docs/doxygen/overviews/scrolling.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        scrolling.h
   3 // Purpose:     topic overview
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /*!
  10
  11 @page overview_scrolling Scrolling Overview
  12
  13 Classes:
  14 @li wxWindow
  15 @li wxScrolledWindow
  16 @li wxScrollBar
  17
  18 Scrollbars come in various guises in wxWidgets. All windows have the potential
  19 to show a vertical scrollbar and/or a horizontal scrollbar: it is a basic
  20 capability of a window. However, in practice, not all windows do make use of
  21 scrollbars, such as a single-line wxTextCtrl.
  22
  23 Because any class derived from wxWindow may have scrollbars, there are
  24 functions to manipulate the scrollbars and event handlers to intercept scroll
  25 events. But just because a window generates a scroll event, doesn't mean that
  26 the window necessarily handles it and physically scrolls the window. The base
  27 class wxWindow in fact doesn't have any default functionality to handle scroll
  28 events. If you created a wxWindow object with scrollbars, and then clicked on
  29 the scrollbars, nothing at all would happen. This is deliberate, because the
  30 @e interpretation of scroll events varies from one window class to another.
  31
  32 wxScrolledWindow (formerly wxCanvas) is an example of a window that adds
  33 functionality to make scrolling really work. It assumes that scrolling happens
  34 in consistent units, not different-sized jumps, and that page size is
  35 represented by the visible portion of the window. It is suited to drawing
  36 applications, but perhaps not so suitable for a sophisticated editor in which
  37 the amount scrolled may vary according to the size of text on a given line. For
  38 this, you would derive from wxWindow and implement scrolling yourself. wxGrid
  39 is an example of a class that implements its own scrolling, largely because
  40 columns and rows can vary in size.
  41
  42
  43 @section overview_scrolling_model The Scrollbar Model
  44
  45 The function wxWindow::SetScrollbar gives a clue about the way a scrollbar is
  46 modeled. This function takes the following arguments:
  47
  48 @beginTable
  49 @row2col{ @c orientation , Which scrollbar: wxVERTICAL or wxHORIZONTAL. }
  50 @row2col{ @c position , The position of the scrollbar in scroll units. }
  51 @row2col{ @c visible , The size of the visible portion of the scrollbar,
  52                        in scroll units. }
  53 @row2col{ @c range , The maximum position of the scrollbar. }
  54 @row2col{ @c refresh , Whether the scrollbar should be repainted. }
  55 @endTable
  56
  57 @c orientation determines whether we're talking about the built-in horizontal
  58 or vertical scrollbar.
  59
  60 @c position is simply the position of the 'thumb' (the bit you drag to scroll
  61 around). It is given in scroll units, and so is relative to the total range of
  62 the scrollbar.
  63
  64 @c visible gives the number of scroll units that represents the portion of the
  65 window currently visible. Normally, a scrollbar is capable of indicating this
  66 visually by showing a different length of thumb.
  67
  68 @c range is the maximum value of the scrollbar, where zero is the start
  69 position. You choose the units that suit you, so if you wanted to display text
  70 that has 100 lines, you would set this to 100. Note that this doesn't have to
  71 correspond to the number of pixels scrolled - it is up to you how you actually
  72 show the contents of the window.
  73
  74 @c refresh just indicates whether the scrollbar should be repainted immediately
  75 or not.
  76
  77
  78 @section overview_scrolling_example An Example
  79
  80 Let's say you wish to display 50 lines of text, using the same font. The window
  81 is sized so that you can only see 16 lines at a time. You would use:
  82
  83 @code
  84 SetScrollbar(wxVERTICAL, 0, 16, 50);
  85 @endcode
  86
  87 Note that with the window at this size, the thumb position can never go above
  88 50 minus 16, or 34. You can determine how many lines are currently visible by
  89 dividing the current view size by the character height in pixels.
  90
  91 When defining your own scrollbar behaviour, you will always need to recalculate
  92 the scrollbar settings when the window size changes. You could therefore put
  93 your scrollbar calculations and SetScrollbar call into a function named
  94 AdjustScrollbars, which can be called initially and also from your wxSizeEvent
  95 handler function.
  96
  97 */
  98