[!NOTE] This is one of 190 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

About

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.

Status

STABLE - used in production

Search or submit any issues for this package

Related packages

• @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

Installation

yarn add @thi.ng/hiccup-canvas
Copy

ES module import:

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

Skypack documentation

For Node.js REPL:

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

Package sizes (brotli'd, pre-treeshake): ESM: 2.53 KB

Dependencies

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

Usage examples

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
	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

API

Generated API docs

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

SVG conversion

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 can be done like so:

import { asSvg, svgDoc, group, circle } from "@thi.ng/geom";
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" }),
]);

// draw to canvas
draw(canvas.getContext("2d"), dots);

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

Supported shape types

In the near future, factory functions for these shape types will be provided...

Group

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

Attributes defined at group level are inherited by child elements.

Definition group

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

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

Circle

["circle", attribs, [x, y], radius]
Copy

Circular arc

["arc", attribs, [x, y], radius, startAngle, endAngle, anticlockwise?]
Copy

Only circular arcs are supported in this format. Please see note about differences to SVG.

Ellipse / elliptic arc

["ellipse", attribs, [x, y], [rx, ry], axisTheta?, start?, end?, ccw?]
Copy

Rect

["rect", attribs, [x, y], w, h, radius?]
Copy

If radius is given, creates a rounded rectangle. radius will be clamped to Math.min(w, h)/2.

Line

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

Horizontal Line

["hline", attribs, y]
Copy

Vertical Line

["vline", attribs, x]
Copy

Polyline / Polygon

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

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

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

Always closed, can be filled and/or stroked.

Path

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

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.

SVG paths with arc segments

IMPORTANT: Currently, due to differences between SVG and canvas API arc handling, SVG paths containing arc segments are NOT compatible with the above format. This issue is being worked on, but in the meantime, to use such paths, these should first be converted to use cubics or polygon / polyline. E.g. here using @thi.ng/geom:

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

// path w/ arc segments (*not* usable by hiccup-canvas)
const a = pathFromSvg("M0,0H80A20,20,0,0,1,100,20V30A20,20,0,0,1,80,50")[0];

// normalized to only use cubic curves (usable by hiccup-canvas)
const b = normalizedPath(a);

// converted to polyline (usable by hiccup-canvas)
const c = asPolyline(a);

asSvg(b);
// <path d="M0.00,0.00C26.67,0.00,53.33,0.00,80.00,0.00C..."/>

asSvg(c);
// <polyline fill="none" points="0.00,0.00 80.00,0.00 81.57,0.06..."/>
Copy

Points

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

The following shape specific attributes are used:

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

Text

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

Image

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

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

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], ...]
]
Copy

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

Using flat, packed vertex buffers

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,...]]
Copy

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...]]
Copy

Attributes

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

Color attributes

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

String

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

Number

Interpreted as ARGB hex value:

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

Array

Interpreted as float RGB(A):

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

@thi.ng/color values

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 transformations

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 matrix

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

Override transform

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

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) }
Copy

Translation

{ translate: [x, y] }
Copy

Scaling

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

Rotation

{ rotate: theta } // in radians
Copy

Special attributes

Background fill

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.

Background clear

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.

Authors

• 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
}
Copy

License

© 2018 - 2024 Karsten Schmidt // Apache License 2.0