term

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 Go to latest Published: Jan 10, 2026 License: Apache-2.0 Imports: 11 Imported by: 0

Documentation

Overview

Package term provides terminal management for VT220-compatible terminals. It handles character set designation, invocation (shifting), and provides an io.Writer interface for encoding UTF-8 text to the terminal's character set.

Index

Constants

This section is empty.

Variables

View Source 
var (
	// ErrInvalidRegister is returned when an invalid register index is specified.
	ErrInvalidRegister = errors.New("invalid register index")

	// ErrNilGraphicSet is returned when attempting to designate a nil graphic set.
	ErrNilGraphicSet = errors.New("graphic set is nil")

	// ErrUnknownGraphicSet is returned when a graphic set name is not found
	// in the repertoire.
	ErrUnknownGraphicSet = errors.New("graphic set not found in repertoire")

	// ErrNRCInMultinational is returned when attempting to designate an NRC
	// (National Replacement Character) set while in multinational mode.
	// NRC sets require 7-bit national mode and cannot be used in 8-bit
	// multinational mode.
	ErrNRCInMultinational = errors.New("NRC sets cannot be used in multinational mode")
)

Functions

This section is empty.

Types

type AttrBuilder 

type AttrBuilder struct {
	// contains filtered or unexported fields
}

AttrBuilder provides a fluent interface for building attributed strings. Use VT220.Attr() to create an AttrBuilder, chain attribute methods, then call Print/Printf/Println for direct output or Bprint/Bprintf/Bprintln for composed output. 

func (a *AttrBuilder) Blink() *AttrBuilder

Blink enables the blink attribute.

func (*AttrBuilder) Bold 

func (a *AttrBuilder) Bold() *AttrBuilder

Bold enables the bold attribute.

func (*AttrBuilder) Bprint 

func (a *AttrBuilder) Bprint(args ...any) []byte

Bprint formats using the default formats for its operands and returns the resulting byte slice with SGR attribute sequences. Spaces are added between operands when neither is a string.

func (*AttrBuilder) Bprintf 

func (a *AttrBuilder) Bprintf(format string, args ...any) []byte

Bprintf formats according to a format specifier and returns the resulting byte slice with SGR attribute sequences.

func (*AttrBuilder) Bprintln 

func (a *AttrBuilder) Bprintln(args ...any) []byte

Bprintln formats using the default formats for its operands and returns the resulting byte slice with SGR attribute sequences. Spaces are always added between operands and a newline is appended.

func (*AttrBuilder) Negative 

func (a *AttrBuilder) Negative() *AttrBuilder

Negative enables the negative/reverse video attribute.

func (*AttrBuilder) Print 

func (a *AttrBuilder) Print(args ...any) (int, error)

Print formats using the default formats for its operands and writes the attributed string to the terminal.

func (*AttrBuilder) Printf 

func (a *AttrBuilder) Printf(format string, args ...any) (int, error)

Printf formats according to a format specifier and writes the attributed string to the terminal.

func (*AttrBuilder) Println 

func (a *AttrBuilder) Println(args ...any) (int, error)

Println formats using the default formats for its operands and writes the attributed string to the terminal. Spaces are always added between operands and a newline is appended.

func (*AttrBuilder) Underline 

func (a *AttrBuilder) Underline() *AttrBuilder

Underline enables the underline attribute.

type CharSetMode 

type CharSetMode int

CharSetMode represents the terminal's character set operating mode. 

const (
	// Multinational is 8-bit DEC Multinational Character Set mode.
	// This is the default mode and supports the full 8-bit character range.
	// NRC (National Replacement Character) sets cannot be used in this mode.
	Multinational CharSetMode = iota

	// National is 7-bit National Replacement Character mode.
	// This mode is required for NRC sets but is incompatible with 8-bit
	// multinational keyboards and character sets.
	National
)

func (CharSetMode) String 

func (m CharSetMode) String() string

String returns a human-readable name for the character set mode.

type VT220 

type VT220 struct {
	// contains filtered or unexported fields
}

VT220 represents a VT220 terminal's character set state. It manages four graphic registers (G0-G3) and tracks which registers are currently invoked into GL (left, 7-bit) and GR (right, 8-bit).

func New 

func New(w io.Writer) *VT220

New creates a new VT220 terminal manager with the given output writer. It initializes with the standard VT220 defaults:

  • G0: ASCII (invoked into GL)
  • G1: DEC Supplemental (invoked into GR)
  • G2: DEC Special Graphics
  • G3: DEC Special Graphics
  • Mode: Multinational
  • Equivalence encoding: disabled

func NewWithConfig 

func NewWithConfig(w io.Writer, cfg VTConfig) *VT220

NewWithConfig creates a new VT220 terminal manager with the given output writer and configuration options. It initializes with the standard VT220 defaults for registers:

