read_fonts/tables/
instance_record.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
//! An fvar InstanceRecord

use types::{BigEndian, Fixed, FixedSize, NameId};

#[cfg(feature = "experimental_traverse")]
use crate::traversal::{Field, RecordResolver, SomeRecord};
use crate::{ComputeSize, FontData, FontReadWithArgs, ReadArgs, ReadError};

/// The [InstanceRecord](https://learn.microsoft.com/en-us/typography/opentype/spec/fvar#instancerecord)
#[derive(Clone, Debug)]
pub struct InstanceRecord<'a> {
    /// The name ID for entries in the 'name' table that provide subfamily names for this instance.
    pub subfamily_name_id: NameId,
    /// Reserved for future use — set to 0.
    pub flags: u16,
    /// The coordinates array for this instance.
    pub coordinates: &'a [BigEndian<Fixed>],
    /// Optional. The name ID for entries in the 'name' table that provide PostScript names for this instance.
    pub post_script_name_id: Option<NameId>,
}

impl ReadArgs for InstanceRecord<'_> {
    type Args = (u16, u16);
}

impl<'a> InstanceRecord<'a> {
    /// Parse an instance record with a known axis_count and instance_size
    pub fn read(
        data: FontData<'a>,
        axis_count: u16,
        instance_size: u16,
    ) -> Result<Self, ReadError> {
        let args = (axis_count, instance_size);
        Self::read_with_args(data, &args)
    }
}

impl<'a> FontReadWithArgs<'a> for InstanceRecord<'a> {
    fn read_with_args(data: FontData<'a>, args: &Self::Args) -> Result<Self, ReadError> {
        let axis_count = args.0 as usize;
        let instance_size = args.1 as usize;
        let mut cursor = data.cursor();
        let subfamily_name_id = cursor.read()?;
        let flags = cursor.read()?;
        let coordinates = cursor.read_array(axis_count)?;
        // Size of common fields (subfamily_name_id and flags) plus axis coordinates.
        let common_byte_len = u16::RAW_BYTE_LEN * 2 + (axis_count * Fixed::RAW_BYTE_LEN);
        // The instance contains a post_script_name_id field if the instance size is greater than
        // or equal to the common size plus the 2 bytes for the optional field.
        let has_post_script_name_id = instance_size >= common_byte_len + u16::RAW_BYTE_LEN;
        let post_script_name_id = if has_post_script_name_id {
            let id: NameId = cursor.read()?;
            // From <https://learn.microsoft.com/en-us/typography/opentype/spec/fvar#instancerecord>:
            // "If the value is 0xFFFF, then the value is ignored, and no
            // PostScript name equivalent is provided for the instance."
            (id.to_u16() != 0xFFFF).then_some(id)
        } else {
            None
        };
        Ok(InstanceRecord {
            subfamily_name_id,
            flags,
            coordinates,
            post_script_name_id,
        })
    }
}

impl ComputeSize for InstanceRecord<'_> {
    #[inline]
    fn compute_size(args: &(u16, u16)) -> Result<usize, ReadError> {
        Ok(args.1 as usize)
    }
}

#[cfg(feature = "experimental_traverse")]
impl<'a> InstanceRecord<'a> {
    pub(crate) fn get_field(&self, idx: usize, _data: FontData<'a>) -> Option<Field<'a>> {
        match idx {
            0 => Some(Field::new("subfamily_name_id", self.subfamily_name_id)),
            1 => Some(Field::new("flags", self.flags)),
            2 => Some(Field::new("coordinates", self.coordinates)),
            3 => Some(Field::new("post_script_name_id", self.post_script_name_id?)),
            _ => None,
        }
    }
}

#[cfg(feature = "experimental_traverse")]
impl<'a> SomeRecord<'a> for InstanceRecord<'a> {
    fn traverse(self, data: FontData<'a>) -> RecordResolver<'a> {
        RecordResolver {
            name: "InstanceRecord",
            data,
            get_field: Box::new(move |idx, data| self.get_field(idx, data)),
        }
    }
}