STEP: Implementation ported from BambuStudio:

CMake handling is different

STEP: Removed preprocessing stage

STEP: Small refactoring

STEP: Bigger refactoring

STEP: Changed naming on loaded object and volumes:
If the STEP contains exactly one named volume, the object and its first
volume will both have that name. Otherwise, filename w/o suffix is used
as object name and volumes are named using names from the STEP (if there
is none, untranslated "PartN" string is used).

STEP: Load the libraries dynamically on Win

wip

src/libslic3r/Format/STEP.cpp

@@ -0,0 +1,110 @@
+#include "STEP.hpp"
+#include "occt_wrapper/OCCTWrapper.hpp"
+
+#include "libslic3r/Model.hpp"
+#include "libslic3r/TriangleMesh.hpp"
+
+#include <string>
+#include <functional>
+
+#ifdef _WIN32
+    #include<windows.h>
+#else
+    #include<occt_wrapper/OCCTWrapper.hpp>
+    #include <dlfcn.h>
+#endif
+
+
+namespace Slic3r {
+
+LoadStepFn get_load_step_fn()
+{
+    static LoadStepFn load_step_fn = nullptr;
+
+    if (!load_step_fn) {
+#ifdef _WIN32
+        HMODULE module = LoadLibraryW(L"OCCTWrapper.dll");
+        if (module == NULL)
+            throw Slic3r::RuntimeError("Cannot load OCCTWrapper.dll");
+
+        try {
+            const char* fn_name = "load_step_internal";
+            FARPROC farproc = GetProcAddress(module, fn_name);
+            if (! farproc) {
+                DWORD ec = GetLastError();
+                throw Slic3r::RuntimeError(std::string("Cannot load function from OCCTWrapper.dll: ") + fn_name
+                                           + "\n\nError code: " + std::to_string(ec));
+            }
+            load_step_fn = reinterpret_cast<LoadStepFn>(farproc);
+        } catch (const Slic3r::RuntimeError&) {
+            FreeLibrary(module);
+            throw;
+        }
+#else
+        void *plugin_ptr = dlopen("OCCTWrapper.so", RTLD_NOW | RTLD_GLOBAL);
+
+        if (plugin_ptr) {
+            load_step_fn = reinterpret_cast<LoadStepFn>(dlsym(plugin_ptr, "load_step_internal"));
+            if (!load_step_fn) {
+                dlclose(plugin_ptr);
+            }
+        }
+#endif
+    }
+
+    return load_step_fn;
+}
+
+bool load_step(const char *path, Model *model /*BBS:, ImportStepProgressFn proFn*/)
+{
+    OCCTResult occt_object;
+
+    LoadStepFn load_step_fn = get_load_step_fn();
+
+    if (!load_step_fn)
+        return false;
+
+    load_step_fn(path, &occt_object);
+
+    assert(! occt_object.volumes.empty());
+    
+    assert(boost::algorithm::iends_with(occt_object.object_name, ".stp")
+        || boost::algorithm::iends_with(occt_object.object_name, ".step"));
+    occt_object.object_name.erase(occt_object.object_name.find("."));
+    assert(! occt_object.object_name.empty());
+
+
+    ModelObject* new_object = model->add_object();
+    new_object->input_file = path;
+    if (new_object->volumes.size() == 1 && ! occt_object.volumes.front().volume_name.empty())
+        new_object->name = new_object->volumes.front()->name;
+    else
+        new_object->name = occt_object.object_name;
+
+
+    for (size_t i=0; i<occt_object.volumes.size(); ++i) {
+        indexed_triangle_set its;
+        for (size_t j=0; j<occt_object.volumes[i].vertices.size(); ++j)
+            its.vertices.emplace_back(Vec3f(occt_object.volumes[i].vertices[j][0],
+                                            occt_object.volumes[i].vertices[j][1],
+                                            occt_object.volumes[i].vertices[j][2]));
+        for (size_t j=0; j<occt_object.volumes[i].indices.size(); ++j)
+            its.indices.emplace_back(Vec3i(occt_object.volumes[i].indices[j][0],
+                                           occt_object.volumes[i].indices[j][1],
+                                           occt_object.volumes[i].indices[j][2]));
+        its_merge_vertices(its, true);
+        TriangleMesh triangle_mesh(std::move(its));
+        ModelVolume* new_volume = new_object->add_volume(std::move(triangle_mesh));
+
+        new_volume->name = occt_object.volumes[i].volume_name.empty()
+                       ? std::string("Part") + std::to_string(i+1)
+                       : occt_object.volumes[i].volume_name;
+        new_volume->source.input_file = path;
+        new_volume->source.object_idx = (int)model->objects.size() - 1;
+        new_volume->source.volume_idx = (int)new_object->volumes.size() - 1;
+    }
+
+    return true;
+}
+
+}; // namespace Slic3r

src/libslic3r/Format/STEP.hpp

@@ -0,0 +1,19 @@
+// Original implementation of STEP format import created by Bambulab.
+// https://github.com/bambulab/BambuStudio
+// Forked off commit 1555904, modified by Prusa Research.
+
+#ifndef slic3r_Format_STEP_hpp_
+#define slic3r_Format_STEP_hpp_
+
+namespace Slic3r {
+
+class Model;
+
+//typedef std::function<void(int load_stage, int current, int total, bool& cancel)> ImportStepProgressFn;
+
+// Load a step file into a provided model.
+extern bool load_step(const char *path_str, Model *model /*LMBBS:, ImportStepProgressFn proFn = nullptr*/);
+
+}; // namespace Slic3r
+
+#endif /* slic3r_Format_STEP_hpp_ */