Graphite - Text Tool
I have implemented the text tool for Graphite, a work in progress vector editor written in the Rust programming language with Web Assembly. Text is stored as a new type of layer that contains a string. When the user is editing the text, the string is rendered as an editable HTML div element for proper OS input handling. This was challenging as the behaviour for these editable DIVs changes in different browsers, with Chromium based browsers inserting extra new lines and not showing an insertion mark when the text input was empty, however Keavon helped me to debug these issues.
When the text is not editable, it is rendered as a spline so that it can be edited. In order to do this, I used ttf-parser, the standard in Rust for parsing font files, which provides a query for glyphs as well as enabling you to get at their raw curve data, as bezier curves so no work was needed to convert them to Graphite's svg based paths. I also used used RustyBuzz, a Rust port of HarfBuzz, in order to shape the text. Shaping involves finding the correct glyphs, including any ligatures specified by the font, common examples including 'ff' and 'fi', as well as computing the positions and advances of each glyph, taking into account kerning, which subtly moves glyphs, for example putting a V and A closer together - 'VA'.
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