gerber_jobfile_writer.cpp

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/*
 * This program source code file is part of KiCad, a free EDA CAD application.
 *
 * Copyright (C) 2018 Jean_Pierre Charras <jp.charras at wanadoo.fr>
 * Copyright (C) 1992-2022 KiCad Developers, see AUTHORS.txt for contributors.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, you may find one here:
 * http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
 * or you may search the http://www.gnu.org website for the version 2 license,
 * or you may write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
 */

#include <fstream>
#include <iomanip>
#include <vector>

#include <build_version.h>
#include <locale_io.h>
#include <pcb_edit_frame.h>
#include <plotters/plotter.h>

#include <board.h>
#include <board_design_settings.h>
#include <footprint.h>
#include <pad.h>
#include <pcb_track.h>
#include <zone.h>

#include <board_stackup_manager/stackup_predefined_prms.h>
#include <gbr_metadata.h>
#include <gerber_jobfile_writer.h>
#include <pcbplot.h>
#include <reporter.h>
#include <wildcards_and_files_ext.h>


GERBER_JOBFILE_WRITER::GERBER_JOBFILE_WRITER( BOARD* aPcb, REPORTER* aReporter )
{
 m_pcb = aPcb;
 m_reporter = aReporter;
 m_conversionUnits = 1.0 / IU_PER_MM; // Gerber units = mm
}

std::string GERBER_JOBFILE_WRITER::formatStringFromUTF32( const wxString& aText )
{
 std::string fmt_text; // the text after UTF32 to UTF8 conversion

 for( unsigned long letter : aText )
 {
 if( letter >= ' ' && letter <= 0x7F )
 fmt_text += char( letter );
 else
 {
 char buff[16];
 sprintf( buff, "\\u%4.4lX", letter );
 fmt_text += buff;
 }
 }
 return fmt_text;
}


enum ONSIDE GERBER_JOBFILE_WRITER::hasSilkLayers()
{
 int flag = SIDE_NONE;

 for( unsigned ii = 0; ii < m_params.m_LayerId.size(); ii++ )
 {
 if( m_params.m_LayerId[ii] == B_SilkS )
 flag |= SIDE_BOTTOM;

 if( m_params.m_LayerId[ii] == F_SilkS )
 flag |= SIDE_TOP;
 }

 return (enum ONSIDE) flag;
}


enum ONSIDE GERBER_JOBFILE_WRITER::hasSolderMasks()
{
 int flag = SIDE_NONE;

 for( unsigned ii = 0; ii < m_params.m_LayerId.size(); ii++ )
 {
 if( m_params.m_LayerId[ii] == B_Mask )
 flag |= SIDE_BOTTOM;

 if( m_params.m_LayerId[ii] == F_Mask )
 flag |= SIDE_TOP;
 }

 return (enum ONSIDE) flag;
}

const char* GERBER_JOBFILE_WRITER::sideKeyValue( enum ONSIDE aValue )
{
 // return the key associated to sides used for some layers
 // "No, TopOnly, BotOnly or Both"
 const char* value = nullptr;

 switch( aValue )
 {
 case SIDE_NONE:
 value = "No";
 break;

 case SIDE_TOP:
 value = "TopOnly";
 break;

 case SIDE_BOTTOM:
 value = "BotOnly";
 break;

 case SIDE_BOTH:
 value = "Both";
 break;
 }

 return value;
}


bool GERBER_JOBFILE_WRITER::CreateJobFile( const wxString& aFullFilename )
{
 bool success;
 wxString msg;

 success = WriteJSONJobFile( aFullFilename );

 if( !success )
 {
 if( m_reporter )
 {
 msg.Printf( _( "Failed to create file '%s'." ), aFullFilename );
 m_reporter->Report( msg, RPT_SEVERITY_ERROR );
 }
 }
 else if( m_reporter )
 {
 msg.Printf( _( "Created Gerber job file '%s'." ), aFullFilename );
 m_reporter->Report( msg, RPT_SEVERITY_ACTION );
 }

 return success;
}


void GERBER_JOBFILE_WRITER::addJSONHeader()
{
 wxString text;

 m_json["Header"] = {
 {
 "GenerationSoftware",
 {
 { "Vendor", "KiCad" },
 { "Application", "Pcbnew" },
 { "Version", GetBuildVersion() }
 }
 },
 {
 // The attribute value must conform to the full version of the ISO 8601
 // date and time format, including time and time zone.
 "CreationDate", GbrMakeCreationDateAttributeString( GBR_NC_STRING_FORMAT_GBRJOB )
 }
 };
}


bool GERBER_JOBFILE_WRITER::WriteJSONJobFile( const wxString& aFullFilename )
{
 // Note: in Gerber job file, dimensions are in mm, and are floating numbers
 std::ofstream file( aFullFilename.ToUTF8() );

