[!NOTE] This is one of 192 standalone projects, maintained as part of the @thi.ng/umbrella monorepo and anti-framework.

🚀 Please help me to work full-time on these projects by sponsoring me on GitHub. Thank you! ❤️

• About
• Status
• Related packages
• Installation
• Dependencies
• Usage examples
• API
• SVG conversion
• Supported shape types
  • Group
  • Definition group
  • Circle / circular arc
  • Ellipse / elliptic arc
  • Rect
  • Line
  • Horizontal Line
  • Vertical Line
  • Polyline / Polygon
  • Path
    • SVG paths with arc segments
  • Points
  • Text
  • Image
  • Gradients
  • Using flat, packed vertex buffers
• Attributes
  • Color attributes
    • String
    • Number
    • Array
    • @thi.ng/color values
  • Coordinate transformations
    • Transform matrix
    • Override transform
    • Translation
    • Scaling
    • Rotation
  • Special attributes
    • Background fill
    • Background clear
• Authors
• License

Hiccup shape tree renderer for vanilla Canvas 2D contexts. This is a support package for @thi.ng/hiccup.

This package provides a simple draw() function, which accepts a scene tree of different shape types in @thi.ng/hiccup syntax/format (i.e. nested arrays, IToHiccup implementations) and then translates these into canvas API draw calls.

STABLE - used in production

Search or submit any issues for this package

• @thi.ng/hdom-canvas - @thi.ng/hdom component wrapper for declarative canvas scenegraphs
• @thi.ng/hiccup - HTML/SVG/XML serialization of nested data structures, iterables & closures

yarn add @thi.ng/hiccup-canvas

ESM import:

import * as hc from "@thi.ng/hiccup-canvas";

Browser ESM import:

<script type="module" src="https://esm.run/@thi.ng/hiccup-canvas"></script>

JSDelivr documentation

For Node.js REPL:

const hc = await import("@thi.ng/hiccup-canvas");

Package sizes (brotli'd, pre-treeshake): ESM: 2.54 KB

• @thi.ng/api
• @thi.ng/checks
• @thi.ng/color
• @thi.ng/geom-arc
• @thi.ng/math
• @thi.ng/pixel
• @thi.ng/vectors

Several projects in this repo's /examples directory are using this package:

Screenshot	Description	Live demo	Source
	Self-modifying, animated typographic grid with emergent complex patterns	Demo	Source
	Fiber-based cooperative multitasking basics	Demo	Source
	Shape conversions & operations using polygons with holes	Demo	Source
	geom-fuzz basic shape & fill examples	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
	Animated arcs & drawing using hiccup-canvas	Demo	Source
	Basic hiccup-based canvas drawing	Demo	Source
	Animated, iterative polygon subdivisions & visualization	Demo	Source

Generated API docs

The shape tree given to draw() MUST consist of well-formed, normalized hiccup syntax (incl. objects implementing the IToHiccup() interface, like the shape types provided by @thi.ng/geom).

Even though the shape element names & syntax are intentionally very similar (largely the same) to SVG elements, for performance reasons all geometry data given to each shape remains un-stringified (only styling attributes can be strings). However, the @thi.ng/hiccup-svg package provides a convertTree() function which takes the arguably more "raw" shape format used by this package and converts an entire shape tree into SVG compatible & serializable format.

It's very likely (and recommended) you're using the shape type provided @thi.ng/geom, in which case these can be provided as-is to this package's draw() function and SVG conversion (from the same geometry) can be done like so:

import { asSvg, svgDoc, group, circle } from "@thi.ng/geom";
import { canvas2d } from "@thi.ng/canvas";
import { draw } from "@thi.ng/hiccup-canvas";

const dots = group({}, [
    circle([100, 100], 20, { fill: "red" }),
    circle([140, 100], 20, { fill: "green" }),
    circle([160, 100], 20, { fill: "blue" }),
]);

const { ctx } = canvas2d(200, 200, document.body);

// draw geometry group to canvas
draw(ctx, dots);

// convert to SVG
// (unless given, width, height and viewBox will be auto-computed)
asSvg(svgDoc({}, dots))

["g", attribs, child1, child2, ...]

