Bracket a toolchange's own gcode against FanMover splitting its moves (#15904)

FanMover could split a move inside change_filament_gcode to place a delayed fan command. It computed the split point from the last position the G-code set, but on Bambu printers the firmware moves the head during the T command, so the inserted waypoint sent the head to a spot the template never visits (#15789).

Both toolchange paths, set_extruder() and the Type1 append_tcr(), now wrap the template output in ;_FAN_MOVER_SKIP_START/END tags when fan speed-up or kick-start is on. FanMover keeps fan commands inside them where they are and drops the tags from the output. multifilament_config() also sizes the per-filament options that the wipe tower reads by index.

src/libslic3r/GCode.cpp

@@ -1033,6 +1033,15 @@ static std::vector<Vec2d> get_path_of_change_filament(const Print& print)
         return buf;
     }
 
+    // FanMover consumes these markers (and drops them) to avoid splitting a G1 inside custom gcode.
+    // Only written when FanMover runs, the same gate as its construction in GCode::process_layers.
+    static std::string wrap_custom_gcode_for_fan_mover(const FullPrintConfig &config, const std::string &gcode)
+    {
+        if (config.fan_speedup_time.value == 0 && config.fan_kickstart.value <= 0)
+            return gcode;
+        return ";_FAN_MOVER_SKIP_START\n" + gcode + ";_FAN_MOVER_SKIP_END\n";
+    }
+
     std::string WipeTowerIntegration::append_tcr(GCode& gcodegen, const WipeTower::ToolChangeResult& tcr, int new_filament_id, double z) const
     {
         if (new_filament_id != -1 && new_filament_id != tcr.new_tool)
@@ -1384,6 +1393,9 @@ static std::vector<Vec2d> get_path_of_change_filament(const Print& print)
             toolchange_gcode_str = gcodegen.placeholder_parser_process("change_filament_gcode", change_filament_gcode, new_filament_id, &config);
 
             check_add_eol(toolchange_gcode_str);
+            // Type1 wipe tower path (every BBL printer): bracket the same way set_extruder() does,
+            // so FanMover doesn't split a G1 inside this custom gcode either.
+            toolchange_gcode_str = wrap_custom_gcode_for_fan_mover(gcodegen.config(), toolchange_gcode_str);
 
             //BBS
             {
@@ -10895,7 +10907,8 @@ std::string GCode::set_extruder(unsigned int new_filament_id, double print_z, bo
 
         toolchange_gcode_parsed = placeholder_parser_process("change_filament_gcode", change_filament_gcode, new_filament_id, &dyn_config);
         check_add_eol(toolchange_gcode_parsed);
-        gcode += toolchange_gcode_parsed;
+        // toolchange_gcode_parsed is still read below (get_last_z_from_gcode, custom_gcode_changes_tool).
+        gcode += wrap_custom_gcode_for_fan_mover(m_config, toolchange_gcode_parsed);
 
         //BBS
         {

src/libslic3r/GCode/FanMover.cpp

@@ -445,6 +445,11 @@ void FanMover::_process_gcode_line(GCodeReader& reader, const GCodeReader::GCode
                 std::string extrusion_string = line.raw().substr(6, line.raw().size() - 6);
                 current_role = ExtrusionEntity::string_to_role(extrusion_string);
             }
+            if (line.raw().rfind(";_FAN_MOVER_SKIP_", 0) == 0) {
+                // Internal markers: read here, then dropped from the output.
+                m_is_custom_gcode = line.raw().rfind(";_FAN_MOVER_SKIP_START", 0) == 0;
+                time = -1;
+            }
             if (line.raw().size() > 16) {
                 if (line.raw().rfind("; custom gcode", 0) != std::string::npos) {
                     if (line.raw().rfind("; custom gcode end", 0) != std::string::npos)

tests/fff_print/test_helpers.cpp

@@ -223,7 +223,10 @@ DynamicPrintConfig multifilament_config(unsigned int filaments, std::initializer
 	// These are read by filament id during export but absent from filament_option_keys(),
 	// so set_num_filaments leaves them size 1; size them too, else out-of-range access.
 	const auto &defaults = FullPrintConfig::defaults();
-	for (const char *key : { "filament_type", "filament_vendor", "filament_start_gcode" })
+	for (const char *key : { "filament_type", "filament_vendor", "filament_start_gcode", "filament_change_length", "filament_change_length_nc",
+	                         "filament_ramming_travel_time", "filament_ramming_travel_time_nc",
+	                         "filament_ramming_volumetric_speed", "filament_ramming_volumetric_speed_nc",
+	                         "nozzle_temperature", "nozzle_temperature_initial_layer" })
 		static_cast<ConfigOptionVectorBase *>(config.option(key, true))->resize(filaments, defaults.option(key));
 
 	// flush_volumes_matrix must be sized filaments*filaments or export rejects it.

