subsetter 0.2.3

Reduces the size and coverage of OpenType fonts.
Documentation 
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//! The `maxp` table contains the number of glyphs (and some additional information
//! depending on the version). All we need to do is rewrite the number of glyphs, the rest
//! can be copied from the old table.

use super::*;

pub fn subset(ctx: &mut Context) -> Result<()> {
    const POST_TRUETYPE_VERSION: u32 = 0x00010000;
    const POST_CFF_VERSION: u32 = 0x00005000;

    let maxp = ctx.expect_table(Tag::MAXP).ok_or(MalformedFont)?;
    let mut r = Reader::new(maxp);
    // Version
    let _ = r.read::<u32>().ok_or(MalformedFont)?;
    // number of glyphs
    r.read::<u16>().ok_or(MalformedFont)?;

    let version = match ctx.flavor {
        FontFlavor::TrueType => POST_TRUETYPE_VERSION,
        FontFlavor::Cff => POST_CFF_VERSION,
        // Since we convert to TrueType.
        FontFlavor::Cff2 => POST_TRUETYPE_VERSION,
    };

    let mut sub_maxp = Writer::new();
    sub_maxp.write::<u32>(version);
    sub_maxp.write::<u16>(ctx.mapper.num_gids());

    if version == POST_TRUETYPE_VERSION {
        if let Some(custom_data) = &ctx.custom_maxp_data {
            sub_maxp.write::<u16>(custom_data.max_points);
            sub_maxp.write::<u16>(custom_data.max_contours);
            sub_maxp.write::<u16>(custom_data.max_composite_points);
            sub_maxp.write::<u16>(custom_data.max_composite_contours);
            sub_maxp.write::<u16>(custom_data.max_zones);
            sub_maxp.write::<u16>(custom_data.max_twilight_points);
            sub_maxp.write::<u16>(custom_data.max_storage);
            sub_maxp.write::<u16>(custom_data.max_function_defs);
            sub_maxp.write::<u16>(custom_data.max_instruction_defs);
            sub_maxp.write::<u16>(custom_data.max_stack_elements);
            sub_maxp.write::<u16>(custom_data.max_size_of_instructions);
            sub_maxp.write::<u16>(custom_data.max_component_elements);
            sub_maxp.write::<u16>(custom_data.max_component_depth);
        } else {
            sub_maxp.extend(r.tail().ok_or(MalformedFont)?);
        }
    }

    ctx.push(Tag::MAXP, sub_maxp.finish());
    Ok(())
}

// When converting CFF2 to TTF, we need to write a version 1.0 MAXP table.
pub(crate) struct MaxpData {
    pub(crate) max_points: u16,
    pub(crate) max_contours: u16,
    max_composite_points: u16,
    max_composite_contours: u16,
    max_zones: u16,
    max_twilight_points: u16,
    max_storage: u16,
    max_function_defs: u16,
    max_instruction_defs: u16,
    max_stack_elements: u16,
    max_size_of_instructions: u16,
    max_component_elements: u16,
    max_component_depth: u16,
}

impl Default for MaxpData {
    fn default() -> Self {
        Self {
            max_points: 0,
            max_contours: 0,
            max_composite_points: 0,
            max_composite_contours: 0,
            max_zones: 1,
            max_twilight_points: 0,
            max_storage: 0,
            max_function_defs: 0,
            max_instruction_defs: 0,
            max_stack_elements: 0,
            max_size_of_instructions: 0,
            max_component_elements: 0,
            // Could probably be 0 too since we only use simple glyphs when converting?
            max_component_depth: 1,
        }
    }
}