Attributes defined at group level are inherited by child elements.

["defs", {}, def1, def2, ...]

Special group / container for gradient definitions. If used, should always come first in a scene tree.

["circle", attribs, [x, y], radius, startTheta?, endTheta?, ccw?]

Angles in radians. Please see note about SVG support.

["ellipse", attribs, [x, y], [rx, ry], axisTheta?, startTheta?, endTheta?, ccw?]

Angles in radians. Please see note about SVG support.

["rect", attribs, [x, y], w, h, radii?]

If radii is given, creates a rounded rectangle. See Canvas API roundRect() for possible radius values.

["line", attribs, [x1, y1], [x2, y2]]

["hline", attribs, y]

["vline", attribs, x]

["polyline", attribs, [[x1, y1], [x2, y2], [x3, y3]...]]

Always non-filled (even if fill attrib is given or inherited)

["polygon", attribs, [[x1, y1], [x2, y2], [x3, y3]...]]

Always closed, can be filled and/or stroked.

["path", attribs, [seg1, seg2, ...]]

Path segments are tuples of [type, [x,y]...]. The following segment types are supported and (as with SVG), absolute and relative versions can be used. Relative versions use lowercase letters and are always relative to the end point of the previous segment. The first segment (usually of type "M") must be absolute.

[!IMPORTANT] Prior to v3.0.0, only circular arc segments were supported and used the A/a identifier, which actually should have been reserved for SVG-style elliptic arcs (as is the case now). In the unlikely event you've been using paths with circular arc segments, you'll need to update these to use R/r segment types instead.

Reference about the params for arc segments:

• circular arc
• elliptic arc

Since v3.0.0 this package supports both circular and elliptic arc path segments, however only the latter segment type is compatible with SVG (circular arcs are only supported by the HTML Canvas API). We recommended to use one of the available path constructor functions in @thi.ng/geom to create individual arcs or paths which ensure SVG compatibility:

Arcs:

• arc()
• arcFrom2Points()

Paths:

• pathFromSvg()
• pathBuilder()
• pathFromCubics()
• normalizedPath()
• roundedRect()

import { asPolyline, asSvg, normalizedPath, pathFromSVG, roundedRect } from "@thi.ng/geom";

// path w/ elliptic arc segments (for 2 of the corners)
const a = roundedRect([0, 0], [100, 100], [0, 40]);

console.log(asSvg(a));
// <path d="M0,0H60A40,40,0,0,1,100,40V100H40A40,40,0,0,1,0,60.000V0z"/>

// normalize path to only use cubic curves
const b = normalizedPath(a);

console.log(asSvg(b));
// <path d="M0,0C20,0,40,0,60,0C82.091,0,100,17.909,100,40C100,60,100,80,100,100C80,100,60,100,40,100C17.909,100,0.000,82.091,0,60.000C0,40,0,20,0,0z"/>

// convert/sample path as polyline
// (some paths have multiple boundaries, here we only want the first)
const c = asPolyline(a, { dist: 20 })[0];

console.log(asSvg(c));
// <polyline fill="none" points="0,0 20,0 40,0 60,0 79.168,4.924 93.644,18.410 99.889,37.186 100,40 100,60 100,80 100,100 80,100 60,100 40,100 20.832,95.076 6.356,81.590 0.111,62.814 0,60 0,40 0,20 0,0"/>

["points", attribs, [[x1,y1], [x2,y2],...]]

The following shape specific attributes are used:

• shape: circle or rect (default)
• size: point size (radius for circles, width for rects) - default: 1

["text", attribs, [x,y], "body...", maxWidth?]

["img", { width?, height? }, img, dpos, spos?, ssize?]

IMPORTANT: Since v2.0.0 this element has new/changed args...

img MUST be an HTML image, canvas or video element. dpos, spos, ssize are 2D vectors. The latter two are optional, as are width and height attribs. Defaults:

• width - original image width
• height - original image height
• spos - [0,0]
• ssize - [width, height]

Note: For SVG conversion spos & ssize will be ignored. Sub-image blitting is not supported in SVG.

