Chapter 7 calls provenance "the basis of hit-testing, selection, and
back-reference navigation in the UI" and defers the renderer details to a
companion. An editor needs more than the trace it already has: a structured map
from a rendered primitive to its layout object and its score object, with a
selectable shape, so a click or drag resolves to something to select without the
GUI re-deriving geometry or guessing the chain.
RenderIR::hit_test_map() (new hittest.rs) builds that map: one HitRegion per glyph
primitive and per stroke, each carrying the full chain -- rendered primitive ->
layout object (stable_id) -> score object (source) -- plus the synthesis kind and
a selectable HitShape:
- HitShape::Box: a glyph's IR bounding_box placed by its position and any
transform (corners mapped through the same placement the SVG renderer applies,
so the region aligns with the drawn glyph; I-4a made the IR bbox contain the
ink).
- HitShape::Segment: a stroke's segment with a half-width (half its thickness).
Queries: HitShape::contains (point-in-shape, click) and intersects_rect (an exact
capsule-vs-rectangle test for drag, not just AABB overlap, so a diagonal stroke
whose bounding box clips a corner is not falsely selected); HitTestMap::hit(point)
returns regions topmost-first (paint order: layer, glyph-over-stroke, index) and
within(rect) returns the drag selection in ascending paint order.
Two deliberate boundaries: shapes are in staff-space WORLD coordinates (the same
frame as RenderPrimitive.position, before any renderer's world->screen transform),
so the contract is renderer-independent and a GUI applies the inverse of the same
transform its renderer uses; and a glyph's region is its IR bounding_box, not the
render-only outline.
Tested at the RenderIR boundary (8 tests): box/segment contains + aabb; world-box
placement incl. an affine transform; coverage + provenance-chain preservation over
the real pipeline; click-on-a-notehead resolves to its Pitch; topmost-first point
hits; exact (not AABB-only) drag intersection; paint-ordered drag results. Full
gate green: build, fmt, clippy, 595 tests, conformance scale 1.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Levi Neuwirth
cb92d890ec