create repo

.gitignore

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+/target
+Cargo.lock

Cargo.toml

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+[package]
+name = "parley"
+version = "0.1.0"
+authors = ["Chad Brokaw <[email protected]>"]
+license = "MIT OR Apache-2.0"
+edition = "2018"
+
+[dependencies]

LICENSE-APACHE

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LICENSE-MIT

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+Copyright (c) 2020 Chad Brokaw
+
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
+documentation files (the "Software"), to deal in the
+Software without restriction, including without
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+
+The above copyright notice and this permission notice
+shall be included in all copies or substantial portions
+of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.

README.md

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+This is a nascent project for implementing a rich text layout engine backed
+by the [swash](https://github.com/dfrg/swash) crate and implementing the 
+[piet](https://github.com/linebender/piet) text API.

doc/design.md

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+## Typography is the new black
+
+High quality typography, once the domain of static layout generators such as TeX
+and derivatives, has commanded increasing significance in the last decade among 
+real time text engines and as such has received long needed resources and 
+attention from specification groups, web browser developers and platform
+vendors. These efforts have reinvigorated the landscape, producing more 
+sophisticated text APIs, new OpenType specifications, increased investment
+in font production technologies and a wide corpus of beautiful, comprehensive fonts
+supporting modern features. Perhaps more importantly, there has been a strong
+focus on extending global access to computing through both more robust font 
+fallback systems and Google's ever-expanding collection of Noto fonts supporting
+world-wide scripts and languages.
+
+## Portable, safe rich text layout
+
+While modern text layout engines have grown quite sophisticated, they are unfortunately
+limited to platform specific applications, requiring cross-platform code (or even
+cross-platform toolkits) to specialize their text rendering implementations for
+each supported operating system. An increasingly popular option to side-step this problem
+is to use an abstraction wrapping an embedded web browser such as Electron. This
+has advantages if your application is already using a wide range of web technologies, 
+but becomes a large, complicated, overbearing dependency otherwise.
+
+In addition, while platform specific text engines and web browsers consist of high quality,
+well-tested code produced by incredibly talented developers, they are all ultimately large 
+and complex codebases implemented in C++ which is a fundamentally unsafe language. The Rust
+language has proven to be a high performance, safe alternative to C++.
+
+Given the platform specific nature of current text engines, and the unsafe implementation
+language, the obvious course of action is to build a new, cross-platform, open source text
+layout engine in Rust. 
+
+## Design overview
+
+The Rust ecosystem comprises a large collection of high quality crates, specifically in
+the domains of networking and servers. The graphics situation is fairly nascent which
+leads to challenges in bootstrapping projects, but also opportunities to lay a robust
+foundation for future work. The Druid project is a particularly interesting offering for
+UI development and its underlying abstraction for 2D graphics, piet, is a very promising
+API that is a leading contender for coalescing development efforts in the graphics
+domain. As the author of swash, a new crate providing font parsing and complex text shaping,
+my goal is to bridge the two, building a text layout engine that is based on the swash
+primitives and exposes the piet text API.
+
+Rich text layout is a complex process involving cross-cutting concerns across a wide 
+swath of both the Unicode and OpenType specifications interleaved with design intent, 
+available resources, internationalization considerations, and performance. Broadly, the
+process can be represented by a pipeline consisting of the following phases:
+
+* Bidirectional processing: identifies spans of text containing runs of mixed directionality
+and assigns specific "levels" according the Unicode Bidirectional Algorithm (UAX #9).
+These levels are used to determine the directionality of text and to ultimately reorder
+runs later in the pipeline.
+
+* Itemization: splits a paragraph into runs that are appropriate for shaping. This takes
+Unicode scripts, locales, BiDi levels, fonts and other text attributes into account.
+
+* Font selection/fallback: selects an appropriate font for each run based on desired 
+font attributes, script, locale and character coverage. Ideally, this will select the
+font specified by the user, but will prioritize selecting for appropriate coverage and
+readable text (no tofu). This stage can break runs produced by itemization if necessary.
+
+* Shaping: converts each run of characters into a sequence of positioned glyphs using 
+the selected font and based on writing system rules and selected features. This will be
+provided by the swash crate.
+
+* Line breaking: breaks runs to fit within some desired maximum extent based on the 
+Unicode Line Breaking Algorithm (UAX #14). Reorders glyph runs per-line according to the
+previously computed BiDi levels. Computes final layout of lines and glyphs.
+
+Ultimately, the purpose of this project is to take the input specified by the piet text
+API and apply the above pipeline, producing a final paragraph layout suitable for
+hit-testing and rendering. Appropriate data structures and algorithms for implementing
+such will be chosen and documented as development proceeds.
+
+## Extensions to the piet text API
+
+The piet text API currently provides a fairly minimal set of attributes to provide text
+rendering across the range of supported backends. This project initially proposes three
+specific additions to the API.
+
+With respect to text attributes, there is strong desire to offer both OpenType feature
+selectors and variation axes settings. The specific design of such to be discussed and agreed
+upon with the piet maintainer.
+
+To provide proper hit-testing and selection of bidirectional text, the API will also
+require support for some form of affinity with regard to the bounds of a selection.
+This might require a more sophisticated selection API beyond the currently supported
+Unicode scalar offsets.
+
+If time permits, additional features might include user specified letter, word, and
+line spacing and customizable decorations such as custom offsets, sizes, and
+colors for underline and strikeout strokes.
+
+## Further considerations
+
+There exist some nice-to-have layout features that are out of scope for the current development
+cycle of this project-- specifically, more sophisticated segmentation using a 
+dictionary based approach for languages such as Thai and shaper/dictionary driven
+hyphenation and justification.
+
+Additionally, font selection and fallback for this project will be provided by a related
+library that provides a pre-baked collection of well-known platform specific fonts with
+appropriate script coverage. This is a fairly simple and robust solution, but there are
+opportunities for future work in more efficient integration with platform font libraries
+without taking on large dependencies. This would require cross-vendor coordination and is
+also out of scope for this project.

src/lib.rs

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+