Changing the Style of the Main Window

The style of Viewer's main window can be changed using the Windows SetWindowLong() function. The prototype for SetWindowLong() is where hwnd is the handle of the window, nOffset is the offset of the value to change, and nVal is the new value for the offset. Further documentation for the SetWindowLong() function can be found in the documentation for the Windows 3.1 Software Development Kit (SDK). To change the window style, the value -16 (which is the value of the Windows constant GWL_STYLE) should be specified for nOffset. The possible values for nVal are combinations of: These values would be combined simply by or'ing them together. Each call to SetWindowLong() completely replaces the previous styles for the window with the new styles specified in the nVal parameter. By default, the main Viewer window has the styles WS_VISIBLE, WS_CLIPSIBLINGS, WS_CLIPCHILDREN, WS_CAPTION, WS_SYSMENU, WS_THICKFRAME, WS_MINIMIZEBOX, and WS_MAXIMIZEBOX (that is, nVal=0x16CF0000).

To use SetWindowLong() from Viewer, it must be registered in the [CONFIG] section of the .MVP file as follows: SetWindowLong() can then be called from anywhere within the title with hwndApp as the first parameter, -16 as the second parameter, and the appropriate new style value in the third parameter. Microsoft recommends always including the WS_VISIBLE, WS_CLIPSIBLINGS, and WS_CLIPCHILDREN styles in the new value. That means the value of nVal would always be at least 0x16000000.

Note that SetWindowLong() is registered with the first parameter as an unsigned long (U) even though the SetWindowLong() function properly takes an HWND, which is an unsigned short int (u) in Windows 3.1, as the first parameter. SetWindowLong() must be registered this way if the internal hwndApp variable, which is an unsigned long, is to be passed to it. Because of the way arguments are passed, SetWindowLong() will still work correctly; the high word of hwndApp, which is zero-filled, will be ignored. However, if an unsigned short value will be passed to SetWindowLong(), then RegisterRoutine() must specify "u" for the first parameter. A Viewer title could obtain an unsigned short window handle by calling one of the Windows functions such as GetParent().

To remove the maximize box from the main Viewer window, the SetWindowLong() call would look as follows: To cause the main window frame to be redrawn immediately after the change to its style, you may need to call the Windows function SetWindowPos(). It can be registered as follows and then it can be called from anywhere within the title as follows: The SetWindowPos() call above is equivalent to calling SetWindowPos(hwndApp,0,0,0,0,0,SWP_DRAWFRAME | SWP_NOMOVE | SWP_NOSIZE | SWP_NOZORDER) using the Windows constants defined in the WINDOWS.H include file from the Windows SDK.

The following list describes the styles mentioned above:

WS_BORDER - Creates a window that has a border.

WS_CAPTION - Creates a window that has a title bar (implies the WS_BORDER style). This style cannot be used with the WS_DLGFRAME style.

WS_CLIPCHILDREN - Excludes the area occupied by child windows when drawing within the parent window. Used when creating the parent window.

WS_CLIPSIBLINGS - Clips child windows relative to each other; that is, when a particular child window receives a paint message, the WS_CLIPSIBLINGS style clips all other overlapped child windows out of the region of the child window to be updated. (If WS_CLIPSIBLINGS is not specified and child windows overlap, it is possible, when drawing within the client area of a child window, to draw within the client area of a neighboring child window.) For use with the WS_CHILD style only.

WS_DISABLED - Creates a window that is initially disabled.

WS_DLGFRAME - Creates a window with a double border but no title.

WS_HSCROLL - Creates a window that has a horizontal scroll bar.

WS_MAXIMIZE - Creates a window of maximum size.

WS_MAXIMIZEBOX - Creates a window that has a Maximize button.

WS_MINIMIZE - Creates a window that is initially minimized. For use with the WS_OVERLAPPED style only.

WS_MINIMIZEBOX - Creates a window that has a Minimize button.

WS_SYSMENU - Creates a window that has a System-menu box in its title bar. Used only for windows with title bars.

WS_THICKFRAME - Creates a window with a thick frame that can be used to size the window.

WS_VISIBLE - Creates a window that is initially visible. This applies to overlapped, child, and pop-up windows. For overlapped windows, the y parameter is used as a ShowWindow function parameter.

WS_VSCROLL - Creates a window that has a vertical scroll bar.

Note that one can determine the current styles of the main Viewer window using the Spy utility shipped with the Windows SDK. Choose Window\Window from Spy's menu. Then position the cursor over the main Viewer window. Spy will display the style of the window in the last line of the "Spy Window" dialog box.