fansiterm

README

FANSITERM

Fake (virtual) ANSI TERMinal.

Fansiterm is a golang package for implementing a partially compatible ANSI terminal, rendered to an image.Image (really, a golang.org/x/image/draw.Image). This is suitable for the graphical back-end of a virtual terminal emulator.

The intent is for implementing a terminal on micro controllers connected to graphical displays. This provides an easy way to make a TUI for the micro controller and take advantage of packages like github.com/charmbracelet/bubbletea or for making a simple dumb terminal-type device.

Overview

The (*fansiterm.Device) object implements io.Writer. (*fansiterm.Device).Render implements image.Draw. To push data (text) to the terminal, you simply call Write() against the Device object.

The text isn't buffered anywhere, if you need the text or want to implement more advanced features like scrolling, that's up to whatever is writing to (*fansiterm).Device. Incomplete escape sequences will be buffered and it's possible to "hang" the terminal by sending an incomplete sequence and then overloading the system memory. This is inline with how actual physical dumb terminals of yore worked.

If you want to push your own graphics or other operations, you can draw directly to the (*fansiterm.Device).Render object as well, as it implements draw.Image.

If Device is initialized with a nil image buffer, it allocates its own buffer. Otherwise, you can pass a draw.Image object (like what the driver for an OLED or TFT screen provides you) to it and any Write()s to the (*fansiterm.Device) will be immediately rendered to the backing screen. Whether the screen buffers image data and needs to be manually blitted is screen driver dependent.

For use with microcontrollers, you'll want to pass it the pseudo-buffer provided by the screen driver, as chances are your MCU does not have enough ram for a single frame buffer--in addition to the memory used for all the tiles and the rest of the program.

Features

• Cursor styles: Block, Beam, Underscore
• Bell is supported: a callback is provided for when the terminal receives a \a (bell character). So you could trigger a beep via a speaker and PWM or blink an LED or blink the backlight, etc.
• Standard cursor manipulation supported.
• Regular, Bold, and "italic" Font (italics are reasonably faked by rotating individual tiles)
• Underline, Double Underline, Strike-through
• Several "TileSets" come built-in: inconsolata, Fira Code Nerd Mono, x3270, julia mono, and fansi
• Tool to generate additional tilesets from TTF fonts is included: look in tiles/ and tiles/gentileset/
• Custom Tile loading for alternate character set (shift-out character set, commonly used for line-drawing/pseudo graphics)
• Tiles are rendered using an 8-bit Alpha mask, allowing for clean blending and anti-aliased rendering of glyphs.
• 4-bit (with extended codes for bright / high intensity) color; 256-Color; True Color (24 bit).

Non-Features

The main purpose of this package is for use on rather low-power microcontrollers, so some standard features for terminal emulators are not implemented.

• Blinking text and blink cursors
  • this would require a some kind of timer-callback. As it is, fansiterm is only using CPU when bytes are being written to it.
• Resizable Text
  • Right now, the pre-rendered inconsolata.Regular8x16 and inconsolata.Bold8x16 are used.
  • It's possible to use basicfont.Regular7x13, but you have to give up bold support.
• Hardware acceleration. Fansiterm remains agnostic of what it's rendering to and thus can't take advantage of any double-buffers or hardware-cursors on its own. Backwards compatible PRs to improve hardware support / hardware acceleration are very much welcome.
  • Okay, I lied a little bit. By using the interfaces from github.com/sparques/gfx, like Filler, Scroller, and RegionScroller, we can get "hardware acceleration." It's not really hardware acceleration, but when the underlying device can use more efficient algorithms (for example, sending a specific "Fill" command to the display, or even just manipulating video memory directly) you can get much improved performance. Using the pure-Go software implementation of Scroll and Fill, it took an arbitrary amount of lines over two minutes to render. With the Scroller and Fill interfaces supported, that same amount of lines takes slightly more than 2 seconds. (And a "real" Terminal emulator takes about 0.03 seconds. Fansi don't mean fast.)

TODO

• General Clean Up (Device struct is a bit of a mess) Always more to be done, but I'm relatively happy with things now.
• Package documentation
  • Reviewing the package documentation now shows me I have far too much exported. A major to do is only have things exported if they actually need to be exported.
• Test on real hardware
• 1-bit color/rendering support for very-very-constrained systems
• More configurable font / better font configuration Now using a purpose-built Tile system.
  • Better, user-oriented font config system: The means are in place, now just have to make it easy to use.
• Optimize drawing/rendering routines This has been greatly improved.
  • Add in hardware accel / filling rectangle support (some hardware can fill rectangles more efficiently than the equivalent single-pixel-pushing)
• Standardize / settle upon an API
  • Limit your interactions to the io.Write() interface.
• Modify gentileset utility to only dump specific ranges--currently any of the "Nerd" fonts included (Fira, x3270, and julia) use too much RAM to actually load onto an RP2040.

