From 6975b5d84cd2000365237e1cbb384ab40b8f47ba Mon Sep 17 00:00:00 2001
From: Rodrigo Faselli <162915171+RF47@users.noreply.github.com>
Date: Tue, 7 Apr 2026 11:25:28 -0300
Subject: [PATCH] =?UTF-8?q?=F0=9F=92=A5Fix=20crash=20-=20inconsistent=20dr?=
 =?UTF-8?q?aft=20shield=20layer=20height=20(#12937)?=
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* Fix crash-inconsistent draft shield

* Skip empty skirt G-code and fix skirt_done handling

Track whether a skirt was actually generated for the current print Z and avoid appending empty skirt G-code. Only pop m_skirt_done when a skirt was emitted to prevent corrupting skirt state across multiple instances per layer. Also use a temporary string (moved into the main gcode) to detect emptiness before updating state. Preserves existing first-layer clearing behavior.
---
 src/libslic3r/GCode.cpp | 36 +++++++++++++++++++++++++++---------
 1 file changed, 27 insertions(+), 9 deletions(-)

diff --git a/src/libslic3r/GCode.cpp b/src/libslic3r/GCode.cpp
index ba47fac081..ed7f153ab3 100644
--- a/src/libslic3r/GCode.cpp
+++ b/src/libslic3r/GCode.cpp
@@ -5137,19 +5137,37 @@ LayerResult GCode::process_layer(
             if (is_anything_overridden && print_wipe_extrusions == 0)
                 gcode+="; PURGING FINISHED\n";
 
+            bool skirt_generated_for_current_print_z = false;
+
             for (InstanceToPrint &instance_to_print : instances_to_print) {
                 if (print.config().skirt_type == stPerObject && 
                     !instance_to_print.print_object.object_skirt().empty() &&
-                    print.config().print_sequence == PrintSequence::ByLayer
-                    &&
-                    (layer.id() < print.config().skirt_height || print.config().draft_shield == DraftShield::dsEnabled))
+                    print.config().print_sequence == PrintSequence::ByLayer)
                 {
-                    if (first_layer)
-                        m_skirt_done.clear();
-                    const Point& offset = instance_to_print.print_object.instances()[instance_to_print.instance_id].shift;
-                    gcode += generate_skirt(print, instance_to_print.print_object.object_skirt(), offset, instance_to_print.print_object.config().skirt_start_angle, layer_tools, layer, extruder_id);
-                    if (instances_to_print.size() > 1 && &instance_to_print != &*(instances_to_print.end() - 1))
-                        m_skirt_done.pop_back();
+                    const LayerToPrint& layer_to_print = layers[instance_to_print.layer_id];
+                    const Layer* skirt_layer = layer_to_print.object_layer;
+                    if (skirt_layer == nullptr && layer_to_print.support_layer != nullptr &&
+                        layer_to_print.support_layer->id() < layer_to_print.support_layer->object()->slicing_parameters().raft_layers()) {
+                        skirt_layer = layer_to_print.support_layer;
+                    }
+
+                    if (skirt_layer != nullptr &&
+                        (skirt_layer->id() < print.config().skirt_height || print.config().draft_shield == DraftShield::dsEnabled)) {
+                        const bool skirt_first_layer = (skirt_layer->id() == 0 && std::abs(skirt_layer->bottom_z()) < EPSILON);
+                        if (skirt_first_layer)
+                            m_skirt_done.clear();
+
+                        if (skirt_generated_for_current_print_z && !m_skirt_done.empty())
+                            m_skirt_done.pop_back();
+
+                        const Point& offset      = instance_to_print.print_object.instances()[instance_to_print.instance_id].shift;
+                        std::string  skirt_gcode = generate_skirt(print, instance_to_print.print_object.object_skirt(), offset,
+                                                                  instance_to_print.print_object.config().skirt_start_angle, layer_tools,
+                                                                  *skirt_layer, extruder_id);
+                        if (!skirt_gcode.empty())
+                            skirt_generated_for_current_print_z = true;
+                        gcode += std::move(skirt_gcode);
+                    }
                 }
                 
                 const auto& inst = instance_to_print.print_object.instances()[instance_to_print.instance_id];