Why when I blit to a mem dc or a mem bmp, and then blit the mem dc to the screen...

Nothing at all:

Code:

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HBITMAP hOldMemBmp= (HBITMAP)::SelectObject(imageDC, hBmp);

::StretchBlt(a::hdcMem, 0, 0, 800, 600, imageDC, 0, 0, BmpW, BmpH, SRCCOPY);

::BitBlt(hDC, invalLocation->left, invalLocation->top,
        invalLocation->right-invalLocation->left,
        invalLocation->bottom-invalLocation->top, a::hdcMem, 0, 0, SRCCOPY);

---

Black screen:

Code:

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HBITMAP hOldMemBmp= (HBITMAP)::SelectObject(imageDC, hBmp);

::StretchBlt(hMemBmp, 0, 0, 800, 600, imageDC, 0, 0, BmpW, BmpH, SRCCOPY);

a::hOldBmp= (HBITMAP)::SelectObject(a::hdcMem, hMemBmp);

::BitBlt(hDC, invalLocation->left, invalLocation->top,
        invalLocation->right-invalLocation->left,
        invalLocation->bottom-invalLocation->top, a::hdcMem, 0, 0, SRCCOPY);

---

I took another look at this post:
http://www.experts-exchange.com/CXO/..._20027366.html
and saw that I had to select the mem bmp to the mem dc and then draw to the mem dc.