METHODS
            OO interface

  Graph::ChartSVG->new
        Create a new Chart

        possible parameters are :

    active_size
        an array ref with x,y size of the active graph ( without the reserved border for label )
    
    bg_color
      an hex color for the global background color
 
    frame
      a Frame object to surround the active part of the graph

    grid
      a Grid oject to add to the graph
  
    overlay
     a Overlay to add on top of the graph ( useful to enhance a period in alarm )
  
    layer
     a Layer object
  
    border
     a Border object ( = some extra space to fit aroubd the active graph to allow label.
                    This increase the actual_size and create the total_size)
 
    tag
     a Tag objet ( if missing create a automatically incremented one )
 
    glyph
     a Glyph object to add on the graph ( like a arrow to point at the end of the current data )
    
    my $graph = Graph::ChartSVG->new( active_size => \@size, bg_color =>
    'FCF4C6', frame => $f, png_tag => 1 );

  Frame->new
    color
     a hex color of the frame
 
    thickness
     thickness of the frame

    my $f = Frame->new( color => 'ff0000', thickness => 3 );

  Border->new
    top
     space between the active part of the graph and the top of the image
 
    bottom
     space between the active part of the graph and the bottom of the image
 
    left
     space between the active part of the graph and the left of the image

    right
    space between the active part of the graph and the right of the image

    my $b = Border->new( top => 200, bottom => 100, left => 80, right => 200
    );

  $graph->border
    method to add or change a border on the graph

  Data->new
     create a new set of data 
 
    type
     the type of graph used for that data set.
     could be :
 
        line

        a normal line

        line_up

        a line with zero starting at the middle of the active graph with
        increasing value in the top direction

        line_down

        a line with zero starting at the middle of the active graph with
        increasing value in the bottom direction

        bar

        a filled graph

        bar_up

        a filled graph with zero starting at the middle of the active graph
        with increasing value in the top direction

        bar_down

        a filled graph with zero starting at the middle of the active graph
        with increasing value in the bottom direction

        line_stack

        a set of line stacked under each other

        line_stack_up

        a set of line stacked under each other with zero starting at the
        middle of the active graph with increasing value in the top
        direction

        line_stack_down

        a set of line stacked under each otherwith zero starting at the
        middle of the active graph with increasing value in the bottom
        direction

        bar_stack

        a set of filled graph stacked under each other

        bar_stack_up

        a set of filled graph stacked under each other with zero starting at
        the middle of the active graph with increasing value in the top
        direction

        bar_stack_down

        a set of filled graph stacked under each other with zero starting at
        the middle of the active graph with increasing value in the bottom
        direction

    color
    the hex color of the graph

    if Data is stack type, it should be a array ref with all the hex color

    thickness
    the thickness of the line used

    in bar the thickness of the border

    label
    a label to set to the SVG object

    offset
    a vertical offset ( where the zero start )

    example:
        my $l = Data->new( type => 'line', color => 'ff9800A0', thickness => 3, label => 'oblique' ,  offset    => 50 );

  $l->data_set( ... )
    include a set of data to a Data object

    it is an array ref with all data

    or an array ref of array ref for the stack type of Graph

    example:
      $l->data_set( \@data1 );
  
  $graph->add( ... )
    add a element in the graph

    the element could be:

        data_set

        Glyph

        Overlay

    example:
     $graph->add( $l );
 
    method to add an object to a graph

  graph->grid( 
    debord => ...,
    x => Grid_object,
    y = > Grid_object,
    )
        $graph->grid(

            Grid->new(
                debord => Border->new( # the debord size of the grid ( = the grid is greater than the active size )
                    top => 20, 
                    bottom => 10, 
                    left => 10,
                    right => 10 ), 

                x => Grid_def->new(         # label on the left border of the graph
                    color     => '1292FF',
                    number    => 10,
                    thickness => 2,
                    label     => Label->new(
                        font  => 'verdana',
                        color => '0000ff',
                        size  => 15,
                        text  => \@text,    # a array ref with all the text to set on the left border of the graph
                        space => 10,        # space between the end of the label and the start of the grid
                        align => 'right',
                        rotation => -30,
                    ),
                        label2 => Label->new(   # label on the right border of the graph
                        font  => 'times',
                        color => '0000ff',
                        s ize  => 20,
                        text  => \@text2,
                        space => 10,
                        # align => 'right',
                        # rotation => -45,
                    ),
                ),

