1.8.4 Processing Scroll Messages

A window that permits scrolling needs a standard scroll bar or a scroll-bar control to let the user generate scrolling requests, and it needs a window procedure to process the WM_HSCROLL and WM_VSCROLL messages that represent the scrolling requests. Although the result of a scrolling request depends entirely on how the window processes it, a window typically carries out a scroll operation by moving through the application's displayed information in some direction from the current location or to a known beginning or end and by displaying the data at the new location. For example, a word-processing application can scroll to the next line, the next page, or to the end of the document.