Make outline font min segment length configurable

This was hard coded at 10IU, which was way too small for pcbnew and
still too small for schematic editor.  Instead, we set a default of 50
and allow the user to adjust (smaller for less powerful machines)

Fixes https://gitlab.com/kicad/code/kicad/-/issues/16568

common/advanced_config.cpp

@@ -103,6 +103,7 @@ static const wxChar EnableGit[] = wxT( "EnableGit" );
 static const wxChar EnableEeschemaPrintCairo[] = wxT( "EnableEeschemaPrintCairo" );
 static const wxChar DisambiguationTime[] = wxT( "DisambiguationTime" );
 static const wxChar PcbSelectionVisibilityRatio[] = wxT( "PcbSelectionVisibilityRatio" );
+static const wxChar MinimumSegmentLength[] = wxT( "MinimumSegmentLength" );
 } // namespace KEYS
 
 
@@ -245,6 +246,8 @@ ADVANCED_CFG::ADVANCED_CFG()
 
     m_PcbSelectionVisibilityRatio = 1.0;
 
+    m_MinimumSegmentLength      = 50;
+
     loadFromConfigFile();
 }
 
@@ -437,6 +440,10 @@ void ADVANCED_CFG::loadSettings( wxConfigBase& aCfg )
                                                   &m_PcbSelectionVisibilityRatio,
                                                   m_PcbSelectionVisibilityRatio, 0.0, 1.0 ) );
 
+    configParams.push_back( new PARAM_CFG_INT( true, AC_KEYS::MinimumSegmentLength,
+                                                  &m_MinimumSegmentLength,
+                                                  m_MinimumSegmentLength, 10, 1000 ) );
+
     // Special case for trace mask setting...we just grab them and set them immediately
     // Because we even use wxLogTrace inside of advanced config
     wxString traceMasks;

common/font/outline_decomposer.cpp

@@ -24,6 +24,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
  */
 
+#include <advanced_config.h>
 #include <font/outline_decomposer.h>
 #include <bezier_curves.h>
 
@@ -176,10 +177,8 @@ bool OUTLINE_DECOMPOSER::approximateCubicBezierCurve( GLYPH_POINTS&       aResul
 {
     wxASSERT( aCubicBezier.size() == 4 );
 
-    // minimumSegmentLength defines the "smoothness" of the
-    // curve-to-straight-segments conversion: the larger, the coarser
-    // TODO: find out what the minimum segment length should really be!
-    constexpr int minimumSegmentLength = 10;
+
+    static int minimumSegmentLength = ADVANCED_CFG::GetCfg().m_MinimumSegmentLength;
     BEZIER_POLY   converter( aCubicBezier );
     converter.GetPoly( aResult, minimumSegmentLength );
 

include/advanced_config.h

@@ -498,6 +498,17 @@ public:
      * Default value: 1
      */
     double m_PcbSelectionVisibilityRatio;
+
+    /**
+     * Length of the minimum segment for the outline decomposer.  This is in IU, so
+     * it is nm in pcbnew and 100nm in eeschema.
+     *
+     * Setting name: "MinimumSegmentLength"
+     * Valid values: 10 to 1000
+     * Default value: 50
+     */
+    int m_MinimumSegmentLength;
+
 ///@}