Fix Qt scrollbar grippers 1.1: Fix control detection

mods/fix-qt-scrollbar-grippers.wh.cpp

@@ -2,7 +2,7 @@
 // @id              fix-qt-scrollbar-grippers
 // @name            Fix Qt scrollbar grippers
 // @description     Fixes scrollbar grippers in Qt 6.1+
-// @version         1.0
+// @version         1.1
 // @author          kawapure
 // @github          https://github.com/kawapure
 // @twitter         https://twitter.com/kawaipure
@@ -32,31 +32,45 @@ for injection.
 
 In Windhawk, go to the "Advanced" tab and scroll down to 
 "Custom process inclusion list". In that box, put the filename of the `.exe`. 
-The mod will immediately apply to those programs after you click "Save". 
+The mod will immediately apply to those programs after you click "Save", although the best results usually require a restart
+of that program because Qt may cache the bitmap, causing the element to sometimes appear unmodified.
 */
 // ==/WindhawkModReadme==
 
 #include <windhawk_api.h>
 #include <windhawk_utils.h>
 #include <uxtheme.h>
 #include <vsstyle.h>
+#include <winerror.h>
+
+// Undocumented export from UXTheme to get the class from a theme handle.
+HRESULT STDMETHODCALLTYPE (*GetThemeClass)(HTHEME hTheme, LPCWSTR pszClassIdList, int cchClass);
 
 using DrawThemeBackgroundEx_t = decltype(&DrawThemeBackgroundEx);
 DrawThemeBackgroundEx_t DrawThemeBackgroundEx_orig;
 HRESULT WINAPI DrawThemeBackgroundEx_hook(HTHEME hTheme, HDC hdc, int iPartId, int iStateId, LPCRECT pRect, const DTBGOPTS *pOptions)
 {
     HRESULT result = DrawThemeBackgroundEx_orig(hTheme, hdc, iPartId, iStateId, pRect, pOptions);
 
-    if (iPartId == SBP_THUMBBTNHORZ || iPartId == SBP_THUMBBTNVERT)
+    WCHAR szClassName[512];
+    HRESULT hrGetString = GetThemeClass(hTheme, szClassName, 512);
+
+    if (
+        SUCCEEDED(hrGetString) &&
+        wcsicmp(szClassName, L"ScrollBar") == 0 &&
+        (iPartId == SBP_THUMBBTNHORZ || iPartId == SBP_THUMBBTNVERT)
+    )
     {
         if (iPartId == SBP_THUMBBTNHORZ)
             Wh_Log(L"dtb: is SBP_THUMBBTNHORZ");
         else if (iPartId == SBP_THUMBBTNVERT)
             Wh_Log(L"dtb: is SBP_THUMBBTNVERT");
 
+        Wh_Log(L"iStateId: %d", iStateId);
+
         int gripperPart = iPartId == SBP_THUMBBTNHORZ
-                ? SBP_GRIPPERHORZ
-                : SBP_GRIPPERVERT;
+            ? SBP_GRIPPERHORZ
+            : SBP_GRIPPERVERT;
 
         SIZE gripperSize = { 0 };
         GetThemePartSize(hTheme, hdc, gripperPart, iStateId, nullptr, TS_TRUE, &gripperSize);
@@ -67,6 +81,7 @@ HRESULT WINAPI DrawThemeBackgroundEx_hook(HTHEME hTheme, HDC hdc, int iPartId, i
         )
         {
             Wh_Log(L"drawing gripper");
+            Wh_Log(L"is dimensions %dx%d", pRect->right - pRect->left, pRect->bottom - pRect->top);
 
             DrawThemeBackground(hTheme, hdc, gripperPart, iStateId, pRect, nullptr);
         }
@@ -81,11 +96,35 @@ BOOL Wh_ModInit()
 {
     Wh_Log(L"Init");
 
-    Wh_SetFunctionHook(
+    HMODULE hModUxtheme = GetModuleHandleW(L"uxtheme.dll");
+
+    if (!hModUxtheme)
+    {
+        Wh_Log(L"UXTheme module not loaded. Mod failed to load.");
+        return FALSE;
+    }
+
+    // UXTheme ordinal export #74 = GetThemeClass: Gets the class name opened by that theme handle.
+    *(void **)&GetThemeClass = (void *)GetProcAddress(hModUxtheme, MAKEINTRESOURCEA(74));
+
+    if (!GetThemeClass)
+    {
+        Wh_Log(
+            L"GetThemeClass not exported by UXTheme. The mod may not be compatible with "
+            L"your version of Windows."
+        );
+        return FALSE;
+    }
+
+    if (!Wh_SetFunctionHook(
         (void *)DrawThemeBackgroundEx,
         (void *)DrawThemeBackgroundEx_hook,
         (void **)&DrawThemeBackgroundEx_orig
-    );
+    ))
+    {
+        Wh_Log(L"Failed to install DrawThemeBackgroundEx hooks. Mod failed to load.");
+        return FALSE;
+    }
 
     return TRUE;
 }