Feature scope

[dhardy]

#1 leaves the target feature scope unclear. This issue is not a development plan or goal, but merely an attempt to add perspective on what/where the project is.

Unfortunately there are few clear dividing lines between features in terms of complexity, thus grouping of items here is somewhat arbitrary.

Basic features:

• Simple typesetting with kerning
• Line wrapping
• Basic alignment
• (Simple) justified text

Advanced text features:

• Hyphenation
• Advanced justified text: e.g. Arabic justification should increase inter-letter distance, extending the baseline
• Bi-directional text support: breaking into "level runs" and reordering
• Glyph mirroring
• Shaping
• Rotated text (could be done downstream)
• Vertical text support
• Emot-icons
• Shaper and formatting inter-mixing: supporting format changes within a shaped run

Font features:

• Font fallback
• Font discovery: current approach is a hack ignoring system configuration
• Font face selection from family: done but sub-optimal API
• Variable fonts, font synthesis
• Small-caps text

Text interaction:

• Cursor position from index
• Visual-order navigation via Left/Right keys
• Mouse-coordinate to nearest text-index
• Better than O(n) text editing
• Intra-ligature cursor position

Text formatting:

• Highlighting (implemented but buggy)
• Highlighting via format tokens
• Formatted text selecting font size and face/family
• Underline and strike-through
• Interactive formatting (e.g. hyperlinks should have mouse-hover effect and be clickable)
• Non-contact underline

Text parsing is mostly orthogonal to other features; never-the-less having an easy way to construct formatted texts is useful:

• BiDi breaking
• Markdown (basic)
• Simplified HTML?

Rendering is mostly out-of-scope, but some features are supported:

• Basic glyph rastering
• (RGB) sub-pixel rendering (probably not worthwhile now that high-res displays are common)
• Cache-friendly raster-target descriptor supporting sub-pixel positioning
• Hinting / grid-fitting

Layout:

• Inter-paragraph spacing (beyond an empty line)
• Tabs (basic implementation but too limited to call done)
• Embedding: supporting arbitrary content embedded within text flow
• Composibility: supporting text or complex content over multiple Text/TextDisplay objects (possibly better supported by a downstream library)

Non-text objects (likely beyond scope):

• Horizontal rules
• Tables
• Quote background box

There is no desired scope or use-case, but it is very unlikely that all the above will be implemented. Notes:

• Font discovery, font synthesis, variable font support, hinting and rastering are all complex features which will never be implemented in this crate (but may have API wrapping a foreign impl)
• Unclear how to handle indentation/tabs and inter-paragraph spaces. Possibly allow formatting tokens to specify indent/v-skip?