent parts. But I can see the first Image through the second Image. I can't use fillRect because I I want to see the Background of the CWnd Object behind it. Is it possible to clear the CWnd so that I have a "transparent" Background as it is on creation? I am using two CImage Objects and two png Images On Mousemove I change the CImage Pointer mp_ActiveBook to the second CImage Object and onMouseleave I switch the pointer again and call OnPaint void CLitBoardItem::OnPaint() { CPaintDC dc(this); // device context for painting CRect rect; Invalidate(1); DrawItem(); CWnd::OnPaint(); } int CLitBoardItem::DrawItem(void) { CWindowDC pDC(this); mp_ActiveBook->AlphaBlend(pDC.m_hDC,0,0,255,0); return 0; } Thanks for Answers Manu
From: Seetharam on 1 Mar 2010 09:25 >>I can't use fillRect because I I want to see the Background of the CWnd Object behind it. Is your window background transparent so that you see contents of your desktop/windows behind it? If not, then before drawing your new image in the window, just do a fill rect with whatever color/background the window background needs to be. -Seetharam
From: Joseph M. Newcomer on 1 Mar 2010 11:31 See below... On Mon, 1 Mar 2010 14:16:34 +0100, "Manuel Hoeger" <Manuel.Hoeger(a)physik.stud.uni-erlangen.de> wrote: >Hi, > >I want to overdraw an Image on a CWnd Object with a second Image including >transparent parts. >But I can see the first Image through the second Image. **** Define what you mean by this. You said you wanted transparent parts, which means you will be able to see the first image through the second, at least at the transparent parts. Or are you seeing it in some other way? Are you creating a transparent window in some way, or using alpha blending? The only alpha blending I see is 255 (100%, no transparency). **** > >I can't use fillRect because I I want to see the Background of the CWnd >Object behind it. **** You wouldn't use FillRect to draw a picture **** > >Is it possible to clear the CWnd so that I have a "transparent" Background >as it is on creation? **** Override OnEraseBkgnd and do nothing. In OnPaint, do nothing if there is nothing to draw. **** > > > >I am using two CImage Objects and two png Images >On Mousemove I change the CImage Pointer mp_ActiveBook to the second CImage >Object and onMouseleave I switch the pointer again and call OnPaint **** I hope you do NOT "call" OnPaint. If you did switch pointers OnPaint(); it cannot POSSIBLY work, ever. So whatever you are getting is no indication of correct behavior. If, on the other hand, you did switch pointers Invalidate(); UpdateWindow(); then it should work. So if you are doing the first, you get undefined results, and you won't know what you have until you fix it to represent the second form. When a WM_PAINT message is issued, the clipping region of the window has been computed properly, and the clipping areas are all you can draw into. If you just call OnPaint, there is no clipping area (it is actually undefined), so who knows what's going to happen? I don't, except that it will not be right. **** > > >void CLitBoardItem::OnPaint() >{ > CPaintDC dc(this); // device context for painting > CRect rect; > Invalidate(1); **** This is clearly a mistake, in several ways Invalidate() takes a BOOL operator, e.g., TRUE or FALSE. Why you would write an integer there escapes me. The default argument is TRUE, so no argument needs to be supplied You would NEVER call Invalidate() in an OnPaint handler because the whole POINT of OnPaint is to revalidate! **** > > DrawItem(); > > CWnd::OnPaint(); ***** You should not be calling CWnd::OnPaint. ***** > > >} > >int CLitBoardItem::DrawItem(void) >{ > CWindowDC pDC(this); > mp_ActiveBook->AlphaBlend(pDC.m_hDC,0,0,255,0); **** This seems overkill; you are effectively doing a BitBlt/SRC_COPY. And note that the last argument of AlphaBlend must either be omitted, or be AC_SRC_OVER; I have NO IDEA how you could imagine that "0" could possibly make sense here. Read the documentation! At no point does it EVER indicate that "0" is a valid value for the last parameter. And NEVER, EVER "look inside" a header file to find what a symbolic value is so you can write the integer instead of the specified name! Note that you didn't have to write 255 either; that's the default! **** > return 0; >} > > >Thanks for Answers > >Manu Joseph M. Newcomer [MVP] email: newcomer(a)flounder.com Web: http://www.flounder.com MVP Tips: http://www.flounder.com/mvp_tips.htm
