From ef60fb2e593ef30a6776cf1859dbd4ebfb14e81c Mon Sep 17 00:00:00 2001
From: Timo Kreuzer <timo.kreuzer@reactos.org>
Date: Thu, 8 Jan 2026 11:45:53 +0200
Subject: [PATCH] [GDITOOLS] Improve ChangeScreenBpp utility function

---
 modules/rostests/apitests/gditools/gditools.c | 30 ++++++++++++++++---
 modules/rostests/apitests/gditools/gditools.h |  2 +-
 .../apitests/win32u/ntgdi/NtGdiBitBlt.c       |  6 ++--
 .../apitests/win32u/ntgdi/NtGdiLineTo.c       | 10 +++----
 4 files changed, 34 insertions(+), 14 deletions(-)

diff --git a/modules/rostests/apitests/gditools/gditools.c b/modules/rostests/apitests/gditools/gditools.c
index 8292ef81dd4..6fa13983f94 100644
--- a/modules/rostests/apitests/gditools/gditools.c
+++ b/modules/rostests/apitests/gditools/gditools.c
@@ -106,10 +106,24 @@ GdiGetHandleUserData(
     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) };
 
@@ -119,18 +133,26 @@ ChangeScreenBpp(
         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;
 }
 
diff --git a/modules/rostests/apitests/gditools/gditools.h b/modules/rostests/apitests/gditools/gditools.h
index b48241816c4..547396bd8c0 100644
--- a/modules/rostests/apitests/gditools/gditools.h
+++ b/modules/rostests/apitests/gditools/gditools.h
@@ -44,4 +44,4 @@ GdiGetHandleUserData(
 BOOL
 ChangeScreenBpp(
     _In_ ULONG cBitsPixel,
-    _Out_ PULONG pcOldBitsPixel);
+    _Out_ PDEVMODEW pdmOld);
diff --git a/modules/rostests/apitests/win32u/ntgdi/NtGdiBitBlt.c b/modules/rostests/apitests/win32u/ntgdi/NtGdiBitBlt.c
index 91947602a7e..59437a3a559 100644
--- a/modules/rostests/apitests/win32u/ntgdi/NtGdiBitBlt.c
+++ b/modules/rostests/apitests/win32u/ntgdi/NtGdiBitBlt.c
@@ -355,8 +355,8 @@ START_TEST(NtGdiBitBlt)
 {
     ok(GdiToolsInit(), "GdiToolsInit failed\n");
 
-    ULONG cBitsPixel;
-    ChangeScreenBpp(32, &cBitsPixel);
+    DEVMODEW dmOld;
+    ChangeScreenBpp(32, &dmOld);
 
     ghdcDDB1 = CreateCompatibleDC(NULL);
     SelectObject(ghdcDDB1, ghbmp1);
@@ -371,5 +371,5 @@ START_TEST(NtGdiBitBlt)
     gbUseCLR_INVALID = FALSE;
     Test_NtGdiBitBlt_1BPP();
 
-    ChangeScreenBpp(cBitsPixel, &cBitsPixel);
+    ChangeDisplaySettingsW(&dmOld, 0);
 }
diff --git a/modules/rostests/apitests/win32u/ntgdi/NtGdiLineTo.c b/modules/rostests/apitests/win32u/ntgdi/NtGdiLineTo.c
index e916a7f30c8..fbd353466e1 100644
--- a/modules/rostests/apitests/win32u/ntgdi/NtGdiLineTo.c
+++ b/modules/rostests/apitests/win32u/ntgdi/NtGdiLineTo.c
@@ -10,7 +10,7 @@
 
 #define DIBINDEX(n) MAKELONG((n),0x10FF)
 
-static HDC ghdcDDB1, ghdcDDB32;
+static HDC ghdcDDB1;
 
 static
 COLORREF
@@ -186,18 +186,16 @@ START_TEST(NtGdiLineTo)
 {
     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);
 }