Add WinStructWordSize<> helper and use it

This is similar to WinStruct<> but initializes dwSize and not cbSize
struct member.

In the future we should auto-detect the xxSize existence in WinStruct
using either SFINAE or, preferably, concepts, but for now keep things
simple.

include/wx/msw/private.h

@@ -195,6 +195,23 @@ struct WinStruct : public T
     }
 };
 
+// Life wouldn't be fun if Windows didn't call the size member differently in
+// different structs, so define the equivalent of the above for the ones where
+// it's called dwSize.
+//
+// When we can require C++17 or preferably C++20 we could merge this with
+// WinStruct by detecting the presence of cbSize/dwSize member using SFINAE,
+// but for now just define it separately to keep things simple.
+template <class T>
+struct WinStructWordSize : public T
+{
+    WinStructWordSize()
+    {
+        wxZeroMemory(*this);
+
+        this->dwSize = sizeof(T);
+    }
+};
 
 // Macros for converting wxString to the type expected by API functions.
 //

src/msw/darkmode.cpp

@@ -774,8 +774,7 @@ HandleMenuMessage(WXLRESULT* result,
                 // We have to specify the text colour explicitly as by default
                 // black would be used, making the menu label unreadable on the
                 // (almost) black background.
-                DTTOPTS textOpts;
-                textOpts.dwSize = sizeof(textOpts);
+                WinStructWordSize<DTTOPTS> textOpts;
                 textOpts.dwFlags = DTT_TEXTCOLOR;
                 textOpts.crText = wxColourToRGB(GetMenuColour(colText));
 

src/msw/datecontrols.cpp

@@ -51,8 +51,7 @@ bool wxMSWDateControls::CheckInitialization()
         // it's enough to give the error only once
         s_initResult = false;
 
-        INITCOMMONCONTROLSEX icex;
-        icex.dwSize = sizeof(icex);
+        WinStructWordSize<INITCOMMONCONTROLSEX> icex;
         icex.dwICC = ICC_DATE_CLASSES;
 
         // see comment in wxApp::GetComCtl32Version() explaining the

src/msw/joystick.cpp

@@ -266,9 +266,8 @@ bool wxJoystick::GetButtonState(unsigned id) const
 int wxJoystick::GetPOVPosition() const
 {
 #ifndef NO_JOYGETPOSEX
-    JOYINFOEX joyInfo;
+    WinStructWordSize<JOYINFOEX> joyInfo;
     joyInfo.dwFlags = JOY_RETURNPOV;
-    joyInfo.dwSize = sizeof(joyInfo);
     MMRESULT res = joyGetPosEx(m_joystick, & joyInfo);
     if (res == JOYERR_NOERROR )
     {
@@ -288,9 +287,8 @@ int wxJoystick::GetPOVPosition() const
 int wxJoystick::GetPOVCTSPosition() const
 {
 #ifndef NO_JOYGETPOSEX
-    JOYINFOEX joyInfo;
+    WinStructWordSize<JOYINFOEX> joyInfo;
     joyInfo.dwFlags = JOY_RETURNPOVCTS;
-    joyInfo.dwSize = sizeof(joyInfo);
     MMRESULT res = joyGetPosEx(m_joystick, & joyInfo);
     if (res == JOYERR_NOERROR )
     {
@@ -306,9 +304,8 @@ int wxJoystick::GetPOVCTSPosition() const
 int wxJoystick::GetRudderPosition() const
 {
 #ifndef NO_JOYGETPOSEX
-    JOYINFOEX joyInfo;
+    WinStructWordSize<JOYINFOEX> joyInfo;
     joyInfo.dwFlags = JOY_RETURNR;
-    joyInfo.dwSize = sizeof(joyInfo);
     MMRESULT res = joyGetPosEx(m_joystick, & joyInfo);
     if (res == JOYERR_NOERROR )
     {
@@ -324,9 +321,8 @@ int wxJoystick::GetRudderPosition() const
 int wxJoystick::GetUPosition() const
 {
 #ifndef NO_JOYGETPOSEX
-    JOYINFOEX joyInfo;
+    WinStructWordSize<JOYINFOEX> joyInfo;
     joyInfo.dwFlags = JOY_RETURNU;
-    joyInfo.dwSize = sizeof(joyInfo);
     MMRESULT res = joyGetPosEx(m_joystick, & joyInfo);
     if (res == JOYERR_NOERROR )
     {
@@ -342,9 +338,8 @@ int wxJoystick::GetUPosition() const
 int wxJoystick::GetVPosition() const
 {
 #ifndef NO_JOYGETPOSEX
-    JOYINFOEX joyInfo;
+    WinStructWordSize<JOYINFOEX> joyInfo;
     joyInfo.dwFlags = JOY_RETURNV;
-    joyInfo.dwSize = sizeof(joyInfo);
     MMRESULT res = joyGetPosEx(m_joystick, & joyInfo);
     if (res == JOYERR_NOERROR )
     {

