star-drawing

SVG drawing canvas web component for StarHTML and Datastar.

One app.register() call gives you a <drawing-canvas> custom element with drawing, shape, text, and annotation tools — plus a reactive toolbar wired to the canvas state. Built on starelements, so each canvas instance gets its own scoped signal namespace.

Why?

Adding a drawing surface to a web app typically means choosing a JS canvas library, wiring up toolbars, managing undo state, and handling pointer events yourself. star-drawing wraps all of that into a single starelements component — import it, register it, and you have a working canvas with 10 tools, undo/redo, keyboard shortcuts, and collaboration hooks.

Features

• Full drawing toolkit — pen, highlighter, line, arrow, rectangle, ellipse, diamond, text, and eraser tools out of the box.
• WYSIWYG text editing — click to place text, edit inline with font family, size, and alignment options.
• Toolbar presets — drawing_toolbar() for the full suite, annotation_toolbar() for markup, diagram_toolbar() for shapes and connectors.
• Undo/redo and keyboard shortcuts — Ctrl+Z, Ctrl+Y, Delete, Ctrl+A, Ctrl+D, and arrow-key nudging all wired up.
• SVG export/import — export_svg() and import_svg() for serialization and persistence.
• Scoped signals — built on starelements, so each canvas instance has its own signal namespace. No cross-instance interference.
• Collaboration-ready — onElementChange callback and applyRemoteChanges method for syncing state across clients.
• Configurable palettes — stroke colors, fill colors, highlighter colors, width presets, font options, and arrowhead styles are all customizable.
• Readonly mode — set the readonly attribute for view-only canvases.
• Skeleton loading — shimmer placeholder shown until the component initializes, preventing layout shift.

Installation

Requires Python 3.12+ and StarHTML.

pip install star-drawing

Quick Start

from starhtml import *
from star_drawing import DrawingCanvas, drawing_toolbar

app, rt = star_app()
app.register(DrawingCanvas)

@rt("/")
def index():
    canvas = DrawingCanvas(cls="drawing-container")
    return Div(
        drawing_toolbar(canvas),
        canvas,
    )

serve()

This gives you a full-featured drawing canvas with all tools, color palettes, style options, and undo/redo.

Toolbar Presets

For focused use cases, use a preset instead of the full toolbar:

# Annotation — pen, highlighter, eraser only
annotation_toolbar(canvas)

# Diagramming — select, shapes, lines, arrows, text
diagram_toolbar(canvas)

Both presets accept the same keyword arguments as drawing_toolbar() for further customization.

Configuration

Attributes on <drawing-canvas> control defaults:

Set these as element attributes in Python:

DrawingCanvas(
    default_tool="select",
    default_stroke_color="#3568d4",
    default_stroke_width=4,
    readonly=True,
)

Toolbar Customization

drawing_toolbar() accepts keyword arguments to override defaults:

drawing_toolbar(
    canvas,
    tools=("pen", "line", "rect", "text"),        # subset of tools to show
    show_colors=True,                               # color palette panel
    show_styles=True,                               # style options panel
    show_undo=True,                                 # undo/redo/clear buttons
    color_palette=[("#000", "Black"), ("#fff", "White")],
    width_presets=(1, 2, 4, 8),
)

Development

TypeScript sources live in typescript/ and are bundled with bun:

bun run build                          # build drawing-canvas.js
bun run dev                            # watch mode

uv run ruff check src/ tests/          # lint Python
uv run ruff format --check src/        # check formatting
npx tsc --noEmit                       # type-check TypeScript

The hatch build hook runs bun run build automatically during pip install / uv build, so the generated JS is never checked into git.

License

Apache 2.0