 LOCALE_IO dummy;

 m_json = nlohmann::ordered_json( {} );

 // output the job file header
 addJSONHeader();

 // Add the General Specs
 addJSONGeneralSpecs();

 // Job file support a few design rules:
 addJSONDesignRules();

 // output the gerber file list:
 addJSONFilesAttributes();

 // output the board stackup:
 addJSONMaterialStackup();

 file << std::setw( 2 ) << m_json << std::endl;

 return true;
}


double GERBER_JOBFILE_WRITER::mapValue( double aUiValue )
{
 // A helper function to convert aUiValue in Json units (mm) and to have
 // 4 digits in Json in mantissa when using %g to print it
 // i.e. displays values truncated in 0.1 microns.
 // This is enough for a Json file
 char buffer[128];
 sprintf( buffer, "%.4f", aUiValue * m_conversionUnits );

 long double output;
 sscanf( buffer, "%Lg", &output );

 return output;

}


void GERBER_JOBFILE_WRITER::addJSONGeneralSpecs()
{
 m_json["GeneralSpecs"] = nlohmann::ordered_json( {} );
 m_json["GeneralSpecs"]["ProjectId"] = nlohmann::ordered_json( {} );

 // Creates the ProjectId. Format is (from Gerber file format doc):
 // ProjectId,<project id>,<project GUID>,<revision id>*%
 // <project id> is the name of the project, restricted to basic ASCII symbols only,
 // and comma not accepted
 // All illegal chars will be replaced by underscore
 // Rem: <project id> accepts only ASCII 7 code (only basic ASCII codes are allowed in gerber files).
 //
 // <project GUID> is a string which is an unique id of a project.
 // However Kicad does not handle such a project GUID, so it is built from the board name
 wxFileName fn = m_pcb->GetFileName();
 wxString msg = fn.GetFullName();

 // Build a <project GUID>, from the board name
 wxString guid = GbrMakeProjectGUIDfromString( msg );

 // build the <project id> string: this is the board short filename (without ext)
 // and all non ASCII chars are replaced by '_', to be compatible with .gbr files.
 msg = fn.GetName();

 // build the <rec> string. All non ASCII chars and comma are replaced by '_'
 wxString rev = ExpandTextVars( m_pcb->GetTitleBlock().GetRevision(), m_pcb->GetProject() );

 if( rev.IsEmpty() )
 rev = wxT( "rev?" );

 m_json["GeneralSpecs"]["ProjectId"]["Name"] = msg.ToAscii();
 m_json["GeneralSpecs"]["ProjectId"]["GUID"] = guid;
 m_json["GeneralSpecs"]["ProjectId"]["Revision"] = rev.ToAscii();

 // output the board size in mm:
 EDA_RECT brect = m_pcb->GetBoardEdgesBoundingBox();

 m_json["GeneralSpecs"]["Size"]["X"] = mapValue( brect.GetWidth() );
 m_json["GeneralSpecs"]["Size"]["Y"] = mapValue( brect.GetHeight() );


 // Add some data to the JSON header, GeneralSpecs:
 // number of copper layers
 m_json["GeneralSpecs"]["LayerNumber"] = m_pcb->GetCopperLayerCount();

 // Board thickness
 m_json["GeneralSpecs"]["BoardThickness"] =
 mapValue( m_pcb->GetDesignSettings().GetBoardThickness() );

