Plotters (especially DXF) add more precision when plotting arcs (and others)

- in DXF coordinates were using 6 digits for coordinate mantissa: this is not
enough for coord in inches. Now use 16 digits
- Arc( VECTOR2I& aCentre, EDA_ANGLE& aStartAngle, EDA_ANGLE& aEndAngle, ...)
was using integers for coord. This creates significant errors for start point
and end points of the arc. Now the center is given in double, and its position
is calculated from angle end points (and radius) to do not generate a position error
for these end points (previously the error could be 20 ... 50 nm)
Fixes #15056
https://gitlab.com/kicad/code/kicad/-/issues/15056

common/plotters/DXF_plotter.cpp

@@ -30,6 +30,7 @@
 #include <string_utils.h>
 #include <convert_basic_shapes_to_polygon.h>
 #include <trigo.h>
+#include <fmt/core.h>
 
 /**
  * Oblique angle for DXF native text
@@ -146,6 +147,26 @@ void DXF_PLOTTER::SetUnits( DXF_UNITS aUnit )
 }
 
 
+// convert aValue to a string, and remove trailing zeros
+// In DXF files coordinates need a high precision: at least 9 digits when given
+// in inches and 7 digits when in mm.
+// So we use 16 digits and remove trailing 0 (if any)
+static std::string formatCoord( double aValue )
+{
+    std::string buf;
+
+    buf = fmt::format( "{:.16f}", aValue );
+
+    // remove trailing zeros
+    while( !buf.empty() && buf[buf.size() - 1] == '0' )
+    {
+        buf.pop_back();
+    }
+
+    return buf;
+}
+
+
 void DXF_PLOTTER::SetViewport( const VECTOR2I& aOffset, double aIusPerDecimil,
                                double aScale, bool aMirror )
 {
@@ -437,22 +458,28 @@ void DXF_PLOTTER::Circle( const VECTOR2I& centre, int diameter, FILL_T fill, int
 
         if( fill == FILL_T::NO_FILL )
         {
-            fprintf( m_outputFile, "0\nCIRCLE\n8\n%s\n10\n%g\n20\n%g\n40\n%g\n",
+            fprintf( m_outputFile, "0\nCIRCLE\n8\n%s\n10\n%s\n20\n%s\n40\n%s\n",
                      TO_UTF8( cname ),
-                     centre_dev.x, centre_dev.y, radius );
+                     formatCoord( centre_dev.x ).c_str(),
+                     formatCoord( centre_dev.y ).c_str(),
+                     formatCoord( radius ).c_str() );
         }
         else if( fill == FILL_T::FILLED_SHAPE )
         {
             double r = radius*0.5;
             fprintf( m_outputFile, "0\nPOLYLINE\n" );
             fprintf( m_outputFile, "8\n%s\n66\n1\n70\n1\n", TO_UTF8( cname ) );
-            fprintf( m_outputFile, "40\n%g\n41\n%g\n", radius, radius);
+            fprintf( m_outputFile, "40\n%s\n41\n%s\n",
+                                    formatCoord( radius ).c_str(),
+                                    formatCoord( radius ).c_str() );
             fprintf( m_outputFile, "0\nVERTEX\n8\n%s\n", TO_UTF8( cname ) );
-            fprintf( m_outputFile, "10\n%g\n 20\n%g\n42\n1.0\n",
-                     centre_dev.x-r, centre_dev.y );
+            fprintf( m_outputFile, "10\n%s\n 20\n%s\n42\n1.0\n",
+                                    formatCoord( centre_dev.x-r ).c_str(),
+                                    formatCoord( centre_dev.y ).c_str() );
             fprintf( m_outputFile, "0\nVERTEX\n8\n%s\n", TO_UTF8( cname ) );
-            fprintf( m_outputFile, "10\n%g\n 20\n%g\n42\n1.0\n",
-                     centre_dev.x+r, centre_dev.y );
+            fprintf( m_outputFile, "10\n%s\n 20\n%s\n42\n1.0\n",
+                                    formatCoord( centre_dev.x+r ).c_str(),
+                                    formatCoord( centre_dev.y ).c_str() );
             fprintf( m_outputFile, "0\nSEQEND\n");
         }
     }
@@ -578,9 +605,12 @@ void DXF_PLOTTER::PenTo( const VECTOR2I& pos, char plume )
         // DXF LINE
         wxString    cname = getDXFColorName( m_currentColor );
         const char* lname = getDXFLineType( static_cast<PLOT_DASH_TYPE>( m_currentLineType ) );
-        fprintf( m_outputFile, "0\nLINE\n8\n%s\n6\n%s\n10\n%g\n20\n%g\n11\n%g\n21\n%g\n",
+        fprintf( m_outputFile, "0\nLINE\n8\n%s\n6\n%s\n10\n%s\n20\n%s\n11\n%s\n21\n%s\n",
                  TO_UTF8( cname ), lname,
-                 pen_lastpos_dev.x, pen_lastpos_dev.y, pos_dev.x, pos_dev.y );
+                 formatCoord( pen_lastpos_dev.x ).c_str(),
+                 formatCoord( pen_lastpos_dev.y ).c_str(),
+                 formatCoord( pos_dev.x ).c_str(),
+                 formatCoord( pos_dev.y ).c_str() );
     }
 
