class HexaPDF::Layout::Box

Included Modules

The base class for all layout boxes.

Box Model

HexaPDF uses the following box model:

  • Each box can specify a width and height. Padding and border are inside, the margin outside of this rectangle.

  • The content_width and content_height accessors can be used to get the width and height of the content box without padding and the border.

  • If width or height is set to zero, they are determined automatically during layouting.


Each subclass should only take keyword arguments on initialization so that the boxes can be instantiated from the common convenience method HexaPDF::Document::Layout#box. To use this facility subclasses need to be registered with the configuration option ‘’.

The methods supports_position_flow?, empty?, fit or fit_content, split or split_content, and draw or draw_content need to be customized according to the subclass’s use case (also see the documentation of the methods besides the informatione below):


If the subclass supports the value :flow of the ‘position’ style property, this method needs to be overridden to return true.


This method should return true if the subclass won’t draw anything when draw is called.


This method should return true if fitting was successful. Additionally, the @fit_successful instance variable needs to be set to the fit result as it is used in split.

The default implementation provides code common to most use-cases and delegates the specifics to the fit_content method which needs to return true if fitting was successful.


This method splits the content so that the current region is used as good as possible. The default implementation should be fine for most use-cases, so only split_content needs to be implemented. The method create_split_box should be used for getting a basic cloned box.


This method draws the content and the default implementation already handles things like drawing the border and background. So it should not be overridden. The box specific drawing commands should be implemented in the draw_content method.

This base class provides various private helper methods for use in the above methods:

reserved_width, reserved_height

Returns the width respectively the height of the reserved space inside the box that is used for the border and padding.

reserved_width_left, reserved_width_right, reserved_height_top,


Returns the reserved space inside the box at the specified edge (left, right, top, bottom).

update_content_width, update_content_height

Takes a block that should return the content width respectively height and sets the box’s width respectively height accordingly.


Creates a new box based on this one and resets the internal data back to their original values.

The keyword argument split_box_value (defaults to true) is used to set the +@split_box+ variable to make the new box aware that it is a split box. This can be set to any other truthy value to convey more meaning.



The height of the box, including padding and/or borders.


Hash with custom properties. The keys should be strings and can be arbitrary.

This can be used to store arbitrary information on boxes for later use. For example, a generic style layer could use one or more custom properties for its work.

The Box class itself uses the following properties:


If this property is set, it needs to be an optional content group dictionary, a String defining an (optionally existing) optional content group dictionary, or an optional content membership dictionary.

The whole content of the box, i.e. including padding, border, background…, is wrapped with the appropriate commands so that the optional content group or membership dictionary specifies whether the content is shown or not.

See: HexaPDF::Type::OptionalContentProperties


The style to be applied.

Only the following properties are used:


The width of the box, including padding and/or borders.

Public Class Methods

create(width: 0, height: 0, content_box: false, style: nil, **style_properties, &block)

Creates a new Box object, using the provided block as drawing block (see ::new).

If content_box is true, the width and height are taken to mean the content width and height and the style’s padding and border are added to them appropriately.

The style argument defines the Style object (see Style::create for details) for the box. Any additional keyword arguments have to be style properties and are applied to the style object.

new(width: 0, height: 0, style: nil, properties: nil) {|canv, box| block} → box

Creates a new Box object with the given width and height that uses the provided block when it is asked to draw itself on a canvas (see draw).

Since the final location of the box is not known beforehand, the drawing operations inside the block should draw inside the rectangle (0, 0, content_width, content_height) - note that the width and height of the box may not be known beforehand.

Public Instance Methods


The height of the content box, i.e. without padding and/or borders.


The width of the content box, i.e. without padding and/or borders.

draw(canvas, x, y)

Draws the content of the box onto the canvas at the position (x, y).

The coordinate system is translated so that the origin is at the bottom left corner of the **content box** during the drawing operations when +@draw_block+ is used.

The block specified when creating the box is invoked with the canvas and the box as arguments. Subclasses can specify an on-demand drawing method by setting the +@draw_block+ instance variable to nil or a valid block. This is useful to avoid unnecessary set-up operations when the block does nothing.

Alternatively, if a draw_content method is defined, this method is called.


Returns true if no drawing operations are performed.

fit(available_width, available_height, frame)

Fits the box into the frame and returns true if fitting was successful.

The arguments available_width and available_height are the width and height of the current region of the frame, adjusted for this box. The frame itself is provided as third argument.

The default implementation uses the given available width and height for the box width and height if they were initially set to 0. Otherwise the intially specified dimensions are used. Then the fit_content method is called which allows sub-classes to fit their content.

The following variables are set that may later be used during splitting or drawing:

  • (@fit_x, @fit_y): The lower-left corner of the content box where fitting was done. Can be used to adjust the drawing position in draw/#draw_content if necessary.

  • @fit_successful: true if fitting was successful.

split(available_width, available_height, frame)

Tries to split the box into two, the first of which needs to fit into the current region of the frame, and returns the parts as array.

If the first item in the result array is not nil, it needs to be this box and it means that even when fit fails, a part of the box may still fit. Note that fit should not be called before draw on the first box since it is already fitted. If not even a part of this box fits into the current region, nil should be returned as the first array element.

Possible return values:


The box fully fits into the current region.

[nil, self]

The box can’t be split or no part of the box fits into the current region.

[self, new_box]

A part of the box fits and a new box is returned for the rest.

This default implementation provides the basic functionality based on the fit result that should be sufficient for most subclasses; only split_content needs to be implemented if necessary.


Returns the set truthy value if this is a split box, i.e. the rest of another box after it was split.


Returns false since a basic box doesn’t support the ‘position’ style property value :flow.