antsy

Antsy

Antsy is a library that provides a canvas for drawing full-color (xterm-256) text and generating the ANSI/xterm codes to efficiently paint it into a terminal. It remembers the previous state after each paint operation, so as you update the canvas, it generates only the minimal codes necessary for the update.

It's like a modern typescript implementation of the lower half of ncurses.

var antsy = require("antsy");
var canvas = new antsy.Canvas(80, 24);
var region = canvas.all();
region.at(0, 23).backgroundColor("#000080").write("i am on a blue background!");

// now write it out to the terminal!
// generates: '\e[37m\e[40m\e[2J\e[H\e[23B\e[44mi am on a blue background!\e[H'
process.stdout.write(canvas.paint());

region.at(10, 23).color("#ff0").write("BLUE");

// now update that word!
// generates: '\e[24;11H\e[38;5;11mBLUE\e[H'
process.stdout.write(canvas.paint());

That's all it does. The intent is that this would be enough to build a widget library on top of, if you want, by using a separate Canvas for each widget, drawing them into the main canvas in z-buffer order, and calling paint() to generate the diff as ANSI/xterm codes. (Check test_canvas.ts for an example.)

xterm-256

All modern terminals support 256-color "xterm" control codes, so antsy uses them. There's an exhaustive explanation of the encoding in the docs/ folder.

Antsy uses an incredibly fast, state-of-the-art hylaean algorithm for determining the closest "xterm" color to a 24-bit web-style color code. You can use it yourself via the exported get_color function:

var color = antsy.get_color("#ffffff"); // 15

It also understands the three-letter alternate forms ("f00") and a basic set of American color names ("teal", "brown", and so on).

Canvas

Antsy models a screen (or framebuffer) as a "canvas" which generates the ANSI codes, and clip regions which support drawing commands.

• new Canvas(cols: number, rows: number)

  Create a new canvas with a framebuffer of the requested size. It will be cleared to white-on-black.

• all(): Region

  Return a new clipping/drawing region that covers the entire canvas.

• clip(x1: number, y1: number, x2: number, y2: number): Region

  Return a new clipping/drawing region that begins at x1, y1 inclusive and ends at x2, y2 exclusive. For example, clip(4, 3, 10, 5) will return a region with an origin at column 4 (counting from 0), row 3, and is 6 columns wide and 2 columns tall. The point (0, 0) in the region will map to (4, 3) in the canvas.

• paint(): string

  Return the ANSI codes that will paint the current canvas contents, since the last call. Each call to paint() caches the current canvas state, so that future updates only paint the parts of the screen that have changed since last time.

• paintInline(): string

  Return the ANSI codes that will paint the current canvas contents as if the screen was in an unknown (dirty) state. Every glyph and color will be rendered, separated by linefeeds, without cursor manipulation. This may be useful for rendering small canvases that are meant to be embedded in other displays or output that doesn't know about the canvas.

Region

A clip region maps a rectangle of the canvas, and can be drawn on.

• all(): Region

  Return this region. This method exists only to match the method on Canvas.

• clip(x1: number, y1: number, x2: number, y2: number): Region

  Return a new clipping/drawing region that's possibly smaller than the current one. It can't expand to cover more than the current region.

• color(fg?: string | number, bg?: string | number): this

• backgroundColor(bg: string | number): this

  Change the foreground (and optionally the background) color to match either a name or an HTML-style hex string like #ff0088.

• at(x: number, y: number): this

  Move the local cursor. Coordinates are zero-based.

• clear(): this

  Clear the entire region to the current background color.

• write(s: string): this

  Write a string to the current cursor coordinates. Text will wrap within the region if necessary. If text goes past the bottom line of the region, it will be scrolled.

• draw(other: Region): this

  Copy a region from another canvas into this region. If the other region is larger than this one, it will be clipped. The other region is always drawn into this one at (0, 0): to draw into another coordinate, clip the region first. You can use this to give each UX element ("widget") its own canvas, and draw them into a region of the canvas representing the screen.

• scrollUp(rows: number = 1): this

• scrollDown(rows: number = 1): this

• scrollLeft(cols: number = 1): this

• scrollRight(cols: number = 1): this

  Scroll the region horizontally or vertically. "Up" means the characters shift up (like a scrolling terminal), and "down", "left", and "right" have similar meanings. New areas are filled with the current background color.

• moveCursor(x: number = this.cursorX, y: number = this.cursorY): this

  Move the screen's physical block cursor, either to an explicit cell, or to the current cursor location. This causes paint() to emit codes to move the cursor after all other drawing is done.

Grid layout

A region can be dynamically split into smaller regions using a set of grid constraints.

