VT Sequences

We need to filter and build the VT sequences.

In your own terminal emulator, VT sequences are the power of any terminal emulator found in literally every PC.

This feature provides several filtering and manipulation tools which allow you to perform these operations on strings that contain escape sequences under the Terminaux.Sequences namespace.

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VT sequence types

Each type of VT sequence contain their own class files that stores sequence generation functions based on the given action and argument. Here are a list of supported sequence types:

Sequence type	Description
APC sequences	Application program command
C1 sequences	8-bit control characters
CSI sequences	Controls beginning with control sequence introducer
DCS sequences	Device control
ESC sequences	Controls beginning with ESC
OSC sequences	Operating system command sequences
PM sequences	Privacy message

To learn more about these sequences, visit the below page:

ctlseqs(ms)invisible-island.net

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Usage

Place the using Terminaux.Sequences; clause at the top of the file that you want to call these functions in. You need to put the class name VtSequenceTools before the function name mentioned above so that it looks like this:

char EscapeChar = Convert.ToChar(0x1b);
string vtSequence1 = $"{EscapeChar}[38;5;43m";
string filtered = VtSequenceTools.FilterVTSequences($"Hello!{vtSequence1}");
TextWriterRaw.WritePlain(filtered);

Here are some of the common tools. Expand one of the expandables to get more info.

Available functions

Currently, these tools are provided:

Function	Description
FilterVTSequences()	Filters all of the VT sequences that are of either a single type or of multiple types
MatchVTSequences()	Matches all of the VT sequences that are of either a single type or of multiple types
IsMatchVTSequences()	Does the string contain all of the VT sequences or a VT sequence of one or more types?
IsMatchVTSequencesSpecific()	Does the string contain all of the VT sequences or a VT sequence of any specific type?
SplitVTSequences()	Splits all of the VT sequences that are either of a single type or of multiple types
DetermineTypeFromText()	Determines the VT sequence type from the given text

Sequence builder

Terminaux offers a Builder namespace that contains building blocks for building a VT sequence for your console applications.

It starts with VtSequenceBasicChars which allows you to get a variety of starting-point characters for your VT sequence in case you want to manually build the sequence yourself.

Here are the available characters:

Character code	Character number	Character property
BEL	\x07	BellChar
BS	\x08	BackspaceChar
CR	\x0D	CarriageReturnChar
ENQ	\x05	ReturnTerminalStatusChar
FF	\x0C	FormFeedChar
LF	\x0A	LineFeedChar
SI	\x0F	StandardCharacterSetChar
SO	\x0E	AlternateCharacterSetChar
SP	" "	SpaceChar
TAB	\x09	HorizontalTabChar
VT	\x0B	VerticalTabChar
ESC	\x1B	EscapeChar
ST	\x9C	StChar
CSI	\x9B	CsiChar
OSC	\x9D	OSCChar
APC	\x9F	APCChar
DCS	\x90	DCSChar
PM	\x9E	PMChar

The builder also provides a powerful tool which allows you to build almost any VT sequence using only the arguments and the specific type of VT sequence (Character attributes for example). This tool is found inside the VtSequenceBuilderTools class under the Terminaux.Sequences.Builder namespace.

Currently, it provides these tools:

Function	Description	Returns
BuildVtSequence()	Builds a VT sequence	A string consisting of a VT sequence of the requested type with the requested arguments
DetermineTypesFromSequence()	Determines the types from a VT sequence	An enumerable containing a list of types and specific types

Operations

When Terminaux tokenizes all VT sequences found in a target text, one of the below operations happen.

There are currently four types of operations.

Operation
Filtering	FilterVTSequences() replaces the found sequences with blanks. You can optionally replace it with something, like a text, a syntax, or even another VT sequence.
Matching	MatchVTSequences() gets all the matched sequences. You can then wrap the values in the for or the foreach loop to get information for each sequence.
Querying	IsMatchVTSequences() checks the text to see if any part of the text is a VT sequence.
	IsMatchVTSequencesSpecific() checks the text for any specific VT sequence type.
Splitting	SplitVTSequences() splits the text with the VT sequences as delimiters.

Usage in console writers for Mono

All console writers internally use the VT sequence filtering tools, like GetFilteredPositions(), to be able to determine the exact text position. This is to work around Linux Mono installs that report wrong position when VT sequences are appended.

This workaround was not necessary as of the modern .NET implementation, but the workaround is still in place, because Terminaux targets .NET Standard, which means that it can be used for .NET Framework console projects, and, thus, Mono on Linux.

It works by seeking through every visible letter from the text in the form of "advancing" so that GetFilteredPositions() can make sure that the filtered positions are actually correct and sought "to the last letter" rather than "past the last letter" that Mono and the normal Console.Write() and Console.WriteLine() functions were suffering.