exstyle

Exstyle, short for extended window style, refers to a set of bit flags that extend the basic window style used by the Win32 API when creating or modifying windows. These extended styles are defined as WS_EX_ constants and alter aspects of a window’s appearance and behavior beyond the standard style flags.

Usage and mechanisms

Extended window styles are supplied to window creation functions such as CreateWindowEx. They can also be read or modified later with GetWindowLongPtr (or GetWindowLong in older code) using the GWLP_EXSTYLE index, and changed with SetWindowLongPtr. Some changes apply immediately, while others may require the window to be destroyed and recreated or a redraw to take effect.

Common extended styles

- WS_EX_DLGMODALFRAME: creates a dialog-like border around the window.

- WS_EX_TOPMOST: keeps the window above non-topmost windows.

- WS_EX_TOOLWINDOW: creates a tool window with a smaller presence in the taskbar and in the Z order.

- WS_EX_CLIENTEDGE and WS_EX_WINDOWEDGE: provide sunken or raised borders for the window frame.

- WS_EX_LAYERED: enables layered windows for per-pixel transparency or color-key transparency.

- WS_EX_TRANSPARENT: allows mouse events to pass through to windows underneath in certain scenarios.

- WS_EX_ACCEPTFILES: enables drag-and-drop of files to the window (WM_DROPFILES).

- WS_EX_NOACTIVATE: prevents the window from activating when clicked.

- WS_EX_APPWINDOW: ensures the window appears in the taskbar for top-level windows.

- WS_EX_RTLREADING and related flags: support for right-to-left languages.

Notes and limitations

Exstyles are Windows-specific. Some styles only apply to top-level windows, others interact with standard styles in complex ways. Some changes require recreating the window or additional redrawing to take effect; others can be toggled at runtime but may not be supported across all Windows versions. Layered and transparency-related exstyles often have additional requirements and performance considerations.