feat(imex): effective_physical_extruder_map helper + diagnostic no-filament tooltip

Centralize the project→printer→printer_extruder_id fallback for the physical
extruder map. PrintApply, PartPlate (ghost color + cache key), Plater (tooltip
+ click gate) all previously open-coded the three-step lookup, and each handled
the "pem unset, derive from pei" case slightly differently — an IDEX printer
without an explicit pem could paint an UNPRINTABLE_COLOR ghost even though the
slicer would have derived a valid mapping.

- IMEXHelpers: add effective_physical_extruder_map(explicit_pem, pei) and a
  PresetBundle overload that wraps the project→printer precedence.
- PrintApply: use the helper in place of the inline pei→pem normalization.
- PartPlate / Plater: call the PresetBundle overload at every ghost-color,
  ghost-cache-key, tooltip, and click-gate site.
- Plater::format_imex_ghost_tooltip: when no filament resolves to a head,
  surface an actionable message directing the user to extend the extruder
  count in the Machine tab, instead of the generic "(no filament routed)".
- IMEXFilamentPickerPopover: hold m_pem by value so callers can pass a
  stack-local derived pem without lifetime worries.
- Tests: 5 new cases covering explicit-wins, default-pem fallback, null
  inputs, and the IDEX ghost-color regression that motivated this.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/libslic3r/IMEXHelpers.cpp

@@ -6,8 +6,33 @@
 #include <sstream>
 #include <unordered_set>
 
+#include "libslic3r/PresetBundle.hpp"
+
 namespace Slic3r {
 
+ConfigOptionInts effective_physical_extruder_map(const ConfigOptionInts* explicit_pem,
+                                                  const ConfigOptionInts* printer_extruder_id)
+{
+    if (explicit_pem && explicit_pem->values.size() >= 2)
+        return *explicit_pem;
+    ConfigOptionInts derived;
+    if (printer_extruder_id) {
+        derived.values.reserve(printer_extruder_id->values.size());
+        for (int v : printer_extruder_id->values)
+            derived.values.push_back(v - 1);
+    }
+    return derived;
+}
+
+ConfigOptionInts effective_physical_extruder_map(const PresetBundle& pb)
+{
+    const ConfigOptionInts* explicit_pem = pb.project_config.option<ConfigOptionInts>("physical_extruder_map");
+    if (!explicit_pem || explicit_pem->values.size() < 2)
+        explicit_pem = pb.printers.get_edited_preset().config.option<ConfigOptionInts>("physical_extruder_map");
+    const ConfigOptionInts* pei = pb.printers.get_edited_preset().config.option<ConfigOptionInts>("printer_extruder_id");
+    return effective_physical_extruder_map(explicit_pem, pei);
+}
+
 int first_filament_for_physical_head(const ConfigOptionInts& pem, int physical)
 {
     const auto& v = pem.values;

src/libslic3r/IMEXHelpers.hpp

@@ -11,6 +11,25 @@
 
 namespace Slic3r {
 
+class PresetBundle;
+
+// Returns the effective physical_extruder_map given an optionally-explicit map and
+// the printer's `printer_extruder_id`. If `explicit_pem` has size >= 2 the caller
+// authored one, and it is returned verbatim. Otherwise the map is auto-derived
+// from `printer_extruder_id` by converting each 1-indexed value to 0-indexed.
+// Returns an empty ConfigOptionInts if neither source yields any values.
+// Slice-time (PrintApply) and GUI ghost-color paths both call this so a printer
+// profile without an explicit pem still gets a consistent mapping.
+ConfigOptionInts effective_physical_extruder_map(const ConfigOptionInts* explicit_pem,
+                                                  const ConfigOptionInts* printer_extruder_id);
+
+// GUI overload: resolves the effective pem from a live PresetBundle using the
+// project_config → printer preset fallback, then derives from printer_extruder_id
+// if neither holds a user-authored map (size >= 2). Use this instead of open-coding
+// the lookup at ghost-color, tooltip, click-gate, and cache-key call sites so they
+// all agree on what the slicer will see.
+ConfigOptionInts effective_physical_extruder_map(const PresetBundle& pb);
+
 // Returns the lowest 0-based logical filament index L such that pem[L] == physical.
 // Returns -1 if no filament routes to `physical`.
 // Degenerate case: an empty pem returns 0 when `physical == 0` (identity-on-head-0

src/libslic3r/PrintApply.cpp

@@ -1,4 +1,5 @@
 #include "ClipperUtils.hpp"
+#include "IMEXHelpers.hpp"
 #include "Model.hpp"
 #include "Print.hpp"
 