Gradients MUST be defined within a root-level defs group, which itself MUST be given prior to any other shapes. Use the $ prefix to refer to a gradient in a fill or stroke attribute, e.g. {stroke: "$foo" }

["linearGradient",
    {id: "foo", from: [x1,y1], to: [x2, y2]},
    [[offset1, color1], [offset2, color2], ...]
]

["radialGradient",
    {id: "foo", from: [x1,y1], to: [x2, y2], r1: r1, r2: r2 },
    [[offset1, color1], [offset2, color2], ...]
]

The points, polyline and polygon shape types also provide alternative versions, each allowing the use of a single packed buffer (e.g. typed array) for all point coordinates instead of individual arrays/views per vertex. This much simplifies & speeds up WASM interop usecases, which can now skip creating vector views of a vertexbuffer memory region.

["packedPoints", attribs, [x1,y1, x2,y2,...]]

["packedPolyline", attribs, [x1,y1, x2,y2,...]]

["packedPolygon", attribs, [x1,y1, x2,y2,...]]

Optional start index, number of points, component & element stride lengths (i.e. the number of indices between each vector x/y component and/or each point respectively) can be given as attributes and thus these packaged shapes support both AOS and SOA memory layouts/arrangements.

Options & defaults:

• start: start index = 0
• num: number of vertices = (array_length - start) / estride
• cstride: component stride = 1
• estride: element stride = 2

["packedPoints", { cstride: 1, estride: 4 },
    [x1, y1, 0, 0, x2, y2, 0, 0, ...]]

["packedPoints", { offset: 8, num: 3, cstride: 4, estride: 1 },
    [0, 0, 0, 0, 0, 0, 0, 0, x1, x2, x3, 0, y1, y2, y3, 0...]]

Some attributes use different names than their actual names in the CanvasRenderingContext2D:

Color conversions are only applied to fill, stroke, shadowColor attributes and color stops provided to gradient definitions.

String color attribs prefixed with $ are replaced with url(#...) refs (e.g. to refer to gradients), else used as is (untransformed)

Interpreted as ARGB hex value:

{ fill: 0xffaabbcc } => { fill: "#aabbcc" }

Interpreted as float RGB(A):

{ fill: [1, 0.8, 0.6, 0.4] } => { fill: "rgba(255,204,153,0.40)" }

Colors defined via the @thi.ng/color package can be automatically converted to CSS color strings:

{ fill: hcya(0.1666, 1, 0.8859) } => { fill: "#ffff00" }

Coordinate system transformations can be achieved via the following attributes (for groups and individual shapes). Nested transformations are supported.

If using a combination of translate, scale and/or rotate attribs, the order of application is always TRS.

{ transform: [xx, xy, yx, yy, ox, oy] }

{ setTransform: [xx, xy, yx, yy, ox, oy] }

Similar to transform but completely overrides transformation matrix, rather than concatenating with existing one.

See MDN docs for further details.

Also see the 2x3 matrix functions in the @thi.ng/matrices package for creating different kinds of transformation matrices, e.g.

{ transform: skewX23([], Math.PI / 12) }

{ translate: [x, y] }

{ scale: [x, y] } // non-uniform
{ scale: x } // uniform

{ rotate: theta } // in radians

The special __background attribute can be used to fill the entire canvas with a given background color. The attribute only makes sense if attached to the root group/shape and can take the same values as any other color attribs.

The special __clear boolean attribute is used to force clearing of the canvas before drawing. This attrib takes priority over __background and it too only should be attached to the root group/shape. By default the canvas is not being cleared.

• Karsten Schmidt

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

@misc{thing-hiccup-canvas,
  title = "@thi.ng/hiccup-canvas",
  author = "Karsten Schmidt",
  note = "https://thi.ng/hiccup-canvas",
  year = 2018
}

© 2018 - 2024 Karsten Schmidt // Apache License 2.0