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Automatic Syntax Highlighting

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Brandon Desjarlais edited this page Dec 27, 2023 · 3 revisions

Far and away the most popular use for Scintilla is to display and edit source code. Out-of-the-box, Scintilla comes with syntax highlighting support for over 100 different languages. Chances are that the language you want to edit is already supported.

NOTE: At tool has been created by user @uf6429 to aid in the creation of some of the syntax highlighting code presented below. You can find the "ScintillaNET Kitchen" at https://github.com/uuf6429/ScintillaNET-Kitchen.

Selecting a Lexer

A language processor is referred to as a 'lexer' in Scintilla. Without going too much into parser theory, it's important to know that a lexer performs lexical analysis of a language, not syntatic analysis (parsing). In short, this means that the language support provided by Scintilla is enough to break the text into tokens and provide syntax highlighting, but not interpret what those tokens mean or whether they form an actual program. The distinction is important because developers using Scintilla often want to know how they can highlight incorrect code. Scintilla doesn't do that. If you want more than basic syntax highlighting, you'll need to couple Scintilla with a parser or even a background compiler.

To inform Scintilla what the current language is you must set the LexerName property to the appropriate string value. In some cases multiple languages share the same LexerName value because these language share the same lexical grammar. For example, the Cpp lexer not only provides language support for C++, but all for C, C#, Java, JavaScript and others--because they are lexically similar. In our example we want to do C# syntax highlighting so we'll use the Cpp lexer.

scintilla.LexerName = "cpp";

Defining Styles

The process of doing syntax highlighting in Scintilla is referred to as styling. When the text is styled, runs of text are assigned a numeric style definition in the Styles collection. For example, keywords may be assigned the style definition 1, while operators may be assigned the definition 2. It's entirely up to the lexer how this is done. Once done, however, you are then free to determine what style 1 or 2 look like. The lexer assigns the styles, but you define the style appearance. To make it easier to know which styles definitions a lexer will use, the Style object contains static constants that coincide with each Lexer enumeration value. For example, if we were using the Cpp lexer and wanted to set the style for single-line comments (//...) we would use the Style.Cpp.CommentLine constant to set the appropriate style in the Styles collection:

scintilla.Styles[Style.Cpp.CommentLine].Font = "Consolas";
scintilla.Styles[Style.Cpp.CommentLine].Size = 10;
scintilla.Styles[Style.Cpp.CommentLine].ForeColor = Color.FromArgb(0, 128, 0); // Green

To set the string style we would:

scintilla.Styles[Style.Cpp.String].Font = "Consolas";
scintilla.Styles[Style.Cpp.String].Size = 10;
scintilla.Styles[Style.Cpp.String].ForeColor = Color.FromArgb(163, 21, 21); // Red

To set the styles for number tokens we would do the same thing using the Style.Cpp.Number constant. For operators, we would use Style.Cpp.Operator, and so on.

If you use your imagination you will begin to see how doing this for each possible lexer token could be tedious. There is a lot of repetition. To reduce the amount of code you have to write Scintilla provides a way of setting a single style and then applying its appearance to every style in the collection. The general process is to:

  • Reset the Default style using StyleResetDefault.
  • Configure the Default style with all common properties.
  • Use the StyleClearAll method to apply the Default style to all styles.
  • Set any individual style properties

Using that time saving approach, we can set the appearance of our C# lexer styles like so:

// Configuring the default style with properties
// we have common to every lexer style saves time.
scintilla.StyleResetDefault();
scintilla.Styles[Style.Default].Font = "Consolas";
scintilla.Styles[Style.Default].Size = 10;
scintilla.StyleClearAll();

// Configure the CPP (C#) lexer styles
scintilla.Styles[Style.Cpp.Default].ForeColor = Color.Silver;
scintilla.Styles[Style.Cpp.Comment].ForeColor = Color.FromArgb(0, 128, 0); // Green
scintilla.Styles[Style.Cpp.CommentLine].ForeColor = Color.FromArgb(0, 128, 0); // Green
scintilla.Styles[Style.Cpp.CommentLineDoc].ForeColor = Color.FromArgb(128, 128, 128); // Gray
scintilla.Styles[Style.Cpp.Number].ForeColor = Color.Olive;
scintilla.Styles[Style.Cpp.Word].ForeColor = Color.Blue;
scintilla.Styles[Style.Cpp.Word2].ForeColor = Color.Blue;
scintilla.Styles[Style.Cpp.String].ForeColor = Color.FromArgb(163, 21, 21); // Red
scintilla.Styles[Style.Cpp.Character].ForeColor = Color.FromArgb(163, 21, 21); // Red
scintilla.Styles[Style.Cpp.Verbatim].ForeColor = Color.FromArgb(163, 21, 21); // Red
scintilla.Styles[Style.Cpp.StringEol].BackColor = Color.Pink;
scintilla.Styles[Style.Cpp.Operator].ForeColor = Color.Purple;
scintilla.Styles[Style.Cpp.Preprocessor].ForeColor = Color.Maroon;

Setting Keywords

The last thing we need to do to provide syntax highlighting is to inform the lexer what the language keywords and identifiers are. Since languages can often add keywords year after year, or because a lexer may sometimes be used for more than one language, it makes sense to make the keyword list configurable.

