This project is part of the @thi.ng/umbrella monorepo.

• About
• Status
• Related packages
• Installation
• Dependencies
• Usage examples
• API
  • Canvas creation
  • Format identifiers
    • Colors
    • Variations
    • Combined formats
  • String conversion format presets
  • Stroke styles
  • Clipping
  • Drawing functions
  • Image functions
  • Text functions
  • Bars & bar charts
  • Tables
  • 3D wireframe cube example
• Authors
• License

About

Text based canvas, drawing, tables with arbitrary formatting (incl. ANSI/HTML).

Status

STABLE - used in production

Search or submit any issues for this package

Related packages

• @thi.ng/text-format - Customizable color text formatting with presets for ANSI & HTML

Installation

yarn add @thi.ng/text-canvas

ES module import:

<script type="module" src="https://cdn.skypack.dev/@thi.ng/text-canvas"></script>

Skypack documentation

For Node.js REPL:

# with flag only for < v16
node --experimental-repl-await

> const textCanvas = await import("@thi.ng/text-canvas");

Package sizes (gzipped, pre-treeshake): ESM: 5.65 KB

Dependencies

• @thi.ng/api
• @thi.ng/arrays
• @thi.ng/checks
• @thi.ng/errors
• @thi.ng/geom-clip-line
• @thi.ng/math
• @thi.ng/strings
• @thi.ng/text-format
• @thi.ng/transducers

Usage examples

Several demos in this repo's /examples directory are using this package.

A selection:

Screenshot	Description	Live demo	Source
	3D wireframe textmode demo	Demo	Source
	Textmode image warping w/ 16bit color output	Demo	Source

API

Generated API docs

Canvas creation

const c = canvas(width, height, format?, style?);

Format identifiers

The text canvas stores all characters in a Uint32Array with the lower 16 bits used for the UTF-16 code and the upper 16 bits for abitrary formatting data. The package utilizes format identifier constants and formatters from the @thi.ng/text-format package, which are tailored for the included ANSI & HTML formatters, but users are free to choose use any other system (but then will also need to implement a custom string formatter impl).

The default format ID layout used by text canvas is as shown:

Most drawing functions accept an optional format arg, but a default format can also be set via setFormat(canvas, formatID).

The format IDs defined in @thi.ng/text-format are only compatible with these formatters (also supplied by that package):

• FMT_ANSI16
• FMT_HTML_INLINE_CSS
• FMT_HTML_TACHYONS

All constants and other formatters are also discussed in detail in the @thi.ng/text-format readme.

Colors

These color IDs MUST be prefixed with either FG_ (foreground) or BG_ (background):

• BLACK
• RED
• GREEN
• YELLOW
• BLUE
• MAGENTA
• CYAN
• GRAY
• WHITE
• LIGHT_GRAY
• LIGHT_RED
• LIGHT_GREEN
• LIGHT_YELLOW
• LIGHT_BLUE
• LIGHT_MAGENTA
• LIGHT_CYAN

Variations

• BOLD
• DIM
• UNDERLINE

Combined formats

Format IDs can be combined via the binary OR operator (|), e.g.:

setFormat(canvas, FG_BLACK | BG_LIGHT_CYAN | BOLD | UNDERLINE);

String conversion format presets

Canvas-to-string conversion is completely customizable via the StringFormat interface. Currently the following presets are supplied (in the @thi.ng/text-format package):

• FMT_ANSI16 - translate built-in format IDs to 4-bit ANSI escape sequences
• FMT_ANSI256 - uses all 16 format bits for fg & bg colors (ANSI esc sequences)
• FMT_ANSI565 - uses all 16 format bits for RGB565 fg colors (ANSI esc sequences)
• FMT_ANSI_RAW - verbatim use of format IDs to ANSI sequences
• FMT_HTML_INLINE_CSS - HTML <span> elements with inline CSS
• FMT_HTML_TACHYONS - HTML <span> elements with Tachyons CSS class names
• FMT_HTML565 - HTML <span> elements with RGB565 color coding
• FMT_NONE - dummy formatter outputting plain text only (all format information discarded, e.g. for NO_COLOR support)

// Terminal
console.log(formatCanvas(canvas, FMT_ANSI16));
// or
console.log(formatCanvas(canvas, FMT_ANSI256));

