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5 <head>
9 <title>
10 Scintilla and SciTE
11 </title>
12 </head>
15 <tr>
16 <td>
18 </td>
19 <td>
21 Component Design</font></a>
22 </td>
23 </tr>
24 </table>
25 <h2>
26 Top level structure
27 </h2>
28 <p>
29 Scintilla consists of three major layers of C++ code
30 </p>
31 <ul>
32 <li>
33 Portability Library
34 </li>
35 <li>
36 Core Code
37 </li>
38 <li>
39 Platform Events and API
40 </li>
41 </ul>
42 <p>
43 The primary purpose of this structure is to separate the platform dependent code from the
44 platform independent core code. This makes it easier to port Scintilla to a new platform and
45 ensures that most readers of the code do not have to deal with platform details. To minimise
46 portability problems and avoid code bloat, a conservative subset of C++ is used in Scintilla
47 with no exception handling, run time type information or use of the standard C++
48 library and with limited use of templates.
49 </p>
50 <p>
51 The currently supported platforms, Windows, GTK+/Linux and wxWindows are fairly similar in
52 many ways.
53 Each has windows, menus and bitmaps. These features generally work in similar ways so each
54 has a way to move a window or draw a red line. Sometimes one platform requires a sequence of
55 calls rather than a single call. At other times, the differences are more profound. Reading
56 the Windows clipboard occurs synchronously but reading the GTK+ clipboard requires a request
57 call that will be asynchronously answered with a message containing the clipboard data.
59 </p>
60 <br />
61 <h3>
62 Portability Library
63 </h3>
64 <p>
65 This is a fairly small and thin layer over the platform's native capabilities.
66 </p>
67 <p>
68 The portability library is defined in Platform.h and is implemented once for each platform.
69 PlatWin.cxx defines the Windows variants of the methods and PlatGTK.cxx the GTK+ variants.
70 </p>
71 <p>
72 Several of the classes here hold platform specific object identifiers and act as proxies to
73 these platform objects. Most client code can thus manipulate the platform objects without
74 caring which is the current platform. Sometimes client code needs access to the underlying
75 object identifiers and this is provided by the GetID method. The underlying types of the
76 platform specific identifiers are typedefed to common names to allow them to be transferred
77 around in client code where needed.
78 </p>
79 <h4>
80 Point, PRectangle
81 </h4>
82 <p>
83 These are simple classes provided to hold the commonly used geometric primitives. A
84 PRectangle follows the Mac / Windows convention of not including its bottom and right sides
85 instead of including all its sides as is normal in GTK+. It is not called Rectangle as this may be
86 the name of a macro on Windows.
87 </p>
88 <h4>
89 Colour, ColourPair, Palette
90 </h4>
91 <p>
92 Colour holds a platform specific colour identifier - COLORREF for Windows and GdkColor for
93 GTK+. The red, green and blue components that make up the colour are limited to the 8 bits of
94 precision available on Windows. ColourPairs are used because not all possible colours are
95 always available. Using an 8 bit colour mode, which is a common setting for both Windows and
96 GTK+, only 256 colours are possible on the display. Thus when an application asks for a dull
99 have to use the limited set of already available colours.
100 </p>
101 A Palette object holds a set of colour pairs and can make the appropriate calls to ask to
102 allocate these colours and to see what the platform has decided will be allowed.
103 <h4>
104 Font
105 </h4>
106 <p>
107 Font holds a platform specific font identifier - HFONT for Windows, GdkFont* for GTK+. It
108 does not own the identifier and so will not delete the platform font object in its
109 destructor. Client code should call Destroy at appropriate times.
110 </p>
111 <h4>
112 Surface
113 </h4>
114 <p>
115 Surface is an abstraction over each platform's concept of somewhere that graphical drawing
116 operations can be done. It may wrap an already created drawing place such as a window or be
117 used to create a bitmap that can be drawn into and later copied onto another surface. On
118 Windows it wraps a HDC and possibly a HBITMAP. On GTK+ it wraps a GdkDrawable* and possibly a
119 GdkPixmap*. Other platform specific objects are created (and correctly destroyed) whenever
120 required to perform drawing actions.
121 </p>
122 <p>
123 Drawing operations provided include drawing filled and unfilled polygons, lines, rectangles,
124 ellipses and text. The height and width of text as well as other details can be measured.
125 Operations can be clipped to a rectangle. Most of the calls are stateless with all parameters
126 being passed at each call. The exception to this is line drawing which is performed by
127 calling MoveTo and then LineTo.
128 </p>
129 <h4>
130 Window
131 </h4>
132 <p>
133 Window acts as a proxy to a platform window allowing operations such as showing, moving,
134 redrawing, and destroying to be performed. It contains a platform specific window identifier
135 - HWND for Windows, GtkWidget* for GTK+.
