Phase 3 rework: Compare pre-selects checked presets

- DiffPresetDialog::show() overload takes left/right preset names
- Batch management Compare button passes first two checked presets
- Compare dialog opens on top without closing batch management
- Existing show() behavior unchanged for other callers

Author: adele-with-a-b

src/slic3r/GUI/UnsavedChangesDialog.cpp

@@ -2098,6 +2098,23 @@ void DiffPresetDialog::show(Preset::Type type /* = Preset::TYPE_INVALID*/)
     Show();
 }
 
+void DiffPresetDialog::show(Preset::Type type, const std::string &left, const std::string &right)
+{
+    show(type);
+
+    // Pre-select the requested presets in the combo boxes
+    for (auto &preset_combos : m_preset_combos) {
+        if (preset_combos.presets_left->get_type() != type)
+            continue;
+        if (!left.empty())
+            preset_combos.presets_left->update(left);
+        if (!right.empty())
+            preset_combos.presets_right->update(right);
+        break;
+    }
+    update_tree();
+}
+
 void DiffPresetDialog::update_presets(Preset::Type type)
 {
     m_pr_technology = m_preset_bundle_left.get()->printers.get_edited_preset().printer_technology();

src/slic3r/GUI/UnsavedChangesDialog.hpp

@@ -449,6 +449,7 @@ class DiffPresetDialog : public DPIDialog
     ~DiffPresetDialog(){};
 
     void                    show(Preset::Type type = Preset::TYPE_INVALID);
+    void                    show(Preset::Type type, const std::string &left, const std::string &right);
     void                    update_presets(Preset::Type type = Preset::TYPE_INVALID);
 
 protected:

src/slic3r/GUI/UserPresetsDialog.cpp

@@ -97,8 +97,10 @@ UserPresetsDialog::UserPresetsDialog(wxWindow *parent)
     m_button_compare->SetTextColorNormal(wxColor("#00AE42"));
     m_button_compare->Bind(wxEVT_COMMAND_BUTTON_CLICKED, [this](auto &) {
         Preset::Type types[] = {Preset::TYPE_PRINTER, Preset::TYPE_FILAMENT, Preset::TYPE_PRINT};
-        this->EndModal(wxID_OK);
-        wxGetApp().mainframe->diff_dialog.show(types[m_collection]);
+        std::string left, right;
+        if (m_checked_presets.size() >= 1) left = m_checked_presets[0];
+        if (m_checked_presets.size() >= 2) right = m_checked_presets[1];
+        wxGetApp().mainframe->diff_dialog.show(types[m_collection], left, right);
     });
 
     wxSizer *sizer_bottom = new wxBoxSizer(wxHORIZONTAL);