tests/fff_print/test_multifilament.cpp

@@ -315,6 +315,79 @@ TEST_CASE("Per-object wall filament override is honored", "[MultiFilament]")
     CHECK(tools_for_role(gcode, "infill")    == std::set<int>{ 0 }); // infill not overridden: stays on F1
 }
 
+// FanMover's guard against splitting a G1 inside custom gcode keys off the ";_FAN_MOVER_SKIP_START/END"
+// markers GCode::set_extruder() must emit around change_filament_gcode's output. Direct
+// toolchanges and Type2's wipe-tower toolchange (append_tcr2() calls set_extruder()) both go
+// through it; Type1's wipe-tower toolchange (WipeTowerIntegration::append_tcr(), append_tcr2's only
+// sibling caller of change_filament_gcode) needs the same bracketing of its own.
+TEST_CASE("Toolchange gcode is bracketed against FanMover splitting its moves", "[MultiFilament]")
+{
+    const std::string custom_gcode = "; fan full\nM106 P1 S255\nM400 S3\nG1 X77 F5000\nG1 X91 F3000\n";
+
+    // "direct": no prime tower, GCode::set_extruder() runs the toolchange. By-object sequencing
+    // with a per-object filament override is what makes one happen at all without a tower.
+    // "type1": a Type1 prime tower routes the toolchange through WipeTowerIntegration::append_tcr()
+    // instead (append_tcr2, Type2's equivalent, itself calls set_extruder() - so Type2 needs no
+    // separate case here).
+    const std::string path = GENERATE(as<std::string>{}, "direct", "type1");
+    CAPTURE(path);
+
+    std::string gcode_str;
+    if (path == "direct") {
+        const std::vector<std::vector<Slic3r::ConfigBase::SetDeserializeItem>> per_object_overrides = {
+            {}, { { "outer_wall_filament_id", "2" }, { "inner_wall_filament_id", "2" } }
+        };
+        DynamicPrintConfig config = multifilament_config(2, {
+            { "skirt_loops",           0 },
+            { "brim_type",             "no_brim" },
+            { "print_sequence",        "by object" },
+            { "change_filament_gcode", custom_gcode },
+            { "fan_speedup_time",      0.5 },
+            { "fan_kickstart",         0.1 },
+        });
+        gcode_str = slice_with_object_overrides({ cube(20), cube(20) }, config, per_object_overrides);
+    } else {
+        const std::vector<std::vector<Slic3r::ConfigBase::SetDeserializeItem>> per_object_overrides = {
+            { { "extruder", "1" } }, { { "extruder", "2" } }
+        };
+        DynamicPrintConfig config = multifilament_config(2, {
+            { "change_filament_gcode", custom_gcode },
+            { "fan_speedup_time",      0.5 },
+            { "fan_kickstart",         0.1 },
+            { "enable_prime_tower",    true },
+            { "wipe_tower_type",       "type1" },
+            { "prime_tower_width",     35 },
+            { "wipe_tower_x",          120 },
+            { "wipe_tower_y",          120 },
+            { "printable_area",        "0x0,200x0,200x200,0x200" },
+            { "skirt_loops",           0 },
+            { "brim_type",             "no_brim" },
+        });
+        gcode_str = slice_with_object_overrides({ cube(20), cube(20) }, config, per_object_overrides);
+    }
+
+    // The resolved-settings config footer echoes "change_filament_gcode = ..." with its value
+    // escaped, so drop it before counting or its own copy of "G1 X77 F5000" is miscounted.
+    const size_t footer_start = gcode_str.find("; CONFIG_BLOCK_START");
+    REQUIRE(footer_start != std::string::npos);
+    gcode_str.erase(footer_start);
+
+    auto count_occurrences = [](const std::string &haystack, const std::string &needle) {
+        size_t count = 0, pos = 0;
+        while ((pos = haystack.find(needle, pos)) != std::string::npos) {
+            ++count;
+            pos += needle.size();
+        }
+        return count;
+    };
+    const size_t total_waypoints = count_occurrences(gcode_str, "G1 X77 F5000");
+    const size_t bracketed       = count_occurrences(gcode_str, "M400 S3\nG1 X77 F5000");
+    REQUIRE(total_waypoints > 0);
+    CHECK(bracketed == total_waypoints);
+    // FanMover drops its own markers; only the start-of-print toolchange, which it never processes, keeps them.
+    CHECK(count_occurrences(gcode_str, ";_FAN_MOVER_SKIP_START") <= 1);
+}
+
 // With wait_for_temp_on_wipe_tower the blocking M109 moves from right after the Tn command to
 // a stop point parked beside the wipe tower (heat-up drool falls next to the tower, not onto
 // its top): tagged with _WAIT_FOR_TEMP_ON_WIPE_TOWER, after the toolchange and before the