Future

I want to keep a very stripped down, bare-bones version of fansiterm that will work on very resource constrained microcontrollers. However, I'm very open to having a more featureful v2 that is suitable for using as a back-end for something as full blown as desktop terminal emulator.

Screenshot

The screenshot demonstrates:

• FANSITERM is colored using inverted VGA color ( SGR CSI34;7m ) and is also bold (SGR CSI1m).
• The trademark character (™) is present in inconsolata.Regular8x16 and rendered correctly here.
• On either end of FANSITERM are custom tiles, defined using 8x16 pixel PNGs, in the fansi TileSet (fansiterm/tiles/fansi) and set to represent the characters '(' and ')' in the alternate character set (activated with the SHIFT-OUT byte, 0x0E, and deactivated with SHIFT-IN byte, 0x0F).
• Custom rounded-end-cap tiles are used to surround 433 MHz and KHz, also via alternate character set (and mapped to '{' and '}').
• The distance between 'Freq:' and '443 MHz' and 'Bandwidth:' and '005 KHz' are managed via tab characters.
• The gradient bar is implemented using 24-bit True Color and an on-the-fly generated gradient tile.
• Finally, the cursor is a block style cursor. All cursor shapes are implemented by inverting the colors they land over top.
• This is a 240x135 pixel. While 240 is evenly divisible by 8, 135 is not divisible by 16. The terminal is automatically centered. (It is a TODO item to add customizable offset).

htop Screenshot

Yes. Htop works.

See Also

I found out about this when nearly done with this project:

https://github.com/tinygo-org/tinyterm

Same basic idea--tinyterm is a (tiny)go implementation of a terminal. Tinyterm is meant to be a minimal implementation to aid in troubleshooting projects. Fansiterm is meant to be the main interface / visual subsystem.

Tinyterm is specifically for tinygo, but fansiterm will work anywhere regular go will.

Documentation

Index

• Variables
• func DecodeImageData(data []rune) (image.Image, error)
• func NewColorSystem(m color.Model) *colorSystem
• type Attr
• type Color
  • func NewColor(r, g, b, a uint8) Color
  • func NewOpaqueColor(r, g, b uint8) Color
  • func (c Color) At(int, int) color.Color
  • func (c Color) Bounds() image.Rectangle
  • func (c Color) ColorModel() color.Model
  • func (c Color) Convert(cin color.Color) color.Color
• type Colorizer
  • func (c Colorizer) RGBA() (r, g, b, a uint32)
• type Config
• type Cursor
  • func (c *Cursor) ColsRemaining() int
  • func (c *Cursor) MoveAbs(x, y int)
  • func (c *Cursor) MoveRel(x, y int)
  • func (c *Cursor) RestorePos()
  • func (c *Cursor) SavePos()
• type Device
  • func New(cols, rows int, buf draw.Image) *Device
  • func NewAtResolution(x, y int, buf draw.Image) *Device
  • func NewWithBuf(buf draw.Image) *Device
  • func (d *Device) Clear(x1, y1, x2, y2 int)
  • func (d *Device) GetReader() (rd io.Reader)
  • func (d *Device) Image() image.Image
  • func (d *Device) RenderRune(sym rune) (width int)
  • func (d *Device) Reset()
  • func (d *Device) Scroll(rowAmount int)
  • func (d *Device) SetAttrDefault(attr Attr)
  • func (d *Device) SetCursorStyle(style cursorRectFunc)
  • func (d *Device) UpdateAttr()
  • func (d *Device) VectorScrollCells(c1, r1, c2, r2, cn, rn int)
  • func (d *Device) VisualBell()
  • func (d *Device) Write(data []byte) (n int, err error)
  • func (d *Device) WriteAt(p []byte, off int64) (n int, err error)
• type Property
• type RGBColor
  • func (c RGBColor) RGBA() (r, g, b, a uint32)
• type RGBImage
  • func NewRGBImage(r image.Rectangle) *RGBImage
  • func (p *RGBImage) At(x, y int) color.Color
  • func (p *RGBImage) Bounds() image.Rectangle
  • func (p *RGBImage) ColorModel() color.Model
  • func (p *RGBImage) Set(x, y int, c color.Color)
• type Render
  • func (r Render) Bounds() image.Rectangle
  • func (r *Render) Fill(region image.Rectangle, c color.Color)
  • func (r *Render) RegionScroll(region image.Rectangle, pixAmt int)
  • func (r *Render) Scroll(pixAmt int)
  • func (r Render) Set(x, y int, c color.Color)
  • func (r *Render) VectorScroll(region image.Rectangle, vector image.Point)

Variables

var (
	// ShowEsc if set to true (default false) prints to stdout escape sequences as received by fansiterm
	ShowEsc bool
	// ShowUnhandled if set to true (default false) prints to stdout escape sequencies that fansiterm does not actually handle.
	ShowUnhandled bool
)

var (
	// CursorBlock, CursorBeam, and CursorUnderscore are the 3 cursor display options.
	CursorBlock      = blockRect
	CursorBeam       = beamRect
	CursorUnderscore = underscoreRect
)

var ConfigDefault = Config{
	TabSize:             8,
	StrikethroughHeight: 7,
	BoldColors:          true,
}

ConfigDefault is used to initialize (*Device).Config. These are the config values fansiterm uses when initializing a terminal.