// Browser
const el = document.createElement("pre");
el.innerHTML = formatCanvas(canvas, FMT_HTML_TACHYONS);

Stroke styles

Built-in style presets:

• STYLE_ASCII
• STYLE_THIN
• STYLE_THIN_ROUNDED
• STYLE_DASHED
• STYLE_DASHED_ROUNDED
• STYLE_DOUBLE

Functions:

• beginStyle(canvas, style)
• endStyle(canvas)

Clipping

All drawing operations are constrained to the currently active clipping rect (by default full canvas). The canvas maintains a stack of such clipping regions, each newly pushed one being intersected with the previous top-of-stack rect:

• beginClip(canvas, x, y, w, h) - push new clip rect
• endClip(canvas) - restore previous clip rect

┌──────────────────┐
│ A                │
│         ╔════════╗─────────┐
│         ║        ║         │
│         ║ A & B  ║         │
│         ║        ║         │
└─────────╚════════╝         │
          │                B │
          └──────────────────┘

Drawing functions

• line

• hline

• vline

• circle

• clear

• fillRect

• strokeRect

Image functions

• blit
• resize
• extract
• scrollV
• image / imageRaw / imageCanvas565 / imageString565
• imageBraille / imageCanvasBraille / imageStringBraille

import { RGB565 } from "@thi.ng/pixel";
import { read } from "@thi.ng/pixel-io-netpbm";

// resize non-proportionally (to compensate
// for character aspect ratio, YMMV)
const img = read(readFileSync("chroma-rings.ppm"))
  .resize(32, 32 / 2.25)
  .as(RGB565)

// requires an ANSI 24bit compatible terminal
console.log(imageString565(img));

Text functions

• textLine
• textLines
• textColumn (word wrapped)
• textBox (word wrapped)

Bars & bar charts

The following are string builders only, draw result via text functions:

• barHorizontal
• barVertical
• barChartHStr
• barChartVStr

Tables

Tables support individual column width, automatic (or user defined) row heights, cell padding, as well as global and per-cell formats and the following border style options:

Border style	Result
Border.ALL
Border.NONE
Border.H
Border.V
Border.FRAME
Border.FRAME_H
Border.FRAME_V

Table cell contents will be word-wrapped. By default, individual words longer than the configured cell width will be truncated, but can be forced to wrap by enabling the hard option (see example below).

import { repeatedly } from "@thi.ng/transducers";
import * as tc from "@thi.ng/text-canvas";
import * as tf from "@thi.ng/text-format";

// generate 20 random values
const data = repeatedly(() => Math.random(), 20)
// format as bar chart string
const chart = tc.barChartHStr(4, data, 0, 1);

// create text canvas
const canvas = new tc.Canvas(64, 20);

// create table
tc.table(
    canvas,
    0,
    0,
    {
        // column defs
        cols: [{ width: 4 }, { width: 20 }, { width: 8 }],
        // default cell format
        format: tf.FG_BLACK | tf.BG_LIGHT_CYAN,
        // default format for header cells (1st row)
        formatHead: tf.FG_RED | tf.BG_LIGHT_CYAN | tf.BOLD | tf.UNDERLINE,
        // border line style
        style: tc.STYLE_DASHED_ROUNDED,
        // border mode
        border: tc.Border.ALL,
        // internal cell padding [h,v]
        padding: [1, 0],
        // hard word wrap
        hard: true,
    },
    // table contents (row major)
    // each cell either a string or RawCell object
    [
        ["ID", "Main", "Comment"],
        [
            "0001",
            { body: chart, format: tf.FG_BLUE | tf.BG_LIGHT_CYAN },
            "This is a test!"
        ],
        ["0002", "Random data plot", "Word wrapped content"],
        ["0003", { body: "More details...", height: 4 }, ""]
    ]
);

// output as ANSI formatted string
console.log(tc.formatCanvas(canvas, tf.FMT_ANSI16));

For even more detailed control, tables can also be pre-initialized prior to creation of the canvas via initTable() and then drawn via drawTable(). The initTable function returns an object also containing the computed table size (width, height keys) which can then be used to create a canvas with the required size...

