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Feature: Add inward wipe for external perimeters (#15407)

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Valerii Bokhan
2026-09-15 20:01:39 -03:00
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# Wipe inward — High Level Design
## Purpose and scope
Wipe inward reduces reheating of fresh plastic and visible seam artifacts by
moving the hot nozzle toward adjacent printed material during the external-wall
wipe. Wipe marks are especially visible at layer heights below 0.1 mm.
The option applies only to wipes after external walls, including walls around
holes. It does not offset wipes after inner walls, infill or supports. For an
outer contour the move is inward; for a hole it is away from the hole, toward
the surrounding material. The path must remain supported by material that is
already present when the wipe executes.
The operation belongs to G-code generation. It uses extrusion paths, their actual
widths and their print order. Changing its settings invalidates G-code export
while preserving the sliced geometry.
## Settings and eligibility
`wipe_inward` defaults to disabled and requires Wipe while retracting to be
enabled for the active filament. `wipe_inward_distance` defaults to 50% of the
actual external-wall extrusion width; it also accepts an absolute distance in
millimeters. Using the path width makes Auto width and Arachne's variable widths
meaningful. The effective offset is limited by that width and the spacing to the
adjacent wall. A zero distance disables the offset.
Only external perimeters with a suitable, previously printed inner perimeter
are eligible. A configured wall count alone cannot establish eligibility:
the local geometry may contain fewer walls, and walls scheduled later do not
provide support. Outer/Inner wall order therefore normally retains the regular
wipe path.
Retraction and pressure advance calibrations disable inward wiping so it cannot
mask the behavior being measured. The calibration settings turn it off, and
G-code generation enforces this even if a profile or object override enables it.
## Path selection and support
The planner identifies an adjacent inner perimeter on the material side of the
outgoing wall. Contour winding and the distinction between outer contours and
holes establish a preferred direction; local printed geometry resolves ambiguous
or self-touching contours.
Candidate paths offset or translate the portion needed for the configured wipe
distance. A wide seam gap can prevent a supported forward path; following the
incoming printed wall backwards is also a candidate. If translating that wall
cannot provide a complete wipe around a curve, the planner tries an offset of
the reversed wall. Direction checks allow coordinate-rounding error at a
perpendicular entry, while rejecting actual backtracking. The planner checks the
complete executable path, including its connector from the nozzle position,
against the current and earlier printed perimeters. Nearby endpoints alone do
not establish support across a gap.
Each region accumulates its printed perimeter prefix once, in extrusion order.
Every entity contributes its geometry only after it is printed, and the prefix
is discarded when the region ends. This collection is skipped when inward wiping
is disabled or its configured distance is zero. A mixed inner-wall loop remains
an eligible target even when its first path is an overhang: ordinary inner-wall
paths elsewhere in the loop identify it. Likewise, an external loop with an
overhanging start remains eligible when other segments identify the external
wall. It is available for support checks but is not an inner-wall target.
Candidate-specific support filtering and AABB trees are built only for eligible
external loops, then reused across their candidate paths.
Material-side validation applies with or without a seam gap. Along each
candidate, local wall normals point toward the adjacent printed inner wall;
samples on the opposite side are rejected even when they remain close enough
to the external wall to pass the support check. This uses the open wall geometry
without treating it as a closed polygon. Full paths at a zero-gap seam also
retain clearance from the external wall after their initial connector. At a
clipped corner, another branch can be closer than the requested offset, so
material-side and support checks apply without that additional clearance rule.
An accepted candidate replaces the stored wipe path as a whole. A short direct
inward move is also eligible when longer candidates fail validation. It may
waive full wall clearance, but must pass the material-side check. Its initial
direction is checked from the actual nozzle position after any loop pre-move;
the original wall endpoint is retained separately for intersection checks. It takes
priority over the alternate offset when the preferred and translated paths
are unusable. A longer reversed path may replace the selected candidate only
when its distance to the target inner wall is no worse within tolerance.
## Fallback to the regular wipe
The original wipe path is retained when:
- No suitable adjacent inner wall has already been printed near the seam. This
includes single-wall areas, locally missing inner walls and normally Outer/Inner
wall order. A distant wall or a wall on the air side does not qualify.