Functions

func DecodeImageData

func DecodeImageData(data []rune) (image.Image, error)

DecodeImageData accepts base64 encoded data and attempts to decode it as an image, returning the image.

func NewColorSystem

func NewColorSystem(m color.Model) *colorSystem

NewColorSystem instantiates and initializes a *colorSystem. Fansiterm (*Device) uses colorSystem as its palette as well as using it to ensure our working colors are already in the native format for the backing buffer.

Types

type Attr

type Attr struct {
	Bold            bool
	Underline       bool
	DoubleUnderline bool
	Strike          bool
	Blink           bool
	Reversed        bool
	Italic          bool
	Conceal         bool
	Fg              Color
	Bg              Color
}

type Color

type Color struct {
	color.Color
}

Color both implements color.Color and image.Image. image.Image needs a color.Model, so for convenience's sake, Color also implements color.Model so it can simply have ColorModel() return itself. The main purpose of Color is so there is no need to instantiate an image.Unform everytime we need to draw something in a particular color.

func NewColor

func NewColor(r, g, b, a uint8) Color

NewColor returns a new Color.

func NewOpaqueColor

func NewOpaqueColor(r, g, b uint8) Color

NewOpaqueColor returns a Color that has a fully opaque alpha value.

func (Color) At

func (c Color) At(int, int) color.Color

At implements image.Image

func (Color) Bounds

func (c Color) Bounds() image.Rectangle

Bounds implements image.Image

func (Color) ColorModel

func (c Color) ColorModel() color.Model

ColorModel implements image.Image

func (Color) Convert

func (c Color) Convert(cin color.Color) color.Color

type Colorizer

type Colorizer func() color.RGBA

the tinygo.org/x/drivers/pixel package has a somewhat incompatible color interface with the color.Color interface. This type definition and it's associated function allows a pixel.Color's RGBA method to be cast so that it implements the color.Color interface. Example: pixelColor := pixel.NewColor[pixel.RGB888](127,127,127) drawImage.Set(xPos,yPos, Colorizer(pixelColor.RGBA))

func (Colorizer) RGBA

func (c Colorizer) RGBA() (r, g, b, a uint32)

type Config

type Config struct {
	TabSize             int
	StrikethroughHeight int
	CursorStyle         int
	CursorBlink         bool
	BoldColors          bool
}

type Cursor

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

Cursor is used to track the cursor.

func (*Cursor) ColsRemaining

func (c *Cursor) ColsRemaining() int

ColsRemaining returns how many columns are remaining until EOL

func (*Cursor) MoveAbs

func (c *Cursor) MoveAbs(x, y int)

func (*Cursor) MoveRel

func (c *Cursor) MoveRel(x, y int)

func (*Cursor) RestorePos

func (c *Cursor) RestorePos()

func (*Cursor) SavePos

func (c *Cursor) SavePos()

type Device

type Device struct {
	// BellFunc is called if it is non-null and the terminal would
	// display a bell character
	BellFunc func()

	// Config species the runtime configurable features of fansiterm.
	Config Config

	// Render collects together all the graphical rendering fields.
	Render Render

	// Miscellaneous properties, like "Window Title"
	Properties map[Property]string

	// Output specifies the program attached to the terminal. This should be the
	// same interface that the input mechanism (whatever that may be) uses to write
	// to the program. On POSIX systems, this would be equivalent to Stdin.
	// Default is io.Discard. Setting to nil will cause Escape Sequences that
	// write a response to panic.
	Output io.Writer

	sync.Mutex
	// contains filtered or unexported fields
}

Device implements a virtual terminal. It supports being io.Write()n to. It handles the cursor and processing of sequences.

func New

func New(cols, rows int, buf draw.Image) *Device

New returns an initialized *Device. If buf is nil, an internal buffer is used. Otherwise if you specify a hardware backed draw.Image, writes to Device will immediately be written to the backing hardware--whether this is instaneous or buffered is up to the device and the device driver.