                y => Grid_def->new(
                    color     => '00fff0',
                    number    => $VERT_GRID,
                    thickness => 1,
                    label     => Label->new(  # label on the left bottom of the graph
                        font     => 'verdana',
                        color    => 'ff00ff',
                        size     => 14,
                        text     => \@DATE,
                        space    => 10,
                        rotation => -30,
                        align    => 'right',
                    ),
                    label2 => Label->new( # label on the left top of the graph
                        font         => 'verdana',
                        font_scaling => 0.558,
                        color        => 'B283FF',
                        size         => 16,
                        text         => \@DATE2,
                        align        => 'right',
                        space        => 0,
                        rotation     => -30,
                    ),
                )
            )
        );

  $graph->label( label_name);
    search for the layer with the label = label_name

    in array context return ( ref_data, layer_level) in scalar context
    return ref_data

    (ref_data = an array ref with the data set )

     my ( $Mal, $Mlan ) = $graph->label( 'src_all' );
 
  $graph->move( from, to );
    Move a speciied layer to another level.

    the other layer are shifted to allow the insert

  Glyph->new
    3 type of glyph are available:

    'line' draw a polyline or polygon 'text' draw a text 'image' include a
    PNG image Embeded in the SVG

    To draw an arrow:

        my $g1 = Glyph->new(
            x        => $graph->border->left ,  
            y        =>$graph->active_size->[1] +$graph->border->bottom ,       
            type     => 'line',
            filled   => 1,                  # if 1 = fill the polygon ( be sure to correctly close the path )
            color    => '0faFff',
            data_set => [
                {
                    data => [ [ 0, 0 ], [ 8, 10 ], [ 0, 10 ], [ 0, 10 + 20 ], [ 0, 10 ], [ -8, 10 ], [ 0, 0 ] ], # the list of point to create the polyline
                    thickness => 3
                }
            ]
        );

    To write 2 text label ( in one Glyph )

            $g = Glyph->new(
                label =>'label_max',
                x => 100 ,
                y        =>200,
                type     => 'text',
                color    =>0xff0000,
                size     => 9,                              # if the glyph's type is 'text', this is the font size
                font     => 'Verdana',                      # the TrueType font to use
                data_set => [                               # the data set contain an array with all the text to plot followed by the relative position + the optional rotation
                    {
                        text   => "hello text 1",
                        x      => 0,                                # the relative position in x for that specific text
                        y      => 15,                               # the relative position in yfor that specific text
                        anchor => 'end',                                    # the text anchor ( could be  start, middle or end )
                        rotation => -45,                            # a rotation in ° in trigonometric direction ( anti-clock )
                        style => 'oblique'                          # could be      normal (default) ,| italic = oblique
                    },
                    {
                        text =>"Bye text 2",
                        x      => 60,                                # the relative position in x for that specific text
                        y      => 15,                              # the relative position in yfor that specific text
                        anchor => 'end',
                        # rotation => -45,
                        style => 'oblique'
                    },
                ],
            );
        
     To inlude a PNG image ( the image is encoded with MIME::Base64 )
      
             $g = Glyph->new(
                label => 'port_label',
                x     => $graph->active_size->[0] + $graph->border->left + 250,
                y     => $graph->active_size->[1] + $graph->border->top+$graph->border->bottom  -4,
                type  => 'image',
                data_set => [    
                    {
                        image  => $img_bin,   
                        x      => 0,
                        y      => -5,
                        width  => $buf_x,           # the width of the image
                        height => $buf_y,           # the height of the image
                    },
                ],
            ); 
        
  $graph>image
    return the SVG image ( to be writed in a file )

        open( my $IMG, '>', $file_svg ) or die $!;
        binmode $IMG;
        print $IMG $graph>image;
        close $IMG;
    
    !!!! This object is only available after the render method !!!!

  $graph->render
    create the SVG from all the objects

