WMSIZE

WMSIZE is an informal term that appears in some programming contexts as a reference to the Windows message WM_SIZE. It is not an official Windows API constant; WM_SIZE is the canonical name used by the Windows API. In practice, WMSIZE may be used in code comments, documentation, or as a local alias, but developers should rely on WM_SIZE for official references.

WM_SIZE is a Windows message sent to a window when the size of the window changes, such as when the user resizes, minimizes, maximizes, or restores the window. The message is delivered to the window procedure as part of the standard Windows message loop. The wParam parameter indicates the type of resizing, with common values including SIZE_RESTORED, SIZE_MINIMIZED, SIZE_MAXIMIZED, SIZE_MAXSHOW, and SIZE_MAXHIDE. The lParam parameter carries the new width and height of the client area, with the width stored in the low-order word and the height in the high-order word.

Typical handling of WM_SIZE involves updating window layout and child controls, reallocating resources, or triggering layout recalculations to reflect the new client area. Applications may also respond by redrawing content, adjusting scroll bars, or initiating layout logic specific to the new size.

In summary, while WMSIZE may appear as a shorthand in some contexts, the official Windows message is WM_SIZE. Understanding WM_SIZE and its parameters is essential for implementing responsive window layouts and proper UI behavior in Windows applications.