[GDITOOLS] Improve ChangeScreenBpp utility function

modules/rostests/apitests/gditools/gditools.c

···
     return pentry->pUser;
 }
 
+VOID
+PrintAvailableDisplayModes(void)
+{
+    DEVMODEW dm = { .dmSize = sizeof(dm) };
+    ULONG iMode = 0;
+
+    printf("Available display modes:\n");
+    while (EnumDisplaySettingsW(NULL, iMode++, &dm))
+    {
+        printf("  %ux%u @ %u bpp, freq: %u Hz\n",
+               dm.dmPelsWidth, dm.dmPelsHeight, dm.dmBitsPerPel, dm.dmDisplayFrequency);
+    }
+}
+
 BOOL
 ChangeScreenBpp(
     _In_ ULONG cBitsPixel,
-    _Out_ PULONG pcOldBitsPixel)
+    _Out_ PDEVMODEW pdmOld)
 {
     DEVMODEW dm = { .dmSize = sizeof(dm) };
 
···
         return FALSE;
     }
 
-    *pcOldBitsPixel = dm.dmBitsPerPel;
+    printf("ChangeScreenBpp(%lu): Old display settings: %ux%u @ %u bpp\n",
+           cBitsPixel, dm.dmPelsWidth, dm.dmPelsHeight, dm.dmBitsPerPel);
+
+    *pdmOld = dm;
 
     if (dm.dmBitsPerPel != cBitsPixel)
     {
         dm.dmBitsPerPel = cBitsPixel;
-        if (ChangeDisplaySettingsExW(NULL, &dm, NULL, CDS_UPDATEREGISTRY | CDS_GLOBAL, NULL) != DISP_CHANGE_SUCCESSFUL)
+        if (ChangeDisplaySettingsW(&dm, 0) != DISP_CHANGE_SUCCESSFUL)
         {
-            printf("Failed to change display settings to %lu bpp. Current bpp: %u\n", cBitsPixel, *pcOldBitsPixel);
+            printf("Failed to change display settings.\n");
+            PrintAvailableDisplayModes();
             return FALSE;
         }
     }
+
+    EnumDisplaySettingsW(NULL, ENUM_CURRENT_SETTINGS, &dm);
+    printf("ChangeScreenBpp(%lu): New display settings: %ux%u @ %u bpp\n",
+           cBitsPixel, dm.dmPelsWidth, dm.dmPelsHeight, dm.dmBitsPerPel);
 
     return TRUE;
 }

modules/rostests/apitests/gditools/gditools.h

···
 BOOL
 ChangeScreenBpp(
     _In_ ULONG cBitsPixel,
-    _Out_ PULONG pcOldBitsPixel);
+    _Out_ PDEVMODEW pdmOld);

modules/rostests/apitests/win32u/ntgdi/NtGdiBitBlt.c

···
 {
     ok(GdiToolsInit(), "GdiToolsInit failed\n");
 
-    ULONG cBitsPixel;
-    ChangeScreenBpp(32, &cBitsPixel);
+    DEVMODEW dmOld;
+    ChangeScreenBpp(32, &dmOld);
 
     ghdcDDB1 = CreateCompatibleDC(NULL);
     SelectObject(ghdcDDB1, ghbmp1);
···
     gbUseCLR_INVALID = FALSE;
     Test_NtGdiBitBlt_1BPP();
 
-    ChangeScreenBpp(cBitsPixel, &cBitsPixel);
+    ChangeDisplaySettingsW(&dmOld, 0);
 }

modules/rostests/apitests/win32u/ntgdi/NtGdiLineTo.c

···
 
 #define DIBINDEX(n) MAKELONG((n),0x10FF)
 
-static HDC ghdcDDB1, ghdcDDB32;
+static HDC ghdcDDB1;
 
 static
 COLORREF
···
 {
     ok(GdiToolsInit(), "GdiToolsInit failed\n");
 
-    ULONG cBitsPixel;
-    ChangeScreenBpp(32, &cBitsPixel);
+    DEVMODEW dmOld;
+    ChangeScreenBpp(32, &dmOld);
 
     ghdcDDB1 = CreateCompatibleDC(NULL);
     ok(SelectObject(ghdcDDB1, ghbmp1) != NULL, "SelectObject failed\n");
-    ghdcDDB32 = CreateCompatibleDC(NULL);
-    ok(SelectObject(ghdcDDB32, ghbmp32) != NULL, "SelectObject failed\n");
 
     Test_NtGdiLineTo_1BPP_BW(ghdcDDB1);
     Test_NtGdiLineTo_1BPP_BW(ghdcDIB1);
     Test_NtGdiLineTo_1BPP_BW(ghdcDIB1_InvCol);
     Test_NtGdiLineTo_1BPP_RB();
 
-    ChangeScreenBpp(cBitsPixel, &cBitsPixel);
+    ChangeDisplaySettingsW(&dmOld, 0);
 }