cosmic-text/src/swash.rs

// SPDX-License-Identifier: MIT OR Apache-2.0

use std::collections::HashMap;
use swash::scale::{ScaleContext, image::Content};
use swash::scale::{Render, Source, StrikeWith};
use swash::zeno::{Format, Vector};

use crate::{CacheKey, Color, FontSystem};

pub use swash::scale::image::{Content as SwashContent, Image as SwashImage};

fn swash_image<'a>(font_system: &'a FontSystem, context: &mut ScaleContext, cache_key: CacheKey) -> Option<SwashImage> {
    let font = match font_system.get_font(cache_key.font_id) {
        Some(some) => some,
        None => {
            log::warn!("did not find font {:?}", cache_key.font_id);
            return None;
        },
    };

    // Build the scaler
    let mut scaler = context
        .builder(font.as_swash())
        .size(cache_key.font_size as f32)
        .hint(true)
        .build();

    // Compute the fractional offset-- you'll likely want to quantize this
    // in a real renderer
    let offset =
        Vector::new(cache_key.x_bin.as_float(), cache_key.y_bin.as_float());

    // Select our source order
    Render::new(&[
        // Color outline with the first palette
        Source::ColorOutline(0),
        // Color bitmap with best fit selection mode
        Source::ColorBitmap(StrikeWith::BestFit),
        // Standard scalable outline
        Source::Outline,
    ])
    // Select a subpixel format
    .format(Format::Alpha)
    // Apply the fractional offset
    .offset(offset)
    // Render the image
    .render(&mut scaler, cache_key.glyph_id)
}

/// Cache for rasterizing with the swash scaler
pub struct SwashCache<'a> {
    font_system: &'a FontSystem,
    context: ScaleContext,
    pub image_cache: HashMap<CacheKey, Option<SwashImage>>,
}

impl<'a> SwashCache<'a> {
    /// Create a new swash cache
    pub fn new(font_system: &'a FontSystem) -> Self {
        Self {
            font_system: font_system,
            context: ScaleContext::new(),
            image_cache: HashMap::new()
        }
    }

    /// Create a swash Image from a cache key, without caching results
    pub fn get_image_uncached(&mut self, cache_key: CacheKey) -> Option<SwashImage> {
        swash_image(self.font_system, &mut self.context, cache_key)
    }

    /// Create a swash Image from a cache key, caching results
    pub fn get_image(&mut self, cache_key: CacheKey) -> &Option<SwashImage> {
        self.image_cache.entry(cache_key).or_insert_with(|| {
            swash_image(self.font_system, &mut self.context, cache_key)
        })
    }

    /// Enumerate pixels in an Image, use `with_image` for better performance
    pub fn with_pixels<F: FnMut(i32, i32, Color)>(
        &mut self,
        cache_key: CacheKey,
        base: Color,
        mut f: F
    ) {
        if let Some(image) = self.get_image(cache_key) {
            let x = image.placement.left;
            let y = -image.placement.top;

            match image.content {
                Content::Mask => {
                    let mut i = 0;
                    for off_y in 0..image.placement.height as i32 {
                        for off_x in 0..image.placement.width as i32 {
                            //TODO: blend base alpha?
                            f(
                                x + off_x,
                                y + off_y,
                                Color(
                                    ((image.data[i] as u32) << 24) |
                                    base.0 & 0xFFFFFF
                                )
                            );
                            i += 1;
                        }
                    }
                }
                Content::Color => {
                    let mut i = 0;
                    for off_y in 0..image.placement.height as i32 {
                        for off_x in 0..image.placement.width as i32 {
                            //TODO: blend base alpha?
                            f(
                                x + off_x,
                                y + off_y,
                                Color::rgba(
                                    image.data[i],
                                    image.data[i + 1],
                                    image.data[i + 2],
                                    image.data[i + 3]
                                )
                            );
                            i += 4;
                        }
                    }
                }
                Content::SubpixelMask => {
                    log::warn!("TODO: SubpixelMask");
                }
            }
        }
    }
}