 // Copper finish
 const BOARD_STACKUP brd_stackup = m_pcb->GetDesignSettings().GetStackupDescriptor();

 if( !brd_stackup.m_FinishType.IsEmpty() )
 m_json["GeneralSpecs"]["Finish"] = brd_stackup.m_FinishType;

 if( brd_stackup.m_HasDielectricConstrains )
 m_json["GeneralSpecs"]["ImpedanceControlled"] = true;

 if( brd_stackup.m_CastellatedPads )
 m_json["GeneralSpecs"]["Castellated"] = true;

 if( brd_stackup.m_EdgePlating )
 m_json["GeneralSpecs"]["EdgePlating"] = true;

 if( brd_stackup.m_EdgeConnectorConstraints )
 {
 m_json["GeneralSpecs"]["EdgeConnector"] = true;

 m_json["GeneralSpecs"]["EdgeConnectorBevelled"] =
 ( brd_stackup.m_EdgeConnectorConstraints == BS_EDGE_CONNECTOR_BEVELLED );
 }

#if 0 // Not yet in use
 /* The board type according to IPC-2221. There are six primary board types:
 - Type 1 - Single-sided
 - Type 2 - Double-sided
 - Type 3 - Multilayer, TH components only
 - Type 4 - Multilayer, with TH, blind and/or buried vias.
 - Type 5 - Multilayer metal-core board, TH components only
 - Type 6 - Multilayer metal-core
 */
 m_json["GeneralSpecs"]["IPC-2221-Type"] = 4;

 /* Via protection: key words:
 Ia Tented - Single-sided
 Ib Tented - Double-sided
 IIa Tented and Covered - Single-sided
 IIb Tented and Covered - Double-sided
 IIIa Plugged - Single-sided
 IIIb Plugged - Double-sided
 IVa Plugged and Covered - Single-sided
 IVb Plugged and Covered - Double-sided
 V Filled (fully plugged)
 VI Filled and Covered
 VIII Filled and Capped
 None...No protection
 */
 m_json["GeneralSpecs"]["ViaProtection"] = "Ib";
#endif
}


void GERBER_JOBFILE_WRITER::addJSONFilesAttributes()
{
 // Add the Files Attributes section in JSON format to m_JSONbuffer
 m_json["FilesAttributes"] = nlohmann::ordered_json::array();

 for( unsigned ii = 0; ii < m_params.m_GerberFileList.GetCount(); ii++ )
 {
 wxString& name = m_params.m_GerberFileList[ii];
 PCB_LAYER_ID layer = m_params.m_LayerId[ii];
 wxString gbr_layer_id;
 bool skip_file = false; // true to skip files which should not be in job file
 const char* polarity = "Positive";

 nlohmann::ordered_json file_json;

 if( layer <= B_Cu )
 {
 gbr_layer_id = wxT( "Copper,L" );

 if( layer == B_Cu )
 gbr_layer_id << m_pcb->GetCopperLayerCount();
 else
 gbr_layer_id << layer + 1;

 gbr_layer_id << wxT( "," );

 if( layer == B_Cu )
 gbr_layer_id << wxT( "Bot" );
 else if( layer == F_Cu )
 gbr_layer_id << wxT( "Top" );
 else
 gbr_layer_id << wxT( "Inr" );
 }

 else
 {
 switch( layer )
 {
 case B_Adhes:
 gbr_layer_id = wxT( "Glue,Bot" );
 break;
 case F_Adhes:
 gbr_layer_id = wxT( "Glue,Top" );
 break;

 case B_Paste:
 gbr_layer_id = wxT( "SolderPaste,Bot" );
 break;
 case F_Paste:
 gbr_layer_id = wxT( "SolderPaste,Top" );
 break;

 case B_SilkS:
 gbr_layer_id = wxT( "Legend,Bot" );
 break;
 case F_SilkS:
 gbr_layer_id = wxT( "Legend,Top" );
 break;

 case B_Mask:
 gbr_layer_id = wxT( "SolderMask,Bot" );
 polarity = "Negative";
 break;
 case F_Mask:
 gbr_layer_id = wxT( "SolderMask,Top" );
 polarity = "Negative";
 break;

 case Edge_Cuts:
 gbr_layer_id = wxT( "Profile" );
 break;

 case B_Fab:
 gbr_layer_id = wxT( "AssemblyDrawing,Bot" );
 break;
 case F_Fab:
 gbr_layer_id = wxT( "AssemblyDrawing,Top" );
 break;

 case Margin:
 case B_CrtYd:
 case F_CrtYd:
 skip_file = true;
 break;

