Crate rotulus_layout 

The layout engine behind the Rotulus chat view.

Everything between “a message arrives” and “the view knows what pixels to put where”, with no GTK, no GLib and no Pango, so all of it runs under cargo test on display-less CI. The widget that consumes it is rotulus; see docs/design.md.

  Message  ──parse──▶  ParsedText (text + Spans)
     │                        │
     │                   layout_message ──▶ LayoutCache (height, LineBoxes)
     ▼                        │
  ChatBuffer ◀────────────────┘
     │  rows + HeightIndex + ScrollAnchor
     ▼
  view: "which rows are visible, and how tall is everything"

What this replaces, and why

HexChat’s xtext widget lays out on a uniform grid: every row is fontsize × subline_count, the scroll adjustment’s unit is fractional text lines, and hit-testing is y / fontsize. That assumption is wired through the whole widget, and every feature added to it late had to work around it — inline media reserves ceil(image_height / fontsize) blank text rows and paints a texture across them, which is why selection drags through empty space and the marker line draws above an image rather than across it.

Four things here are deliberate departures:

• Parse once. Styling is resolved at append into span::Spans. xtext re-ran its escape state machine over every visible byte on every render pass and separately built a run list at append that the render path then ignored.
• Pixels, not lines. index::HeightIndex gives O(log n) pixel↔row in both directions over genuinely variable heights.
• Anchor, not offset. anchor::ScrollAnchor pins the viewport to a row. Resize, zoom, history backfill, scrollback trim and a late-arriving image decode then all preserve reading position for free, rather than each needing its own compensation.
• Lazy layout. A width or font change invalidates without recomputing, so resize costs O(visible). xtext’s gtk_xtext_calc_lines re-wraps the entire scrollback.

Measurement

measure::TextMeasure is the seam. The view supplies a Pango implementation; tests supply measure::FixedMeasure, where every character is N pixels wide, so wrap assertions are exact rather than font-dependent. The trait’s unit of work is a run, never a character — xtext measured per character through a full Pango round trip each time, and the trait shape makes repeating that impossible.

Input vocabularies

Style arrives as runs from the application, already resolved, so the engine decodes no in-band escapes and nothing a remote user sends can restyle a row. markdown is the one vocabulary it parses itself: an inline subset, rendered on display and transmitted literally. linkify finds URLs, against a scheme list the application owns.

Re-exports

pub use anchor::Gravity;

pub use anchor::ScrollAnchor;

pub use buffer::ChatBuffer;

pub use buffer::MIN_INDENT;

pub use index::HeightIndex;

pub use linkify::Linkifier;

pub use linkify::DEFAULT_SCHEMES;

pub use markdown::scan_delims;

pub use markdown::SourceSpan;

pub use measure::FixedMeasure;

pub use measure::FontMetrics;

pub use measure::TextMeasure;

pub use message::Block;

pub use message::Blocks;

pub use message::GroupKey;

pub use message::ImageSize;

pub use message::LoadMoreDirection;

pub use message::Message;

pub use message::MessageFlags;

pub use message::MessageId;

pub use message::MessageKind;

pub use message::Speaker;

pub use search::find_all;

pub use search::Match;

pub use search::SearchState;

pub use select::Caret;

pub use select::RowSelection;

pub use select::Selection;

pub use span::Attrs;

pub use span::ColorRef;

pub use span::Link;

pub use span::LinkId;

pub use span::ParsedText;

pub use span::Span;

pub use span::Style;

pub use wrap::AvatarBox;

pub use wrap::LayoutCache;

pub use wrap::LayoutGeneration;

pub use wrap::LayoutParams;

pub use wrap::LineBox;

pub use wrap::LineSource;

Modules

anchor

Scroll position, expressed as a row rather than a pixel.

buffer

The buffer: rows, marks, lazy layout, trim.

index

The height index: pixel position ↔ row, in O(log n).

linkify

Finding links in plain text.

markdown

The markdown inline scanner.

measure

Text measurement, abstracted.

message

The structured message model.

search

In-buffer search: find every occurrence of a needle, and a cursor over the results.

select

Selection: hit-testing, the selection range, and text extraction.

span

Styled text runs.

wrap

Line breaking and per-message layout.