Ebox

Ebox is a standalone Text/Box layout engine for Emacs. It owns text measurement, box geometry, row/column/flex/Grid layout, retained rendering, and incremental buffer publication. Use the sibling ETAF package when an application also needs Components, reactive state, behaviors, or lifecycle.

Install

Ebox requires Emacs 29.1 or newer, ECSS 0.1.0 or newer, and TP 1.0.1 or newer. A package manager should install the declared dependencies. For sibling source checkouts, add the three directories to load-path, then load Ebox:

(add-to-list 'load-path "/path/to/ecss")
(add-to-list 'load-path "/path/to/tp")
(add-to-list 'load-path "/path/to/ebox")
(require 'ebox)

Loading Ebox does not create a buffer or build native code.

First render

The ordinary author model has seven entries: a string, text, box, row, column, flex, and grid. Children are nested directly; there is no second field-based child syntax.

(require 'ebox)

(ebox-render-to-buffer
 "*Ebox Example*"
 (ebox-build
  '(column :padding ((lh 1) (ch 2))
           :border ((px 1) solid "#8A93A6")
           (text :color "#263244" "Hello Ebox")
           (row :item-gap (ch 1)
                (box "Left")
                (box "Right")))))

Use ebox-build for the public author DSL. Framework integrations may instead assemble typed nodes with one ebox-source-builder, then seal the forest and its source generation as one CanonicalEboxInput; that evaluated API is not a second author grammar.

Typed Box construction containing ebox-child-range descriptors passes its open builder explicitly as :source-builder. The builder must own the Box and its immediate children's source handles; an empty Range still requires an open builder. It is used only during construction. To compose an existing canonical input, use ebox-canonical-input-roots and ebox-canonical-input-import-roots; frameworks must not access private canonical fields or dynamic context.

Layout choices

• box creates a normal visual box.
• row and column provide simple one-axis composition.
• flex distributes space and supports wrapping.
• grid provides two-dimensional tracks and placement.
• A bare string is the short form of (text "...").

Flex and Grid participation properties belong directly to a child box. They do not require a wrapper node.

Box geometry uses (unit number): px, %, vw, vh, ch, and lh. For example, :width (ch 80) and :height (calc (- (vh 100) (lh 1))) mean an 80-zero-glyph width and a viewport height minus one line height. calc, min, max, and clamp compose lengths at layout time. Size keywords such as auto and bare fit-content stay symbols. Old bare lengths, singleton pixel lists, and viewport keywords are rejected. Units are checked against the property axis at construction, including every branch of a size function. See the shared unit-constraint table for the allowed combinations, keyword defaults, percentage references, and vertical line quantization. An empty Box has zero automatic content height; use (box :height (lh 1)) to reserve a blank line.

Native interaction

Text and every Box form accept four explicit node capabilities: :help-echo for a string or native help function, :pointer for a native pointer shape, :hover-style for restricted color and text-decoration paint, and :keymap for a native Emacs keymap. Box help, pointer, and keymap cover its content, padding, and border; they exclude that Box's margin and structural newlines. Hover shares the declaring node's paint across text and padding, excluding physical left/right borders. Nested explicit values override enclosing capabilities; explicit nil clears one capability.

Use ebox-help-create to adapt a zero-argument business function to native help with the hovered buffer as its context. Use ebox-keymap-create to bind ordinary zero-argument callbacks to activation keys or custom keys; it supplies the clicked window's buffer for mouse commands. Use ebox-region-update with a semantic ID in the current mounted buffer or an explicit region handle to replace or clear these capabilities. Native keymaps support independent Ebox interactions; application state, focus navigation, and command behavior remain the author's responsibility. See the interaction guide and the Playground's interaction lab.

Render and update

• ebox-render returns propertized text without publishing a live buffer.
• ebox-render-to-buffer mounts a retained surface.
• ebox-commit atomically publishes a newly built canonical input.
• ebox-buffer-update-report returns the last successful update report.
• ebox-rerender-buffer-with-context applies an explicit viewport change.
• ebox-surface-buffer-snapshot explicitly exports the current committed :input, :revision, and :mount-id as one plist.

Ebox copies canonical input before assigning runtime identity, so one built value may be mounted in multiple buffers without sharing live ownership.

Snapshots traverse exported data and TP's latest retained diagnostic report only when requested; ordinary updates do not create them. Their canonical input remains usable after later updates or unmounting. Mutable node data and interaction keymaps are detached, while immutable source facts and opaque capabilities (callbacks, records) retain identity. The display environment and external capabilities are not frozen. Querying during a TP transaction or after unmounting signals an error. Compare both mount ID and revision when identifying a committed generation; remounting can restart revision numbers.

Ebox registers rollback-capable state only through TP's public structured participant API. TP 1.0.1 supports the consumer-first migration protocol; TP 2.0.0 publishes the final v2-only protocol. Missing or malformed structured participant capability stops Ebox loading instead of selecting a compatibility writer.

Optional native module

The Rust module accelerates eligible reflow work. It is optional and has an exact Elisp fallback. Ebox never builds it while loading.

(ebox-native-status)
(ebox-native-build)

Verification

make load EMACS=/Applications/Emacs.app/Contents/MacOS/Emacs
make compile EMACS=/Applications/Emacs.app/Contents/MacOS/Emacs
make docs-contract-tests EMACS=/Applications/Emacs.app/Contents/MacOS/Emacs
make interaction-tests EMACS=/Applications/Emacs.app/Contents/MacOS/Emacs
make c1b-contract-tests EMACS=/Applications/Emacs.app/Contents/MacOS/Emacs
make check EMACS=/Applications/Emacs.app/Contents/MacOS/Emacs
make native-rust-tests

See the user guide, the public API reference, and the sibling ebox-playground examples.