how can I clear overlay after using transparentblt

[gurucplusplus]

I use transparentblt to display an overlay color image? ::TransparentBlt(pDC->GetSafeHdc(),upperLeftX, upperLeftY, width, height, paintMemory.GetSafeHdc(),0,0,width,height,RGB(0,0,0)) ; where paintMemory is contains color pixels using method call paintMemory.SetPixel(CPoint(x,y),RGB(255,0,0); the color image is display correctly. How can I clear this overlay?

[Mark Salsbery]

gurucplusplus wrote:

How can I clear this overlay?

Draw something else over the top of it? I'm curious why you use the CDC class but you go through the extra trouble of extracting the HDCs from the CDC objects to call a GDI API directly instead of using the CDC method CDC::TrasparentBlt()...? Mark

Mark Salsbery Microsoft MVP - Visual C++ :java:

[gurucplusplus]

I am not sure what you mean? Can you give me an example?

[Mark Salsbery]

It depends on what you mean by "clear this overlay" For the TransparentBlt call... ::TransparentBlt(pDC->GetSafeHdc(),upperLeftX,upperLeftY, width, height,                        paintMemory.GetSafeHdc(),0,0,width,height,RGB(0,0,0)) ; could be pDC->TransparentBlt(upperLeftX, upperLeftY, width, height,                              &paintMemory,0,0,width,height,RGB(0,0,0)) ; Mark

Mark Salsbery Microsoft MVP - Visual C++ :java:

[gurucplusplus]

For my application, I display paintMemory using ::transparentBlt in red using paintMemory.SetPixel(point(x,y),RGB(255,0,0)) But I don't know how to clear this paintMemory to transparency by reseting paintMemory.SetPixel(point(x,y),RGB(0,0,0)). I have an greyimage display in the background and would like to paint an color image using paintMemory to paint a color on top of this image without destructing the content of the greyimage. Once I draw complete I would like to see this greyimage background back by clearing the painMemory by setting color of paintMemory pixel back to color RGB(0,0,0). But It doesn't work.

[Mark Salsbery]

gurucplusplus wrote:

But I don't know how to clear this paintMemory to transparency by reseting paintMemory.SetPixel(point(x,y),RGB(0,0,0)).

paintMemory is a memory DC, correct? An easier and possibly faster way to clear the entire bitmap associated with the DC is something like:    paintMemory.FillSolidRect(0, 0, BitmapWidth, BitmapHeight(), RGB(0, 0, 0)); What's not working? Mark

Mark Salsbery Microsoft MVP - Visual C++ :java:

[gurucplusplus]

paintMemory is a memory DC. Let do an example. I implement the following: painMemory.FillSolidRect(0,0,BitmapWidth,BitmapHeight(),RGB(255,0,0)); ::TransparentBlt(pDC->GetSafeHdc(),m_upperLeftX, 0,BitmapWidth,0,BitmapHeight, paintMemory.GetSafeHdc(),0,0,BitmapWidth,BitmapHeight,RGB(0,0,0)); // At this point I see the overlay image is red. // Then next is try to clear this overlay painMemory from red to RGB(0,0,0) painMemory.FillSolidRect(0,0,BitmapWidth,BitmapHeight(),RGB(0,0,0)); ::TransparentBlt(pDC->GetSafeHdc(),m_upperLeftX, 0,BitmapWidth,0,BitmapHeight, paintMemory.GetSafeHdc(),0,0,BitmapWidth,BitmapHeight,RGB(0,0,0)); // At this point I still see the overly image is red instead of black I need solution for this ASAP. Thanks

[Mark Salsbery]

Are you drawing to the screen?  Is this code in a WM_PAINT message handler (OnPaint())? You can't erase - you need to redraw what was "underneath" the red. Mark

Mark Salsbery Microsoft MVP - Visual C++ :java:

[gurucplusplus]

Yes, I draw to the screen. I add WM_PAINT message handler OnPaint() as you suggested as shown CMyView::OnPaint() { CPaintDC dc(this); // device context for painting OnPrepareDC(&dc); OnDraw(&dc); } And OnDraw(CDC pDC) I have GDI method to draw image on screen that always works. After I implement OnPaint(). It still doesn't redraw image underneath the red. Please Help!

[Mark Salsbery]

I didn't suggest anything - I was asking. You don't need an OnPaint override in a view since there's OnDraw(). You do, however, need to draw whatever you want to appear. You can't draw something to the screen and then erase it, expecting to see what was underneath it. It's up to you to redraw the window without the overlay. You can force a window to repaint by invalidating a portion (or all) of the window with one of the Invalidate___() methods/APIs. That will cause your OnDraw() to be called, where you can draw whatever you want to appear on the window. Mark

Mark Salsbery Microsoft MVP - Visual C++ :java: