From 8c101d5f281ba670a3af2663302fe3dc7fb15283 Mon Sep 17 00:00:00 2001
From: ruevs <dpr@ruevs.com>
Date: Wed, 3 Mar 2021 20:51:56 +0200
Subject: [PATCH] Fix tangent constraints of curves.

This fixes a regression introduced in  96958f466395148ee7f0a252222a2a27e7345c22
(https://github.com/solvespace/solvespace/pull/833.)
Three `return` statements got "swallowed" by the newly created functions.
(e.g .https://github.com/solvespace/solvespace/commit/96958f466395148ee7f0a252222a2a27e7345c22#diff-49abc03ed071148c0ebae0c64aafb625fa6223135f77aeecdb47dab4cf8b940cL638 )

Because of this it was possible to constrain arcs and cubics tangent to
each other or line segments, without them sharing an endpoint.

This kind of worked, but always chose the "starting" points of the curves
and lines. In the future this can be turned into a feature. See the
discussion in #937.
---
 src/constraint.cpp | 27 ++++++++++++++++++---------
 src/sketch.h       |  6 +++---
 2 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/src/constraint.cpp b/src/constraint.cpp
index 93831731..435fc3ac 100644
--- a/src/constraint.cpp
+++ b/src/constraint.cpp
@@ -127,7 +127,7 @@ hConstraint Constraint::ConstrainCoincident(hEntity ptA, hEntity ptB) {
         Entity::NO_ENTITY, Entity::NO_ENTITY, /*other=*/false, /*other2=*/false);
 }
 
-void Constraint::ConstrainArcLineTangent(Constraint *c, Entity *line, Entity *arc) {
+bool Constraint::ConstrainArcLineTangent(Constraint *c, Entity *line, Entity *arc) {
     Vector l0 = SK.GetEntity(line->point[0])->PointGetNum(),
            l1 = SK.GetEntity(line->point[1])->PointGetNum();
     Vector a1 = SK.GetEntity(arc->point[1])->PointGetNum(),
@@ -140,11 +140,12 @@ void Constraint::ConstrainArcLineTangent(Constraint *c, Entity *line, Entity *ar
         Error(_("The tangent arc and line segment must share an "
                 "endpoint. Constrain them with Constrain -> "
                 "On Point before constraining tangent."));
-        return;
+        return false;
     }
+    return true;
 }
 
-void Constraint::ConstrainCubicLineTangent(Constraint *c, Entity *line, Entity *cubic) {
+bool Constraint::ConstrainCubicLineTangent(Constraint *c, Entity *line, Entity *cubic) {
     Vector l0 = SK.GetEntity(line->point[0])->PointGetNum(),
            l1 = SK.GetEntity(line->point[1])->PointGetNum();
     Vector as = cubic->CubicGetStartNum(),
@@ -158,11 +159,12 @@ void Constraint::ConstrainCubicLineTangent(Constraint *c, Entity *line, Entity *
         Error(_("The tangent cubic and line segment must share an "
                 "endpoint. Constrain them with Constrain -> "
                 "On Point before constraining tangent."));
-        return;
+        return false;
     }
+    return true;
 }
 
-void Constraint::ConstrainCurveCurveTangent(Constraint *c, Entity *eA, Entity *eB) {
+bool Constraint::ConstrainCurveCurveTangent(Constraint *c, Entity *eA, Entity *eB) {
     Vector as = eA->EndpointStart(),
            af = eA->EndpointFinish(),
            bs = eB->EndpointStart(),
@@ -183,8 +185,9 @@ void Constraint::ConstrainCurveCurveTangent(Constraint *c, Entity *eA, Entity *e
         Error(_("The curves must share an endpoint. Constrain them "
                 "with Constrain -> On Point before constraining "
                 "tangent."));
-        return;
+        return false;
     }
+    return true;
 }
 
 void Constraint::MenuConstrain(Command id) {
@@ -690,7 +693,9 @@ void Constraint::MenuConstrain(Command id) {
                 if(line->type == Entity::Type::ARC_OF_CIRCLE) {
                     swap(line, arc);
                 }
-                ConstrainArcLineTangent(&c, line, arc);
+                if(!ConstrainArcLineTangent(&c, line, arc)) {
+                    return;
+                }
                 c.type = Type::ARC_LINE_TANGENT;
                 c.entityA = arc->h;
                 c.entityB = line->h;
@@ -700,7 +705,9 @@ void Constraint::MenuConstrain(Command id) {
                 if(line->type == Entity::Type::CUBIC) {
                     swap(line, cubic);
                 }
-                ConstrainCubicLineTangent(&c, line, cubic);
+                if(!ConstrainCubicLineTangent(&c, line, cubic)) {
+                    return;
+                }
                 c.type = Type::CUBIC_LINE_TANGENT;
                 c.entityA = cubic->h;
                 c.entityB = line->h;
@@ -711,7 +718,9 @@ void Constraint::MenuConstrain(Command id) {
                 }
                 Entity *eA = SK.GetEntity(gs.entity[0]),
                        *eB = SK.GetEntity(gs.entity[1]);
-                ConstrainCurveCurveTangent(&c, eA, eB);
+                if(!ConstrainCurveCurveTangent(&c, eA, eB)) {
+                    return;
+                }
                 c.type = Type::CURVE_CURVE_TANGENT;
                 c.entityA = eA->h;
                 c.entityB = eB->h;
diff --git a/src/sketch.h b/src/sketch.h
index 83773749..903e638f 100644
--- a/src/sketch.h
+++ b/src/sketch.h
@@ -790,9 +790,9 @@ public:
     static hConstraint TryConstrain(Constraint::Type type, hEntity ptA, hEntity ptB,
                                     hEntity entityA, hEntity entityB = Entity::NO_ENTITY,
                                     bool other = false, bool other2 = false);
-    static void ConstrainArcLineTangent(Constraint *c, Entity *line, Entity *arc);
-    static void ConstrainCubicLineTangent(Constraint *c, Entity *line, Entity *cubic);
-    static void ConstrainCurveCurveTangent(Constraint *c, Entity *eA, Entity *eB);
+    static bool ConstrainArcLineTangent(Constraint *c, Entity *line, Entity *arc);
+    static bool ConstrainCubicLineTangent(Constraint *c, Entity *line, Entity *cubic);
+    static bool ConstrainCurveCurveTangent(Constraint *c, Entity *eA, Entity *eB);
 };
 
 class hEquation {