Since each Scintilla lexer is like a program until itself the number of keyword sets and the definition of each one vary from lexer to lexer. To determine what keyword sets a lexer supports you can call the DescribeKeywordSets method. This prints a human readable explanation of how many sets the current Lexer supports and what each means:

scintilla.Lexer = Lexer.Cpp;
Console.WriteLine(scintilla.DescribeKeywordSets());

// Outputs:
// Primary keywords and identifiers
// Secondary keywords and identifiers
// Documentation comment keywords
// Global classes and typedefs
// Preprocessor definitions
// Task marker and error marker keywords

Based on the output of DescribeKeywordSets I can determine that the first two sets are what I'm interested in for supporting general purpose C# syntax highlighting. To set a set of keywords you call the SetKeywords method. What 'primary' and 'secondary' means in the keyword set description is up to a bit of interpretation, but I'll break it down so that primary keywords are C# language keywords and secondary keywords are known .NET types. To set those I would call:

scintilla.SetKeywords(0, "abstract as base break case catch checked continue default delegate do else event explicit extern false finally fixed for foreach goto if implicit in interface internal is lock namespace new null object operator out override params private protected public readonly ref return sealed sizeof stackalloc switch this throw true try typeof unchecked unsafe using virtual while");
scintilla.SetKeywords(1, "bool byte char class const decimal double enum float int long sbyte short static string struct uint ulong ushort void");

NOTE: Keywords in a keyword set can be separated by any combination of whitespace (space, tab, '\r', '\n') characters.

Wondering where I got the list of keywords above? I typically pull them from the SciTE project .properties files -- a companion to Scintilla. The same could be done looking at the Notepad++ langs.model.xml file or any number of other text editors if you wanted to avoid going through the documentation for a language.

Complete Recipe

The complete recipe below will give you C# syntax highlighting using colors roughly equivalent to the Visual Studio defaults.

// Configuring the default style with properties
// we have common to every lexer style saves time.
scintilla.StyleResetDefault();
scintilla.Styles[Style.Default].Font = "Consolas";
scintilla.Styles[Style.Default].Size = 10;
scintilla.StyleClearAll();

// Configure the CPP (C#) lexer styles
scintilla.Styles[Style.Cpp.Default].ForeColor = Color.Silver;
scintilla.Styles[Style.Cpp.Comment].ForeColor = Color.FromArgb(0, 128, 0); // Green
scintilla.Styles[Style.Cpp.CommentLine].ForeColor = Color.FromArgb(0, 128, 0); // Green
scintilla.Styles[Style.Cpp.CommentLineDoc].ForeColor = Color.FromArgb(128, 128, 128); // Gray
scintilla.Styles[Style.Cpp.Number].ForeColor = Color.Olive;
scintilla.Styles[Style.Cpp.Word].ForeColor = Color.Blue;
scintilla.Styles[Style.Cpp.Word2].ForeColor = Color.Blue;
scintilla.Styles[Style.Cpp.String].ForeColor = Color.FromArgb(163, 21, 21); // Red
scintilla.Styles[Style.Cpp.Character].ForeColor = Color.FromArgb(163, 21, 21); // Red
scintilla.Styles[Style.Cpp.Verbatim].ForeColor = Color.FromArgb(163, 21, 21); // Red
scintilla.Styles[Style.Cpp.StringEol].BackColor = Color.Pink;
scintilla.Styles[Style.Cpp.Operator].ForeColor = Color.Purple;
scintilla.Styles[Style.Cpp.Preprocessor].ForeColor = Color.Maroon;
scintilla.LexerName = "cpp";

// Set the keywords
scintilla.SetKeywords(0, "abstract as base break case catch checked continue default delegate do else event explicit extern false finally fixed for foreach goto if implicit in interface internal is lock namespace new null object operator out override params private protected public readonly ref return sealed sizeof stackalloc switch this throw true try typeof unchecked unsafe using virtual while");
scintilla.SetKeywords(1, "bool byte char class const decimal double enum float int long sbyte short static string struct uint ulong ushort void");

NOTE: Our Wiki includes a number of User-Submitted Recipes that illustrate syntax highlighting in combination with other language features.

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