From 85b4b25278c0acf85c6f35cb347c672f273dec5d Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Sun, 16 Apr 2017 02:12:31 +0000
Subject: [PATCH] Fix a crash changing g->meshCombine when g->type!=EXTRUDE.

---
 CHANGELOG.md        |  7 +++++++
 src/textscreens.cpp | 16 +++++++++-------
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3b84f47..9add68a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -84,6 +84,13 @@ Bugs fixed:
     as a source group also gets forced to triangle mesh.
   * Paste Transformed with a negative scale does not invert arcs.
 
+2.x
+---
+
+Bug fixes:
+  * Do not crash when changing an unconstrained lathe group between
+    union and difference modes.
+
 2.3
 ---
 
diff --git a/src/textscreens.cpp b/src/textscreens.cpp
index 9998583..8be0096 100644
--- a/src/textscreens.cpp
+++ b/src/textscreens.cpp
@@ -188,13 +188,15 @@ void TextWindow::ScreenChangeGroupOption(int link, uint32_t v) {
         case 'K': g->skipFirst = false; break;
 
         case 'c':
-            // When an extrude group is first created, it's positioned for a union
-            // extrusion. If no constraints were added, flip it when we switch between
-            // union and difference modes to avoid manual work doing the smae.
-            if(g->meshCombine != (Group::CombineAs)v && g->GetNumConstraints() == 0 &&
-               ((Group::CombineAs)v == Group::CombineAs::DIFFERENCE ||
-                g->meshCombine == Group::CombineAs::DIFFERENCE)) {
-                g->ExtrusionForceVectorTo(g->ExtrusionGetVector().Negated());
+            if(g->type == Group::Type::EXTRUDE) {
+                // When an extrude group is first created, it's positioned for a union
+                // extrusion. If no constraints were added, flip it when we switch between
+                // union and difference modes to avoid manual work doing the smae.
+                if(g->meshCombine != (Group::CombineAs)v && g->GetNumConstraints() == 0 &&
+                        ((Group::CombineAs)v == Group::CombineAs::DIFFERENCE ||
+                        g->meshCombine == Group::CombineAs::DIFFERENCE)) {
+                    g->ExtrusionForceVectorTo(g->ExtrusionGetVector().Negated());
+                }
             }
             g->meshCombine = (Group::CombineAs)v;
             break;