136 </p>
137 <h4>
138 ListBox
139 </h4>
140 <p>
141 ListBox is a subclass of Window and acts as a proxy to a platform listbox adding methods for
142 operations such as adding, retrieving, and selecting items.
143 </p>
144 <h4>
145 Menu
146 </h4>
147 <p>
148 Menu is a small helper class for constructing popup menus. It contains the platform specific
149 menu identifier - HMENU for Windows, GtkItemFactory* for GTK+. Most of the work in
150 constructing menus requires access to platform events and so is done in the Platform Events
151 and API layer.
152 </p>
153 <h4>
154 Platform
155 </h4>
156 <p>
157 The Platform class is used to access the facilities of the platform. System wide parameters
158 such as double click speed and chrome colour are available from Platform. Utility functions
159 such as DebugPrintf are also available from Platform.
160 </p>
161 <h3>
162 Core Code
163 </h3>
164 <p>
165 The bulk of Scintilla's code is platform independent. This is made up of the CellBuffer,
166 ContractionState, Document, Editor, Indicator, LineMarker, Style, ViewStyle, KeyMap,
167 ScintillaBase, CallTip,
168 and AutoComplete primary classes.
169 </p>
170 <h4>
171 CellBuffer
172 </h4>
173 <p>
174 A CellBuffer holds text and styling information, the undo stack, the assignment of line
175 markers to lines, and the fold structure.
176 </p>
177 <p>
178 A cell contains a character byte and its associated style byte. The current state of the
179 cell buffer is the sequence of cells that make up the text and a sequence of line information
180 containing the starting position of each line and any markers assigned to each line.
181 </p>
182 <p>
183 The undo stack holds a sequence of actions on the cell buffer. Each action is one of a text
184 insertion, a text deletion or an undo start action. The start actions are used to group
185 sequences of text insertions and deletions together so they can be undone together. To
186 perform an undo operation, each insertion or deletion is undone in reverse sequence.
187 Similarly, redo reapplies each action to the buffer in sequence. Whenever a character is
188 inserted in the buffer either directly through a call such as InsertString or through undo or
189 redo, its styling byte is initially set to zero. Client code is responsible for styling each
190 character whenever convenient. Styling information is not stored in undo actions.
191 </p>
192 <h4>
193 Document
194 </h4>
195 <p>
196 A document contains a CellBuffer and deals with some higher level abstractions such as
197 words, DBCS character sequences and line end character sequences. It is responsible for
198 managing the styling process and for notifying other objects when changes occur to the
199 document.
200 </p>
201 <h4>
202 Editor
203 </h4>
204 <p>
205 The Editor object is central to Scintilla. It is responsible for displaying a document and
206 responding to user actions and requests from the container. It uses ContractionState, Indicator,
207 LineMarker, Style, and ViewStyle objects to display the document and a KeyMap class to
208 map key presses to functions.
209 The visibility of each line is kept in the ContractionState which is also responsible for mapping
210 from display lines to documents lines and vice versa.
211 </p>
212 <p>
213 There may be multiple Editor objects attached to one Document object. Changes to a
214 document are broadcast to the editors through the DocWatcher mechanism.
215 </p>
216 <h4>
217 ScintillaBase
218 </h4>
219 <p>
220 ScintillaBase is a subclass of Editor and adds extra windowing features including display of
221 calltips, autocompletion lists and context menus. These features use CallTip and AutoComplete
222 objects. This class is optional so a lightweight implementation of Scintilla may bypass it if
223 the added functionality is not required.
224 </p>
225 <h3>
226 Platform Events and API
227 </h3>
228 <p>
229 Each platform uses different mechanisms for receiving events. On Windows, events are
230 received through messages and COM. On GTK+, callback functions are used.
231 </p>
232 <p>
233 For each platform, a class is derived from ScintillaBase (and thus from Editor). This is
234 ScintillaWin on Windows and ScintillaGTK on GTK+. These classes are responsible for
235 connecting to the platforms event mechanism and also to implement some virtual methods in
236 Editor and ScintillaBase which are different on the platforms. For example, this layer has to
237 support this difference between the synchronous Windows clipboard and the asynchronous GTK+
238 clipboard.
239 </p>
240 <p>
241 The external API is defined in this layer as each platform has different preferred styles of
242 API - messages on Windows and function calls on GTK+. This also allows multiple APIs to be
243 defined on a platform. The currently available API on GTK+ is similar to the Windows API and
244 does not follow platform conventions well. A second API could be implemented here that did
245 follow platform conventions.
246 </p>
247 </body>
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