- The requested or available offset, or the configured wipe distance, is zero
or too small at the geometry's coordinate precision.
- Degenerate geometry prevents construction of a usable candidate, or all
candidates fail the checks for printed support, direction, wall clearance or
the connector from the actual nozzle position. This can occur at tight corners,
narrow features or seam gaps.
Corners and seam gaps do not automatically trigger fallback: an offset,
translated, reversed or short direct inward path may still be valid. The regular
wipe is retained only when no candidate is accepted.
Fallback uses the path and retraction rules for `wipe_inward` disabled.
Wipe while retracting must still be enabled for a wipe to occur; `wipe_on_loops`
remains controlled by its own setting.
## Interaction with Wipe on loop
`wipe_on_loops` is an independent option that makes a short move before leaving
an external loop. It can operate with `wipe_inward` disabled. When both options
are enabled, its destination is the starting position for the inward wipe.
The loop move samples the outgoing and incoming paths by distance across path
boundaries. The sampling distance is bounded by the nozzle diameter and one
quarter of the total path length. It samples the outgoing path at up to 20% of
the nozzle diameter and rotates that point around the seam through one third
of the material-side corner angle. For a closed square outer contour, this
produces a move of 20% of the nozzle diameter at 30 degrees into the corner.
Coincident samples or degenerate angles suppress the move.
The nozzle position stored by G-code generation must match the emitted loop
move. Both travel planning and wipe execution depend on this position, including
when Wipe inward is disabled.
With a seam gap, a loop move may advance past the inward offset's original entry.
If that alone makes the connector backtrack, the entry advances to the nozzle's
projection on the offset. The planner extends the source as needed to preserve
the configured wipe length and validates the new connector and complete path.
Joins that already backtrack across the seam gap are not adjusted this way.
## Execution and retraction
The stored wipe path uses a sentinel first point. Execution starts from the
actual nozzle position and proceeds to the second stored point. Path selection,
support validation and wipe-length calculation must all use this same executable
geometry, especially after a Wipe on loop move.
An accepted inward path executes at the end of the external loop, after any
Wipe on loop move, without retracting filament. It consumes the stored path and
updates the nozzle position before travel planning. A short travel to the next
wall cannot discard this wipe or force a retraction or Z-hop. Subsequent travel
uses the normal minimum-travel threshold and retraction/lift settings from the
new position. The regular wipe, including fallback, remains deferred until a
normal retraction uses it.
Retraction is divided into portions before, during and after wiping. The amount
that can be retracted during the wipe depends on its executable length, wipe
speed and the active filament's retraction speed. Fractional retraction speeds
are retained in this calculation. For a 2 mm wipe at 100 mm/s and a retraction
speed of 25.5 mm/s, the wipe can retract 0.51 mm. With a total retraction of 0.8 mm
and both before/after percentages set to zero, the remaining 0.29 mm is retracted
before wiping. This split applies to regular deferred wipes, including fallback;
an accepted inward wipe executes separately without retraction.
## Implementation and verification
- [GCode.cpp](../../src/libslic3r/GCode.cpp) integrates path selection, nozzle
position and retraction; [Print.cpp](../../src/libslic3r/Print.cpp) controls
invalidation, and [PrintConfig.cpp](../../src/libslic3r/PrintConfig.cpp) defines
the settings.
- [WipePathHelpers](../../src/libslic3r/GCode/WipePathHelpers.hpp) implements path
sampling, offset selection and support checks.
- [Geometry tests](../../tests/libslic3r/test_wipe_path.cpp) cover support,
degenerate paths, contour and hole orientations, and exact loop-move geometry
across path subdivisions.
- [FFF tests](../../tests/fff_print/test_wipe.cpp) cover emitted trajectories,
fallback, minimum-travel retraction and Z-hop rules, and export invalidation.
With Wipe inward disabled, they check the loop move's direction and magnitude
for Classic and Arachne, the subsequent wipe's start and length, and fractional
retraction splitting in absolute and relative E modes.
Loop-move checks use reserved role/wipe markers and extrusion state, and run
with human-readable G-code comments both enabled and disabled.