* Drawing W06a: exact orthographic hidden lines for the analytic subset (#2455)
crates/geom/src/hlr (L0): prepare once per body, then hidden_lines for a
scene of placed bodies. Edges and face silhouettes are projected from their
exact curves, split where projections cross, and each piece is classified by
rays toward the viewer against the trimmed faces: visible, hidden or
explicitly uncertain, never guessed. Planes, cylinders, cones, spheres and
tori are supported whether stored as analytic records, revolutions or spline
patches; freeform faces are reported and make what they could hide
uncertain. Screen geometry is Seg2 with the W01a accuracy vocabulary: exact
lines and conic arcs where the projection is exact, bounded chords
otherwise. docs/drawing-hlr.md holds the contract and its limits.
* geom/hlr: handle the brep records main gained in #3093
Main's exact model storage (#3093) added Curve::SurfaceIntersection,
Surface::PlaneThrough and Surface::PlacedRevolution, and the HLR matches on
the records no longer compiled. A plane through three points is a plane: it
is trimmed and intersected as one, and a box stored that way draws the same
bits as one with axis-stored planes. The procedural intersection curve and
the placed revolution (whose affine placement may scale it unevenly) are
refused by prepare as not supported yet, until the kernel adapter handles
them. The records' positions move with the body's centre like the others.
* geom/hlr: pad plane faces' boxes, so a plane record off by rounding still hides
Plane faces took the box of their boundary chords unpadded, flat along the
normal. When the plane record and its edges disagree by rounding (a unit cube's
top plane one ulp above its edges, a 100 mm cube's 1e-11), the ray toward the
viewer reached the plane just outside that box, the slab test culled the hit,
and the back edges came out Visible with no doubt. Every face's box is now
padded by 1e-6 of its size, as curved faces' boxes already were. Reported by
DevonHope on #2457.
* geom/hlr: limits from review: trim samples, scene extent, crossing pairs, surface groups
From DevonHope's review of #2457:
- Options::trim_samples must be 1 to MAX_TRIM_SAMPLES (4096).
- Placed bodies must stay within MAX_COORDINATE (1e12 mm, as section and brep
bound stored numbers). Placements 1e200 apart made the scene's size infinite
and every tolerance taken from it with it, so everything came out Visible.
- The crossing search counts its candidate pairs before it starts and meets
each pair only in the first grid cell the two segments share, instead of
keeping a set of the pairs met, which could outgrow wasm's 4 GB before the
500 million pair budget tripped. The same pairs in the same order.
- prepare groups faces on one quadric or torus by comparing each face with
the faces of its kind whose size agrees to the tolerance (sorted), not with
every face; at most 50 million comparisons. prepare_cancellable polls a
cancel callback between edges, faces and comparisons.
* geom/hlr: boundary chords on a grid, and no fine pass over coincident curved chords
The cost items of DevonHope's review of #2457:
- Every ray hit asked how far it lies from its face's boundary by scanning all
of the face's chords (4096 per circle; a plate's face with 256 holes has
about a million). The chords are now bucketed on a uniform grid over the
boundary's box, cells at least as long as the longest chord, and the test
looks only at the cells around the point. It finds exactly the chords the
scan finds.
- Chords of two curved curves that lie on each other end to end (aligned holes
seen along their axes) were cut into 16 by 16 pieces and intersected, to
find crossings that are only noise within the curves' tolerance. They are
now skipped; visibility changes where a coincident run starts or ends, and
chords that only partly overlap still find those.
- Fixtures: a plate with holes, coaxial cylinders seen along their axis, and
300 placements.
* geom/hlr: pad boxes by the body's coordinates too; coincident chords only to rounding
Review of the previous commits found two holes:
- The padding grew with the face's size, but rounding grows with where the body
was modelled: a 0.001 mm cube 1e7 mm out, its top plane one step (1.9e-9 mm)
above its edges, still had its hit culled. The pad now adds 1e-12 of the
body's offset.
- Two chords were taken for coincident when their ends lay within each other's
sag, which in a coarse scene can hide real crossings: an arc can bulge across
a line 1 mm off its chord twice. Only chords that coincide to rounding are
skipped now; identical projections, the costly case, still are.
* geom/hlr: coincident curves meeting at shared sample points do not cross
Timing the review's scenes showed that skipping coincident chords was not
enough: chords of two coincident curves also touch end to end at every sample
point they share, and each touch was a crossing to refine and split at. 64
coaxial cylinders seen along their axis gave 8.3 million crossings (19 s), 64
cylinders one behind another along the line of sight 4.2 million (214 s;
before these commits the crossing budget refused it). A touch at a shared
sample point is now dropped when the two curves also coincide, to rounding, on
both sides of it. Where a coincident run starts or ends one side differs, and
the touch is kept.
* geom/hlr: the own-face margin allows for rounding where a body was modelled
The far 0.001 mm cube of the previous commit showed a second effect of records
rounded at large coordinates: its top plane, one ulp (1.9e-9 mm) above its
edges, hid the top edges themselves, because a ray leaving an edge met its own
face 3.2e-9 mm along, past the own-face margin of 1e-6 of the face (1.4e-9).
The margin now also covers 1e-14 of the body's offset (about 45 ulps of its
coordinates), which only matters for parts far smaller than their distance
from the origin.
* geom/hlr: no parity test for a hit on the boundary, where it is uncertain anyway
* docs/drawing-hlr: the fixtures of the review's second round
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Co-authored-by: MateuszSychXpl <151755914+MateuszSychXpl@users.noreply.github.com>
Mateusz SychandMateuszSychXpl
ebafe07487