Taskbar10: Better TaskbarSd handling. (#4020)

- Invisible mode (2) now supports ep_taskbar. We do this by completely overriding WM_PAINT and WM_PRINTCLIENT when this mode is active, instead of null-ing the HTHEME.
- Disabled mode (1) now hides the window instead of returning 0 (width/height value depending on taskbar orientation) in message 0x464 (calculate minimum size). Fortunately CTrayNotify handles the visibility of the button, therefore this also fixes tab navigation when the button is hidden.

ExplorerPatcher/dllmain.c

@@ -5047,6 +5047,23 @@ __declspec(dllexport) BOOL explorer_SetChildWindowNoActivateHook(HWND hWnd)
 
 #pragma region "Hide Show desktop button"
 #if WITH_MAIN_PATCHER
+DWORD GetTaskbarSd()
+{
+    DWORD dwVal = 1, dwSize = sizeof(DWORD);
+    if (SHRegGetValueFromHKCUHKLMFunc && SHRegGetValueFromHKCUHKLMFunc(
+        TEXT("SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Advanced"),
+        TEXT("TaskbarSd"),
+        SRRF_RT_REG_DWORD,
+        NULL,
+        &dwVal,
+        &dwSize
+    ) == ERROR_SUCCESS)
+    {
+        return dwVal;
+    }
+    return 1; // Visible
+}
+
 INT64 ShowDesktopSubclassProc(
     _In_ HWND   hWnd,
     _In_ UINT   uMsg,
@@ -5056,31 +5073,60 @@ INT64 ShowDesktopSubclassProc(
     DWORD_PTR   dwRefData
 )
 {
-    if (uMsg == WM_NCDESTROY)
-    {
-        RemoveWindowSubclass(hWnd, ShowDesktopSubclassProc, ShowDesktopSubclassProc);
-    }
-    else if (uMsg == WM_USER + 100)
+    switch (uMsg)
     {
-        LRESULT lRes = DefSubclassProc(hWnd, uMsg, wParam, lParam);
-        if (lRes > 0)
+        case WM_NCDESTROY:
         {
-            DWORD dwVal = 0, dwSize = sizeof(DWORD);
-            if (SHRegGetValueFromHKCUHKLMFunc && SHRegGetValueFromHKCUHKLMFunc(
-                TEXT("SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Advanced"),
-                TEXT("TaskbarSd"),
-                SRRF_RT_REG_DWORD,
-                NULL,
-                &dwVal,
-                (LPDWORD)(&dwSize)
-            ) == ERROR_SUCCESS && !dwVal)
+            RemoveWindowSubclass(hWnd, ShowDesktopSubclassProc, ShowDesktopSubclassProc);
+            break;
+        }
+        case WM_PAINT:
+        case WM_PRINTCLIENT:
+        {
+            HANDLE h_dwTaskbarSd = GetPropW(hWnd, L"EP_TaskbarSd");
+            if (h_dwTaskbarSd)
             {
-                lRes = 0;
+                DWORD dwTaskbarSd = (DWORD)h_dwTaskbarSd - 1;
+                if (dwTaskbarSd == 2) // Invisible
+                {
+                    PAINTSTRUCT ps;
+                    HDC hdc = BeginPaint(hWnd, &ps);
+                    if (hdc)
+                    {
+                        HDC hdcPaint;
+                        HPAINTBUFFER hBufferedPaint = BeginBufferedPaint(hdc, &ps.rcPaint, BPBF_TOPDOWNDIB, NULL, &hdcPaint);
+                        if (hBufferedPaint)
+                        {
+                            if (IsThemeActive())
+                            {
+                                DrawThemeParentBackground(hWnd, hdcPaint, NULL);
+                            }
+                            else
+                            {
+                                RECT rc;
+                                GetClientRect(hWnd, &rc);
+                                FillRect(hdc, &rc, (HBRUSH)(COLOR_BTNFACE + 1));
+                            }
+                            EndBufferedPaint(hBufferedPaint, TRUE);
+                        }
+                        EndPaint(hWnd, &ps);
+                    }
+                    return 0;
+                }
             }
-            else if (dwVal) PostMessageW(hWnd, 794, 0, 0);
+            break;
+        }
+        case WM_THEMECHANGED:
+        case WM_SETTINGCHANGE:
+        {
+            LRESULT lRes = DefSubclassProc(hWnd, uMsg, wParam, lParam);
+            DWORD dwTaskbarSd = GetTaskbarSd();
+            SetPropW(hWnd, L"EP_TaskbarSd", (HANDLE)(dwTaskbarSd + 1));
+            ShowWindow(hWnd, dwTaskbarSd != 0 ? SW_SHOW : SW_HIDE);
+            return lRes;
         }
-        return lRes;
     }
+
     return DefSubclassProc(hWnd, uMsg, wParam, lParam);
 }
 #endif
@@ -7295,13 +7341,6 @@ HTHEME explorer_OpenThemeDataForDpi(
         }
         return hTheme;
     }
-    else if ((*((WORD*)&(pszClassList)+1)) && !wcscmp(pszClassList, L"TaskbarShowDesktop"))
-    {
-        DWORD dwVal = 0, dwSize = sizeof(DWORD);
-        RegGetValueW(HKEY_CURRENT_USER, L"Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Advanced", L"TaskbarSD", RRF_RT_REG_DWORD, NULL, &dwVal, &dwSize);
-        if (dwVal == 2) return NULL;
-        return OpenThemeDataForDpi(hwnd, pszClassList, dpi);
-    }
 
     // task list - Taskband2 from CTaskListWnd::_HandleThemeChanged
     if (bClassicThemeMitigations && (*((WORD*)&(pszClassList)+1)) && !wcscmp(pszClassList, L"Taskband2"))