Question

I am trying to make a radio button control with a transparent background using only Win32 when themes are enabled. The reason for doing this is to allow a radio button to be placed over an image and have the image show (rather than the grey default control background).

What happens out of the box is that the control will have the grey default control background and the standard method of changing this by handling either WM_CTLCOLORSTATIC or WM_CTLCOLORBTN as shown below does not work:

case WM_CTLCOLORSTATIC:
    hdcStatic = (HDC)wParam;

    SetTextColor(hdcStatic, RGB(0,0,0)); 
    SetBkMode(hdcStatic,TRANSPARENT);

    return (LRESULT)GetStockObject(NULL_BRUSH);
    break;  

My research so far indicates that Owner Draw is the only way to achieve this. I’ve managed to get most of the way with an Owner Draw radio button – with the code below I have a radio button and a transparent background (the background is set in WM_CTLCOLORBTN). However, the edges of the radio check are cut off using this method – I can get them back by uncommenting the call to the function DrawThemeParentBackgroundEx but this breaks the transparency.

void DrawRadioControl(HWND hwnd, HTHEME hTheme, HDC dc, bool checked, RECT rcItem)
{
    if (hTheme)
    {
      static const int cb_size = 13;

      RECT bgRect, textRect;
      HFONT font = (HFONT)SendMessageW(hwnd, WM_GETFONT, 0, 0);
      WCHAR *text = L"Experiment";

      DWORD state = ((checked) ? RBS_CHECKEDNORMAL : RBS_UNCHECKEDNORMAL) | ((bMouseOverButton) ? RBS_HOT : 0); 

      GetClientRect(hwnd, &bgRect);
      GetThemeBackgroundContentRect(hTheme, dc, BP_RADIOBUTTON, state, &bgRect, &textRect);

      DWORD dtFlags = DT_VCENTER | DT_SINGLELINE;

      if (dtFlags & DT_SINGLELINE) /* Center the checkbox / radio button to the text. */
         bgRect.top = bgRect.top + (textRect.bottom - textRect.top - cb_size) / 2;

      /* adjust for the check/radio marker */
      bgRect.bottom = bgRect.top + cb_size;
      bgRect.right = bgRect.left + cb_size;
      textRect.left = bgRect.right + 6;

      //Uncommenting this line will fix the button corners but breaks transparency
      //DrawThemeParentBackgroundEx(hwnd, dc, DTPB_USECTLCOLORSTATIC, NULL);

      DrawThemeBackground(hTheme, dc, BP_RADIOBUTTON, state, &bgRect, NULL);
      if (text)
      {
          DrawThemeText(hTheme, dc, BP_RADIOBUTTON, state, text, lstrlenW(text), dtFlags, 0, &textRect);

      }

   }
   else
   {
       // Code for rendering the radio when themes are not present
   }

}

The method above is called from WM_DRAWITEM as shown below:

case WM_DRAWITEM:
{
    LPDRAWITEMSTRUCT pDIS = (LPDRAWITEMSTRUCT)lParam;
    hTheme = OpenThemeData(hDlg, L"BUTTON");    

    HDC dc = pDIS->hDC;

    wchar_t sCaption[100];
    GetWindowText(GetDlgItem(hDlg, pDIS->CtlID), sCaption, 100);
    std::wstring staticText(sCaption);

    DrawRadioControl(pDIS->hwndItem, hTheme, dc, radio_group.IsButtonChecked(pDIS->CtlID), pDIS->rcItem, staticText);                               

    SetBkMode(dc, TRANSPARENT);
    SetTextColor(hdcStatic, RGB(0,0,0));                                
    return TRUE;

}                           

So my question is two parts I suppose:

1. Have I missed some other way to achieve my desired result?
2. Is it possible to fix the clipped button corners issue with my code and still have a transparent background

Answer 1

After looking at this on and off for nearly three months I’ve finally found a solution that I’m pleased with. What I eventually found was that the radio button edges were for some reason not being drawn by the routine within WM_DRAWITEM but that if I invalidated the radio button control’s parent in a rectangle around the control, they appeared.