 case Dwgs_User:
 case Cmts_User:
 case Eco1_User:
 case Eco2_User:
 case User_1:
 case User_2:
 case User_3:
 case User_4:
 case User_5:
 case User_6:
 case User_7:
 case User_8:
 case User_9:
 gbr_layer_id = wxT( "Other,User" );
 break;

 default:
 skip_file = true;

 if( m_reporter )
 m_reporter->Report( wxT( "Unexpected layer id in job file" ), RPT_SEVERITY_ERROR );

 break;
 }
 }

 if( !skip_file )
 {
 // name can contain non ASCII7 chars.
 // Ensure the name is JSON compatible.
 std::string strname = formatStringFromUTF32( name );

 file_json["Path"] = strname.c_str();
 file_json["FileFunction"] = gbr_layer_id;
 file_json["FilePolarity"] = polarity;

 m_json["FilesAttributes"] += file_json;
 }
 }
}


void GERBER_JOBFILE_WRITER::addJSONDesignRules()
{
 // Add the Design Rules section in JSON format to m_JSONbuffer
 // Job file support a few design rules:
 const BOARD_DESIGN_SETTINGS& dsnSettings = m_pcb->GetDesignSettings();
 NETCLASS defaultNC = *dsnSettings.GetDefault();
 int minclearanceOuter = defaultNC.GetClearance();
 bool hasInnerLayers = m_pcb->GetCopperLayerCount() > 2;

 // Search a smaller clearance in other net classes, if any.
 for( const std::pair<const wxString, NETCLASSPTR>& entry : dsnSettings.GetNetClasses() )
 minclearanceOuter = std::min( minclearanceOuter, entry.second->GetClearance() );

 // job file knows different clearance types.
 // Kicad knows only one clearance for pads and tracks
 int minclearance_track2track = minclearanceOuter;

 // However, pads can have a specific clearance defined for a pad or a footprint,
 // and min clearance can be dependent on layers.
 // Search for a minimal pad clearance:
 int minPadClearanceOuter = defaultNC.GetClearance();
 int minPadClearanceInner = defaultNC.GetClearance();

 for( FOOTPRINT* footprint : m_pcb->Footprints() )
 {
 for( PAD* pad : footprint->Pads() )
 {
 for( PCB_LAYER_ID layer : pad->GetLayerSet().Seq() )
 {
 int padClearance = pad->GetOwnClearance( layer );

 if( layer == B_Cu || layer == F_Cu )
 minPadClearanceOuter = std::min( minPadClearanceOuter, padClearance );
 else
 minPadClearanceInner = std::min( minPadClearanceInner, padClearance );
 }
 }
 }

 m_json["DesignRules"] = { {
 { "Layers", "Outer" },
 { "PadToPad", mapValue( minPadClearanceOuter ) },
 { "PadToTrack", mapValue( minPadClearanceOuter ) },
 { "TrackToTrack", mapValue( minclearance_track2track ) }
 } };

 // Until this is changed in Kicad, use the same value for internal tracks
 int minclearanceInner = minclearanceOuter;

 // Output the minimal track width
 int mintrackWidthOuter = INT_MAX;
 int mintrackWidthInner = INT_MAX;

 for( PCB_TRACK* track : m_pcb->Tracks() )
 {
 if( track->Type() == PCB_VIA_T )
 continue;

 if( track->GetLayer() == B_Cu || track->GetLayer() == F_Cu )
 mintrackWidthOuter = std::min( mintrackWidthOuter, track->GetWidth() );
 else
 mintrackWidthInner = std::min( mintrackWidthInner, track->GetWidth() );
 }

 if( mintrackWidthOuter != INT_MAX )
 m_json["DesignRules"][0]["MinLineWidth"] = mapValue( mintrackWidthOuter );

