iText Core/Community for .NET

iText supports dynamic margins and automatic footnote management through the PageMarginBoxes and PageMarginContent classes.

Dynamic Margins

You can adjust page margins on the fly using the SectionBreak element or by setting margins via Document#setPageMargins. The DocumentRenderer#computeLayoutMargins method reserves this space at the start of a new page.

Footnotes

Footnotes are handled automatically within paragraphs:

• Anchors: FootnoteAnchor is added to a paragraph.
• Placement: The engine checks if there is enough space at the bottom of the current area for the corresponding Footnote. If not, it reduces the available layout area and triggers a relayout.
• Tagging:
  • The anchor in the text is tagged as Reference (or Lbl in PDF 2.0).
  • The footnote text is tagged as Note (or FENote in PDF 2.0).
  • The label inside the footnote is tagged as Lbl.

Multicol layouting allows for horizontal content layouting within a fixed height, similar to a newspaper.

Using MulticolContainer

To implement this, use the MulticolContainer class.

• Role: It acts as an aggregator for content that should be laid out in columns and stores properties like Property#COLUMN_COUNT or Property#COLUMN_WIDTH.
• Constraint: A MulticolContainer instance must have exactly one child, which represents the entire block of content to be distributed into columns.

How it works

The MulticolRenderer performs a balancing algorithm:

1. Calculates column count and width.
2. Performs a temporary layout with infinite height to estimate column height.
3. Iteratively adjusts the height (up to MulticolRenderer#MAX_RELAYOUT_COUNT times) until all content fits into the columns.
4. Enables TREAT_AS_CONTINUOUS_CONTAINER to ensure continuous layout between columns.

The Layout module transforms abstract model elements (like Paragraph, Table, or List) into low-level PDF drawing operations. This process is handled by a rendering engine that separates the model structure from the rendering logic.

Key Abstractions

• Model Elements (IElement): Objects like Text, Paragraph, and Table that represent the structure of your document. You build a tree of these elements in your code.
• Renderers (IRenderer): Internal classes (e.g., ParagraphRenderer, TableRenderer) that handle the actual placement and drawing of elements. While usually used internally, you can subclass them to customize rendering behavior.
• Property Containers (IPropertyContainer): An interface implemented by both IElement and IRenderer. It uses a map-based system to store and inherit properties (like font size or color) across the element/renderer tree, which is more memory-efficient than standard fields.

The Rendering Lifecycle

1. Tree Construction: You build a tree of IElement objects (e.g., adding a Paragraph to a Div).
2. Renderer Conversion: The engine calls IElement#createRendererSubTree to convert the element tree into a corresponding tree of renderers via a depth-first traversal.
3. Layout Phase: The engine calls Layout() on the renderers. This calculates the position and area (LayoutBBox) each element occupies. If an element doesn't fit on a page, it is split into a split renderer (the part that fits) and an overflow renderer (the part to be moved to the next page).
4. Draw Phase: Once layout is complete, Draw() is called to generate the actual PDF syntax and drawing instructions.

Div container = new Div();
Paragraph paragraph = new Paragraph("New paragraph.");
container.add(paragraph);