Struct GlyphInfo

#[repr(C)]
pub struct GlyphInfo {
    pub glyph_id: u32,
    pub cluster: u32,
    /* private fields */
}

A glyph info.

Structure that holds information about the glyphs and their relation to input text.

HarfBuzz calls this hb_glyph_info_t. See the documentation and source.

Fields

glyph_id: u32

A selected glyph.

Guarantee to be <= u16::MAX.

cluster: u32

An index to the start of the grapheme cluster in the original string.

Read more on clusters.

Implementations

impl GlyphInfo

pub fn unsafe_to_break(&self) -> bool

Indicates that if input text is broken at the beginning of the cluster this glyph is part of, then both sides need to be re-shaped, as the result might be different.

On the flip side, it means that when this flag is not present, then it’s safe to break the glyph-run at the beginning of this cluster, and the two sides represent the exact same result one would get if breaking input text at the beginning of this cluster and shaping the two sides separately. This can be used to optimize paragraph layout, by avoiding re-shaping of each line after line-breaking, or limiting the reshaping to a small piece around the breaking point only.

pub fn unsafe_to_concat(&self) -> bool

Indicates that if input text is changed on one side of the beginning of the cluster this glyph is part of, then the shaping results for the other side might change. Note that the absence of this flag will NOT by itself mean that it IS safe to concat text. Only two pieces of text both of which clear of this flag can be concatenated safely.

This can be used to optimize paragraph layout, by avoiding re-shaping of each line after line-breaking, by limiting the reshaping to a small piece around the breaking position only, even if the breaking position carries the unsafe-to-break flag or when hyphenation or other text transformation happens at line-break position, in the following way:

1. Iterate back from the line-break position until the first cluster start position that is NOT unsafe-to-concat.
2. Shape the segment from there till the end of line.
3. Check whether the resulting glyph-run also is clear of the unsafe-to-concat at its start-of-text position; if it is, just splice it into place and the line is shaped; If not, move on to a position further back that is clear of unsafe-to-concat and retry from there, and repeat.

At the start of next line a similar algorithm can be implemented. That is:

1. Iterate forward from the line-break position until the first cluster start position that is NOT unsafe-to-concat.
2. Shape the segment from beginning of the line to that position.
3. Check whether the resulting glyph-run also is clear of the unsafe-to-concat at its end-of-text position; if it is, just splice it into place and the beginning is shaped; If not, move on to a position further forward that is clear of unsafe-to-concat and retry up to there, and repeat. A slight complication will arise in the implementation of the algorithm above, because while our buffer API has a way to return flags for position corresponding to start-of-text, there is currently no position corresponding to end-of-text. This limitation can be alleviated by shaping more text than needed and looking for unsafe-to-concat flag within text clusters. The unsafe-to-break flag will always imply this flag. To use this flag, you must enable the buffer flag BufferFlags::PRODUCE_UNSAFE_TO_CONCAT during shaping, otherwise the buffer flag will not be reliably produced.

pub fn safe_to_insert_tatweel(&self) -> bool

In scripts that use elongation (Arabic, Mongolian, Syriac, etc.), this flag signifies that it is safe to insert a U+0640 TATWEEL character before this cluster for elongation. This flag does not determine the script-specific elongation places, but only when it is safe to do the elongation without interrupting text shaping.

Trait Implementations

impl Clone for GlyphInfo

fn clone(&self) -> GlyphInfo

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for GlyphInfo

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for GlyphInfo

fn default() -> GlyphInfo

Returns the “default value” for a type.

impl Zeroable for GlyphInfo

fn zeroed() -> Self

Calls zeroed.

impl Copy for GlyphInfo

impl Pod for GlyphInfo