mirror of
https://github.com/scratchfoundation/bgfx.git
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250 lines
11 KiB
HTML
250 lines
11 KiB
HTML
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<?xml version="1.0"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta name="generator" content="HTML Tidy, see www.w3.org" />
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<meta name="generator" content="SciTE" />
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
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<title>
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Scintilla and SciTE
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</title>
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</head>
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<body bgcolor="#FFFFFF" text="#000000">
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<table bgcolor="#000000" width="100%" cellspacing="0" cellpadding="0" border="0">
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<tr>
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<td>
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<img src="SciTEIco.png" border="3" height="64" width="64" alt="Scintilla icon" />
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</td>
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<td>
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<a href="index.html" style="color:white;text-decoration:none"><font size="5">Scintilla
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Component Design</font></a>
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</td>
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</tr>
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</table>
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<h2>
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Top level structure
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</h2>
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<p>
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Scintilla consists of three major layers of C++ code
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</p>
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<ul>
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<li>
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Portability Library
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</li>
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<li>
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Core Code
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</li>
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<li>
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Platform Events and API
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</li>
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</ul>
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<p>
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The primary purpose of this structure is to separate the platform dependent code from the
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platform independent core code. This makes it easier to port Scintilla to a new platform and
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ensures that most readers of the code do not have to deal with platform details. To minimise
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portability problems and avoid code bloat, a conservative subset of C++ is used in Scintilla
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with no exception handling, run time type information or use of the standard C++
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library and with limited use of templates.
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</p>
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<p>
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The currently supported platforms, Windows, GTK+/Linux and wxWindows are fairly similar in
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many ways.
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Each has windows, menus and bitmaps. These features generally work in similar ways so each
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has a way to move a window or draw a red line. Sometimes one platform requires a sequence of
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calls rather than a single call. At other times, the differences are more profound. Reading
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the Windows clipboard occurs synchronously but reading the GTK+ clipboard requires a request
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call that will be asynchronously answered with a message containing the clipboard data.
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The wxWindows platform is available from the <a href="http://wxwindows.org/">wxWindows site</a>
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</p>
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<br />
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<h3>
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Portability Library
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</h3>
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<p>
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This is a fairly small and thin layer over the platform's native capabilities.
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</p>
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<p>
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The portability library is defined in Platform.h and is implemented once for each platform.
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PlatWin.cxx defines the Windows variants of the methods and PlatGTK.cxx the GTK+ variants.
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</p>
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<p>
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Several of the classes here hold platform specific object identifiers and act as proxies to
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these platform objects. Most client code can thus manipulate the platform objects without
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caring which is the current platform. Sometimes client code needs access to the underlying
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object identifiers and this is provided by the GetID method. The underlying types of the
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platform specific identifiers are typedefed to common names to allow them to be transferred
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around in client code where needed.
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</p>
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<h4>
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Point, PRectangle
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</h4>
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<p>
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These are simple classes provided to hold the commonly used geometric primitives. A
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PRectangle follows the Mac / Windows convention of not including its bottom and right sides
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instead of including all its sides as is normal in GTK+. It is not called Rectangle as this may be
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the name of a macro on Windows.
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</p>
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<h4>
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Colour, ColourPair, Palette
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</h4>
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<p>
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Colour holds a platform specific colour identifier - COLORREF for Windows and GdkColor for
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GTK+. The red, green and blue components that make up the colour are limited to the 8 bits of
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precision available on Windows. ColourPairs are used because not all possible colours are
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always available. Using an 8 bit colour mode, which is a common setting for both Windows and
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GTK+, only 256 colours are possible on the display. Thus when an application asks for a dull
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red, say #400000, it may only be allocated an already available colour such as #800000 or
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#330000. With 16 or 2 colour modes even less choice is available and the application will
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have to use the limited set of already available colours.
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</p>
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A Palette object holds a set of colour pairs and can make the appropriate calls to ask to
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allocate these colours and to see what the platform has decided will be allowed.
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<h4>
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Font
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</h4>
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<p>
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Font holds a platform specific font identifier - HFONT for Windows, GdkFont* for GTK+. It
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does not own the identifier and so will not delete the platform font object in its
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destructor. Client code should call Destroy at appropriate times.
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</p>
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<h4>
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Surface
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</h4>
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<p>
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Surface is an abstraction over each platform's concept of somewhere that graphical drawing
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operations can be done. It may wrap an already created drawing place such as a window or be
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used to create a bitmap that can be drawn into and later copied onto another surface. On
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Windows it wraps a HDC and possibly a HBITMAP. On GTK+ it wraps a GdkDrawable* and possibly a
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GdkPixmap*. Other platform specific objects are created (and correctly destroyed) whenever
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required to perform drawing actions.
