ClearType ruins transparency

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I have a bitmap which background needs to be replaced with part of another bitmap. Everything works fine until I enable ClearFont on my WindowsXP.

In order to explain my problem better, let us label first bitmap as bmpDestination and second as bmpSource.

Here[^] is how the bmpSource looks like.

Here[^] is how bmpDestination looks like.

And here[^] is the incorrect result of their combining when ClearType is on.

ClearType alters some parts of the text background color, so they aren't white anymore ( RGB( 255, 255, 255 ) ) but a combination of white and text color.

I am using BitBlt() and monochrome bitmap to create a mask, and to simulate transparency. I have tried using TransparentBlt() too, but got the same result.

How can I combine bmpSource and bmpDestination, when ClearType is enabled, so I can create correct result ?

Thank you for your help.

Best regards.

Posted 10-May-14 14:54pm

AlwaysLearningNewStuff

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leon de boer · Answer 1 · 2014-05-10T16:15:00

I added this to your previous post it got messy so you probably missed it.

There are ways around it but they are all slow and give different results which you have to choose between. There is no perfect solution because it is a bug or over-sight in windows Cleartype implementation.

I played around and I came to the exact same conclusions as this author

http://theartofdev.wordpress.com/2014/04/21/text-rendering-methods-comparison-or-gdi-vs-gdi-revised/[^]

Conclusions

-GDI text rendering provides the best visual quality but doesn’t support transparent background.
-Native GDI rendering provides the best performance.
-GDI+ with anti-aliasing and typographic format provides the best performance and visual quality for transparent background rendering.
-GraphicsPath rendering method visual quality4 and performance is disappointing.
-Text rendered in each rendering method is visually different.
-As Microsoft will improve their fonts and display resolution (DPI) will raise, GDI+ text rendering will improve to a point where GDI has no significant visual benefit.

leon de boer · Answer 2 · 2014-05-11T08:35:00

I have studied carefully the code from your previous answer and managed to handle WM_WINDOWPOSCHANGED properly for multiple windows but I can not handle slight flickering.

What is causing the flicker is the way the listbox draws each item you need to do you own drawing to solve the problem there are plenty of articles on listbox flicker and solving it.

Ok to do the font simply attach the font if you need to the window .. so lets look at specific code.

First make a text string we are going to call the property in out case "FONT"

//this is the property title of the FONT to attach to our window
#define TEXTPROP TEXT("FONT")

Next handle WM_FONT

case WM_SETFONT:
LOGFONT lf;
HFONT OldFont, Newfont;
GetObject((HFONT)wParam, sizeof(lf), &lf);                  // Get proposed font
if (lf.lfQuality != NONANTIALIASED_QUALITY){                // If its antialiased we can't use
	lf.lfQuality = NONANTIALIASED_QUALITY;              // So change it to non antialiased
	Newfont = CreateFontIndirect(&lf);                  // Create a new font 
	OldFont = (HFONT) GetProp(hwnd, TEXTPROP);	    // Get the old font
	if (OldFont != 0) DeleteObject(OldFont);            // If valid delete it
	SetProp(hwnd, TEXTPROP, (HANDLE)Newfont);           // Set new font to window property
} else Newfont = (HFONT) wParam;                            // Use the font provided
return ::DefSubclassProc( hwnd, WM_SETFONT, (WPARAM)Newfont, lParam); // Treat it as usual

Your responsibility to delete any font WM_SETFONT created in NCDESTROY

case WM_NCDESTROY: 
   HFONT Font = (HFONT) GetProp(hwnd, TEXTPROP);           // Fetch the font property
   if (Font != 0) DeleteObject(Font);                      // If valid delete the font 
   RemoveProp(hwnd, TEXTPROP);                             // Remove the window property   
   ::RemoveWindowSubclass(hwnd, TreeProc, 0 );
   return ::DefSubclassProc( hwnd, message, wParam, lParam);

It now handles the WM_FONT like any normal window.