@@ -1168,11 +1169,8 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
     {
         auto* pem = new_full_config.option<ConfigOptionInts>("physical_extruder_map", true);
         const auto* pei = new_full_config.option<ConfigOptionInts>("printer_extruder_id");
-        if (pem && pei && !pei->values.empty() && pem->values.size() <= 1) {
-            pem->values.clear();
-            for (int v : pei->values)
-                pem->values.push_back(v - 1); // convert 1-indexed extruder IDs to 0-indexed
-        }
+        if (pem)
+            pem->values = effective_physical_extruder_map(pem, pei).values;
     }
 
     m_ori_full_print_config = new_full_config;

src/slic3r/GUI/IMEXFilamentPickerPopover.hpp

@@ -30,7 +30,10 @@ private:
     void on_filament_selected(int slot_1_based);
 
     PartPlate*              m_plate;
-    const ConfigOptionInts& m_pem;
+    // Owned by value: callers may pass a stack-local derived pem
+    // (e.g. effective_physical_extruder_map result) that won't outlive
+    // the popover's async lifetime.
+    ConfigOptionInts        m_pem;
     int                     m_physical_head;
     CommitCallback          m_on_commit;
 

src/slic3r/GUI/PartPlate.cpp

@@ -438,14 +438,9 @@ ColorRGBA PartPlate::get_imex_head_filament_color(int physical_head) const
     if (!pb)
         return GLVolume::UNPRINTABLE_COLOR;
 
-    const ConfigOptionInts* pem = pb->project_config.option<ConfigOptionInts>("physical_extruder_map");
-    if (!pem || pem->values.size() < 2)
-        pem = pb->printers.get_edited_preset().config.option<ConfigOptionInts>("physical_extruder_map");
-    if (!pem)
-        return GLVolume::UNPRINTABLE_COLOR;
-
+    const ConfigOptionInts pem = effective_physical_extruder_map(*pb);
     const auto plate_map = get_imex_head_filament_map();
-    const int logical = resolve_filament_for_head(plate_map, *pem, physical_head);
+    const int logical = resolve_filament_for_head(plate_map, pem, physical_head);
     if (logical < 0)
         return GLVolume::UNPRINTABLE_COLOR;
 
@@ -979,13 +974,11 @@ std::string PartPlate::build_imex_ghost_cache_key() const
     if (k.empty()) return "";  // ghost-off when zones-off
 
     if (auto* pb = wxGetApp().preset_bundle) {
-        const ConfigOptionInts* pem = pb->project_config.option<ConfigOptionInts>("physical_extruder_map");
-        if (!pem || pem->values.size() < 2)
-            pem = pb->printers.get_edited_preset().config.option<ConfigOptionInts>("physical_extruder_map");
-        if (pem) {
-            k += "|pem";
-            for (int v : pem->values) { k += ':'; k += std::to_string(v); }
-        }
+        // Keyed on the effective pem (project → printer → pei-derived) so a printer
+        // swap that only changes printer_extruder_id still invalidates the ghost cache.
+        const ConfigOptionInts pem = effective_physical_extruder_map(*pb);
+        k += "|pem";
+        for (int v : pem.values) { k += ':'; k += std::to_string(v); }
     }
     k += "|obj";
     for (const auto& oi : obj_to_instance_set)

src/slic3r/GUI/Plater.cpp

@@ -18543,14 +18543,15 @@ Plater::ImexGhostTooltip Plater::format_imex_ghost_tooltip(int physical_head) co
         return t;
     }
 
-    const ConfigOptionInts* pem = wxGetApp().preset_bundle->project_config.option<ConfigOptionInts>("physical_extruder_map");
-    if (!pem || pem->values.size() < 2)
-        pem = wxGetApp().preset_bundle->printers.get_edited_preset().config.option<ConfigOptionInts>("physical_extruder_map");
-
+    const ConfigOptionInts pem = effective_physical_extruder_map(*wxGetApp().preset_bundle);
     const auto map = plate->get_imex_head_filament_map();
-    const int logical = pem ? resolve_filament_for_head(map, *pem, physical_head) : -1;
+    const int logical = resolve_filament_for_head(map, pem, physical_head);
     if (logical < 0) {
-        t.label = "T" + std::to_string(physical_head) + " -> (no filament routed)";
+        // No filament slot resolves to this physical head. Usually means the printer's
+        // extruder count is understated relative to the filament palette (user added a
+        // filament without extending printer_extruder_id in the Machine tab).
+        t.label = "T" + std::to_string(physical_head) + " — no filament routed\n"
+                  "Add an extruder in the Machine tab so this head has a filament slot.";
         return t;
     }
     t.filament_slot_1based = logical + 1;
@@ -18563,13 +18564,10 @@ Plater::ImexGhostTooltip Plater::format_imex_ghost_tooltip(int physical_head) co
 
