65772958b7
delimited by the extrusion stepping and the sloping surface. This leads to a yet different metric from Cura or upstream Slic3r.
218 lines
9.3 KiB
C++
218 lines
9.3 KiB
C++
#include "libslic3r.h"
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#include "Model.hpp"
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#include "TriangleMesh.hpp"
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#include "SlicingAdaptive.hpp"
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#include <boost/log/trivial.hpp>
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// Based on the work of Florens Waserfall (@platch on github)
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// and his paper
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// Florens Wasserfall, Norman Hendrich, Jianwei Zhang:
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// Adaptive Slicing for the FDM Process Revisited
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// 13th IEEE Conference on Automation Science and Engineering (CASE-2017), August 20-23, Xi'an, China. DOI: 10.1109/COASE.2017.8256074
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// https://tams.informatik.uni-hamburg.de/publications/2017/Adaptive%20Slicing%20for%20the%20FDM%20Process%20Revisited.pdf
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// Vojtech believes that there is a bug in @platch's derivation of the triangle area error metric.
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// Following Octave code paints graphs of recommended layer height versus surface slope angle.
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#if 0
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adeg=0:1:85;
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a=adeg*pi/180;
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t=tan(a);
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tsqr=sqrt(tan(a));
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lerr=1./cos(a);
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lerr2=1./(0.3+cos(a));
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plot(adeg, t, 'b', adeg, sqrt(t), 'g', adeg, 0.5 * lerr, 'm', adeg, 0.5 * lerr2, 'r')
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xlabel("angle(deg), 0 - horizontal wall, 90 - vertical wall");
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ylabel("layer height");
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legend("tan(a) as cura - topographic lines distance limit", "sqrt(tan(a)) as PrusaSlicer - error triangle area limit", "old slic3r - max distance metric", "new slic3r - Waserfall paper");
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#endif
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#ifndef NDEBUG
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#define ADAPTIVE_LAYER_HEIGHT_DEBUG
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#endif /* NDEBUG */
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namespace Slic3r
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{
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static inline std::pair<float, float> face_z_span(const stl_facet &f)
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{
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return std::pair<float, float>(
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std::min(std::min(f.vertex[0](2), f.vertex[1](2)), f.vertex[2](2)),
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std::max(std::max(f.vertex[0](2), f.vertex[1](2)), f.vertex[2](2)));
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}
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// By Florens Waserfall aka @platch:
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// This constant essentially describes the volumetric error at the surface which is induced
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// by stacking "elliptic" extrusion threads. It is empirically determined by
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// 1. measuring the surface profile of printed parts to find
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// the ratio between layer height and profile height and then
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// 2. computing the geometric difference between the model-surface and the elliptic profile.
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//
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// The definition of the roughness formula is in
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// https://tams.informatik.uni-hamburg.de/publications/2017/Adaptive%20Slicing%20for%20the%20FDM%20Process%20Revisited.pdf
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// (page 51, formula (8))
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// Currenty @platch's error metric formula is not used.
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static constexpr double SURFACE_CONST = 0.18403;
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// for a given facet, compute maximum height within the allowed surface roughness / stairstepping deviation
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static inline float layer_height_from_slope(const SlicingAdaptive::FaceZ &face, float max_surface_deviation)
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{
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// @platch's formula, see his paper "Adaptive Slicing for the FDM Process Revisited".
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// return float(max_surface_deviation / (SURFACE_CONST + 0.5 * std::abs(normal_z)));
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// Constant stepping in horizontal direction, as used by Cura.
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// return (face.n_cos > 1e-5) ? float(max_surface_deviation * face.n_sin / face.n_cos) : FLT_MAX;
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// Constant error measured as an area of the surface error triangle, Vojtech's formula.
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// return (face.n_cos > 1e-5) ? float(1.44 * max_surface_deviation * sqrt(face.n_sin / face.n_cos)) : FLT_MAX;
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// Constant error measured as an area of the surface error triangle, Vojtech's formula with clamping to roughness at 90 degrees.
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return std::min(max_surface_deviation / 0.184f, (face.n_cos > 1e-5) ? float(1.44 * max_surface_deviation * sqrt(face.n_sin / face.n_cos)) : FLT_MAX);
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// Constant stepping along the surface, equivalent to the "surface roughness" metric by Perez and later Pandey et all, see @platch's paper for references.
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// return float(max_surface_deviation * face.n_sin);
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}
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void SlicingAdaptive::clear()
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{
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m_faces.clear();
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}
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void SlicingAdaptive::prepare(const ModelObject &object)
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{
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this->clear();
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TriangleMesh mesh = object.raw_mesh();
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const ModelInstance &first_instance = *object.instances.front();
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mesh.transform(first_instance.get_matrix(), first_instance.is_left_handed());
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// 1) Collect faces from mesh.
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m_faces.reserve(mesh.stl.stats.number_of_facets);
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for (const stl_facet &face : mesh.stl.facet_start) {
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Vec3f n = face.normal.normalized();
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m_faces.emplace_back(FaceZ({ face_z_span(face), std::abs(n.z()), std::sqrt(n.x() * n.x() + n.y() * n.y()) }));
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}
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// 2) Sort faces lexicographically by their Z span.
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std::sort(m_faces.begin(), m_faces.end(), [](const FaceZ &f1, const FaceZ &f2) { return f1.z_span < f2.z_span; });
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}
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// current_facet is in/out parameter, rememebers the index of the last face of m_faces visited,
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// where this function will start from.
