Window decorations: fixed black line sometimes painted on top of (native) window border on Windows 11 (issue #852)

Windows binaries built and signed locally in clean workspace

CHANGELOG.md

@@ -31,6 +31,8 @@ FlatLaf Change Log
   updated when table width changed and was painted on wrong side in
   right-to-left component orientation).
 - Theme Editor: Fixed occasional empty window on startup on macOS.
+- FlatLaf window decorations: Fixed black line sometimes painted on top of
+  (native) window border on Windows 11. (issue #852)
 
 #### Incompatibilities
 

flatlaf-natives/flatlaf-natives-jna/src/main/java/com/formdev/flatlaf/natives/jna/windows/FlatWindowsNativeWindowBorder.java

@@ -60,8 +60,11 @@ import com.sun.jna.platform.win32.WinDef.LRESULT;
 import com.sun.jna.platform.win32.WinDef.RECT;
 import com.sun.jna.platform.win32.WinDef.UINT_PTR;
 import com.sun.jna.platform.win32.WinDef.WPARAM;
+import com.sun.jna.platform.win32.WinError;
 import com.sun.jna.platform.win32.WinUser.HMONITOR;
 import com.sun.jna.platform.win32.WinUser.WindowProc;
+import com.sun.jna.ptr.IntByReference;
+import com.sun.jna.win32.StdCallLibrary;
 import com.sun.jna.win32.W32APIOptions;
 
 //
@@ -615,6 +618,14 @@ public class FlatWindowsNativeWindowBorder
 					if( hasAutohideTaskbar( ABE_RIGHT, monitorInfo.rcMonitor ) )
 						params.rgrc[0].right--;
 				}
+			} else if( SystemInfo.isWindows_11_orLater ) {
+				// For Windows 11, add border thickness to top, which is necessary to make the whole Java area visible.
+				// This also avoids that a black line is sometimes painted on top window border.
+				// Note: Do not increase top on Windows 10 because this would not hide Windows title bar.
+				IntByReference borderThickness = new IntByReference();
+				if( DWMApi.INSTANCE.DwmGetWindowAttribute( hwnd, DWMApi.DWMWA_VISIBLE_FRAME_BORDER_THICKNESS,
+						borderThickness.getPointer(), 4 ) == WinError.S_OK.intValue() )
+					params.rgrc[0].top += borderThickness.getValue();
 			}
 
 			// write changed params back to native memory
@@ -898,6 +909,18 @@ public class FlatWindowsNativeWindowBorder
 		HBRUSH CreateSolidBrush( DWORD color );
 	}
 
+	//---- interface DWMApi ---------------------------------------------------
+
+	private interface DWMApi
+		extends StdCallLibrary
+	{
+		DWMApi INSTANCE = Native.load( "dwmapi", DWMApi.class, W32APIOptions.DEFAULT_OPTIONS );
+
+		int DWMWA_VISIBLE_FRAME_BORDER_THICKNESS = 37;
+
+		int DwmGetWindowAttribute( HWND hwnd, int dwAttribute, Pointer pvAttribute, int cbAttribute );
+	}
+
 	//---- class NCCALCSIZE_PARAMS --------------------------------------------
 
 	@FieldOrder( { "rgrc" } )

flatlaf-natives/flatlaf-natives-windows/src/main/cpp/FlatWndProc.cpp

@@ -20,6 +20,7 @@
 #include <windows.h>
 #include <windowsx.h>
 #include <shellapi.h>
+#include <dwmapi.h>
 #include <jawt.h>
 #include <jawt_md.h>
 #include "FlatWndProc.h"
@@ -76,6 +77,7 @@ jmethodID FlatWndProc::isFullscreenMID;
 jmethodID FlatWndProc::fireStateChangedLaterOnceMID;
 
 HWNDMap* FlatWndProc::hwndMap;
+DWORD FlatWndProc::osBuildNumber = 0;
 
 #define java_awt_Frame_ICONIFIED			1
 #define java_awt_Frame_MAXIMIZED_BOTH		(4 | 2)
@@ -107,6 +109,14 @@ HWND FlatWndProc::install( JNIEnv *env, jobject obj, jobject window ) {
 			return 0;
 	}
 
+	// get OS build number
+	if( osBuildNumber == 0 ) {
+		OSVERSIONINFO info;
+		info.dwOSVersionInfoSize = sizeof( info );
+		if( ::GetVersionEx( &info ) )
+			osBuildNumber = info.dwBuildNumber;
+	}
+
 	// get window handle
 	HWND hwnd = getWindowHandle( env, window );
 	if( hwnd == NULL || hwndMap->get( hwnd ) != NULL )
@@ -391,6 +401,13 @@ LRESULT FlatWndProc::WmNcCalcSize( HWND hwnd, int uMsg, WPARAM wParam, LPARAM lP
 			if( hasAutohideTaskbar( ABE_RIGHT, monitorInfo.rcMonitor ) )
 				params->rgrc[0].right--;
 		}
+	} else if( osBuildNumber >= 22000 ) {
+		// For Windows 11, add border thickness to top, which is necessary to make the whole Java area visible.
+		// This also avoids that a black line is sometimes painted on top window border.
+		// Note: Do not increase top on Windows 10 because this would not hide Windows title bar.
+		UINT borderThickness = 0;
+		if( ::DwmGetWindowAttribute( hwnd, DWMWA_VISIBLE_FRAME_BORDER_THICKNESS, &borderThickness, sizeof( borderThickness ) ) == S_OK )
+			params->rgrc[0].top += borderThickness;
 	}
 
 	return lResult;

flatlaf-natives/flatlaf-natives-windows/src/main/cpp/FlatWndProc.h

@@ -35,6 +35,7 @@ private:
 	static jmethodID fireStateChangedLaterOnceMID;
 
 	static HWNDMap* hwndMap;
+	static DWORD osBuildNumber;
 
 	JavaVM* jvm;
 	JNIEnv* env; // attached to AWT-Windows/Win32 thread