96 lines
4.1 KiB
C++
96 lines
4.1 KiB
C++
/////////////////////////////////////////////////////////////////////////////
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// Name: scrolling.h
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// Purpose: topic overview
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// Author: wxWidgets team
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// Licence: wxWindows licence
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/////////////////////////////////////////////////////////////////////////////
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/**
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@page overview_scrolling Scrolled Windows
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@tableofcontents
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Scrollbars come in various guises in wxWidgets. All windows have the potential
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to show a vertical scrollbar and/or a horizontal scrollbar: it is a basic
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capability of a window. However, in practice, not all windows do make use of
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scrollbars, such as a single-line wxTextCtrl.
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Because any class derived from wxWindow may have scrollbars, there are
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functions to manipulate the scrollbars and event handlers to intercept scroll
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events. But just because a window generates a scroll event, doesn't mean that
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the window necessarily handles it and physically scrolls the window. The base
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class wxWindow in fact doesn't have any default functionality to handle scroll
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events. If you created a wxWindow object with scrollbars, and then clicked on
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the scrollbars, nothing at all would happen. This is deliberate, because the
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@e interpretation of scroll events varies from one window class to another.
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::wxScrolledWindow (formerly wxCanvas) is an example of a window that adds
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functionality to make scrolling really work. It assumes that scrolling happens
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in consistent units, not different-sized jumps, and that page size is
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represented by the visible portion of the window. It is suited to drawing
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applications, but perhaps not so suitable for a sophisticated editor in which
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the amount scrolled may vary according to the size of text on a given line. For
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this, you would derive from wxWindow and implement scrolling yourself. wxGrid
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is an example of a class that implements its own scrolling, largely because
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columns and rows can vary in size.
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@see wxScrollBar
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@section overview_scrolling_model The Scrollbar Model
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The function wxWindow::SetScrollbar gives a clue about the way a scrollbar is
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modeled. This function takes the following arguments:
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@beginTable
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@row2col{ @c orientation , Which scrollbar: wxVERTICAL or wxHORIZONTAL. }
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@row2col{ @c position , The position of the scrollbar in scroll units. }
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@row2col{ @c visible , The size of the visible portion of the scrollbar,
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in scroll units. }
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@row2col{ @c range , The maximum position of the scrollbar. }
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@row2col{ @c refresh , Whether the scrollbar should be repainted. }
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@endTable
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@c orientation determines whether we're talking about the built-in horizontal
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or vertical scrollbar.
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@c position is simply the position of the 'thumb' (the bit you drag to scroll
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around). It is given in scroll units, and so is relative to the total range of
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the scrollbar.
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@c visible gives the number of scroll units that represents the portion of the
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window currently visible. Normally, a scrollbar is capable of indicating this
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visually by showing a different length of thumb.
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@c range is the maximum value of the scrollbar, where zero is the start
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position. You choose the units that suit you, so if you wanted to display text
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that has 100 lines, you would set this to 100. Note that this doesn't have to
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correspond to the number of pixels scrolled - it is up to you how you actually
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show the contents of the window.
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@c refresh just indicates whether the scrollbar should be repainted immediately
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or not.
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@section overview_scrolling_example An Example
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Let's say you wish to display 50 lines of text, using the same font. The window
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is sized so that you can only see 16 lines at a time. You would use:
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@code
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SetScrollbar(wxVERTICAL, 0, 16, 50);
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@endcode
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Note that with the window at this size, the thumb position can never go above
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50 minus 16, or 34. You can determine how many lines are currently visible by
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dividing the current view size by the character height in pixels.
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When defining your own scrollbar behaviour, you will always need to recalculate
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the scrollbar settings when the window size changes. You could therefore put
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your scrollbar calculations and SetScrollbar call into a function named
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AdjustScrollbars, which can be called initially and also from your wxSizeEvent
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handler function.
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*/
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