 // Output the minimal zone to xx clearance
 // Note: zones can have a zone clearance set to 0
 // if happens, the actual zone clearance is the clearance of its class
 minclearanceOuter = INT_MAX;
 minclearanceInner = INT_MAX;

 for( ZONE* zone : m_pcb->Zones() )
 {
 if( zone->GetIsRuleArea() || !zone->IsOnCopperLayer() )
 continue;

 for( PCB_LAYER_ID layer : zone->GetLayerSet().Seq() )
 {
 int zclerance = zone->GetOwnClearance( layer );

 if( layer == B_Cu || layer == F_Cu )
 minclearanceOuter = std::min( minclearanceOuter, zclerance );
 else
 minclearanceInner = std::min( minclearanceInner, zclerance );
 }
 }

 if( minclearanceOuter != INT_MAX )
 m_json["DesignRules"][0]["TrackToRegion"] = mapValue( minclearanceOuter );

 if( minclearanceOuter != INT_MAX )
 m_json["DesignRules"][0]["RegionToRegion"] = mapValue( minclearanceOuter );

 if( hasInnerLayers )
 {
 m_json["DesignRules"] += nlohmann::ordered_json( {
 { "Layers", "Inner" },
 { "PadToPad", mapValue( minPadClearanceInner ) },
 { "PadToTrack", mapValue( minPadClearanceInner ) },
 { "TrackToTrack", mapValue( minclearance_track2track ) }
 } );

 if( mintrackWidthInner != INT_MAX )
 m_json["DesignRules"][1]["MinLineWidth"] = mapValue( mintrackWidthInner );

 if( minclearanceInner != INT_MAX )
 m_json["DesignRules"][1]["TrackToRegion"] = mapValue( minclearanceInner );

 if( minclearanceInner != INT_MAX )
 m_json["DesignRules"][1]["RegionToRegion"] = mapValue( minclearanceInner );
 }
}


void GERBER_JOBFILE_WRITER::addJSONMaterialStackup()
{
 // Add the Material Stackup section in JSON format to m_JSONbuffer
 m_json["MaterialStackup"] = nlohmann::ordered_json::array();

 // Build the candidates list:
 LSET maskLayer;
 BOARD_STACKUP brd_stackup = m_pcb->GetDesignSettings().GetStackupDescriptor();

 // Ensure brd_stackup is up to date (i.e. no change made by SynchronizeWithBoard() )
 bool uptodate = not brd_stackup.SynchronizeWithBoard( &m_pcb->GetDesignSettings() );

 if( m_reporter && !uptodate && m_pcb->GetDesignSettings().m_HasStackup )
 m_reporter->Report( _( "Board stackup settings not up to date." ), RPT_SEVERITY_ERROR );

 PCB_LAYER_ID last_copper_layer = F_Cu;

 // Generate the list (top to bottom):
 for( int ii = 0; ii < brd_stackup.GetCount(); ++ii )
 {
 BOARD_STACKUP_ITEM* item = brd_stackup.GetStackupLayer( ii );

 int sub_layer_count =
 item->GetType() == BS_ITEM_TYPE_DIELECTRIC ? item->GetSublayersCount() : 1;

 for( int sub_idx = 0; sub_idx < sub_layer_count; sub_idx++ )
 {
 // layer thickness is always in mm
 double thickness = mapValue( item->GetThickness( sub_idx ) );
 wxString layer_type;
 std::string layer_name; // for comment

 nlohmann::ordered_json layer_json;

 switch( item->GetType() )
 {
 case BS_ITEM_TYPE_COPPER:
 layer_type = wxT( "Copper" );
 layer_name = formatStringFromUTF32( m_pcb->GetLayerName( item->GetBrdLayerId() ) );
 last_copper_layer = item->GetBrdLayerId();
 break;

 case BS_ITEM_TYPE_SILKSCREEN:
 layer_type = wxT( "Legend" );
 layer_name = formatStringFromUTF32( item->GetTypeName() );
 break;

 case BS_ITEM_TYPE_SOLDERMASK:
 layer_type = wxT( "SolderMask" );
 layer_name = formatStringFromUTF32( item->GetTypeName() );
 break;

 case BS_ITEM_TYPE_SOLDERPASTE:
 layer_type = wxT( "SolderPaste" );
 layer_name = formatStringFromUTF32( item->GetTypeName() );
 break;

 case BS_ITEM_TYPE_DIELECTRIC:
 layer_type = wxT( "Dielectric" );
 // The option core or prepreg is not added here, as it creates constraints
 // in build process, not necessary wanted.
 if( sub_layer_count > 1 )
 {
 layer_name =
 formatStringFromUTF32( wxString::Format( wxT( "dielectric layer %d - %d/%d" ),
 item->GetDielectricLayerId(), sub_idx + 1, sub_layer_count ) );
 }
 else
 layer_name = formatStringFromUTF32( wxString::Format(
 wxT( "dielectric layer %d" ), item->GetDielectricLayerId() ) );
 break;

