From b905b4eac84b51757285f27f508fe76d162fbe3d Mon Sep 17 00:00:00 2001
From: Alex Shvartzkop <dudesuchamazing@gmail.com>
Date: Wed, 3 Apr 2024 00:39:55 +0300
Subject: [PATCH] Improve moving, rendering and plotting of very small angle
 arcs.

Fixes https://gitlab.com/kicad/code/kicad/-/issues/17110
---
 common/gal/opengl/opengl_gal.cpp   | 16 ++++++++++++++--
 common/plotters/GERBER_plotter.cpp | 17 ++++++++++++++---
 common/plotters/HPGL_plotter.cpp   |  7 +++++++
 common/plotters/plotter.cpp        | 12 ++++++------
 include/tool/grid_helper.h         |  2 +-
 5 files changed, 42 insertions(+), 12 deletions(-)

diff --git a/common/gal/opengl/opengl_gal.cpp b/common/gal/opengl/opengl_gal.cpp
index 2565ffcf0b..3f0198119a 100644
--- a/common/gal/opengl/opengl_gal.cpp
+++ b/common/gal/opengl/opengl_gal.cpp
@@ -1075,9 +1075,21 @@ void OPENGL_GAL::DrawArcSegment( const VECTOR2D& aCenterPoint, double aRadius,
     if( seg_count % 2 != 0 )
         seg_count += 1;
 
+    // Our shaders have trouble rendering null line quads, so delegate this task to DrawSegment.
+    if( seg_count == 0 )
+    {
+        VECTOR2D p_start( aCenterPoint.x + cos( startAngle ) * aRadius,
+                          aCenterPoint.y + sin( startAngle ) * aRadius );
+
+        VECTOR2D p_end( aCenterPoint.x + cos( endAngle ) * aRadius,
+                        aCenterPoint.y + sin( endAngle ) * aRadius );
+
+        DrawSegment( p_start, p_end, aWidth );
+        return;
+    }
+
     // Recalculate alphaIncrement with a even integer number of segment
-    if( seg_count )
-        alphaIncrement = ( endAngle - startAngle ) / seg_count;
+    alphaIncrement = ( endAngle - startAngle ) / seg_count;
 
     Save();
     m_currentManager->Translate( aCenterPoint.x, aCenterPoint.y, 0.0 );
diff --git a/common/plotters/GERBER_plotter.cpp b/common/plotters/GERBER_plotter.cpp
index b59ad9fa44..d7702d17bf 100644
--- a/common/plotters/GERBER_plotter.cpp
+++ b/common/plotters/GERBER_plotter.cpp
@@ -833,10 +833,21 @@ void GERBER_PLOTTER::Arc( const VECTOR2D& aCenter, const EDA_ANGLE& aStartAngle,
 {
     SetCurrentLineWidth( aWidth );
 
-    EDA_ANGLE endAngle = aStartAngle + aAngle;
+    double arcLength = std::abs( aRadius * aAngle.AsRadians() );
 
-    // aFill is not used here.
-    plotArc( aCenter, aStartAngle, endAngle, aRadius, false );
+    if( arcLength < 100 || std::abs( aAngle.AsDegrees() ) < 0.1 )
+    {
+        // Prevent plotting very short arcs as full circles, especially with 4.5 mm precision.
+        // Also reduce the risk of integer overflow issues.
+        polyArc( aCenter, aStartAngle, aAngle, aRadius, aFill, aWidth );
+    }
+    else
+    {
+        EDA_ANGLE endAngle = aStartAngle + aAngle;
+
+        // aFill is not used here.
+        plotArc( aCenter, aStartAngle, endAngle, aRadius, false );
+    }
 }
 
 
diff --git a/common/plotters/HPGL_plotter.cpp b/common/plotters/HPGL_plotter.cpp
index 5d9e07cd70..806ddf0905 100644
--- a/common/plotters/HPGL_plotter.cpp
+++ b/common/plotters/HPGL_plotter.cpp
@@ -565,6 +565,13 @@ void HPGL_PLOTTER::Arc( const VECTOR2D& aCenter, const EDA_ANGLE& aStartAngle,
     if( aRadius <= 0 )
         return;
 
+    // Avoid integer overflow when calculating the center point
+    if( std::abs( aAngle.AsDegrees() ) < 5 )
+    {
+        polyArc( aCenter, aStartAngle, aAngle, aRadius, aFill, aWidth );
+        return;
+    }
+
     double const radius_device       = userToDeviceSize( aRadius );
     double const circumf_device      = 2.0 * M_PI * radius_device;
     double const target_chord_length = m_arcTargetChordLength;
diff --git a/common/plotters/plotter.cpp b/common/plotters/plotter.cpp
index ffa378b5f5..34e72cf877 100644
--- a/common/plotters/plotter.cpp
+++ b/common/plotters/plotter.cpp
@@ -191,8 +191,8 @@ void PLOTTER::polyArc( const VECTOR2D& aCenter, const EDA_ANGLE& aStartAngle,
 
     SetCurrentLineWidth( aWidth );
 
-    start.x = aCenter.x + KiROUND( aRadius * startAngle.Cos() );
-    start.y = aCenter.y + sign * KiROUND( aRadius * startAngle.Sin() );
+    start.x = KiROUND( aCenter.x + aRadius * startAngle.Cos() );
+    start.y = KiROUND( aCenter.y + sign * aRadius * startAngle.Sin() );
 
     if( aFill != FILL_T::NO_FILL )
     {
@@ -206,13 +206,13 @@ void PLOTTER::polyArc( const VECTOR2D& aCenter, const EDA_ANGLE& aStartAngle,
 
     for( EDA_ANGLE ii = startAngle + delta; ii < endAngle; ii += delta )
     {
-        end.x = aCenter.x + KiROUND( aRadius * ii.Cos() );
-        end.y = aCenter.y + sign * KiROUND( aRadius * ii.Sin() );
+        end.x = KiROUND( aCenter.x + aRadius * ii.Cos() );
+        end.y = KiROUND( aCenter.y + sign * aRadius * ii.Sin() );
         LineTo( end );
     }
 
-    end.x = aCenter.x + KiROUND( aRadius * endAngle.Cos() );
-    end.y = aCenter.y + sign * KiROUND( aRadius * endAngle.Sin() );
+    end.x = KiROUND( aCenter.x + aRadius * endAngle.Cos() );
+    end.y = KiROUND( aCenter.y + sign * aRadius * endAngle.Sin() );
 
     if( aFill != FILL_T::NO_FILL )
     {
diff --git a/include/tool/grid_helper.h b/include/tool/grid_helper.h
index 5e87222591..a8af1a2a55 100644
--- a/include/tool/grid_helper.h
+++ b/include/tool/grid_helper.h
@@ -141,7 +141,7 @@ protected:
 
         double Distance( const VECTOR2I& aP ) const
         {
-            return ( aP - pos ).EuclideanNorm();
+            return VECTOR2D( (double) aP.x - pos.x, (double) aP.y - pos.y ).EuclideanNorm();
         }
     };