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Separated infills — High Level Design
Purpose and scope
An object's infill patterns are laid out from one reference point, the center
of the object. When an object groups several parts that do not touch, every
part cuts the same object-wide pattern at a different place, so equal parts get
different infill. separated_infills lays the infill of every connected body
out from the center of that body instead, as if the body were sliced on its own.
The option covers sparse infill, internal solid infill and bridges. Top and
bottom surfaces are left to center_of_surface_pattern, which centers the
Archimedean Chords and Octagram Spiral surface patterns. The option is off by
default; with it off, or for an object made of a single body, no fill changes.
Adaptive Cubic and Support Cubic do not depend on the option: they always fill
each body on its own (see Octree infill).
Bodies
PrintObject::prepare_infill() groups the islands of every layer (lslices)
into 3D connected bodies before bridges are detected, so bridge anchors and
printed infill share one origin. Islands on adjacent layers belong to one body
when their slices overlap. Parts that touch or overlap form one body. Separate
parts, disconnected islands of one mesh, and interleaved parts that never touch,
such as chain links, each form their own. Every island stores the index of its
body in Layer::lslices_separated_component_ids, and
PrintObject::separated_body_bboxes() holds the bounding box of each body over
all its layers.
The pass runs when a region uses separated infills, per-model surface centering or an octree infill pattern. It is skipped when the object has one model part that cannot be split, since a single body already shares the object center.
Centering a fill
infill_body() matches each fill region to the island it overlaps most, among
the islands whose bounding boxes overlap it, and the filler takes the bounding
box of that island's body instead of the object's. The box covers every layer
of the body, which is the box the body gets when sliced alone, so patterns that
depend on its extent as well as its center come out the same too. Bridge
anchoring (Layer::generate_sparse_infill_polylines_for_anchoring()) makes the
same choice, so the anchors match the printed infill.
The patterns follow the body's box in one of two ways:
- Rectilinear and its variants, Line, Grid, Triangles, Tri-hexagon, Cubic,
Quarter Cubic, Lateral Lattice, Lateral Honeycomb and the plane-path patterns
(Hilbert Curve, Archimedean Chords, Octagram Spiral) are laid out from the
box: they phase their lines through its center, and Hilbert Curve and the Zig
Zag links start from its corner.
Fill::extended_object_bounding_box()extends the box about its center, so it also serves a box that is not centered on the origin. - Honeycomb, 3D Honeycomb, Cross Hatch, Gyroid, TPMS-D and TPMS-FK are laid out
from the coordinate origin, which is the object center. They return true from
Fill::aligned_to_origin(), andFill::fill_surface()moves each region so that the box center lands on the origin, fills it, and moves the paths back. With the default box the center is the origin, so nothing moves.
is_separable_infill_pattern() lists these patterns. The settings show the
option only when the sparse infill pattern is one of them.
Octree infill
Adaptive Cubic and Support Cubic take their lines from an octree, laid out from
the center of the mesh it is built from and refined near its surfaces. An
octree of the whole object would lay every part out from the object's center
and refine it near the other parts, so these patterns
(is_octree_infill_pattern()) always fill each body on its own, and the
settings hide the option for them.
For an object of several bodies, PrintObject::prepare_adaptive_infill_data()
builds one octree per body (FillAdaptive::Octrees) from the triangles of that
body only, which is the octree the body gets when sliced alone. Each connected
component of the mesh goes to the body that most of a few sampled triangles lie
on. A sample is taken a layer height inside the solid, behind the triangle, and
looked up in the islands of the nearest layer. Each internal bridge surface goes
to the body of its island. The fill takes the octree of the region's body, from
the same infill_body(). The octree of the whole object is built only for an
object of a single body, or when some body received no triangles, which then
uses it.
Patterns left out
Lightning grows its trees over the whole object, so moving a reference point cannot center it on one body. Concentric and Spiral Inset follow the outline of each region and need no centering.
Solid infill at full density spaces its lines over the extent of each region, so it is already independent of the other bodies. Only bridges, which keep their line spacing, and the plane-path solid patterns depend on the center.