 default:
 break;
 }

 layer_json["Type"] = layer_type;

 if( item->IsColorEditable() && uptodate )
 {
 if( IsPrmSpecified( item->GetColor() ) )
 {
 wxString colorName = item->GetColor();

 if( colorName.StartsWith( wxT( "#" ) ) ) // This is a user defined color.
 {
 // In job file a color can be given by its RGB values (0...255)
 wxColor color( COLOR4D( colorName ).ToColour() );
 colorName.Printf( wxT( "R%dG%dB%d" ),
 color.Red(),
 color.Green(),
 color.Blue() );
 }

 layer_json["Color"] = colorName;
 }
 }

 if( item->IsThicknessEditable() && uptodate )
 layer_json["Thickness"] = thickness;

 if( item->GetType() == BS_ITEM_TYPE_DIELECTRIC )
 {
 if( item->HasMaterialValue() )
 {
 layer_json["Material"] = item->GetMaterial( sub_idx );

 // These constrains are only written if the board has impedance controlled tracks.
 // If the board is not impedance controlled, they are useless.
 // Do not add constrains that create more expensive boards.

 if( brd_stackup.m_HasDielectricConstrains )
 {
 // Generate Epsilon R if > 1.0 (value <= 1.0 means not specified: it is not
 // a possible value
 if( item->GetEpsilonR() > 1.0 )
 layer_json["DielectricConstant"] = item->FormatEpsilonR( sub_idx );

 // Generate LossTangent > 0.0 (value <= 0.0 means not specified: it is not
 // a possible value
 if( item->GetLossTangent() > 0.0 )
 layer_json["LossTangent"] = item->FormatLossTangent( sub_idx );
 }
 }

 PCB_LAYER_ID next_copper_layer = ( PCB_LAYER_ID )( last_copper_layer + 1 );

 // If the next_copper_layer is the last copper layer, the next layer id is B_Cu
 if( next_copper_layer >= m_pcb->GetCopperLayerCount() - 1 )
 next_copper_layer = B_Cu;

 wxString subLayerName;

 if( sub_layer_count > 1 )
 subLayerName.Printf( wxT( " (%d/%d)" ), sub_idx + 1, sub_layer_count );

 wxString name = wxString::Format( wxT( "%s/%s%s" ),
 formatStringFromUTF32( m_pcb->GetLayerName( last_copper_layer ) ),
 formatStringFromUTF32( m_pcb->GetLayerName( next_copper_layer ) ),
 subLayerName );

 layer_json["Name"] = name;

 // Add a comment ("Notes"):
 wxString note;

 note << wxString::Format( wxT( "Type: %s" ), layer_name.c_str() );

 note << wxString::Format( wxT( " (from %s to %s)" ),
 formatStringFromUTF32( m_pcb->GetLayerName( last_copper_layer ) ),
 formatStringFromUTF32( m_pcb->GetLayerName( next_copper_layer ) ) );

 layer_json["Notes"] = note;
 }
 else if( item->GetType() == BS_ITEM_TYPE_SOLDERMASK
 || item->GetType() == BS_ITEM_TYPE_SILKSCREEN )
 {
 if( item->HasMaterialValue() )
 {
 layer_json["Material"] = item->GetMaterial();

 // These constrains are only written if the board has impedance controlled tracks.
 // If the board is not impedance controlled, they are useless.
 // Do not add constrains that create more expensive boards.
 if( brd_stackup.m_HasDielectricConstrains )
 {
 // Generate Epsilon R if > 1.0 (value <= 1.0 means not specified: it is not
 // a possible value
 if( item->GetEpsilonR() > 1.0 )
 layer_json["DielectricConstant"] = item->FormatEpsilonR();

 // Generate LossTangent > 0.0 (value <= 0.0 means not specified: it is not
 // a possible value
 if( item->GetLossTangent() > 0.0 )
 layer_json["LossTangent"] = item->FormatLossTangent();
 }
 }

 layer_json["Name"] = layer_name.c_str();
 }
 else
 {
 layer_json["Name"] = layer_name.c_str();
 }

 m_json["MaterialStackup"].insert( m_json["MaterialStackup"].end(), layer_json );
 }
 }
}