Function fill_glyph 

pub(crate) fn fill_glyph(
    renderer: &mut impl GlyphRenderer,
    prepared_glyph: PreparedGlyph<'_>,
    atlas_cacher: &mut AtlasCacher<'_>,
    outline_cache: &mut OutlineCacheSession<'_>,
)

Fill a prepared glyph, using the glyph atlas when possible and falling back to direct rendering otherwise.