For convenience, the tableCanvas() function can be used to combine these steps and to create an auto-sized canvas with the rendered table as content.

3D wireframe cube example

       ┌───┐
  ┌──────────────────────┐
  │ @thi.ng/text-canvas  │
  │ wireframe cube       │++++++++++
  │                      │          +++++++++++    ┌───┐
  │ x: 0.42              │                     ++++│ 6 │
  │ y: 0.30              │        ┌───┐ ++++++++   └───┘
  └──────────────────────┘++++++++│ 7 │+           +
           +         └───┘        └───┘            +
            +          +           +              +
            +          +           +              +
             +         +           +             +
             +         +          +              +
             +          +         +              +
              +         +         +             +
              +         +         +             +
               +        +        ┌───┐         +
               +         +      +│ 3 │         +
                +       ┌───┐+++ └───┘        +
                +       │ 0 │       +         +
                 +      └───┘        +        +
                 +       +            +      +
                 +       +             +     +
                  +     +               +   +
                  +     +                +  +
                   +    +                 ┌───┐
                   +    +                 │ 2 │
                    +   +               ++└───┘
                    +   +            +++
                     + +           ++
                     + +        +++
                      ++      ++

Code for this above example output (CLI version):

import * as geom from "@thi.ng/geom";
import * as mat from "@thi.ng/matrices";
import * as tc from "@thi.ng/text-canvas";
import * as tf from "@thi.ng/text-format";

const W = 64;
const H = 32;

// create text canvas
const canvas = new tc.Canvas(W, H, tf.BG_BLACK, tf.STYLE_THIN);

// cube corner vertices
const cube = geom.vertices(geom.center(geom.aabb(1))!);

// edge list (vertex indices)
const edges = [
    [0, 1], [1, 2], [2, 3], [3, 0], [4, 5], [5, 6],
    [6, 7], [7, 4], [0, 4], [1, 5], [2, 6], [3, 7]
];

// animated parameters
let rotx = 0;
let roty = 0;

// 3D transformation matrices
const view = mat.lookAt([], [0, 0, 1], [0, 0, 0], [0, 1, 0]);
const proj = mat.perspective([], 90, W / H, 0.1, 10);
const viewp = mat.viewport([], 0, W, H, 0);

setInterval(() => {
    tc.clear(canvas, true);
    // model rotation matrix
    const model = mat.concat(
        [],
        mat.rotationX44([], rotx += 0.01),
        mat.rotationY44([], roty += 0.03)
    );
    // combined model-view-projection matrix
    const mvp = mat.concat([], proj, view, model);
    // draw cube instances
    // project 3D points to 2D viewport (canvas coords)
    const pts = cube.map((p) => mat.project3([], mvp, viewp, p)!);
    // draw cube edges
    for (let e of edges) {
        const a = pts[e[0]];
        const b = pts[e[1]];
        tc.line(canvas, a[0], a[1], b[0], b[1], "+", tf.FG_WHITE | tf.BG_RED);
    }
    // draw vertex labels
    canvas.format = tf.FG_WHITE | tf.BG_BLUE;
    for (let i = 0; i < 8; i++) {
        const p = pts[i];
        tc.textBox(canvas, p[0] - 1, p[1] - 1, 5, 3, ` ${i} `);
    }
    tc.textBox(
        canvas,
        2, 1, 24, -1,
        `@thi.ng/text-canvas wireframe cube\n\nx: ${rotx.toFixed(2)}\ny: ${roty.toFixed(2)}`,
        {
            format: tf.FG_BLACK | tf.BG_LIGHT_CYAN,
            padding: [1, 0]
        }
    );
    // draw canvas
    console.clear();
    // output as ANSI formatted string
    console.log(tc.formatCanvas(canvas, tf.FMT_ANSI16));
    // output as plain text
    // console.log(tc.formatCanvas(canvas));
}, 15);

Authors

Karsten Schmidt

If this project contributes to an academic publication, please cite it as:

@misc{thing-text-canvas,
  title = "@thi.ng/text-canvas",
  author = "Karsten Schmidt",
  note = "https://thi.ng/text-canvas",
  year = 2020
}

License

© 2020 - 2022 Karsten Schmidt // Apache Software License 2.0