Add drawing shape interface to World

[tigercosmos]

Summary

Add shape CRUD management directly into World. All method bodies are stubs (throw runtime_error) — this PR defines the interface only.

Shape hierarchy (C++ templates in World.hpp)

Shape<T> is the abstract base. All shapes live on z=0 using Point3d<T> for rendering pipeline compatibility. Concrete shapes:

• Polygon — closed, arbitrary vertex list (>=3)
• Rectangle — axis-aligned, defined by (x, y, width, height)
• Triangle — 3 vertices
• Circle — center + radius, approximated as n-gon
• Line — single segment between two points
• Polyline — open path (>=2 vertices)
• Ellipse — center + semi-axes, approximated as n-gon

CRUD on World

Op	Methods
Create	add_shape(), add_rectangle(), add_circle(), add_line(), add_triangle(), add_polygon(), add_polyline(), add_ellipse() — returns int32_t shape ID
Read	get_shape(id) — by ID; shapes — all shapes; nshape — count
Update	Via shape object: translate(dx, dy), scale(factor, cx, cy), rotate(angle_deg, cx, cy)
Delete	remove_shape(id), clear_shapes()

Usage

world = mm.WorldFp64()

world.add_rectangle(x=0, y=0, width=10, height=5)
shape = world.get_shape(0)
shape.translate(dx=5, dy=3)
all_shapes = world.shapes  # list of all managed shapes

widget.updateWorld(world)

Files changed

File	What
World.hpp	Shape classes + World shape CRUD
wrap_World.cpp	pybind11 bindings (shapes + World)
core.py	Export shape types
test_pilot_drawing.py	Tests (xfail — stubs only)

Test plan

• make builds successfully
• pre-commit passes (clang-format, flake8, ascii, trailing whitespace)
• Shape polymorphism verified (isinstance(RectangleFp64(...), ShapeFp64) is True)
• tests/test_pilot_drawing.py — 4 tests, all xfail (stubs throw, as expected)
• Existing tests unaffected

🤖 Generated with Claude Code

[tigercosmos]

Key design points highlighted inline.

[tigercosmos]

@yungyuc Please take a look. Thank you.

[yungyuc]

This does not look right. World is the canvas. It is not necessary to have another class inside World for creating geometry objects.

And it is called World so that the geometry objects do not have to be in a surface, but can be in a space. The World is part of the universe module. While we do not have a Universe container yet, it may be a future extension to hold multiple World.

And it is not correct to postfix the names to the geometry entities with 2D (although d should be lower-cased per the naming convention, it is not the point). Polygons, rectangles, triangles, circles, polylines, ellipses are all 2D entities.

The 3d postfix we have for Point, Segment, etc., meant the entities are in 3D space.

I am moving this PR to draft for you to follow up.

[tigercosmos]

Shape base class: Abstract base for all shapes managed by World. Concrete shapes implement draw(World&) to emit segments, plus translate/scale/rotate for the Update part of CRUD (transforms are called on the shape object, not through World).

[tigercosmos]

World shape CRUD: Create — add_shape() and typed helpers (add_rectangle, add_circle, etc.) return an int32_t ID. Read — get_shape(id), nshape. Update — via shape methods (translate/scale/rotate). Delete — remove_shape(id), clear_shapes(). Storage is unordered_map<int32_t, shape_ptr> with sequential IDs for O(1) average lookup.

[tigercosmos]

pybind11 inheritance: Concrete shape wrappers pass Shape<T> as the 4th WrapBase template arg so pybind11 registers the C++ inheritance hierarchy. This enables polymorphic returns from get_shape() and correct isinstance() checks in Python.

[tigercosmos]

Shape types exported here so they are accessible as modmesh.ShapeFp64, modmesh.RectangleFp64, etc.

[tigercosmos]

@yungyuc I have update the interface design based on the review. Please take a look, thanks!