From: Manuel Hoeger on 1 Mar 2010 12:25 > Define what you mean by this. You said you wanted transparent parts, > which means you will > be able to see the first image through the second, at least at the > transparent parts. Or > are you seeing it in some other way? Are you creating a transparent > window in some way, > or using alpha blending? The only alpha blending I see is 255 (100%, no > transparency). Yes I see the first Image through the second. But I actually want to replace one bitmap with the other. and I want to see the background of the parent CWnd. I dont wan't to use alphablending yet, but maybe in future. > Override OnEraseBkgnd and do nothing. In OnPaint, do nothing if there is > nothing to draw. Ok I did. > I hope you do NOT "call" OnPaint. If you did > switch pointers > OnPaint(); > it cannot POSSIBLY work, ever. So whatever you are getting is no > indication of correct > behavior. If, on the other hand, you did Now I don't call OnPaint but DrawItem() directly from OnMouseMove and OnmouseLeave: void CLitBoardItem::OnMouseMove(UINT nFlags, CPoint point) { // TODO: F�gen Sie hier Ihren Meldungsbehandlungscode ein, und/oder benutzen Sie den Standard. mp_ActiveBook=&m_BookImageOpen; DrawItem(); CWnd::OnMouseMove(nFlags, point); } void CLitBoardItem::OnMouseLeave() { m_bMouseTracking = FALSE; mp_ActiveBook=&m_BookImage; DrawItem(); CWnd::OnMouseLeave(); } int CLitBoardItem::DrawItem(void) { CWindowDC pDC(this); CRect rect; Invalidate(); UpdateWindow(); mp_ActiveBook->AlphaBlend(pDC.m_hDC,0,0); return 0; } The OnPaint is now empty.
From: Joseph M. Newcomer on 1 Mar 2010 13:29
You will have to "erase" the original image by writing the transparent pixels over it. What you have done, apparently, works like this. Let T be the transparent color and other letters opaque Current picture TTTabcTTT New picture TTTxTwTTT Result of OnPaint after current image is replaced with new image and repainted: TTTxbwTTT So in this case, you either draw all-transparent or use OnEraseBkgnd to erase to the transparent color. Because the color b was overwritten by a transparent pixel, it remains in place, because you did nothing to make it go away. Remember, the writing of a transparent color is the logical equivalent of an "OR" operation, e.g., 000111001 overwritten using "OR" by the pattern 000101000 leaves you 000111001 So note that bits 0 (rightmost) and 4 do not change, giving the illusion that the older picture is still there. joe On Mon, 1 Mar 2010 18:25:32 +0100, "Manuel Hoeger" <Manuel.Hoeger(a)physik.stud.uni-erlangen.de> wrote: > > >> Define what you mean by this. You said you wanted transparent parts, >> which means you will >> be able to see the first image through the second, at least at the >> transparent parts. Or >> are you seeing it in some other way? Are you creating a transparent >> window in some way, >> or using alpha blending? The only alpha blending I see is 255 (100%, no >> transparency). > >Yes I see the first Image through the second. >But I actually want to replace one bitmap with the other. and I want to >see the background of the parent CWnd. >I dont wan't to use alphablending yet, but maybe in future. > > > >> Override OnEraseBkgnd and do nothing. In OnPaint, do nothing if there is >> nothing to draw. > >Ok I did. > >> I hope you do NOT "call" OnPaint. If you did >> switch pointers >> OnPaint(); >> it cannot POSSIBLY work, ever. So whatever you are getting is no >> indication of correct >> behavior. If, on the other hand, you did >Now I don't call OnPaint but DrawItem() directly from OnMouseMove and >OnmouseLeave: > > >void CLitBoardItem::OnMouseMove(UINT nFlags, CPoint point) >{ > // TODO: F�gen Sie hier Ihren Meldungsbehandlungscode ein, und/oder >benutzen Sie den Standard. > > > mp_ActiveBook=&m_BookImageOpen; > DrawItem(); > > > CWnd::OnMouseMove(nFlags, point); >} > >void CLitBoardItem::OnMouseLeave() >{ > m_bMouseTracking = FALSE; > > mp_ActiveBook=&m_BookImage; > DrawItem(); > > > CWnd::OnMouseLeave(); >} > >int CLitBoardItem::DrawItem(void) >{ > CWindowDC pDC(this); > CRect rect; > > Invalidate(); > UpdateWindow(); > > mp_ActiveBook->AlphaBlend(pDC.m_hDC,0,0); > return 0; >} > >The OnPaint is now empty. > > > Joseph M. Newcomer [MVP] email: newcomer(a)flounder.com Web: http://www.flounder.com MVP Tips: http://www.flounder.com/mvp_tips.htm |