From aebbe807f2d7b9d4c7ed001638e58210b25dedfa Mon Sep 17 00:00:00 2001
From: Arthur <arthur.tang@bambulab.com>
Date: Fri, 10 Mar 2023 21:01:39 +0800
Subject: [PATCH] FIX: update_sequential_clearance may crash due to clipper's
 bug

offset may give empty results.
The previous patch solved the issue that the studio crashes immediately when selecting by-object printing.
This patch solves the issue that the studio crashes when moving objects with mouse after selecting by-object printing.

Jira: STUDIO-2452
Change-Id: Iacd69e67386b0750f24e5af2799ff9c0da130e88
(cherry picked from commit 8ea4379d0b6d61e91bd6704e4b1e8309cb42b924)
---
 src/slic3r/GUI/GLCanvas3D.cpp | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/src/slic3r/GUI/GLCanvas3D.cpp b/src/slic3r/GUI/GLCanvas3D.cpp
index 7756d3680..b0f9b5484 100644
--- a/src/slic3r/GUI/GLCanvas3D.cpp
+++ b/src/slic3r/GUI/GLCanvas3D.cpp
@@ -4964,17 +4964,19 @@ void GLCanvas3D::update_sequential_clearance()
         for (size_t i = 0; i < m_model->objects.size(); ++i) {
             ModelObject* model_object = m_model->objects[i];
             ModelInstance* model_instance0 = model_object->instances.front();
-            Polygon hull_2d = offset(model_object->convex_hull_2d(Geometry::assemble_transform({ 0.0, 0.0, model_instance0->get_offset().z() }, model_instance0->get_rotation(),
+            auto tmp = offset(model_object->convex_hull_2d(Geometry::assemble_transform({ 0.0, 0.0, model_instance0->get_offset().z() }, model_instance0->get_rotation(),
                 model_instance0->get_scaling_factor(), model_instance0->get_mirror())),
                 // Shrink the extruder_clearance_radius a tiny bit, so that if the object arrangement algorithm placed the objects
                 // exactly by satisfying the extruder_clearance_radius, this test will not trigger collision.
                 shrink_factor,
-                jtRound, mitter_limit).front();
-
-            Pointf3s& cache_hull_2d = m_sequential_print_clearance.m_hull_2d_cache.emplace_back(Pointf3s());
-            cache_hull_2d.reserve(hull_2d.points.size());
-            for (const Point& p : hull_2d.points) {
-                cache_hull_2d.emplace_back(unscale<double>(p.x()), unscale<double>(p.y()), 0.0);
+                jtRound, mitter_limit);
+            if (!tmp.empty()) { // tmp may be empty due to clipper's bug, see STUDIO-2452
+                Polygon hull_2d = tmp.front();
+                Pointf3s& cache_hull_2d = m_sequential_print_clearance.m_hull_2d_cache.emplace_back(Pointf3s());
+                cache_hull_2d.reserve(hull_2d.points.size());
+                for (const Point& p : hull_2d.points) {
+                    cache_hull_2d.emplace_back(unscale<double>(p.x()), unscale<double>(p.y()), 0.0);
+                }
             }
         }
         m_sequential_print_clearance_first_displacement = false;