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Fix belt printer phantom extrusion line from Y=0 in preview

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On a belt printer the sliced preview drew a stray extrusion-colored line
from Y~=0 to the model, rendered in the first extrusion role's color. It is
not a travel and does not occur on non-belt printers.

GCodeProcessor::store_move_vertex pins a move's stored Z to the first-layer
height during the start-G-code "prepare" stage. That is a harmless cosmetic
tidy-up on a normal printer, but on a belt printer the designed-view
back-transform couples machine Z into the rendered model Y (the belt tilt
mixes the height and belt-feed axes). Pinning Z back-transforms the last
prepare-stage move (the unretract before the first extrusion) to model
Y ~= 0, and libvgcode then draws a phantom extrusion segment from Y ~= 0 to
the first real toolpath.

Keep the real Z for belt printers (gated on belt_tilt_angle, parsed from the
G-code header before the body) so prepare-stage moves back-transform
correctly. Non-belt processing is byte-identical. The emitted G-code was
already correct; this is a preview-geometry fix.
This commit is contained in:
harrierpigeon
2026-06-29 02:58:58 -05:00
parent 02e313a115
commit a83cd8aa29
1 changed files with 17 additions and 1 deletions
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18
src/libslic3r/GCode/GCodeProcessor.cpp
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@@ -7067,6 +7067,22 @@ void GCodeProcessor::store_move_vertex(EMoveType type, EMovePathType path_type,
m_result.print_statistics.total_travel_distance += m_travel_dist; m_result.print_statistics.total_travel_distance += m_travel_dist;
} }
// During the start G-code "prepare" stage the toolhead Z is not yet a real
// print height on a normal printer, so it is pinned to the first-layer height
// to keep the preview tidy. Belt printers are the exception: there the Z is
// written explicitly by BeltGCodeWriter and the designed-view back-transform
// couples machine Z into the rendered model Y (the belt tilt mixes the height
// and belt-feed axes). Overriding Z therefore back-transforms the last
// prepare-stage move (the unretract before the first extrusion) to model
// Y ~= 0, and the libvgcode path builder then draws a phantom extrusion
// segment from Y ~= 0 to the first real toolpath. Keep the real Z for belt
// printers so prepare-stage moves map correctly. Gated on belt_tilt_angle (set
// from the G-code header before the body is processed) so non-belt processing
// is byte-identical.
const float store_z = (m_processing_start_custom_gcode && m_result.belt_tilt_angle == 0.f)
? m_first_layer_height
: m_end_position[Z] - m_z_offset;
m_result.moves.push_back({ m_result.moves.push_back({
m_last_line_id, m_last_line_id,
type, type,
@@ -7074,7 +7090,7 @@ void GCodeProcessor::store_move_vertex(EMoveType type, EMovePathType path_type,
static_cast<unsigned char>(filament_id), static_cast<unsigned char>(filament_id),
m_cp_color.current, m_cp_color.current,
//BBS: add plate's offset to the rendering vertices //BBS: add plate's offset to the rendering vertices
Vec3f(m_end_position[X] + m_x_offset, m_end_position[Y] + m_y_offset, m_processing_start_custom_gcode ? m_first_layer_height : m_end_position[Z]- m_z_offset) + m_extruder_offsets[filament_id], Vec3f(m_end_position[X] + m_x_offset, m_end_position[Y] + m_y_offset, store_z) + m_extruder_offsets[filament_id],
static_cast<float>(m_end_position[E] - m_start_position[E]), static_cast<float>(m_end_position[E] - m_start_position[E]),
m_feedrate, m_feedrate,
0.0f, // actual feedrate 0.0f, // actual feedrate