ポリゴンのシンボルQgsFillSymbolの設定（構築）はQgsFillSymbolクラスのメソッドcreateSimpleにスタイルを渡して設定する。

内部の色、外周の色を設定する時は

QgsFillSymbol.createSimple({'color': '0,0,0,0','outline_color': '255,0,0,255'})

更に内部のパターンを設定する時は

QgsFillSymbol.createSimple({'color': '0,0,0,0','outline_color': '255,0,0,255','style' : 'diagonal_x'})

設定のキーはQgsSymbolLayer::createを参考

QgsSymbolLayer *QgsSimpleFillSymbolLayer::create( const QgsStringMap &props )
{
  QColor color = DEFAULT_SIMPLEFILL_COLOR;
  Qt::BrushStyle style = DEFAULT_SIMPLEFILL_STYLE;
  QColor strokeColor = DEFAULT_SIMPLEFILL_BORDERCOLOR;
  Qt::PenStyle strokeStyle = DEFAULT_SIMPLEFILL_BORDERSTYLE;
  double strokeWidth = DEFAULT_SIMPLEFILL_BORDERWIDTH;
  Qt::PenJoinStyle penJoinStyle = DEFAULT_SIMPLEFILL_JOINSTYLE;
  QPointF offset;

  if ( props.contains( QStringLiteral( "color" ) ) )
    color = QgsSymbolLayerUtils::decodeColor( props[QStringLiteral( "color" )] );
  if ( props.contains( QStringLiteral( "style" ) ) )
    style = QgsSymbolLayerUtils::decodeBrushStyle( props[QStringLiteral( "style" )] );
  if ( props.contains( QStringLiteral( "color_border" ) ) )
  {
    //pre 2.5 projects used "color_border"
    strokeColor = QgsSymbolLayerUtils::decodeColor( props[QStringLiteral( "color_border" )] );
  }
  else if ( props.contains( QStringLiteral( "outline_color" ) ) )
  {
    strokeColor = QgsSymbolLayerUtils::decodeColor( props[QStringLiteral( "outline_color" )] );
  }
  else if ( props.contains( QStringLiteral( "line_color" ) ) )
  {
    strokeColor = QgsSymbolLayerUtils::decodeColor( props[QStringLiteral( "line_color" )] );
  }

  if ( props.contains( QStringLiteral( "style_border" ) ) )
  {
    //pre 2.5 projects used "style_border"
    strokeStyle = QgsSymbolLayerUtils::decodePenStyle( props[QStringLiteral( "style_border" )] );
  }
  else if ( props.contains( QStringLiteral( "outline_style" ) ) )
  {
    strokeStyle = QgsSymbolLayerUtils::decodePenStyle( props[QStringLiteral( "outline_style" )] );
  }
  else if ( props.contains( QStringLiteral( "line_style" ) ) )
  {
    strokeStyle = QgsSymbolLayerUtils::decodePenStyle( props[QStringLiteral( "line_style" )] );
  }
  if ( props.contains( QStringLiteral( "width_border" ) ) )
  {
    //pre 2.5 projects used "width_border"
    strokeWidth = props[QStringLiteral( "width_border" )].toDouble();
  }
  else if ( props.contains( QStringLiteral( "outline_width" ) ) )
  {
    strokeWidth = props[QStringLiteral( "outline_width" )].toDouble();
  }
  else if ( props.contains( QStringLiteral( "line_width" ) ) )
  {
    strokeWidth = props[QStringLiteral( "line_width" )].toDouble();
  }
  if ( props.contains( QStringLiteral( "offset" ) ) )
    offset = QgsSymbolLayerUtils::decodePoint( props[QStringLiteral( "offset" )] );
  if ( props.contains( QStringLiteral( "joinstyle" ) ) )
    penJoinStyle = QgsSymbolLayerUtils::decodePenJoinStyle( props[QStringLiteral( "joinstyle" )] );