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</p>
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<p>
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Drawing operations provided include drawing filled and unfilled polygons, lines, rectangles,
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ellipses and text. The height and width of text as well as other details can be measured.
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Operations can be clipped to a rectangle. Most of the calls are stateless with all parameters
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being passed at each call. The exception to this is line drawing which is performed by
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calling MoveTo and then LineTo.
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</p>
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<h4>
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Window
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</h4>
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<p>
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Window acts as a proxy to a platform window allowing operations such as showing, moving,
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redrawing, and destroying to be performed. It contains a platform specific window identifier
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- HWND for Windows, GtkWidget* for GTK+.
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</p>
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<h4>
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ListBox
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</h4>
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<p>
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ListBox is a subclass of Window and acts as a proxy to a platform listbox adding methods for
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operations such as adding, retrieving, and selecting items.
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</p>
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<h4>
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Menu
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</h4>
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<p>
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Menu is a small helper class for constructing popup menus. It contains the platform specific
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menu identifier - HMENU for Windows, GtkItemFactory* for GTK+. Most of the work in
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constructing menus requires access to platform events and so is done in the Platform Events
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and API layer.
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</p>
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<h4>
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Platform
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</h4>
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<p>
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The Platform class is used to access the facilities of the platform. System wide parameters
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such as double click speed and chrome colour are available from Platform. Utility functions
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such as DebugPrintf are also available from Platform.
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</p>
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<h3>
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Core Code
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</h3>
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<p>
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The bulk of Scintilla's code is platform independent. This is made up of the CellBuffer,
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ContractionState, Document, Editor, Indicator, LineMarker, Style, ViewStyle, KeyMap,
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ScintillaBase, CallTip,
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and AutoComplete primary classes.
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</p>
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<h4>
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CellBuffer
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</h4>
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<p>
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A CellBuffer holds text and styling information, the undo stack, the assignment of line
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markers to lines, and the fold structure.
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</p>
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<p>
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A cell contains a character byte and its associated style byte. The current state of the
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cell buffer is the sequence of cells that make up the text and a sequence of line information
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containing the starting position of each line and any markers assigned to each line.
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</p>
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<p>
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The undo stack holds a sequence of actions on the cell buffer. Each action is one of a text
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insertion, a text deletion or an undo start action. The start actions are used to group
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sequences of text insertions and deletions together so they can be undone together. To
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perform an undo operation, each insertion or deletion is undone in reverse sequence.
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Similarly, redo reapplies each action to the buffer in sequence. Whenever a character is
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inserted in the buffer either directly through a call such as InsertString or through undo or
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redo, its styling byte is initially set to zero. Client code is responsible for styling each
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character whenever convenient. Styling information is not stored in undo actions.
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</p>
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<h4>
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Document
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</h4>
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<p>
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A document contains a CellBuffer and deals with some higher level abstractions such as
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words, DBCS character sequences and line end character sequences. It is responsible for
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managing the styling process and for notifying other objects when changes occur to the
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document.
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</p>
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<h4>
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Editor
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</h4>
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<p>
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The Editor object is central to Scintilla. It is responsible for displaying a document and
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responding to user actions and requests from the container. It uses ContractionState, Indicator,
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LineMarker, Style, and ViewStyle objects to display the document and a KeyMap class to
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map key presses to functions.
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The visibility of each line is kept in the ContractionState which is also responsible for mapping
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from display lines to documents lines and vice versa.
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</p>
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<p>
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There may be multiple Editor objects attached to one Document object. Changes to a
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document are broadcast to the editors through the DocWatcher mechanism.
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</p>
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<h4>
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ScintillaBase
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</h4>
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<p>
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ScintillaBase is a subclass of Editor and adds extra windowing features including display of
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calltips, autocompletion lists and context menus. These features use CallTip and AutoComplete
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objects. This class is optional so a lightweight implementation of Scintilla may bypass it if
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the added functionality is not required.
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</p>
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<h3>
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Platform Events and API
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</h3>
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<p>
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Each platform uses different mechanisms for receiving events. On Windows, events are
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received through messages and COM. On GTK+, callback functions are used.
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</p>
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<p>
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For each platform, a class is derived from ScintillaBase (and thus from Editor). This is
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ScintillaWin on Windows and ScintillaGTK on GTK+. These classes are responsible for
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connecting to the platforms event mechanism and also to implement some virtual methods in
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Editor and ScintillaBase which are different on the platforms. For example, this layer has to
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support this difference between the synchronous Windows clipboard and the asynchronous GTK+
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clipboard.
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</p>
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<p>
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The external API is defined in this layer as each platform has different preferred styles of
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API - messages on Windows and function calls on GTK+. This also allows multiple APIs to be
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defined on a platform. The currently available API on GTK+ is similar to the Windows API and
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does not follow platform conventions well. A second API could be implemented here that did
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follow platform conventions.
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</p>
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</body>
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</html>
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