Coordinates

Data coordinates are distinct from layout lengths. Numeric graph points are data; width, height, stroke widths, and other lengths use the ordinary units. Unit strings in point coordinates are local lengths: "50%" uses half the corresponding drawing dimension, and "10px" is a pixel offset. They do not pass through data-axis mapping. Bare numeric points keep their data meaning.

For placing elements with pos and anchor, start with Positioning.

infer_coordinates(children, options) returns an immutable {xlim,ylim,flip_x,flip_y} record. An optional core Projection maps coordinate records before the axis mapping. map_point(point, coordinates, size) maps to pixels, returning null if the projection omits the point. unmap_point reverses linear mapping; custom projections and zero-sized frames cannot be inverted. point_bounds, merge_bounds, and data_bounds(element) support inference.

Source mapping accepts numeric records with any named dimensions, or [x,y] tuples. Cartesian bounds and inverse mapping require {x,y} or [x,y]. Non-null mapping results have named {x,y} coordinates. See Point values for the shared input convention and examples using zip and length tuples.

A custom element reports bounds with a static method:

class Mark extends Element { static data_bounds(_props: ElementProps): DataBounds { return { xlim: [0, 10], ylim: [-1, 1] } } static layout(props: ElementProps, query: LayoutQuery) { // Map data with query.coordinates and the selected pixel size here. return make_fragment({ size: shape_size(query.request, query.sizing) }) } }

These helpers and types are exports from gum-jsx-core. The factory form define_element also accepts data_bounds in its fourth options argument. See Custom elements for both forms and inherited hooks.

Ordinary containers contribute descendant bounds. A data_bounds callback is a boundary: returning null excludes the subtree. Graph and Plot use this to isolate their internal data.

LayoutQuery and LayoutContext expose coordinates. query.child accepts a fifth context argument: {coordinates} establishes a context, {coordinates:null} clears it, and omission inherits it. Coordinates participate in layout-cache identity. query.prepare must stay independent of coordinates, requests, and references. The engine transports context; inference and mapping remain element policies.

Use coordinate_point(value, size, query.measure, query.coordinates) when a custom element accepts either numeric data records or tagged local Cartesian lengths. Mapping complete records supports polar and geographic projections; mapping x and y separately with coordinate_length cannot do that. See Projections for the callback contract and examples.