     m_penLastpos = pos;
@@ -626,8 +656,8 @@ void DXF_PLOTTER::ThickSegment( const VECTOR2I& aStart, const VECTOR2I& aEnd, in
 }
 
 
-void DXF_PLOTTER::Arc( const VECTOR2I& aCenter, const EDA_ANGLE& aStartAngle,
-                       const EDA_ANGLE& aEndAngle, int aRadius, FILL_T aFill, int aWidth )
+void DXF_PLOTTER::Arc( const VECTOR2D& aCenter, const EDA_ANGLE& aStartAngle,
+                       const EDA_ANGLE& aEndAngle, double aRadius, FILL_T aFill, int aWidth )
 {
     wxASSERT( m_outputFile );
 
@@ -648,9 +678,11 @@ void DXF_PLOTTER::Arc( const VECTOR2I& aCenter, const EDA_ANGLE& aStartAngle,
     // Emit a DXF ARC entity
     wxString cname = getDXFColorName( m_currentColor );
     fprintf( m_outputFile,
-             "0\nARC\n8\n%s\n10\n%g\n20\n%g\n40\n%g\n50\n%g\n51\n%g\n",
+             "0\nARC\n8\n%s\n10\n%s\n20\n%s\n40\n%s\n50\n%.8f\n51\n%.8f\n",
              TO_UTF8( cname ),
-             centre_device.x, centre_device.y, radius_device,
+             formatCoord( centre_device.x ).c_str(),
+             formatCoord( centre_device.y ).c_str(),
+             formatCoord( radius_device ).c_str(),
              startAngle.AsDegrees(), endAngle.AsDegrees() );
 }
 
@@ -936,21 +968,21 @@ void DXF_PLOTTER::plotOneLineOfText( const VECTOR2I& aPos, const COLOR4D& aColor
              "  8\n"
              "%s\n"          // Layer name
              "  10\n"
-             "%g\n"          // First point X
+             "%s\n"          // First point X
              "  11\n"
-             "%g\n"          // Second point X
+             "%s\n"          // Second point X
              "  20\n"
-             "%g\n"          // First point Y
+             "%s\n"          // First point Y
              "  21\n"
-             "%g\n"          // Second point Y
+             "%s\n"          // Second point Y
              "  40\n"
-             "%g\n"          // Text height
+             "%s\n"          // Text height
              "  41\n"
-             "%g\n"          // Width factor
+             "%s\n"          // Width factor
              "  50\n"
-             "%g\n"          // Rotation
+             "%.8f\n"        // Rotation
              "  51\n"
-             "%g\n"          // Oblique angle
+             "%.8f\n"        // Oblique angle
              "  71\n"
              "%d\n"          // Mirror flags
              "  72\n"
@@ -960,9 +992,9 @@ void DXF_PLOTTER::plotOneLineOfText( const VECTOR2I& aPos, const COLOR4D& aColor
              aAttributes.m_Bold ?
                 (aAttributes.m_Italic ? "KICADBI" : "KICADB")
                 : (aAttributes.m_Italic ? "KICADI" : "KICAD"), TO_UTF8( cname ),
-             origin_dev.x, origin_dev.x,
-             origin_dev.y, origin_dev.y,
-             size_dev.y, fabs( size_dev.x / size_dev.y ),
+             formatCoord( origin_dev.x ).c_str(), formatCoord( origin_dev.x ).c_str(),
+             formatCoord( origin_dev.y ).c_str(), formatCoord( origin_dev.y ).c_str(),
+             formatCoord( size_dev.y ).c_str(), formatCoord( fabs( size_dev.x / size_dev.y ) ).c_str(),
              aAttributes.m_Angle.AsDegrees(),
              aAttributes.m_Italic ? DXF_OBLIQUE_ANGLE : 0,
              aAttributes.m_Mirrored ? 2 : 0, // X mirror flag