Black cockpit canvas + flicker-free pane painting

SS_BLACKRECT paints the system window-frame color - gray on modern
Windows - so the viewscreen child is now a plain STATIC subclassed to
erase true black. The MFD/map panes flickered because Paint() cleared
the on-screen surface before redrawing at the fill cadence; the pane
now composes off screen and lands in a single BitBlt.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

MUNGA_L4/L4MFDVIEW.cpp

@@ -323,11 +323,21 @@ void
 
 	RECT client;
 	GetClientRect((HWND) window, &client);
-	FillRect(hdc, &client, (HBRUSH) GetStockObject(BLACK_BRUSH));
 
-	SetStretchBltMode(hdc, COLORONCOLOR);
+	//---------------------------------------------------------------
+	// Double-buffered: compose the whole pane off screen and blit it
+	// in one operation, otherwise the clear-then-draw sequence
+	// flickers at the repaint cadence.
+	//---------------------------------------------------------------
+	HDC mem = CreateCompatibleDC(hdc);
+	HBITMAP surface = CreateCompatibleBitmap(hdc, client.right, client.bottom);
+	HBITMAP old_surface = (HBITMAP) SelectObject(mem, surface);
+
+	FillRect(mem, &client, (HBRUSH) GetStockObject(BLACK_BRUSH));
+
+	SetStretchBltMode(mem, COLORONCOLOR);
 	StretchDIBits(
-		hdc,
+		mem,
 		displayX, displayY, displayW, displayH,
 		0, 0, sourceWidth, sourceHeight,
 		pixels, (const BITMAPINFO *) blitHeader,
@@ -349,15 +359,21 @@ void
 		rect.bottom = button->y + button->h;
 
 		HBRUSH fill = CreateSolidBrush(ButtonFill(button->amber, level));
-		FillRect(hdc, &rect, fill);
+		FillRect(mem, &rect, fill);
 		DeleteObject(fill);
 
 		HBRUSH frame = CreateSolidBrush(
 			(i == pressedIndex) ? RGB(255, 255, 255) : RGB(48, 48, 48));
-		FrameRect(hdc, &rect, frame);
+		FrameRect(mem, &rect, frame);
 		DeleteObject(frame);
 	}
 
+	BitBlt(hdc, 0, 0, client.right, client.bottom, mem, 0, 0, SRCCOPY);
+
+	SelectObject(mem, old_surface);
+	DeleteObject(surface);
+	DeleteDC(mem);
+
 	EndPaint((HWND) window, &ps);
 }
 

MUNGA_L4/L4VB16.cpp

@@ -3801,6 +3801,26 @@ void
 //########################################################################
 //############################ SVGA640x480x16 ############################
 //########################################################################
+
+//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// Single-window cockpit: the viewscreen child erases true black
+// (SS_BLACKRECT paints the system window-frame gray on modern Windows).
+//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+static WNDPROC gViewscreenBaseProc = NULL;
+
+static LRESULT CALLBACK
+	ViewscreenBlackProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
+{
+	if (message == WM_ERASEBKGND)
+	{
+		RECT client;
+		GetClientRect(hwnd, &client);
+		FillRect((HDC) wParam, &client, (HBRUSH) GetStockObject(BLACK_BRUSH));
+		return 1;
+	}
+	return CallWindowProcA(gViewscreenBaseProc, hwnd, message, wParam, lParam);
+}
+
 SVGA16::SVGA16(
 	int mode,
 	int init_width,
@@ -3916,14 +3936,20 @@ SVGA16::SVGA16(
 
 		if (cockpit != NULL)
 		{
+			// plain STATIC (SS_BLACKRECT actually paints the system
+			// window-frame GRAY on modern Windows), subclassed below to
+			// erase true black
 			cockpitViewscreen = CreateWindowExA(
 				0, "STATIC", "",
-				WS_CHILD | WS_VISIBLE | WS_CLIPSIBLINGS | SS_BLACKRECT,
+				WS_CHILD | WS_VISIBLE | WS_CLIPSIBLINGS,
 				0, 0,
 				view_w, view_h,
 				cockpit, NULL, GetModuleHandleA(NULL), NULL);
 			if (cockpitViewscreen != NULL)
 			{
+				gViewscreenBaseProc = (WNDPROC) SetWindowLongPtrA(
+					cockpitViewscreen, GWLP_WNDPROC,
+					(LONG_PTR) ViewscreenBlackProc);
 				gMainPresentWindow = cockpitViewscreen;
 			}
 		}