Visibility - Win32 Programmer's Reference

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Visibility

A window can be either visible or hidden. Windows displays a visible window on the screen. It hides a hidden window by not drawing it. If a window is visible, the user can supply input to the window and view the window's output. If a window is hidden, it is effectively disabled. A hidden window can process messages from Windows or from other windows, but it cannot process input from the user or display output. An application sets a window's visibility state when creating the window. Later, the application can change the visibility state.

A window is visible when the WS_VISIBLE style is set for the window. By default, the CreateWindowEx function creates a hidden window unless the application specifies the WS_VISIBLE style. Typically, an application sets the WS_VISIBLE style after it has created a window to keep details of the creation process hidden from the user. For example, an application may keep a new window hidden while it customizes the window's appearance. If the WS_VISIBLE style is specified in CreateWindowEx, Windows sends the WM_SHOWWINDOW message to the window after creating the window, but before displaying it.

An application can determine whether a window is visible by using the IsWindowVisible function. An application can show (make visible) or hide a window by using the ShowWindow, SetWindowPos, DeferWindowPos, or SetWindowPlacement function. These functions show or hide a window by setting or removing the WS_VISIBLE style for the window. They also send the WM_SHOWWINDOW message to the window before showing or hiding it.

When an owner window is minimized, Windows automatically hides the associated owned windows. Similarly, when an owner window is restored, Windows automatically shows the associated owned windows. In both cases, Windows sends the WM_SHOWWINDOW message to the owned windows before hiding or showing them. Occasionally, an application may need to hide the owned windows without having to minimize or hide the owner. In this case, the application uses the ShowOwnedPopups function. This function sets or removes the WS_VISIBLE style for all owned windows and sends the WM_SHOWWINDOW message to the owned windows before hiding or showing them. Hiding an owner window has no effect on the visibility state of the owned windows.

When a parent window is visible, its associated child windows are also visible. Similarly, when the parent window is hidden, its child windows are also hidden. Minimizing the parent window has no effect on the visibility state of the child windows; that is, the child windows are minimized along with the parent, but the WS_VISIBLE style is not changed.

Even if a window has the WS_VISIBLE style, the user may not be able to see the window on the screen; other windows may completely overlap it or it may have been moved beyond the edge of the screen. Also, a visible child window is subject to the clipping rules established by its parent-child relationship. If the window's parent window is not visible, it will also not be visible. If the parent window moves beyond the edge of the screen, the child window also moves because a child window is drawn relative to the parent's upper left corner. For example, a user may move the parent window containing the child window far enough off the edge of the screen that the user may not be able to see the child window, even though the child window and its parent window both have the WS_VISIBLE style.

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