From f6f75a6a0d9e3532cf05a2c20e3a00150d5df796 Mon Sep 17 00:00:00 2001
From: Florian Foinant-Willig <flachyjoe@gmail.com>
Date: Mon, 16 Jun 2025 22:25:13 +0200
Subject: [PATCH] Sketcher: Fix circle-line negative distance

---
 src/Mod/Sketcher/App/planegcs/Constraints.cpp      | 14 ++++++++++++--
 src/Mod/Sketcher/Gui/CommandConstraints.cpp        |  8 ++++----
 .../Sketcher/SketcherTests/TestSketcherSolver.py   |  3 +--
 3 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/src/Mod/Sketcher/App/planegcs/Constraints.cpp b/src/Mod/Sketcher/App/planegcs/Constraints.cpp
index d6efa6ec5c..b6f564ca2b 100644
--- a/src/Mod/Sketcher/App/planegcs/Constraints.cpp
+++ b/src/Mod/Sketcher/App/planegcs/Constraints.cpp
@@ -2990,11 +2990,21 @@ void ConstraintC2LDistance::errorgrad(double* err, double* grad, double* param)
     double dh = (darea - h * dlength) / length;
 
     if (err) {
-        *err = *distance() + *circle.rad - h;
+        if (h < *circle.rad) {
+            *err = *circle.rad - *distance() - h;
+        }
+        else {
+            *err = *circle.rad + *distance() - h;
+        }
     }
     else if (grad) {
         if (param == distance() || param == circle.rad) {
-            *grad = 1.0;
+            if (h < *circle.rad) {
+                *grad = -1.0;
+            }
+            else {
+                *grad = 1.0;
+            }
         }
         else {
             *grad = -dh;
diff --git a/src/Mod/Sketcher/Gui/CommandConstraints.cpp b/src/Mod/Sketcher/Gui/CommandConstraints.cpp
index 3619111a05..894cd063c3 100644
--- a/src/Mod/Sketcher/Gui/CommandConstraints.cpp
+++ b/src/Mod/Sketcher/Gui/CommandConstraints.cpp
@@ -2259,10 +2259,10 @@ protected:
                 Base::Vector3d pnt1 = lineSeg->getStartPoint();
                 Base::Vector3d pnt2 = lineSeg->getEndPoint();
                 Base::Vector3d d = pnt2 - pnt1;
-                double ActDist =
-                    std::abs(-center1.x * d.y + center1.y * d.x + pnt1.x * pnt2.y - pnt2.x * pnt1.y)
-                        / d.Length()
-                    - radius1;
+                double ActDist = std::abs(
+                            std::abs(-center1.x * d.y + center1.y * d.x + pnt1.x * pnt2.y - pnt2.x * pnt1.y)
+                            / d.Length()
+                            - radius1);
 
                 Gui::cmdAppObjectArgs(Obj,
                                       "addConstraint(Sketcher.Constraint('Distance',%d,%d,%f))",
diff --git a/src/Mod/Sketcher/SketcherTests/TestSketcherSolver.py b/src/Mod/Sketcher/SketcherTests/TestSketcherSolver.py
index 00c9676ac0..e88c6dc6e7 100644
--- a/src/Mod/Sketcher/SketcherTests/TestSketcherSolver.py
+++ b/src/Mod/Sketcher/SketcherTests/TestSketcherSolver.py
@@ -464,8 +464,7 @@ class TestSketcherSolver(unittest.TestCase):
         sketch.addConstraint(
             [Sketcher.Constraint("Block", c_idx), Sketcher.Constraint("Block", l_idx)]
         )
-        # use a negative distance to tell "line is within the circle"
-        expected_distance = -radius / 2  # note that we don't set this in the constraint below!
+        expected_distance = radius / 2  # note that we don't set this in the constraint below!
         # TODO: addConstraint(constraint) triggers a solve (for godd reasons) however, this way
         # one cannot add non-driving constraints. In contrast, addConstraint(list(constraint))
         # does not solve automatically, thus we use this "overload".