Since I could not find a single good example of this I’m providing the full code (in my own solution I have encapsulated my owner drawn controls into their own class, so you will need to provide some details such as whether the button is checked or not)

This is the creation of the radiobutton (adding it to the parent window) also setting GWL_UserData and subclassing the radiobutton:

HWND hWndControl = CreateWindow( _T("BUTTON"), caption, WS_CHILD | WS_VISIBLE | BS_OWNERDRAW, 
    xPos, yPos, width, height, parentHwnd, (HMENU) id, NULL, NULL);

// Using SetWindowLong and GWL_USERDATA I pass in the this reference, allowing my 
// window proc toknow about the control state such as if it is selected
SetWindowLong( hWndControl, GWL_USERDATA, (LONG)this);

// And subclass the control - the WndProc is shown later
SetWindowSubclass(hWndControl, OwnerDrawControl::WndProc, 0, 0);

Since it is owner draw we need to handle the WM_DRAWITEM message in the parent window proc.

case WM_DRAWITEM:      
{      
    LPDRAWITEMSTRUCT pDIS = (LPDRAWITEMSTRUCT)lParam;      
    hTheme = OpenThemeData(hDlg, L"BUTTON");          

    HDC dc = pDIS->hDC;      

    wchar_t sCaption[100];      
    GetWindowText(GetDlgItem(hDlg, pDIS->CtlID), sCaption, 100);      
    std::wstring staticText(sCaption);      

    // Controller here passes to a class that holds a map of all controls 
    // which then passes on to the correct instance of my owner draw class
    // which has the drawing code I show below
    controller->DrawControl(pDIS->hwndItem, hTheme, dc, pDIS->rcItem, 
        staticText, pDIS->CtlID, pDIS->itemState, pDIS->itemAction);    

    SetBkMode(dc, TRANSPARENT);      
    SetTextColor(hdcStatic, RGB(0,0,0));     

    CloseThemeData(hTheme);                                 
    return TRUE;      

}    

Here is the DrawControl method – it has access to class level variables to allow state to be managed since with owner draw this is not handled automatically.

void OwnerDrawControl::DrawControl(HWND hwnd, HTHEME hTheme, HDC dc, bool checked, RECT rcItem, std::wstring caption, int ctrlId, UINT item_state, UINT item_action)
{   
    // Check if we need to draw themed data    
    if (hTheme)
    {   
        HWND parent = GetParent(hwnd);      

        static const int cb_size = 13;                      

        RECT bgRect, textRect;
        HFONT font = (HFONT)SendMessageW(hwnd, WM_GETFONT, 0, 0);

        DWORD state;

        // This method handles both radio buttons and checkboxes - the enums here
        // are part of my own code, not Windows enums.
        // We also have hot tracking - this is shown in the window subclass later
        if (Type() == RADIO_BUTTON) 
            state = ((checked) ? RBS_CHECKEDNORMAL : RBS_UNCHECKEDNORMAL) | ((is_hot_) ? RBS_HOT : 0);      
        else if (Type() == CHECK_BOX)
            state = ((checked) ? CBS_CHECKEDNORMAL : CBS_UNCHECKEDNORMAL) | ((is_hot_) ? RBS_HOT : 0);      

        GetClientRect(hwnd, &bgRect);

        // the theme type is either BP_RADIOBUTTON or BP_CHECKBOX where these are Windows enums
        DWORD theme_type = ThemeType(); 

        GetThemeBackgroundContentRect(hTheme, dc, theme_type, state, &bgRect, &textRect);

        DWORD dtFlags = DT_VCENTER | DT_SINGLELINE;

        if (dtFlags & DT_SINGLELINE) /* Center the checkbox / radio button to the text. */
            bgRect.top = bgRect.top + (textRect.bottom - textRect.top - cb_size) / 2;

        /* adjust for the check/radio marker */
        // The +3 and +6 are a slight fudge to allow the focus rectangle to show correctly
        bgRect.bottom = bgRect.top + cb_size;
        bgRect.left += 3;
        bgRect.right = bgRect.left + cb_size;       

        textRect.left = bgRect.right + 6;       

        DrawThemeBackground(hTheme, dc, theme_type, state, &bgRect, NULL);          
        DrawThemeText(hTheme, dc, theme_type, state, caption.c_str(), lstrlenW(caption.c_str()), dtFlags, 0, &textRect);                    

        // Draw Focus Rectangle - I still don't really like this, it draw on the parent
        // mainly to work around the way DrawFocus toggles the focus rect on and off.
        // That coupled with some of my other drawing meant this was the only way I found
        // to get a reliable focus effect.
        BOOL bODAEntire = (item_action & ODA_DRAWENTIRE);
        BOOL bIsFocused  = (item_state & ODS_FOCUS);        
        BOOL bDrawFocusRect = !(item_state & ODS_NOFOCUSRECT);

        if (bIsFocused && bDrawFocusRect)
        {
            if ((!bODAEntire))
            {               
                HDC pdc = GetDC(parent);
                RECT prc = GetMappedRectanglePos(hwnd, parent);
                DrawFocus(pdc, prc);                
            }
        }   

    }
      // This handles drawing when we don't have themes
    else
    {
          TEXTMETRIC tm;
          GetTextMetrics(dc, &tm);      

          RECT rect = { rcItem.left , 
              rcItem.top , 
              rcItem.left + tm.tmHeight - 1, 
              rcItem.top + tm.tmHeight - 1};    