 void Plater::on_imex_ghost_click(int physical_head)
 {
-    const ConfigOptionInts* pem = wxGetApp().preset_bundle->project_config.option<ConfigOptionInts>("physical_extruder_map");
-    if (!pem || pem->values.size() < 2)
-        pem = wxGetApp().preset_bundle->printers.get_edited_preset().config.option<ConfigOptionInts>("physical_extruder_map");
-    if (!pem) return;
+    const ConfigOptionInts pem = effective_physical_extruder_map(*wxGetApp().preset_bundle);
 
     int lane_count = 0;
-    for (int pv : pem->values) if (pv == physical_head) ++lane_count;
+    for (int pv : pem.values) if (pv == physical_head) ++lane_count;
     if (lane_count < 2) return;  // single-lane head -> click is a no-op, tooltip conveyed status
 
     PartPlate* plate = p->partplate_list.get_curr_plate();
@@ -18577,7 +18575,7 @@ void Plater::on_imex_ghost_click(int physical_head)
 
     auto* picker = new IMEXFilamentPickerPopover(
         p->view3D->get_canvas3d()->get_wxglcanvas(),
-        plate, *pem, physical_head,
+        plate, pem, physical_head,
         [this]() {
             take_snapshot("edit imex head filament");
             update_project_dirty_from_presets();

tests/libslic3r/test_imex_helpers.cpp

@@ -13,6 +13,42 @@ static ConfigOptionInts make_pem(std::vector<int> v) {
     return o;
 }
 
+TEST_CASE("effective_physical_extruder_map — explicit wins", "[IMEX]") {
+    auto explicit_pem = make_pem({0, 0, 0, 0, 1, 2, 3});
+    auto pei          = make_pem({1, 2, 3, 4}); // would derive to {0,1,2,3}
+    auto out = effective_physical_extruder_map(&explicit_pem, &pei);
+    REQUIRE(out.values == std::vector<int>{0, 0, 0, 0, 1, 2, 3});
+}
+
+TEST_CASE("effective_physical_extruder_map — default pem falls back to pei derive", "[IMEX]") {
+    auto default_pem = make_pem({0});           // size 1, the PrintConfig default
+    auto pei         = make_pem({1, 2});        // 1-indexed IDEX
+    auto out = effective_physical_extruder_map(&default_pem, &pei);
+    REQUIRE(out.values == std::vector<int>{0, 1}); // 1-indexed → 0-indexed
+}
+
+TEST_CASE("effective_physical_extruder_map — null explicit, pei present", "[IMEX]") {
+    auto pei = make_pem({1, 2, 3});
+    auto out = effective_physical_extruder_map(nullptr, &pei);
+    REQUIRE(out.values == std::vector<int>{0, 1, 2});
+}
+
+TEST_CASE("effective_physical_extruder_map — both absent yields empty", "[IMEX]") {
+    auto out = effective_physical_extruder_map(nullptr, nullptr);
+    REQUIRE(out.values.empty());
+}
+
+TEST_CASE("effective_physical_extruder_map — IDEX ghost-color regression guard", "[IMEX]") {
+    // Printer with printer_extruder_id = [1, 2] and no explicit pem (default {0}).
+    // Before the GUI fix, this scenario produced a black ghost on T1 because
+    // first_filament_for_physical_head({0}, 1) == -1.
+    auto default_pem = make_pem({0});
+    auto pei         = make_pem({1, 2});
+    auto pem         = effective_physical_extruder_map(&default_pem, &pei);
+    REQUIRE(first_filament_for_physical_head(pem, 0) == 0);
+    REQUIRE(first_filament_for_physical_head(pem, 1) == 1); // no longer -1
+}
+
 TEST_CASE("first_filament_for_physical_head — identity pem", "[IMEX]") {
     auto pem = make_pem({0, 1, 2, 3});
     REQUIRE(first_filament_for_physical_head(pem, 0) == 0);