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

• About
  • Status
  • BREAKING CHANGES 3.0.0
  • Related packages
• Installation
• Dependencies
• Usage examples
• API
• How it works
  • Restrictions & behavior controls
  • HDPI support
• SVG conversion
• Supported shape types
• Authors
  • Maintainer
  • Contributors
• License

@thi.ng/hdom component wrapper for declarative canvas scenegraphs.

This package provides a re-usable canvas component, which accepts child nodes defining a scene tree of different shape types in standard @thi.ng/hiccup syntax/format (i.e. nested arrays) and then translates these into canvas API draw calls during the hdom update process / cycle.

STABLE - used in production

The actual tree traversal & drawing has been extracted to the new @thi.ng/hiccup-canvas package for better re-usability, also outside without hdom.

• @thi.ng/geom - Functional, polymorphic API for 2D geometry types & SVG generation
• @thi.ng/hdom - Lightweight vanilla ES6 UI component trees with customizable branch-local behaviors
• @thi.ng/hiccup-canvas - Hiccup shape tree renderer for vanilla Canvas 2D contexts
• @thi.ng/hiccup-svg - SVG element functions for @thi.ng/hiccup & @thi.ng/hdom

yarn add @thi.ng/hdom-canvas

// ES module
<script type="module" src="https://unpkg.com/@thi.ng/hdom-canvas?module" crossorigin></script>

// UMD
<script src="https://unpkg.com/@thi.ng/hdom-canvas/lib/index.umd.js" crossorigin></script>

Package sizes (gzipped, pre-treeshake): ESM: 910 bytes / CJS: 979 bytes / UMD: 1.06 KB

• @thi.ng/api
• @thi.ng/checks
• @thi.ng/diff
• @thi.ng/hdom
• @thi.ng/hiccup-canvas

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

A selection:

Screenshot	Description	Live demo	Source
	Interactive inverse FFT toy synth	Demo	Source
	Doodle w/ K-nearest neighbor search result visualization	Demo	Source
	Poisson-disk shape-aware sampling, Voronoi & Minimum Spanning Tree visualization	Demo	Source
	Realtime analog clock demo	Demo	Source
	Interactive pattern drawing demo using transducers	Demo	Source
	2D Bezier curve-guided particle system	Demo	Source
	Various hdom-canvas shape drawing examples & SVG conversion / export	Demo	Source
	Canvas based Immediate Mode GUI components	Demo	Source
	Animated sine plasma effect visualized using contour lines	Demo	Source
	Basic rstream-gestures multi-touch demo	Demo	Source
	Unison wavetable synth with waveform editor	Demo	Source
	Animated Voronoi diagram, cubic splines & SVG download	Demo	Source
	2D scenegraph & shape picking	Demo	Source
	2D scenegraph & image map based geometry manipulation	Demo	Source
	Fork-join worker-based raymarch renderer	Demo	Source

Generated API docs

import { start } from "@thi.ng/hdom";
import { canvas } from "@thi.ng/hdom-canvas";

start(() => {
    const t = Date.now() * 0.001;
    return [canvas, { width: 100, height: 100 },
        ["circle", { fill: "red", stroke: "black" }, [50, 50], 25 + 25 * Math.sin(t)]
    ];
});

Usage with @thi.ng/geom shape primitives:

import { start } from "@thi.ng/hdom";
import { canvas } from "@thi.ng/hdom-canvas";
import * as g from "@thi.ng/geom";

start(() => {
    const t = Date.now() * 0.001;
    return [canvas, { width: 100, height: 100 },
        g.group(
            { translate: [50, 50], fill: "none" },
            [
                g.withAttribs(
                    g.asPolygon(g.circle(50), 6),
                    { rotate: t % Math.PI, stroke: "red" }
                ),
                g.star(25 + 25 * Math.sin(t), 6, [0.5, 1], { stroke: "blue" }),
            ]
        )
    ];
});

The package provides a canvas component which uses the branch-local behavior implementation feature of @thi.ng/hdom v5.0.0 to support virtual SVG-like shape elements / components. These are defined as part of the main UI component tree just like any other component, but are then translated into canvas API draw commands during the hdom update process. Any embedded shape component functions receive the user context object as first arg, just like normal hdom components.

Shape components are expressed in standard hiccup syntax (or as objects implementing the IToHiccup() interface, like the shape types provided by @thi.ng/geom), and with the following...

• Shape component objects with life cycle methods are only partially supported, i.e. only the render & release methods are used.
• For performance reasons release methods are disabled by default. If your shape tree contains stateful components which use the release life cycle method, you'll need to explicitly enable the canvas component's __release control attribute by setting it to true.
• Currently no event listeners can be assigned to shapes (ignored), though this is planned for a future version. The canvas element itself can of course have event handlers as usual.

For best performance it's recommended to ensure all resulting shapes elements are provided in already normalized hiccup format, i.e.

[tag, {attribs}, ...] // or
[tag, null, ...]

That way the __normalize: false control attribute can be added either to the canvas component itself (or to individual shapes / groups), and if present, will skip normalization of that element's children.

Likewise, for animated scenes, the __diff control attribute should be set to false to skip unnecessary diffing and force redraws.

To disable the automatic background clearing of the canvas, set the __clear attribute to false.

[canvas, { width: 100, height: 100, __clear: false }, ...]

The canvas component automatically adjusts its size for HDPI displays by adding CSS width & height properties and pre-scaling the drawing context accordingly before any shapes are processed. For fullscreen canvases simply set the width & height attribs to:

[canvas,
    {
        width: window.innerWidth,
        height: window.innerHeight
    },
    // shapes
    ...
]

Even though the element names & syntax are very similar to SVG elements, for performance reasons all geometry data given to each shape remains un-stringified (only styling attributes are). However, the @thi.ng/hiccup-svg package provides a convertTree() function which takes the arguably more "raw" shape format used by hdom-canvas and converts an entire shape tree into SVG compatible & serializable format. Note: the tree MUST first be normalized (if not already) using hdom-canvas' normalizeTree().

import { serialize } from "@thi.ng/hiccup";
import { convertTree, svg } from "@thi.ng/hiccup-svg";
import { normalizeTree } from "@thi.ng/hdom-canvas";

serialize(
    svg({ width: 100, height: 100},
        convertTree(
            normalizeTree(
                {}, // default normalization options
                ["g",
                    {
                        fill: "red",
                        stroke: "none",
                        translate: [50, 50]
                    },
                    ["circle", {}, [0, 0], 25],
                    ["polygon", { fill: "white" },
                        [[-10,10],[10,10],[0,-10]]
                    ]
                ]
            )
        )
    )
);

<svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="100" height="100">
    <g transform="translate(50.00 50.00)" fill="red" stroke="none">
        <circle cx="0.00" cy="0.00" r="25.00"/>
        <polygon points="-10.00,10.00 10.00,10.00 0.00,-10.00" fill="white"/>
    </g>
</svg>

Please see the @thi.ng/hiccup-canvas README for the full list of supported shapes, gradients, attributes, colors and transformations.

• Karsten Schmidt (@postspectacular)

• Arthur Carabott (@acarabott)

© 2018 - 2020 Karsten Schmidt // Apache Software License 2.0