From a8465cbc8a373f591809b080c26028c489ce9a81 Mon Sep 17 00:00:00 2001
From: EvilSpirit <anandamide@mail.ru>
Date: Wed, 4 May 2016 16:18:13 +0600
Subject: [PATCH] Flip extrusion normal when switching between union and
 difference.

This is done because a meaningful union extrusion is almost never
a meaningful difference extrusion, and saves a bunch of common
manual work.

To avoid creating invalid sketches this isn't done when there are any
constraints.
---
 src/group.cpp       | 20 ++++++++++++++++++++
 src/sketch.h        |  3 +++
 src/textscreens.cpp | 10 +++++++++-
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/src/group.cpp b/src/group.cpp
index 706e5efc..b8ed86c4 100644
--- a/src/group.cpp
+++ b/src/group.cpp
@@ -51,6 +51,26 @@ bool Group::IsVisible(void) {
     return true;
 }
 
+int Group::GetNumConstraints(void) {
+    int num = 0;
+    for(int i = 0; i < SK.constraint.n; i++) {
+        Constraint *c = &SK.constraint.elem[i];
+        if(c->group.v != h.v) continue;
+        num++;
+    }
+    return num;
+}
+
+Vector Group::ExtrusionGetVector() {
+    return Vector::From(h.param(0), h.param(1), h.param(2));
+}
+
+void Group::ExtrusionForceVectorTo(const Vector &v) {
+    SK.GetParam(h.param(0))->val = v.x;
+    SK.GetParam(h.param(1))->val = v.y;
+    SK.GetParam(h.param(2))->val = v.z;
+}
+
 void Group::MenuGroup(int id) {
     Group g = {};
     g.visible = true;
diff --git a/src/sketch.h b/src/sketch.h
index 65e08214..d39e476f 100644
--- a/src/sketch.h
+++ b/src/sketch.h
@@ -236,6 +236,9 @@ public:
     void AddEq(IdList<Equation,hEquation> *l, Expr *expr, int index);
     void GenerateEquations(IdList<Equation,hEquation> *l);
     bool IsVisible(void);
+    int GetNumConstraints();
+    Vector ExtrusionGetVector();
+    void ExtrusionForceVectorTo(const Vector &v);
 
     // Assembling the curves into loops, and into a piecewise linear polygon
     // at the same time.
diff --git a/src/textscreens.cpp b/src/textscreens.cpp
index 5cf4eeb5..09ba5634 100644
--- a/src/textscreens.cpp
+++ b/src/textscreens.cpp
@@ -191,7 +191,15 @@ void TextWindow::ScreenChangeGroupOption(int link, uint32_t v) {
         case 'k': g->skipFirst = true; break;
         case 'K': g->skipFirst = false; break;
 
-        case 'c': g->meshCombine = v; 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 != v && g->GetNumConstraints() == 0) {
+                g->ExtrusionForceVectorTo(g->ExtrusionGetVector().Negated());
+            }
+            g->meshCombine = v;
+            break;
 
         case 'P': g->suppress = !(g->suppress); break;