Finally I put all the creation stuff into a helper function

// ** LdB Consolidate function to create a listbox and do all the repeat stuff
HWND CreateListBox (HWND parent,    // Parent window to insert this control in
		    TCHAR* title,   // List box title text
		    int x, int y,   // x,y co-ordinate of parent for the insert
		    int cx, int cy, // Width and Height of the control
		    int id,	    // Id of the control
 		    HFONT hFont) {  // Handle to any special font (0 = default)
DWORD dwStyle;
HWND TreeView;
  
   TreeView = CreateWindowEx(0, WC_TREEVIEW, title, 
		WS_VISIBLE | WS_CHILD | WS_BORDER 
		| TVS_HASBUTTONS | TVS_HASLINES | TVS_LINESATROOT, 
		x, y, cx, cy,	parent, (HMENU)id, 0, NULL);

   dwStyle = GetWindowLong( TreeView , GWL_STYLE);
   dwStyle |= TVS_CHECKBOXES;
   SetWindowLongPtr( TreeView , GWL_STYLE, dwStyle );
   SetWindowSubclass( TreeView, TreeProc, 0, 0 );
   TreeView_SetBkColor(TreeView, RGB(0xFF, 0, 0xFF));
   // This checks font is not aliased by our handling of WM_FONT
   if (hFont == 0) hFont = (HFONT) SendMessage(TreeView, WM_GETFONT, 0, 0);
   SendMessage(TreeView, WM_SETFONT, (WPARAM)hFont, FALSE);
   return (TreeView);
};

Your creation now looks this simple

HWND TreeView = CreateListBox(hwnd, (TCHAR*)TEXT("Tree View"),
    50, 10, 200, 200, ID_LISTBOX, 0);

leon de boer · Answer 3 · 2014-05-11T09:11:00

Oh I forgot I further improved your redraw and made it compliant to handling WM_PRINTCLIENT itself.

case WM_PAINT:
    {
    // usual stuff
    PAINTSTRUCT ps;
    HDC hdc = BeginPaint( hwnd, &ps );
    // Simply get printclient to paint  
    ::SendMessage(hwnd, WM_PRINTCLIENT,(WPARAM) hdc, (LPARAM)(PRF_CLIENT) ); 
    EndPaint( hwnd, &ps );
    }
    return 0L;
case WM_PRINTCLIENT:
    {
    BITMAPINFO bmi;
    // Get parent client co-ordinates
    RECT rc;
    GetClientRect(GetParent(hwnd), &rc);
    // Create a memory DC
    HDC memDC = CreateCompatibleDC(0);
    // Create a DIB header for parent
    memset(&bmi, 0, sizeof(bmi));
    bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    bmi.bmiHeader.biWidth = rc.right - rc.left;
    bmi.bmiHeader.biHeight = rc.bottom - rc.top;
    bmi.bmiHeader.biBitCount = 24;
    bmi.bmiHeader.biPlanes = 1;
    bmi.bmiHeader.biCompression = BI_RGB;
    // Create a DIB bitmap
    HBITMAP tempBmp = CreateDIBSection(0, &bmi, DIB_RGB_COLORS, 0, 0, 0);
    // Select tempBmp onto DC to force size and DIB change on the DC
    SelectObject(memDC, tempBmp );
    // Put parent background on our memory DC
    ::SendMessage( GetParent(hwnd), WM_PRINTCLIENT, (WPARAM) memDC,  (LPARAM)(PRF_CLIENT));
    // Now we can dispose of the DIB bitmap no longer needed
    DeleteObject(tempBmp);
    // map tree's coordinates to parent window
    POINT ptTreeUL;
    ptTreeUL.x = 0;
    ptTreeUL.y = 0;
    ClientToScreen( hwnd, &ptTreeUL );
    ScreenToClient( GetParent(hwnd), &ptTreeUL );
    GetClientRect( hwnd, &rc);
    // Transfer parent background to given DC
    BitBlt((HDC)wParam, 0, 0,  rc.right-rc.left, rc.bottom-rc.top,
	memDC, ptTreeUL.x, ptTreeUL.y, SRCCOPY );
    // Okay get treeview to draw on our memory DC
    DefSubclassProc(hwnd, WM_PRINTCLIENT, (WPARAM)memDC,  (LPARAM)(PRF_CLIENT));
    // Transfer the treeview DC onto finalDC excluding pink
    TransparentBlt((HDC)wParam, 0, 0, rc.right - rc.left, rc.bottom - rc.top,
	memDC, 0, 0, rc.right - rc.left, rc.bottom - rc.top, RGB(0xFF, 0x00, 0xFF));
    // Finished with MemDC 
    DeleteObject(memDC);
    return (0); 
}

ClearType ruins transparency

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