Given a list of horizontal constraints and a list of vertical constraints, a GridLayout will divide the available space and hand out regions that align with the requested grid. Constraints follow the traditional NextStep model, with the following options:

• fixed size (in cells)
• stretch to consume available space, with a weighting factor, and optional minimum/maximum sizes (in cells)

In other layout engines, fixed is sometimes called "strut" and stretch is sometimes called "spring". The idea is that some rows or columns are a fixed size, and others grow or shrink to fill the rest of the available space.

The weighting factor is best thought of as a poor-man's fraction. The weights of each row (or column) are added together, and each row or column's weight is divided by this total to get the fraction of excess space they'll receive. So if there are two rows with weights 2 and 5, the first row will receive 2/7 of the excess space, and the other will receive 5/7.

For example, to build a simple text UI that has a fixed edit region at the bottom, and a fixed sidebar on the right:

 <-  stretch  -> <- 10 ->
+---------------+-------+
|               |       |   ^
|       A       |   B   |   |
|               |       | stretch
|               |       |   |
|               |       |   v
+---------------+-------+
|           C           |   2
+-----------------------+

...you could use a grid layout with 2 columns and 2 rows. The left column and top row are stretchy:

const grid = new GridLayout(
    region,
    [ GridLayout.stretch(1), GridLayout.fixed(10) ],
    [ GridLayout.stretch(1), GridLayout.fixed(2) ],
);

The regions A, B, and C are then given spans within the grid. A span can cover more than one rows or columns of the grid, like C covers two columns here:

const A = grid.layoutAt(0, 0);
const B = grid.layoutAt(1, 0);
const C = grid.layout(0, 1, 2, 2);

• new GridLayout(region: Region, colConstraints: Constraint[], rowConstraints: Constraint[])

  Create a new grid layout for a region, with the requested number of rows and columns, and constraints for each.

• GridLayout.fixed(cells: number): Constraint

• GridLayout.stretch(factor: number): Constraint

• GridLayout.stretchWithMinimum(factor: number, minimum: number): Constraint

• GridLayout.stretchWithMinMax(factor: number, minimum: number, maximum: number): Constraint

  Define a constraint for the GridLayout constructor, either fixed size or stretchy (with a weighting factor, an optional minimum size, and an optional maximum size).

• update(colConstraints: Constraint[], rowConstraints: Constraint[])

  Change the grid constraints. This will also call resize to resize every region that's been handed out.

• adjustCol(x: number, c: Constraint)

• adjustRow(y: number, c: Constraint)

  Change a specific row or column's constraint. This will also call resize to resize every region that's been handed out.

• layout(x1: number, y1: number, x2: number, y2: number): Region

  Create a region that exactly fits the grid rows and columns from (x1, y1) inclusive to (x2, y2) exclusive.

• layoutAt(x1: number, y1: number): Region

  Create a region that exactly fits a single cell in the grid. This is equivalent to layout(x, y, x + 1, y + 1).

• resize(cols: number, rows: number)

  Recompute the grid boundaries. This is automatically called whenever the grid's region (in the constructor) is resized, and it automatically calls resize on any regions it's handed out in layout, so you probably never need to call this directly.

How it works

Canvas stores two framebuffers: a "current" and a "next" one. They start identical, but all modifications made thru Regions are to the "next" buffer. Each "paint" call compares them and performs steps to make "current" match "next":

1. If clear() was ever called on the entire canvas (canvas.all().clear()), then it emits a code to clear the current buffer to the color of the most recent clear() call.

2. If any region was recently scrolled vertically, it checks to see if scrolling a section of the screen would be cheaper than redrawing those lines. If it would, then it emits the codes to set and scroll that section. ANSI/xterm only support scrolling a range of rows as wide as the screen, not just any rectangular box, so this isn't helpful as often as you'd hope.

3. Finally, it iterates across all the rows that are different, "diffs" them, and redraws the needed segments. If it would be cheaper to emit an "erase to the end of the line" code anywhere along the row, then it will.

After redrawing everything, it emits a code to move the cursor to the desired cell, and the two buffers are now identical. This logic is all in canvas_diff.ts.

To-do

JS/ES cannot currently handle grapheme boundaries of combining marks, or identification of double-wide fixed-width glyphs (like emojis). Grapheme boundaries will be part of a future spec. Heuristics may work for double-wide glyph detection. But until JS/ES support improves, this library will only work well with single-codepoint, single-width glyphs. If that's a bunch of jargon to you: "Stick with the ISO-8859 character sets or ASCII for now." :)

License

Apache 2 (open-source) license, included in LICENSE.txt.

Authors

@robey - Robey Pointer [e-mail]