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Keep the Scarf Seam Free of Sub-Millimetre Segments (#15832)

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A scarf joint split the loop at exactly the scarf length, so the remainder
of the segment the split landed in became the first flat segment, often a
fraction of a millimetre. The seam insertion also leaves segments of a few
micrometres at both ends of the loop, which a scarf extrudes through where a
plain loop would start or stop. With junction deviation the planner treats
such short moves as tight corners, limited by the Z axis acceleration at the
end of the ramp, and slows to a third of the wall speed or nearly halts at
the seam.

Extend the ramp to the next vertex when the remainder would be shorter than
half a scarf step, capped at a millimetre, beyond which planners treat a move
as ordinary; the scarf only grows, never shrinks. Drop the vertex next to the
seam point at either end when that segment is shorter than an eighth of a
common line width, so the loop still starts and ends at the seam; a trimmed
path loses its arc fitting and prints as line segments. Clamp the scarf
length to the trimmed loop so a scarf covering a whole loop still ends at
full flow. The descending pass reuses the same path, so both wedges stay
consistent, and a flat part that would collapse to a single point is dropped.
This commit is contained in:
HanifKoh
2026-09-25 12:32:05 +08:00
committed by GitHub
parent 7cb7465ed8
commit db10c719f6
2 changed files with 180 additions and 2 deletions
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tests/fff_print/test_extrusion_entity.cpp
+101
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@@ -84,3 +84,104 @@ SCENARIO("Polygon flattening", "[ExtrusionEntity]") {
}
}
}
static ExtrusionPaths straight_path(const std::vector<double> &xs)
{
ExtrusionPath path{erExternalPerimeter, 1.0, 0.45f, 0.2f};
for (double x : xs)
path.polyline.append(Point3::new_scale(x, 0., 0.));
return {path};
}
TEST_CASE("Scarf ramp ends on the next loop vertex instead of leaving a short stub", "[ExtrusionEntity]")
{
using Catch::Matchers::WithinAbs;
// A 20 mm scarf in 10 steps: a remainder shorter than half a 2 mm step is snapped forward.
const double slope_length = 20.;
const double max_segment = scale_(slope_length / 10);
SECTION("a 0.09 mm remainder extends the ramp to the vertex") {
ExtrusionPaths paths = straight_path({0., 5., 10., 15., 20.09, 25., 30.});
ExtrusionLoopSloped loop(paths, 0., slope_length, max_segment, 0.);
REQUIRE(loop.starts.size() == 1);
REQUIRE(loop.ends.size() == 1);
REQUIRE(loop.paths.size() == 1);
CHECK_THAT(unscale_(loop.starts.front().polyline.last_point().x()), WithinAbs(20.09, 1e-3));
CHECK_THAT(unscale_(loop.ends.front().polyline.last_point().x()), WithinAbs(20.09, 1e-3));
CHECK_THAT(unscale_(loop.paths.front().polyline.first_point().x()), WithinAbs(20.09, 1e-3));
CHECK_THAT(unscale_(loop.paths.front().polyline.lines().front().length()), WithinAbs(4.91, 1e-3));
}
SECTION("a remainder longer than half a step keeps the exact scarf length") {
ExtrusionPaths paths = straight_path({0., 5., 10., 15., 21.5, 25., 30.});
ExtrusionLoopSloped loop(paths, 0., slope_length, max_segment, 0.);
REQUIRE(loop.starts.size() == 1);
REQUIRE(loop.paths.size() == 1);
CHECK_THAT(unscale_(loop.starts.front().polyline.last_point().x()), WithinAbs(20., 1e-3));
