pydrawcv

An editable, retained-mode 2D drawing library built on NumPy and OpenCV. Create illustrations, procedural graphics, diagrams, freehand strokes, and animation as scene objects; render pixels whenever you need them.

Install pydrawcv; import drawcv. Requires Python 3.12 or newer.

pip install pydrawcv

For this checkout, including the milestone 1 stroke improvements:

pip install -e ".[dev]"
python -m pytest -q

Draw and export an image

from drawcv import (
    Scene, OpenCVRenderer, Line, Circle, Point, Color,
    StrokeStyle, FillStyle, CapStyle,
)

scene = Scene(640, 360, background=Color.white())
node = Circle(center=Point(100, 180), radius=35,
              fill=FillStyle(color=Color(50, 140, 200)))
connection = Line(
    start=Point(150, 180), end=Point(560, 180),
    stroke=StrokeStyle(color=Color(30, 60, 90), width=8,
                       cap_style=CapStyle.BUTT, dash_array=(20, 12)),
)
scene.add(node)
scene.add(connection)
renderer = OpenCVRenderer()
renderer.render(scene).save("diagram.png")

The scene remains editable after export. Canvas.buffer is a uint8 BGR array; Canvas.to_numpy() returns a copy. For transparent PNG output, set a transparent scene background and explicitly request BGRA:

scene.background = Color(0, 0, 0, 0)
transparent = renderer.render(scene, alpha=True)
transparent.save("diagram-transparent.png")
transparent.flatten(Color.white()).save("diagram-white.jpg")

See transparent output and alpha semantics.

Edit, undo, and save the scene

with scene.edit(connection, name="Restyle connection"):
    connection.stroke.width = 12
    connection.stroke.dash_offset = 8

scene.undo()
scene.redo()
assert scene.get(connection.id) is connection

scene.save_json("diagram.drawcv.json")
loaded = Scene.load_json("diagram.drawcv.json")
renderer.render(loaded).save("diagram-loaded.png")

Style and transform assignments reject invalid values without corrupting existing state. Use scene.edit for compound changes and geometry edits, and scene.batch for multiple recorded commands. See reliable edits for rollback guarantees and the limits of raw attribute/list mutation.

New scenes use schema 1.4, including embedded font assets, gradient paints and stroke semantics. Schemas 1.0 through 1.3 load with compatible defaults. Older readers reject 1.4; update readers before sharing new documents with them.

Organize and position objects

Use Group(children=[...]) for transform hierarchies and scene.create_layer(name) plus scene.add(obj, layer=name) for rendering layers. Use scene.select([...]) for collective transforms and scene.find_by_name/tag/type for lookup. Objects have stable IDs, visibility, opacity, z-order, tags, and metadata.

from drawcv import place_right_of

with scene.edit(connection):
    place_right_of(connection, node, gap=20, align="center")

Coordinates start at the top left; x increases rightward, y downward, and positive rotation is clockwise. Local geometry maps through object and ancestor transforms. Stroke widths and dashes remain in screen pixels under scaling and shear. Colors are authored as RGB integers 0–255 with alpha 0–1; OpenCV buffers use BGR. Alpha compositing uses source-over with premultiplied internal surfaces for isolation.

Animate a drawing

from drawcv import Timing

connection.timing = Timing(duration=2)
scene.animate(connection, "stroke.dash_offset", 0, 32, duration=2)
scene.render_at_time(0.75).save("frame.png")

render_at_time restores authored state and does not add history entries. scene.sample(t) deliberately updates the live model. VideoRenderer provides frame iteration, image-sequence export, and video export through OpenCV codecs. Line, Polyline, Arrow, BezierCurve, Path, FreehandStroke, and Arc support progressive reveal. See stroke/progress semantics for closure, transforms, phase anchoring, and the different progress parameterizations.

Examples and reference

Run examples as modules from the repository root:

python -m examples.stroke_styles
python -m examples.progressive_drawing
python -m examples.transparent_output

• Stroke comparison source and editable scene.
• Transparent PNG example and external-composition preview.
• Gradient paints and coordinate contracts; runnable gallery.
• Alpha API and compositing conventions.
• StrokeStyle API and conventions.
• Public API guide.
• Retained font typography: installation, metrics and layout.
• SVG export: editable vectors, raster fallbacks and strict mode; gallery.
• Measured rendering performance; reproducible benchmark commands.
• Typography backend evaluation.
• Reliability and history.
• Prioritized roadmap and verified findings.
• Existing runnable examples: retained editing, groups/selection, freehand, compositing, persistence/history, and animation.

Capabilities and current limits

Raster boundary pixels can differ from earlier releases because caps/joins now have real geometry. These improvements are local source changes; no package has been published by this task.