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Add typeface to shaper md

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Change-Id: I5c1122a10be320e877b2adba992edb58e3ca1f9e
No-Try: true
Docs-Preview: https://skia.org/?cl=444981
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/444981
Reviewed-by: Florin Malita <fmalita@google.com>
Commit-Queue: Mike Reed <reed@google.com>
This commit is contained in:
Mike Reed 2021-09-03 11:59:42 -04:00 committed by SkCQ
parent cbfa34a58c
commit 1eb1f448d5
1 changed files with 30 additions and 9 deletions
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39
site/docs/dev/design/text_shaper.md
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@ -49,6 +49,21 @@ A Block is a descriptor for a run of text. Currently there are two specializatio
added without breaking the design.
```WebIDL
interface Typeface {
// Number or opaque object: Whatever is needed for the client to know exactly
// what font-resource (e.g. file, byte-array, etc.) is being used.
// Without this, the glyph IDs would be meaningless.
//
// This interface is really an “instance” of the font-resource. It includes
// any font-wide modifies that the client (or the shaper) may have requested:
// e.g. variations, synthetic-bold, …
//
// Factories to create Typeface can be described elsewhere. The point here
// is that such a unique identifier exists for each font-asset-instance,
// and that they can be passed around (in/out of the browser), and compared
// to each other.
};
interface TextBlock {
unsigned long length; // number of codepoints in this block
};
@ -147,29 +162,35 @@ array of Runs (either Glyphs or Placeholders for now).
```WebIDL
// Shared by all output runs, specifying the range of code-points that produced
// this run.
// this run. Known subclasses: TextRun, PlaceholderRun.
interface TextRun {
readonly attribute TextIndex startIndex;
readonly attribute TextIndex endIndex;
};
interface OutFont {
attribute Typeface typeface;
attribute double size;
attribute double scaleX?; // 1.0 if not specified
attribute double skewX?: // 0.0 if not specified (for oblique)
interface GlyphRunFont {
// Information to know which font-resource (typeface) to use,
// and at what transformation (size, etc.) to use it.
//
readonly attribute Typeface typeface;
readonly attribute double size;
readonly attribute double scaleX?; // 1.0 if not specified
readonly attribute double skewX?: // 0.0 if not specified (could be a bool)
};
// Corresponds to a FontBlock specified during shaping.
interface GlyphRun : TextRun {
readonly attribute OutFont font;
readonly attribute GlyphRunFont font;
// Information to know what positioned glyphs are in the run,
// and what the corresponding text offsets are for those glyphs.
// These “offsets” are not needed to correctly draw the glyphs, but are needed
// during selections and editing, to know the mapping back to the original text.
//
readonly attribute sequence<unsigned short> glyphs; // N glyphs
readonly attribute sequence<float> positions; // N+1 x,y pairs
readonly attribute sequence<TextIndex> indices; // N+1 indices
};
// Corresponds to a PlaceholderBlock specified during shaping.
interface PlaceholderRun : TextRun {
readonly attribute Rect bounds;
};