wxWidgets/docs/doxygen/overviews/scrolling.h

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// Name:        scrolling
// Purpose:     topic overview
// Author:      wxWidgets team
// RCS-ID:      $Id$
// Licence:     wxWindows license
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/*!

 @page scrolling_overview Scrolling overview

 Classes: #wxWindow, #wxScrolledWindow, #wxIcon, #wxScrollBar.
 Scrollbars come in various guises in wxWidgets. All windows have the potential
 to show a vertical scrollbar and/or a horizontal scrollbar: it is a basic capability of a window.
 However, in practice, not all windows do make use of scrollbars, such as a single-line wxTextCtrl.
 Because any class derived from  #wxWindow may have scrollbars,
 there are functions to manipulate the scrollbars and event handlers to intercept
 scroll events. But just because a window generates a scroll event, doesn't mean
 that the window necessarily handles it and physically scrolls the window. The base class
 wxWindow in fact doesn't have any default functionality to handle scroll events.
 If you created a wxWindow object with scrollbars, and then clicked on the scrollbars, nothing
 at all would happen. This is deliberate, because the @e interpretation of scroll
 events varies from one window class to another.
 #wxScrolledWindow (formerly wxCanvas) is an example of a window that
 adds functionality to make scrolling really work. It assumes that scrolling happens in
 consistent units, not different-sized jumps, and that page size is represented
 by the visible portion of the window. It is suited to drawing applications, but perhaps
 not so suitable for a sophisticated editor in which the amount scrolled may vary according
 to the size of text on a given line. For this, you would derive from wxWindow and
 implement scrolling yourself. #wxGrid is an example of a class
 that implements its own scrolling, largely because columns and rows can vary in size.
 @b The scrollbar model
 The function wxWindow::SetScrollbar gives a clue about
 the way a scrollbar is modeled. This function takes the following arguments:






 orientation




 Which scrollbar: wxVERTICAL or wxHORIZONTAL.





 position




 The position of the scrollbar in scroll units.





 visible




 The size of the visible portion of the scrollbar, in scroll units.





 range




 The maximum position of the scrollbar.





 refresh




 Whether the scrollbar should be repainted.




 @e orientation determines whether we're talking about
 the built-in horizontal or vertical scrollbar.
 @e position is simply the position of the 'thumb' (the bit you drag to scroll around).
 It is given in scroll units, and so is relative to the total range of the scrollbar.
 @e visible gives the number of scroll units that represents the portion of the
 window currently visible. Normally, a scrollbar is capable of indicating this visually
 by showing a different length of thumb.
 @e range is the maximum value of the scrollbar, where zero is the start
 position. You choose the units that suit you,
 so if you wanted to display text that has 100 lines, you would set this to 100.
 Note that this doesn't have to correspond to the number of pixels scrolled - it is
 up to you how you actually show the contents of the window.
 @e refresh just indicates whether the scrollbar should be repainted immediately or not.
 @b An example
 Let's say you wish to display 50 lines of text, using the same font.
 The window is sized so that you can only see 16 lines at a time.
 You would use:

 @code
 SetScrollbar(wxVERTICAL, 0, 16, 50);
 @endcode


 Note that with the window at this size, the thumb position can never go
 above 50 minus 16, or 34.
 You can determine how many lines are currently visible by dividing the current view
 size by the character height in pixels.
 When defining your own scrollbar behaviour, you will always need to recalculate
 the scrollbar settings when the window size changes. You could therefore put your
 scrollbar calculations and SetScrollbar
 call into a function named AdjustScrollbars, which can be called initially and also
 from your #wxSizeEvent handler function.

 */