func NewAtResolution

func NewAtResolution(x, y int, buf draw.Image) *Device

func NewWithBuf

func NewWithBuf(buf draw.Image) *Device

NewWithBuf uses buf as its target. NewWithBuf() will panic if called against a nil buf. If using fansiterm with backing hardware, NewWithBuf is likely the way you want to instantiate fansiterm. If you have buf providing an interface to a 240x135 screen, using the default 8x16 tiles, you can have an 40x8 cell terminal, with 7 rows of pixels leftover. If you want to have those extra 7 rows above the rendered terminal, you can do so like this:

term := NewWithBuf(xform.SubImage(buf,image.Rect(0,0,240,128).Add(0,7)))

Note: you can skip the Add() and just define your rectangle as image.Rect(0,7,240,135), but I find supplying the actual dimensions and then adding an offset to be clearer.

func (*Device) Clear

func (d *Device) Clear(x1, y1, x2, y2 int)

Clear writes a block of current background color in a rectangular shape, specified in units of cells (rows and columns). So (*Device).Clear(0,0, (*Device).cols, (*Device).rows) would clear the whole screen.

func (*Device) GetReader

func (d *Device) GetReader() (rd io.Reader)

GetReader returns an io.Reader that fansiterm will use for output. This uses an io.Pipe under the hood. The write portion of the pipe displaces (*Device).Output. A new pipe is instantiated every time this is called and will displace the old pipe.

func (*Device) Image

func (d *Device) Image() image.Image

func (*Device) RenderRune

func (d *Device) RenderRune(sym rune) (width int)

RenderRune does not do *any* interpretation of escape codes or control characters like \r or \n. It simply renders a single rune at the cursor position. It is up to the caller of RenderRune to process any control sequences / handle non-printing characters.

func (*Device) Reset

func (d *Device) Reset()

func (*Device) Scroll

func (d *Device) Scroll(rowAmount int)

func (*Device) SetAttrDefault

func (d *Device) SetAttrDefault(attr Attr)

func (*Device) SetCursorStyle

func (d *Device) SetCursorStyle(style cursorRectFunc)

SetCursorStyle changes the shape of the cursor. Valid options are CursorBlock, CursorBeam, and CursorUnderscore. CursorBlock is the default.

func (*Device) UpdateAttr

func (d *Device) UpdateAttr()

func (*Device) VectorScrollCells

func (d *Device) VectorScrollCells(c1, r1, c2, r2, cn, rn int)

func (*Device) VisualBell

func (d *Device) VisualBell()

VisualBell inverts the screen for a tenth of a second.

func (*Device) Write

func (d *Device) Write(data []byte) (n int, err error)

Write implements io.Write and is the main way to interract with a (*fansiterm).Device. This is essentially writing to the "terminal." Writes are more or less unbuffered with the exception of escape sequences. If a partial escape sequence is written to Device, the beginning will be bufferred and prepended to the next write. Certain broken escape sequence can potentially block forever.

func (*Device) WriteAt

func (d *Device) WriteAt(p []byte, off int64) (n int, err error)

WriteAt works like calling the save cursor position escape sequence, then the absolute set cursor position escape sequence, writing to the terminal, and then finally restoring cursor position. The offset is just the i'th character on screen. Negative offset values are set to 0, values larger than d.rows * d.cols are set to d.rows*d.cols-1.

type Property

type Property int

const (
	PropertyWindowTitle Property = iota
)

type RGBColor

type RGBColor struct {
	R, G, B uint8
}

func (RGBColor) RGBA

func (c RGBColor) RGBA() (r, g, b, a uint32)

type RGBImage

type RGBImage struct {
	Pix []uint8
	image.Rectangle
}

func NewRGBImage

func NewRGBImage(r image.Rectangle) *RGBImage

func (*RGBImage) At

func (p *RGBImage) At(x, y int) color.Color

func (*RGBImage) Bounds

func (p *RGBImage) Bounds() image.Rectangle

func (*RGBImage) ColorModel

func (p *RGBImage) ColorModel() color.Model

func (*RGBImage) Set

func (p *RGBImage) Set(x, y int, c color.Color)

type Render

type Render struct {
	draw.Image

	CharSet       tiles.Tiler
	AltCharSet    tiles.Tiler
	BoldCharSet   tiles.Tiler
	ItalicCharSet tiles.Tiler

	// DisplayFunc is called after a write to the terminal. This is for some displays that require a flush / blit / sync call.
	DisplayFunc func()
	// contains filtered or unexported fields
}

func (Render) Bounds

func (r Render) Bounds() image.Rectangle

Bounds returns the image.Rectangle that aligns with terminal cell boundaries

func (*Render) Fill

func (r *Render) Fill(region image.Rectangle, c color.Color)

func (*Render) RegionScroll

func (r *Render) RegionScroll(region image.Rectangle, pixAmt int)

func (*Render) Scroll

func (r *Render) Scroll(pixAmt int)

func (Render) Set

func (r Render) Set(x, y int, c color.Color)

func (*Render) VectorScroll

func (r *Render) VectorScroll(region image.Rectangle, vector image.Point)