src/msw/renderer.cpp

@@ -956,8 +956,7 @@ void wxRendererXP::DrawItemText(wxWindow* win,
     {
         RECT rc = ConvertToRECT(dc, rect);
 
-        DTTOPTS textOpts;
-        textOpts.dwSize = sizeof(textOpts);
+        WinStructWordSize<DTTOPTS> textOpts;
         textOpts.dwFlags = DTT_STATEID;
         textOpts.iStateId = itemState;
 

src/msw/taskdlg.cpp

@@ -605,7 +605,8 @@ static void TDPaintText(HDC hdc, const TDPageState& s)
 
         if (!native)
         {
-            DTTOPTS opts = { sizeof(opts) }; opts.dwFlags = DTT_COMPOSITED | DTT_TEXTCOLOR;
+            WinStructWordSize<DTTOPTS> opts;
+            opts.dwFlags = DTT_COMPOSITED | DTT_TEXTCOLOR;
             opts.crText = TDGetTextColour(s, part);
             FillRect(hdc, &rcT, brBg);
             ::DrawThemeTextEx(s.hTD, hdc, part, 0, el.name.c_str(), -1, dtF, &rcT, &opts);
@@ -780,7 +781,8 @@ static LRESULT CALLBACK TDRadioButtonSubclassProc(
         GetWindowTextW(hwnd, text, static_cast<int>(std::size(text)));
         auto gs = hBtn.GetTrueSize(BP_RADIOBUTTON, RBS_UNCHECKEDNORMAL);
         RECT rcT = { gs.x + 2,0,rcC.right,rcC.bottom };
-        DTTOPTS opts = { sizeof(opts) };
+
+        WinStructWordSize<DTTOPTS> opts;
         opts.dwFlags = DTT_COMPOSITED | DTT_TEXTCOLOR;
         opts.crText = TDDarkCol::kTextNormal;
         LOGFONT lf = {};

src/msw/toolbar.cpp

@@ -734,8 +734,7 @@ void wxToolBar::MSWSetDarkOrLightMode(SetMode setmode)
 
     // Update the separator above the toolbar which is drawn partially in
     // white by default and so looks very ugly in dark mode.
-    COLORSCHEME colScheme;
-    colScheme.dwSize = sizeof(COLORSCHEME);
+    WinStructWordSize<COLORSCHEME> colScheme;
     colScheme.clrBtnHighlight =
     colScheme.clrBtnShadow = wxSysColourToRGB(wxSYS_COLOUR_WINDOW);
     ::SendMessage(GetHwnd(), TB_SETCOLORSCHEME, 0, (LPARAM)&colScheme);

src/msw/utils.cpp

@@ -818,9 +818,7 @@ int wxKillAllChildren(long pid, wxSignal sig, wxKillError *krc, int flags)
     }
 
     //Fill in the size of the structure before using it.
-    PROCESSENTRY32 pe;
-    wxZeroMemory(pe);
-    pe.dwSize = sizeof(PROCESSENTRY32);
+    WinStructWordSize<PROCESSENTRY32> pe;
 
     // Walk the snapshot of the processes, and for each process,
     // kill it if its parent is pid.