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246 lines
11 KiB
246 lines
11 KiB
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Scintilla and SciTE |
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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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</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, Cocoa, Qt, and wxWidgets 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 wxWidgets platform is available from the <a href="http://wxwidgets.org/">wxWidgets 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 Geometry.h and 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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ColourDesired |
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</h4> |
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<p> |
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This is a simple class holding an expected colour. It is internally represented as a single |
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32 bit integer in BGR format with 8 bits per colour, but also provides a convenient API to fetch |
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each component separately. |
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As a platform might not be able to represent the exact desired colour if it doesn't have 24 bit |
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depth available, it might not actually represent the exact desired colour but select a best fit |
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that it can actually render. |
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</p> |
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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, PangoFontDescription* 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 cairo_surface_t*. |
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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, GtkMenu* 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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