  • G0: ASCII (invoked into GL)
  • G1: DEC Supplemental (invoked into GR)
  • G2: DEC Special Graphics
  • G3: DEC Special Graphics

func (*VT220) Attr 

func (vt *VT220) Attr() *AttrBuilder

Attr returns a new AttrBuilder for constructing attributed strings.

func (*VT220) Bprint 

func (vt *VT220) Bprint(a ...any) []byte

Bprint formats using the default formats for its operands and returns the resulting byte slice. Spaces are added between operands when neither is a string.

func (*VT220) Bprintf 

func (vt *VT220) Bprintf(format string, a ...any) []byte

Bprintf formats according to a format specifier and returns the resulting byte slice.

func (*VT220) Bprintln 

func (vt *VT220) Bprintln(a ...any) []byte

Bprintln formats using the default formats for its operands and returns the resulting byte slice. Spaces are always added between operands and a newline is appended.

func (*VT220) Designate 

func (vt *VT220) Designate(reg control.RegisterIndex, set *repertoire.GraphicSet) error

Designate designates a graphic set to a register and sends the appropriate SCS (Select Character Set) escape sequence to the terminal. The set must be in the terminal's repertoire. Returns ErrNRCInMultinational if attempting to designate an NRC set while in multinational mode.

func (*VT220) DesignateByName 

func (vt *VT220) DesignateByName(reg control.RegisterIndex, name string) error

DesignateByName designates a graphic set by name from the repertoire.

func (*VT220) DynamicGraphicSet 

func (vt *VT220) DynamicGraphicSet() bool

DynamicGraphicSet returns whether dynamic graphic set selection is enabled.

func (*VT220) GLCodepage 

func (vt *VT220) GLCodepage() *charmap.DynamicCodepage

GLCodepage returns the DynamicCodepage currently active for GL.

func (*VT220) GLGraphicSet 

func (vt *VT220) GLGraphicSet() *repertoire.GraphicSet

GLGraphicSet returns the GraphicSet currently invoked into GL, or nil if none.

func (*VT220) GLRegister 

func (vt *VT220) GLRegister() control.RegisterIndex

GLRegister returns the index of the register currently invoked into GL.

func (*VT220) GRCodepage 

func (vt *VT220) GRCodepage() *charmap.DynamicCodepage

GRCodepage returns the DynamicCodepage currently active for GR.

func (*VT220) GRGraphicSet 

func (vt *VT220) GRGraphicSet() *repertoire.GraphicSet

GRGraphicSet returns the GraphicSet currently invoked into GR, or nil if none.

func (*VT220) GRRegister 

func (vt *VT220) GRRegister() control.RegisterIndex

GRRegister returns the index of the register currently invoked into GR.

func (*VT220) Init 

func (vt *VT220) Init() error

Init sends the initialization sequences to configure the terminal with the current register designations and shift state.

func (*VT220) LockShiftGL 

func (vt *VT220) LockShiftGL(reg control.RegisterIndex) error

LockShiftGL invokes the specified register into GL (left side, 7-bit codes). This sends the appropriate lock shift sequence (LS0, LS1, LS2, or LS3).

func (*VT220) LockShiftGR 

func (vt *VT220) LockShiftGR(reg control.RegisterIndex) error

LockShiftGR invokes the specified register into GR (right side, 8-bit codes). This sends the appropriate lock shift sequence (LS1R, LS2R, or LS3R). G0 cannot be invoked into GR.

func (*VT220) Mode 

func (vt *VT220) Mode() CharSetMode

Mode returns the current character set operating mode.

func (*VT220) Print 

func (vt *VT220) Print(s string) (n int, err error)

Print writes a string to the terminal, encoding it to the current character set.

func (*VT220) Printf 

func (vt *VT220) Printf(format string, a ...any) (n int, err error)

Printf formats according to a format specifier and writes to the terminal, encoding the result to the current character set.

func (*VT220) Println 

func (vt *VT220) Println(a ...any) (n int, err error)

Println formats using the default formats for its operands and writes to standard output. Spaces are always added between operands and a newline is appended. It returns the number of bytes written and any write error encountered.

func (*VT220) Register 

func (vt *VT220) Register(reg control.RegisterIndex) *repertoire.GraphicSet

Register returns the graphic set currently designated to the given register, or nil if the register is empty.

func (*VT220) Reset 

func (vt *VT220) Reset(clearScreen bool) error

Reset performs a soft terminal reset, reinitializing the VT220 to its default state. This sends DECSTR to the terminal and resets the internal register state to defaults:

  • G0: ASCII (invoked into GL)
  • G1: DEC Supplemental (invoked into GR)
  • G2: DEC Special Graphics
  • G3: DEC Special Graphics

If clearScreen is true, the screen is also cleared after the reset.

func (*VT220) SendSequence 

func (vt *VT220) SendSequence(seq control.Sequence) error

SendSequence writes a control sequence to the terminal output.

func (*VT220) SetDynamicGraphicSet 

func (vt *VT220) SetDynamicGraphicSet(enabled bool)

SetDynamicGraphicSet enables or disables dynamic graphic set selection. When enabled, the encoder will check other registers (G2, G3) and use single shifts (SS2, SS3) to output characters that cannot be encoded by the current GL/GR character sets.

func (*VT220) SetMode 

func (vt *VT220) SetMode(mode CharSetMode)

SetMode sets the character set operating mode. Note: This only updates the internal state. Use SetModeWithSequence to also send the appropriate DECNRCM control sequence to the terminal.

func (*VT220) SetModeWithSequence 

func (vt *VT220) SetModeWithSequence(mode CharSetMode) error

SetModeWithSequence sets the character set operating mode and sends the appropriate DECNRCM control sequence to the terminal.

func (*VT220) SingleShift 

func (vt *VT220) SingleShift(reg control.RegisterIndex, b byte) error

SingleShift writes a byte using the character set in the specified register via single shift. Only G2 and G3 support single shifts. Returns ErrInvalidRegister for G0 or G1.

func (*VT220) SingleShiftG2 

func (vt *VT220) SingleShiftG2(b byte) error

SingleShiftG2 writes a byte using the character set in G2 via single shift. The SS2 control is sent followed by the byte, causing the terminal to display the character from G2, then revert to the normal GL mapping.

func (*VT220) SingleShiftG3 

func (vt *VT220) SingleShiftG3(b byte) error

SingleShiftG3 writes a byte using the character set in G3 via single shift. The SS3 control is sent followed by the byte, causing the terminal to display the character from G3, then revert to the normal GL mapping.

func (*VT220) Sprint 

func (vt *VT220) Sprint(a ...any) string

Sprint formats using the default formats for its operands and returns the resulting byte slice. Spaces are added between operands when neither is a string.

func (*VT220) Sprintf 

func (vt *VT220) Sprintf(format string, a ...any) string

Sprintf formats according to a format specifier and returns the resulting string.

func (*VT220) Sprintln 

func (vt *VT220) Sprintln(a ...any) string

Sprintln formats using the default formats for its operands and returns the resulting string. Spaces are always added between operands and a newline is appended.

func (*VT220) UnderlyingWriter 

func (vt *VT220) UnderlyingWriter() io.Writer

UnderlyingWriter returns the underlying output writer.

func (*VT220) Write 

func (vt *VT220) Write(p []byte) (n int, err error)

Write encodes UTF-8 text to the terminal's current character encoding and writes it to the output. This makes VT220 implement io.Writer.

func (*VT220) WriteRaw 

func (vt *VT220) WriteRaw(p []byte) (int, error)

WriteRaw writes bytes directly to the terminal without encoding. Use this for pre-encoded content like attributed strings from AttrBuilder.

func (*VT220) Writer 

func (vt *VT220) Writer() io.Writer

Writer returns an io.Writer that encodes UTF-8 text to the terminal's current character encoding (using both GL and GR). If dynamic graphic set selection is enabled, the writer will also check other registers and use single shifts when needed.

type VTConfig 

type VTConfig struct {
	// Mode specifies the character set operating mode.
	// Multinational (default) supports 8-bit character sets.
	// National mode is required for NRC sets but is 7-bit only.
	Mode CharSetMode

	// UseEquivalence enables equivalence encoding, which maps visually
	// similar characters to their canonical forms during encoding.
	UseEquivalence bool

	// DynamicGraphicSet enables dynamic character set selection during encoding.
	// When a rune cannot be encoded by the current GL/GR character sets,
	// the encoder will check other registers (G2, G3) and use single shifts
	// (SS2, SS3) to output characters from those sets.
	DynamicGraphicSet bool
}

VTConfig holds configuration options for creating a VT220 terminal manager.

Source Files

View all Source files

Directories

Path Synopsis
Package control provides control sequence types and builders for VT220 terminals.
 Package control provides control sequence types and builders for VT220 terminals.
Package repertoire provides the graphics repertoire for VT220 terminals.
 Package repertoire provides the graphics repertoire for VT220 terminals.

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