Support MFC Edit Control in Dark Mode

TestDarkModeDlg.cpp

BOOL CTestDarkModeDlg::OnInitDialog()
{
	__super::OnInitDialog();
  
  // Snipped other code for berevity
  
  // Set the dark mode theme
  SetWindowTheme(GetDlgItem(IDC_EDIT1)->GetSafeHwnd(), L"DarkMode_Explorer", nullptr);
  
  // Tweak to render the border correctly
  SetWindowSubclass(GetDlgItem(IDC_EDIT1)->GetSafeHwnd(), EditSubclassProc, 0, 0);
  
  return TRUE;
}

TestDarkModeDlg.h

// Declare this function outside of the dialog class.

// Subclass procedure for the CEdit control
static LRESULT CALLBACK EditSubclassProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData) {
	switch (uMsg) {
	case WM_NCPAINT: {
		// Draw a custom border
		HDC hdc = GetWindowDC(hWnd);
		RECT rect;
		GetWindowRect(hWnd, &rect);
		OffsetRect(&rect, -rect.left, -rect.top);

		// Determine the border color
		bool hasFocus = (GetFocus() == hWnd);
		COLORREF outerBorderColor = RGB(130, 135, 144); // #828790 in RGB
		COLORREF innerBorderColor = RGB(240, 240, 240); // Light gray like buttons
		COLORREF accentColor = RGB(0, 120, 215); // Example accent color (Windows blue)

		// Draw the outer border
		HPEN hOuterPen = CreatePen(PS_SOLID, 1, outerBorderColor);
		HGDIOBJ hOldPen = SelectObject(hdc, hOuterPen);
		HGDIOBJ hOldBrush = SelectObject(hdc, GetStockObject(NULL_BRUSH));
		Rectangle(hdc, rect.left, rect.top, rect.right, rect.bottom);

		// Draw the inner border
		HPEN hInnerPen = CreatePen(PS_SOLID, 1, innerBorderColor);
		SelectObject(hdc, hInnerPen);
		InflateRect(&rect, -1, -1); // Shrink the rectangle by 1 pixel
		Rectangle(hdc, rect.left, rect.top, rect.right, rect.bottom);

		// Draw the accent color on the bottom edge if focused
		if (hasFocus) {
			HPEN hAccentPen = CreatePen(PS_SOLID, 2, accentColor);
			SelectObject(hdc, hAccentPen);
			MoveToEx(hdc, rect.left, rect.bottom - 1, NULL);
			LineTo(hdc, rect.right, rect.bottom - 1);
			SelectObject(hdc, hInnerPen); // Restore inner pen
			DeleteObject(hAccentPen);
		}

		// Cleanup
		SelectObject(hdc, hOldPen);
		SelectObject(hdc, hOldBrush);
		DeleteObject(hOuterPen);
		DeleteObject(hInnerPen);
		ReleaseDC(hWnd, hdc);
		return 0;
	}
	case WM_SETFOCUS:
	case WM_KILLFOCUS:
		// Redraw the non-client area when focus changes
		RedrawWindow(hWnd, NULL, NULL, RDW_FRAME | RDW_INVALIDATE);
		break;
	case WM_DESTROY:
		// Remove the subclass when the control is destroyed
		RemoveWindowSubclass(hWnd, EditSubclassProc, uIdSubclass);
		break;
	}
	return DefSubclassProc(hWnd, uMsg, wParam, lParam);
}