Entity Wrappers

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lc_plugin::entity contains read-only wrappers for geometry, layers, and cells passed to export plugins. Writer entity callbacks receive these types when WriterController::render_cell() or WriterController::render_cell_in_layer_order() renders drawing content.

The Python database API exposes equivalent geometry objects in linkcad.v1.db, with additional direct database creation and mutation methods for scripting.

Purpose

Entity wrappers provide safe, typed access to host-owned drawing objects during export. They are lightweight views over native LinkCAD objects. Plugin code should read values from them and write output data; it should not store them beyond the callback that provided them.

Geometry Types

`Polygon`

Method	Description
`vertex_count() -> usize`	Number of polygon vertices.
`vertices() -> Vec<Point>`	Polygon vertices in database units.
`is_box() -> bool`	Whether the polygon is a rectangular box.
`has_bulges() -> bool`	Whether any edge has a bulge value.
`bulges() -> Vec<f64>`	Per-edge bulge values, or an empty vector.
`layer() -> Layer`	Owning layer.

`Polyline`

Method	Description
`vertex_count() -> usize`	Number of path vertices.
`vertices() -> Vec<Point>`	Path vertices in database units.
`width() -> Coord`	Path width.
`is_closed() -> bool`	Whether the path is closed.
`layer() -> Layer`	Owning layer.

`Arc`

Method	Description
`center() -> Point`	Arc center.
`radius() -> Coord`	Radius.
`width() -> Coord`	Stroke width.
`start_angle() -> Angle`	Start angle.
`end_angle() -> Angle`	End angle.
`layer() -> Layer`	Owning layer.

`Ellipse`

Method	Description
`center() -> Point`	Center point.
`diameter() -> Coord`	Diameter.
`layer() -> Layer`	Owning layer.

`Donut`

Method	Description
`center() -> Point`	Center point.
`mean_diameter() -> Coord`	Mean diameter of the annulus.
`width() -> Coord`	Ring width.
`layer() -> Layer`	Owning layer.

`Text`

Method	Description
`position() -> Point`	Text position.
`height() -> f64`	Text height.
`width_factor() -> f64`	Horizontal scale factor.
`text() -> String`	Text content.
`font() -> String`	Font name.
`rotation() -> Angle`	Text rotation.
`mirrored_in_x() -> bool`	Whether text is mirrored in X.
`mirrored_in_y() -> bool`	Whether text is mirrored in Y.
`layer() -> Layer`	Owning layer.
`real_property(name: &str) -> Option<f64>`	Read a real-valued text property.
`bool_property(name: &str) -> Option<bool>`	Read a boolean text property.

`Nurbs`

Method	Description
`degree() -> i32`	Curve degree.
`width() -> Coord`	Stroke width.
`knots() -> Vec<f64>`	Knot vector.
`ctrl_points() -> Vec<Point>`	Control points.
`is_rational() -> bool`	Whether weights are present.
`weights() -> Vec<f64>`	Weight vector, or an empty vector for non-rational curves.
`is_periodic() -> bool`	Whether the curve is periodic.
`layer() -> Layer`	Owning layer.

`Ref`

Method	Description
`cell_name() -> String`	Referenced cell name.
`transformation() -> Xform`	Reference transform.
`columns() -> i32`	Reference-array column count.
`rows() -> i32`	Reference-array row count.
`column_spacing() -> Coord`	Reference-array column spacing.
`row_spacing() -> Coord`	Reference-array row spacing.
`layer() -> Layer`	Owning layer.

Layer and Cell Types

`Layer`

Method	Description
`name() -> String`	Layer name.
`color() -> Color`	Display color.
`enabled() -> bool`	Whether the layer is enabled.

Layer properties that require drawing context, such as polarity group, comment, and export number, are available on WriterController.

`Cell`

Method	Description
`name() -> String`	Cell name.

Writer Callback Example

impl Writer for ExampleWriter {
    fn write_file(&mut self, _path: &str, ctrl: &mut WriterController) -> bool {
        let Some(cell) = ctrl.main_cell() else {
            ctrl.log().error("No main cell to export");
            return false;
        };

        ctrl.start_enum_layers(SortOrder::Regular);
        while let Some(layer) = ctrl.next_layer() {
            let xform = ctrl.transformation(false);
            ctrl.render_cell(&cell, &layer, &xform);
        }
        true
    }

    fn write_polygon(&mut self, polygon: &Polygon, fill_rule: FillRule) -> bool {
        let vertices = polygon.vertices();
        let layer_name = polygon.layer().name();
        // Write vertices and layer_name to the output format.
        let _ = (vertices, layer_name, fill_rule);
        true
    }
}

Units and Geometry Primitives

Entity methods return lc_types values such as Point, Angle, Color, Xform, Coord, and Resolution. Coordinates and distances are in LinkCAD database units; convert file-format units at the import/export boundary.