Toolchange Cyclic Order (#14868)

* Toolchange Cyclic Order

* Apply cyclic order to first layer

* Unit test

* Copilot fixes

---------

Co-authored-by: Rodrigo Faselli <162915171+RF47@users.noreply.github.com>

src/libslic3r/GCode/ToolOrdering.cpp

@@ -2735,6 +2735,28 @@ void ToolOrdering::enforce_mixed_component_order()
     }
 }
 
+// Declared in ToolOrdering.hpp (exposed for unit testing).
+std::vector<unsigned int> parse_cyclic_order(const std::string& str, unsigned int number_of_extruders)
+{
+    std::vector<unsigned int> order;
+    for (const std::string& token : split_string(str, ',')) {
+        try {
+            size_t pos      = 0;
+            int    filament = std::stoi(token, &pos); // stoi skips leading whitespace by itself
+            // stoi stops at the first non-digit, so "2x" would parse as 2. Require the whole token to be
+            // consumed (bar trailing whitespace) to drop it like any other garbage.
+            if (token.find_first_not_of(" \t\r\n", pos) != std::string::npos)
+                continue;
+            if (filament >= 1 && (unsigned int)filament <= number_of_extruders
+                && std::find(order.begin(), order.end(), (unsigned int)(filament - 1)) == order.end())
+                order.emplace_back((unsigned int)(filament - 1));
+        } catch (const std::exception&) {
+            // Not a number, ignore it.
+        }
+    }
+    return order;
+}
+
 void ToolOrdering::reorder_extruders_for_minimum_flush_volume(bool reorder_first_layer)
 {
     const PrintConfig* print_config = m_print_config_ptr;
@@ -2832,11 +2854,41 @@ void ToolOrdering::reorder_extruders_for_minimum_flush_volume(bool reorder_first
     const bool use_cyclic_ordering =
         (print_config->toolchange_ordering == ToolChangeOrderingType::Cyclic);
 
+    // By default the first layer keeps its adhesion-optimized order (and any custom first layer
+    // sequence); the cyclic sequence is only forced onto it when the user opts in.
+    const bool cyclic_first_layer = use_cyclic_ordering && print_config->toolchange_cyclic_first_layer.value;
+
+    // Optional user defined cyclic sequence, given as 1-based filament numbers ("3,2,1,4"). Filaments
+    // missing from it keep their ascending order after the listed ones, so a partial or bogus entry
+    // still yields the default cyclic order.
+    const std::vector<unsigned int> cyclic_order =
+        use_cyclic_ordering ? parse_cyclic_order(print_config->toolchange_cyclic_order.value, number_of_extruders)
+                            : std::vector<unsigned int>();
+
+    // Reorder a layer's filaments (0-based) for cyclic ordering: ascending by default, or following the
+    // user defined sequence when one was given. Filaments absent from the sequence keep ascending order
+    // after the listed ones.
+    auto apply_cyclic_order = [&cyclic_order](std::vector<unsigned int>& filaments) {
+        std::sort(filaments.begin(), filaments.end());
+        if (!cyclic_order.empty())
+            std::stable_sort(filaments.begin(), filaments.end(), [&cyclic_order](unsigned int lhs, unsigned int rhs) {
+                auto rank = [&cyclic_order](unsigned int filament) {
+                    return size_t(std::find(cyclic_order.begin(), cyclic_order.end(), filament) - cyclic_order.begin());
+                };
+                return rank(lhs) < rank(rhs);
+            });
+    };
+
     // other_layers_seq: the layer_idx and extruder_idx are base on 1
-    auto get_custom_seq = [&other_layers_seqs, &reorder_first_layer, &first_layer_filaments, &layer_filaments, use_cyclic_ordering](int layer_idx, std::vector<int>& out_seq) -> bool {
+    auto get_custom_seq = [&other_layers_seqs, &reorder_first_layer, &first_layer_filaments, &layer_filaments, use_cyclic_ordering, cyclic_first_layer, &apply_cyclic_order](int layer_idx, std::vector<int>& out_seq) -> bool {
         if (!reorder_first_layer && layer_idx == 0) {
-            out_seq.resize(first_layer_filaments.size());
-            std::transform(first_layer_filaments.begin(), first_layer_filaments.end(), out_seq.begin(), [](auto item) {return item + 1; });
+            // The first layer tool order is already decided (adhesion-optimized, plus any custom first
+            // layer sequence). Only override it with the cyclic sequence when the user opted in.
+            std::vector<unsigned int> ordered = first_layer_filaments;
+            if (cyclic_first_layer)
+                apply_cyclic_order(ordered);
+            out_seq.resize(ordered.size());
+            std::transform(ordered.begin(), ordered.end(), out_seq.begin(), [](auto item) {return int(item) + 1; });
             return true;
         }
         for (size_t idx = other_layers_seqs.size() - 1; idx != size_t(-1); --idx) {
@@ -2847,9 +2899,12 @@ void ToolOrdering::reorder_extruders_for_minimum_flush_volume(bool reorder_first
             }
         }
 
-        if (use_cyclic_ordering && layer_idx >= 0 && size_t(layer_idx) < layer_filaments.size()) {
+        // Skip the first layer here (layer_idx == 0 only reaches this point on the reorder_first_layer
+        // path) unless the user asked for cyclic order on it, so it keeps the default flush ordering.
+        if (use_cyclic_ordering && layer_idx >= 0 && (layer_idx != 0 || cyclic_first_layer)
+            && size_t(layer_idx) < layer_filaments.size()) {
             std::vector<unsigned int> ordered = layer_filaments[size_t(layer_idx)];
-            std::sort(ordered.begin(), ordered.end());
+            apply_cyclic_order(ordered);
             out_seq.resize(ordered.size());
             std::transform(ordered.begin(), ordered.end(), out_seq.begin(), [](auto item) { return int(item) + 1; });
             return true;