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// print_z - the top print surface of the previous layer.
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// returns height of the next layer.
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float SlicingAdaptive::next_layer_height(const float print_z, float quality_factor, size_t ¤t_facet)
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{
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float height = (float)m_slicing_params.max_layer_height;
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float max_surface_deviation;
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{
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#if 0
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// @platch's formula for quality:
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double delta_min = SURFACE_CONST * m_slicing_params.min_layer_height;
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double delta_mid = (SURFACE_CONST + 0.5) * m_slicing_params.layer_height;
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double delta_max = (SURFACE_CONST + 0.5) * m_slicing_params.max_layer_height;
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#else
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// Vojtech's formula for triangle area error metric.
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double delta_min = m_slicing_params.min_layer_height;
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double delta_mid = m_slicing_params.layer_height;
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double delta_max = m_slicing_params.max_layer_height;
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#endif
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max_surface_deviation = (quality_factor < 0.5f) ?
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lerp(delta_min, delta_mid, 2. * quality_factor) :
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lerp(delta_max, delta_mid, 2. * (1. - quality_factor));
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}
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// find all facets intersecting the slice-layer
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size_t ordered_id = current_facet;
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{
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bool first_hit = false;
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for (; ordered_id < m_faces.size(); ++ ordered_id) {
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const std::pair<float, float> &zspan = m_faces[ordered_id].z_span;
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// facet's minimum is higher than slice_z -> end loop
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if (zspan.first >= print_z)
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break;
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// facet's maximum is higher than slice_z -> store the first event for next cusp_height call to begin at this point
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if (zspan.second > print_z) {
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// first event?
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if (! first_hit) {
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first_hit = true;
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current_facet = ordered_id;
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}
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// skip touching facets which could otherwise cause small cusp values
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if (zspan.second < print_z + EPSILON)
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continue;
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// compute cusp-height for this facet and store minimum of all heights
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height = std::min(height, layer_height_from_slope(m_faces[ordered_id], max_surface_deviation));
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}
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}
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}
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// lower height limit due to printer capabilities
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height = std::max(height, float(m_slicing_params.min_layer_height));
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// check for sloped facets inside the determined layer and correct height if necessary
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if (height > float(m_slicing_params.min_layer_height)) {
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for (; ordered_id < m_faces.size(); ++ ordered_id) {
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const std::pair<float, float> &zspan = m_faces[ordered_id].z_span;
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// facet's minimum is higher than slice_z + height -> end loop
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if (zspan.first >= print_z + height)
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break;
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// skip touching facets which could otherwise cause small cusp values
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if (zspan.second < print_z + EPSILON)
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continue;
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// Compute cusp-height for this facet and check against height.
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float reduced_height = layer_height_from_slope(m_faces[ordered_id], max_surface_deviation);
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float z_diff = zspan.first - print_z;
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if (reduced_height < z_diff) {
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assert(z_diff < height + EPSILON);
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// The currently visited triangle's slope limits the next layer height so much, that
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// the lowest point of the currently visible triangle is already above the newly proposed layer height.
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// This means, that we need to limit the layer height so that the offending newly visited triangle
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// is just above of the new layer.
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#ifdef ADAPTIVE_LAYER_HEIGHT_DEBUG
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BOOST_LOG_TRIVIAL(trace) << "cusp computation, height is reduced from " << height << "to " << z_diff << " due to z-diff";
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#endif /* ADAPTIVE_LAYER_HEIGHT_DEBUG */
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height = z_diff;
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} else if (reduced_height < height) {
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#ifdef ADAPTIVE_LAYER_HEIGHT_DEBUG
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BOOST_LOG_TRIVIAL(trace) << "adaptive layer computation: height is reduced from " << height << "to " << reduced_height << " due to higher facet";
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#endif /* ADAPTIVE_LAYER_HEIGHT_DEBUG */
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height = reduced_height;
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}
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}
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// lower height limit due to printer capabilities again
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height = std::max(height, float(m_slicing_params.min_layer_height));
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}
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#ifdef ADAPTIVE_LAYER_HEIGHT_DEBUG
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BOOST_LOG_TRIVIAL(trace) << "adaptive layer computation, layer-bottom at z:" << print_z << ", quality_factor:" << quality_factor << ", resulting layer height:" << height;
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#endif /* ADAPTIVE_LAYER_HEIGHT_DEBUG */
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return height;
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}
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// Returns the distance to the next horizontal facet in Z-dir
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// to consider horizontal object features in slice thickness
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float SlicingAdaptive::horizontal_facet_distance(float z)
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{
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for (size_t i = 0; i < m_faces.size(); ++ i) {
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std::pair<float, float> zspan = m_faces[i].z_span;
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// facet's minimum is higher than max forward distance -> end loop
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if (zspan.first > z + m_slicing_params.max_layer_height)
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break;
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// min_z == max_z -> horizontal facet
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if (zspan.first > z && zspan.first == zspan.second)
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return zspan.first - z;
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}
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// objects maximum?
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return (z + (float)m_slicing_params.max_layer_height > (float)m_slicing_params.object_print_z_height()) ?
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std::max((float)m_slicing_params.object_print_z_height() - z, 0.f) : (float)m_slicing_params.max_layer_height;
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}
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}; // namespace Slic3r
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