CHECK_THAT(unscale_(loop.paths.front().polyline.first_point().x()), WithinAbs(20., 1e-3));
CHECK_THAT(unscale_(loop.paths.front().polyline.lines().front().length()), WithinAbs(1.5, 1e-3));
}
SECTION("the ramp never grows by more than a millimetre, whatever the step size") {
ExtrusionPaths paths = straight_path({0., 5., 10., 15., 21.5, 25., 30.});
ExtrusionLoopSloped loop(paths, 0., slope_length, scale_(slope_length), 0.); // a single 20 mm step
REQUIRE(loop.paths.size() == 1);
CHECK_THAT(unscale_(loop.starts.front().polyline.last_point().x()), WithinAbs(20., 1e-3));
}
SECTION("snapping onto the path's last vertex leaves no single-point flat path") {
ExtrusionPaths paths = straight_path({0., 5., 10., 15., 20.5});
ExtrusionLoopSloped loop(paths, 0., slope_length, max_segment, 0.);
REQUIRE(loop.starts.size() == 1);
CHECK(loop.paths.empty());
CHECK_THAT(unscale_(loop.starts.front().polyline.last_point().x()), WithinAbs(20.5, 1e-3));
}
}
TEST_CASE("Scarf loop drops the micro segments the seam insertion leaves at both ends", "[ExtrusionEntity]")
{
using Catch::Matchers::WithinAbs;
const double slope_length = 20.;
const double max_segment = scale_(slope_length / 10);
SECTION("a 3 um segment at each end of a single path is removed, the seam point stays") {
ExtrusionPaths paths = straight_path({0., 0.003, 5., 10., 15., 21.5, 25., 29.997, 30.});
ExtrusionLoopSloped loop(paths, 0., slope_length, max_segment, 0.);
REQUIRE(loop.starts.size() == 1);
REQUIRE(loop.paths.size() == 1);
const Polyline3 &start = loop.starts.front().polyline;
CHECK_THAT(unscale_(start.first_point().x()), WithinAbs(0., 1e-4));
CHECK_THAT(unscale_(start.lines().front().length()), WithinAbs(1.25, 1e-3)); // 5 mm halved twice
const Polyline3 &flat = loop.paths.front().polyline;
CHECK_THAT(unscale_(flat.last_point().x()), WithinAbs(30., 1e-4));
CHECK_THAT(unscale_(flat.lines().back().length()), WithinAbs(5., 1e-3));
}
SECTION("a micro path of its own is dropped and the neighbour ends at the seam point") {
ExtrusionPaths paths = straight_path({0., 0.003});
ExtrusionPaths rest = straight_path({0.003, 5., 10., 15., 21.5, 25., 30.});
paths.push_back(rest.front());
ExtrusionLoopSloped loop(paths, 0., slope_length, max_segment, 0.);
REQUIRE(loop.starts.size() == 1);
CHECK_THAT(unscale_(loop.starts.front().polyline.first_point().x()), WithinAbs(0., 1e-4));
CHECK_THAT(unscale_(loop.starts.front().polyline.lines().front().length()), WithinAbs(1.25, 1e-3));
}
SECTION("a scarf covering the whole loop still ends at full flow after a trim") {
// The caller sizes the scarf from the untrimmed loop: 10.003 mm here, 10 mm after the trim.
ExtrusionPaths paths = straight_path({0., 0.003, 5., 10.});
ExtrusionLoopSloped loop(paths, 0., 10.003, max_segment, 0.);
REQUIRE(loop.starts.size() == 1);
CHECK(loop.paths.empty());
CHECK_THAT(loop.starts.back().slope_end.e_ratio, WithinAbs(1., 1e-9));
CHECK_THAT(unscale_(loop.starts.back().polyline.last_point().x()), WithinAbs(10., 1e-4));
}
SECTION("segments longer than the tolerance are kept") {
ExtrusionPaths paths = straight_path({0., 0.3, 5., 10., 15., 21.5, 25., 29.7, 30.});
ExtrusionLoopSloped loop(paths, 0., slope_length, max_segment, 0.);
REQUIRE(loop.paths.size() == 1);
CHECK_THAT(unscale_(loop.starts.front().polyline.lines().front().length()), WithinAbs(0.3, 1e-3));
CHECK_THAT(unscale_(loop.paths.front().polyline.lines().back().length()), WithinAbs(0.3, 1e-3));
}
}