  QgsSimpleFillSymbolLayer *sl = new QgsSimpleFillSymbolLayer( color, style, strokeColor, strokeStyle, strokeWidth, penJoinStyle );
  sl->setOffset( offset );
  if ( props.contains( QStringLiteral( "border_width_unit" ) ) )
  {
    sl->setStrokeWidthUnit( QgsUnitTypes::decodeRenderUnit( props[QStringLiteral( "border_width_unit" )] ) );
  }
  else if ( props.contains( QStringLiteral( "outline_width_unit" ) ) )
  {
    sl->setStrokeWidthUnit( QgsUnitTypes::decodeRenderUnit( props[QStringLiteral( "outline_width_unit" )] ) );
  }
  else if ( props.contains( QStringLiteral( "line_width_unit" ) ) )
  {
    sl->setStrokeWidthUnit( QgsUnitTypes::decodeRenderUnit( props[QStringLiteral( "line_width_unit" )] ) );
  }
  if ( props.contains( QStringLiteral( "offset_unit" ) ) )
    sl->setOffsetUnit( QgsUnitTypes::decodeRenderUnit( props[QStringLiteral( "offset_unit" )] ) );

  if ( props.contains( QStringLiteral( "border_width_map_unit_scale" ) ) )
    sl->setStrokeWidthMapUnitScale( QgsSymbolLayerUtils::decodeMapUnitScale( props[QStringLiteral( "border_width_map_unit_scale" )] ) );
  if ( props.contains( QStringLiteral( "offset_map_unit_scale" ) ) )
    sl->setOffsetMapUnitScale( QgsSymbolLayerUtils::decodeMapUnitScale( props[QStringLiteral( "offset_map_unit_scale" )] ) );

  sl->restoreOldDataDefinedProperties( props );

  return sl;
}

設定値はQgsSymbolLayerUtilsを参照

Qt::BrushStyle QgsSymbolLayerUtils::decodeBrushStyle( const QString &str )
{
  if ( str == QLatin1String( "solid" ) ) return Qt::SolidPattern;
  if ( str == QLatin1String( "horizontal" ) ) return Qt::HorPattern;
  if ( str == QLatin1String( "vertical" ) ) return Qt::VerPattern;
  if ( str == QLatin1String( "cross" ) ) return Qt::CrossPattern;
  if ( str == QLatin1String( "b_diagonal" ) ) return Qt::BDiagPattern;
  if ( str == QLatin1String( "f_diagonal" ) ) return Qt::FDiagPattern;
  if ( str == QLatin1String( "diagonal_x" ) ) return Qt::DiagCrossPattern;
  if ( str == QLatin1String( "dense1" ) ) return Qt::Dense1Pattern;
  if ( str == QLatin1String( "dense2" ) ) return Qt::Dense2Pattern;
  if ( str == QLatin1String( "dense3" ) ) return Qt::Dense3Pattern;
  if ( str == QLatin1String( "dense4" ) ) return Qt::Dense4Pattern;
  if ( str == QLatin1String( "dense5" ) ) return Qt::Dense5Pattern;
  if ( str == QLatin1String( "dense6" ) ) return Qt::Dense6Pattern;
  if ( str == QLatin1String( "dense7" ) ) return Qt::Dense7Pattern;
  if ( str == QLatin1String( "no" ) ) return Qt::NoBrush;
  return Qt::SolidPattern;
}

QString QgsSymbolLayerUtils::encodeSldBrushStyle( Qt::BrushStyle style )
{
  switch ( style )
  {
    case Qt::CrossPattern:
      return QStringLiteral( "cross" );
    case Qt::DiagCrossPattern:
      return QStringLiteral( "x" );

    /* The following names are taken from the presentation "GeoServer
     * Cartographic Rendering" by Andrea Aime at the FOSS4G 2010.
     * (see http://2010.foss4g.org/presentations/3588.pdf)
     */
    case Qt::HorPattern:
      return QStringLiteral( "horline" );
    case Qt::VerPattern:
      return QStringLiteral( "line" );
    case Qt::BDiagPattern:
      return QStringLiteral( "slash" );
    case Qt::FDiagPattern:
      return QStringLiteral( "backslash" );

    /* define the other names following the same pattern used above */
    case Qt::Dense1Pattern:
    case Qt::Dense2Pattern:
    case Qt::Dense3Pattern:
    case Qt::Dense4Pattern:
    case Qt::Dense5Pattern:
    case Qt::Dense6Pattern:
    case Qt::Dense7Pattern:
      return QStringLiteral( "brush://%1" ).arg( encodeBrushStyle( style ) );

    default:
      return QString();
  }
}