Phase 1 of bringing the grip vocabulary in line with the standard
CAD convention: drop the per-position-type shape encoding (Diamond
for translate, Circle for parameter) and use a plain square for
every endpoint / vertex / centre grip. The behavioural midpoint vs
vertex distinction stays — it lives on `GripDef::is_midpoint` and
drives `Translate` vs `Absolute` in the grip-edit dispatcher — only
the marker shape collapses.
- `GripShape` keeps `Square`, `Rectangle`, `Triangle`. Diamond /
Circle are gone.
- `GripDef` gains `dir: Option<[f32; 2]>` — a world-XY direction
vector consumed by `Rectangle` to orient the box along its
segment.
- `entities::common` exposes `square_grip`, `center_grip` (same
square marker, flagged as translate), `rectangle_grip(id, world,
dir)` for oriented mid-segment handles, and a kept-for-Phase-2
`triangle_grip`.
- `overlay::GripMarker` / `grips_to_screen[_paper]` thread `dir`
through to the canvas painter; the Rectangle path rotates the
box around the grip centre using the world-XY direction (flipping
the sin for screen-Y).
Every existing `diamond_grip(id, w)` call becomes `center_grip(id,
w)` — the visual change is square-replacing-diamond at line
midpoints / arc midpoints / circle centres / ellipse centres /
viewport / hatch loop centroids / dimension grips / image corners /
multileader / ray / underlay / ole2frame / solid3d.
`LwPolyline` grows a stretch handle on every segment (straight or
arc), drawn as the new oriented rectangle. The grip-edit path
translates both segment endpoints for straight segments and
adjusts the arc bulge from the new midpoint for arc segments.
Existing entity grip definitions already followed the conventional
CAD layout: square at vertices / endpoints, diamond at curve
centres / midpoints, triangle for directional control. Round out
the supported shape vocabulary with the two missing standards so
future entities (polyline straight-segment stretch grips, dimension
parameter grips, …) can pick the right marker without inventing
ad-hoc visuals:
- `GripShape::Rectangle` — direction-aware mid-segment stretch
handle (wider-than-tall box).
- `GripShape::Circle` — parametric control (radius / dimension
value).
New `rectangle_grip` / `circle_grip` helpers in `entities::common`
mirror the existing `square_grip` / `diamond_grip` / `triangle_grip`
constructors. `SelectionCanvas::draw` renders the two new variants;
the previously-used Square / Diamond / Triangle paths are
unchanged. Both new variants carry `#[allow(dead_code)]` until an
entity adopts them.