          DWORD state = ((checked) ? DFCS_CHECKED : 0 ); 

          if (Type() == RADIO_BUTTON) 
              DrawFrameControl(dc, &rect, DFC_BUTTON, DFCS_BUTTONRADIO | state);
          else if (Type() == CHECK_BOX)
              DrawFrameControl(dc, &rect, DFC_BUTTON, DFCS_BUTTONCHECK | state);

          RECT textRect = rcItem;
          textRect.left = rcItem.left + 19;

          SetTextColor(dc, ::GetSysColor(COLOR_BTNTEXT));
          SetBkColor(dc, ::GetSysColor(COLOR_BTNFACE));
          DrawText(dc, caption.c_str(), -1, &textRect, DT_WORDBREAK | DT_TOP);
    }           
}

Next is the window proc that is used to subclass the radio button control – this
is called with all windows messages and handles several before then passing unhandled
ones on to the default proc.

LRESULT OwnerDrawControl::WndProc(HWND hWnd, UINT uMsg, WPARAM wParam,
                               LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData)
{
    // Get the button parent window
    HWND parent = GetParent(hWnd);  

    // The page controller and the OwnerDrawControl hold some information we need to draw
    // correctly, such as if the control is already set hot.
    st_mini::IPageController * controller = GetWinLong<st_mini::IPageController *> (parent);

    // Get the control
    OwnerDrawControl *ctrl = (OwnerDrawControl*)GetWindowLong(hWnd, GWL_USERDATA);

    switch (uMsg)
    {       
        case WM_LBUTTONDOWN:
        if (controller)
        {
            int ctrlId = GetDlgCtrlID(hWnd);

            // OnCommand is where the logic for things like selecting a radiobutton
            // and deselecting the rest of the group lives.
            // We also call our Invalidate method there, which redraws the radio when
            // it is selected. The Invalidate method will be shown last.
            controller->OnCommand(parent, ctrlId, 0);       

            return (0);
        }
        break;
        case WM_LBUTTONDBLCLK:
            // We just treat doubleclicks as clicks
            PostMessage(hWnd, WM_LBUTTONDOWN, wParam, lParam);
            break;
        case WM_MOUSEMOVE:
        {
            if (controller)                 
            {
                // This is our hot tracking allowing us to paint the control
                // correctly when the mouse is over it - it sets flags that get
                // used by the above DrawControl method
                if(!ctrl->IsHot())
                {
                    ctrl->SetHot(true);
                    // We invalidate to repaint
                    ctrl->InvalidateControl();

                    // Track the mouse event - without this the mouse leave message is not sent
                    TRACKMOUSEEVENT tme;
                    tme.cbSize = sizeof(TRACKMOUSEEVENT);
                    tme.dwFlags = TME_LEAVE;
                    tme.hwndTrack = hWnd;

                    TrackMouseEvent(&tme);
                }
            }    
            return (0);
        }
        break;
    case WM_MOUSELEAVE:
    {
        if (controller)
        {
            // Turn off the hot display on the radio
            if(ctrl->IsHot())
            {
                ctrl->SetHot(false);        
                ctrl->InvalidateControl();
            }
        }

        return (0);
    }
    case WM_SETFOCUS:
    {
        ctrl->InvalidateControl();
    }
    case WM_KILLFOCUS:
    {
        RECT rcItem;
        GetClientRect(hWnd, &rcItem);
        HDC dc = GetDC(parent);
        RECT prc = GetMappedRectanglePos(hWnd, parent);
        DrawFocus(dc, prc);

        return (0);
    }
    case WM_ERASEBKGND:
        return 1;
    }
    // Any messages we don't process must be passed onto the original window function
    return DefSubclassProc(hWnd, uMsg, wParam, lParam); 

}

Finally the last little piece of the puzzle is that you need to invalidate the control (redraw it) at the right times. I eventually found that invalidating the parent allowed the drawing to work 100% correctly. This was causing flicker until I realised that I could get away by only invalidating a rectangle as big as the radio check, rather than as big as the whole control including text as I had been.

void InvalidateControl()
{
    // GetMappedRectanglePos is my own helper that uses MapWindowPoints 
    // to take a child control and map it to its parent
    RECT rc = GetMappedRectanglePos(ctrl_, parent_);

    // This was my first go, that caused flicker
    // InvalidateRect(parent_, &rc_, FALSE);    

    // Now I invalidate a smaller rectangle
    rc.right = rc.left + 13;
    InvalidateRect(parent_, &rc, FALSE);                
}

A lot of code and effort for something that should be simple – drawing a themed radio button over a background image. Hopefully the answer will save someone else some pain!

* One big caveat with this is it only works 100% correctly for owner controls that are over a background (such as a fill rectangle or an image). That is ok though, since it is only needed when drawing the radio control over a background.