svg: Use grouping

Uses existing grouping in SVG output.  Sets schematic components as a
grouped element in SVG as well as pcbnew elements per layer.

Fixes: lp:1011754
* https://bugs.launchpad.net/kicad/+bug/1011754

common/plotters/SVG_plotter.cpp

@@ -288,6 +288,24 @@ void SVG_PLOTTER::SetCurrentLineWidth( int width, void* aData )
 }
 
 
+void SVG_PLOTTER::StartBlock( void* aData )
+{
+    std::string* idstr = reinterpret_cast<std::string*>( aData );
+
+    fputs( "<svg:g ", outputFile );
+    if( idstr )
+        fprintf( outputFile, "id=\"%s\"", idstr->c_str() );
+
+    fprintf( outputFile, ">\n" );
+}
+
+
+void SVG_PLOTTER::EndBlock( void* aData )
+{
+    fprintf( outputFile, "</g>\n" );
+}
+
+
 /* initialize m_red, m_green, m_blue ( 0 ... 255)
  * from reduced values r, g ,b ( 0.0 to 1.0 )
  */

eeschema/sch_component.cpp

@@ -1968,6 +1968,7 @@ void SCH_COMPONENT::Plot( PLOTTER* aPlotter )
     if( PART_SPTR part = m_part.lock() )
     {
         temp = GetTransform();
+        aPlotter->StartBlock( nullptr );
 
         part->Plot( aPlotter, GetUnit(), GetConvert(), m_Pos, temp );
 
@@ -1975,6 +1976,8 @@ void SCH_COMPONENT::Plot( PLOTTER* aPlotter )
         {
             m_Fields[i].Plot( aPlotter );
         }
+
+        aPlotter->EndBlock( nullptr );
     }
 }
 

include/plotter.h

@@ -936,6 +936,22 @@ public:
                             double aScaleFactor ) override;
 
     virtual void PenTo( const wxPoint& pos, char plume ) override;
+
+
+    /**
+     * calling this function allows one to define the beginning of a group
+     * of drawing items (used in SVG format to separate components)
+     * @param aData should be a string for the SVG ID tage
+     */
+    virtual void StartBlock( void* aData ) override;
+
+    /**
+     * calling this function allows one to define the end of a group of drawing
+     * items the group is started by StartBlock()
+     * @param aData should be null
+     */
+    virtual void EndBlock( void* aData ) override;
+
     virtual void Text( const wxPoint&              aPos,
                        const COLOR4D               aColor,
                        const wxString&             aText,