Eescheam: plot HPGL: add comments and minor fix.

eeschema/dialogs/dialog_plot_schematic.cpp

@@ -88,7 +88,7 @@ void DIALOG_PLOT_SCHEMATIC::initDlg()
 
     // Set plot or not frame reference option
     m_config->Read( PLOT_FRAME_REFERENCE_KEY, &tmp, true );
-    setPlotFrameRef( true );
+    setPlotFrameRef( tmp );
 
     // Set HPGL plot origin to center of paper of left bottom corner
     m_config->Read( PLOT_HPGL_ORIGIN_KEY, &tmp, false );

eeschema/plot_schematic_HPGL.cpp

@@ -170,7 +170,7 @@ void DIALOG_PLOT_SCHEMATIC::createHPGLFile( bool aPlotAll )
 
         if( GetPlotOriginCenter() )
         {
-            plotOffset.x    = -plotPage.GetWidthIU() / 2;
+            plotOffset.x    = plotPage.GetWidthIU() / 2;
             plotOffset.y    = -plotPage.GetHeightIU() / 2;
         }