Can not obtain dialog's background bitmap from treeview's subclass procedure

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I have a dialog box with a bitmap as background.

I am trying to create transparent treeview so I need to grab the underlying bitmap from treeview's WM_PAINT handler, but I do not know how to do this.

I assume that I will need ScreenToClient and ClientToScreen APIs, but I do not know how to use them.

In my WM_PAINT handler, I have this:

C++

memBmp = CreateCompatibleBitmap( hdc,  // Tree's HDC, got from BeginPaint()
    rcClient.right - rcClient.left,      // tree's client rectangle
    rcClient.bottom - rcClient.top );    // obtained with GetClientRect()

bmpOldFinal = (HBITMAP)SelectObject( memDC, // HDC compatible with tree's HDC
    memBmp );

// capture parent bitmap
HDC pDC = GetDC( GetParent(hwnd) );

// a desperate try to get proper coordinates, 
// based on an example of mouse usage from MSDN
POINT ptTreeUL, ptTreeLR;

ptTreeUL.x = rcClient.left;
ptTreeUL.y = rcClient.top;

ptTreeLR.x = rcClient.right + 1;
ptTreeLR.y = rcClient.bottom + 1;

ClientToScreen( hwnd, &ptTreeUL );
ClientToScreen( hwnd, &ptTreeLR );

// Blit the parent DC into memory DC, here things go wrong
BitBlt( memDC, 0, 0, 
    rcClient.right - rcClient.left, 
    rcClient.bottom - rcClient.top, 
    pDC, 
    ptTreeLR.x - ptTreeUL.x,
    ptTreeLR.y - ptTreeUL.y, SRCCOPY ); 

ReleaseDC( GetParent(hwnd), pDC );

Unfortunately, the coordinates I get are not good, and although I get a part of the bitmap Blited into memory DC it is not the correct part.

How can I blit the underlying portion of the parent background into treeview's memory DC ?

Thank you.

Best regards.

Posted 4-Apr-14 5:55am

AlwaysLearningNewStuff

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KarstenK · Accepted Answer · 2014-04-04T06:58:00

Solution 1

you must transform with the right HWND

C#

HWND hParent = GetParent(hwnd);
ClientToScreen( hwnd, &ptTreeUL );
ClientToScreen( hwnd, &ptTreeLR );

//dont write such code ;-)
ReleaseDC( GetParent(hwnd), pDC );

tip: create the bitmap globally once to improve performance

Posted 4-Apr-14 6:58am

KarstenK

Updated 4-Apr-14 7:01am

v2

Comments

AlwaysLearningNewStuff 4-Apr-14 14:25pm

I have solved my problem:

// capture parent bitmap
HDC pDC = GetDC( GetParent(hwnd) );
 
HWND parent = GetParent(hwnd);

POINT ptTreeUL, ptParentUL; // upper left corner coordinates
 
ptTreeUL.x = rcClient.left;
ptTreeUL.y = rcClient.top;
 
ptParentUL.x = rcParent.left;
ptParentUL.y = rcParent.right;
 
ClientToScreen( hwnd, &ptTreeUL );
ClientToScreen( parent, &ptParentUL );
 
// Blit the parent DC into memory DC
BitBlt( memDC, 0, 0, 
    rcClient.right - rcClient.left, 
    rcClient.bottom - rcClient.top, 
    pDC, 
    ptParentUL.x + ptTreeUL.x,
    ptParentUL.y + ptTreeUL.y, SRCCOPY ); 
 
ReleaseDC( parent, pDC );

You should properly edit your solution so it can be useful to the future generations and those who are fairly inexperienced.

Thank you for the advice ( my 5 as a token of gratitude ).

Best regards.