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    //! This module provides capabilities for managing a cache of rendered glyphs in
    //! GPU memory, with the goal of minimisng the size and frequency of glyph
    //! uploads to GPU memory from the CPU.
    //!
    //! This module is optional, and not compiled by default. To use it enable the
    //! `gpu_cache` feature in your Cargo.toml.
    //!
    //! Typical applications that render directly with hardware graphics APIs (e.g.
    //! games) need text rendering. There is not yet a performant solution for high
    //! quality text rendering directly on the GPU that isn't experimental research
    //! work. Quality is often critical for legibility, so many applications use
    //! text or individual characters that have been rendered on the CPU. This is
    //! done either ahead-of-time, giving a fixed set of fonts, characters, and
    //! sizes that can be used at runtime, or dynamically as text is required. This
    //! latter scenario is more flexible and the focus of this module.
    //!
    //! To minimise the CPU load and texture upload bandwidth saturation, recently
    //! used glyphs should be cached on the GPU for use by future frames. This
    //! module provides a mechanism for maintaining such a cache in the form of a
    //! single packed 2D GPU texture. When a rendered glyph is requested, it is
    //! either retrieved from its location in the texture if it is present or room
    //! is made in the cache (if necessary), the CPU renders the glyph then it is
    //! uploaded into a gap in the texture to be available for GPU rendering. This
    //! cache uses a Least Recently Used (LRU) cache eviction scheme - glyphs in the
    //! cache that have not been used recently are as a rule of thumb not likely to
    //! be used again soon, so they are the best candidates for eviction to make
    //! room for required glyphs.
    //!
    //! The API for the cache does not assume a particular graphics API. The
    //! intended usage is to queue up glyphs that need to be present for the current
    //! frame using `Cache::queue_glyph`, update the cache to ensure that the queued
    //! glyphs are present using `Cache::cache_queued` (providing a function for
    //! uploading pixel data), then when it's time to render call `Cache::rect_for`
    //! to get the UV coordinates in the cache texture for each glyph. For a
    //! concrete use case see the `gpu_cache` example.
    //!
    //! Cache dimensions are immutable. If you need to change the dimensions of the
    //! cache texture (e.g. due to high cache pressure), rebuild a new `Cache`.
    //! Either from scratch or with `CacheBuilder::rebuild`.
    //!
    //! # Example
    //!
    //! ```
    //! # use rusttype::{Font, gpu_cache::Cache, point, Scale};
    //! # use std::error::Error;
    //! # fn example() -> Result<(), Box<Error>> {
    //! # let font_data: &[u8] = include_bytes!("../fonts/dejavu/DejaVuSansMono.ttf");
    //! # let font: Font<'static> = Font::from_bytes(font_data)?;
    //! # let glyph = font.glyph('a').scaled(Scale::uniform(25.0)).positioned(point(0.0, 0.0));
    //! # let glyph2 = glyph.clone();
    //! # let update_gpu_texture = |_, _| {};
    //! // Build a default Cache.
    //! let mut cache = Cache::builder().build();
    //!
    //! // Queue some positioned glyphs needed for the next frame.
    //! cache.queue_glyph(0, glyph);
    //!
    //! // Cache all queued glyphs somewhere in the cache texture.
    //! // If new glyph data has been drawn the closure is called to upload
    //! // the pixel data to GPU memory.
    //! cache.cache_queued(|region, data| update_gpu_texture(region, data))?;
    //!
    //! # let glyph = glyph2;
    //! // Lookup a positioned glyph's texture location
    //! if let Ok(Some((uv_rect, screen_rect))) = cache.rect_for(0, &glyph) {
    //!     // Generate vertex data, etc
    //! }
    //! # Ok(())
    //! # }
    //! ```
    use crate::{point, vector, GlyphId, Point, PositionedGlyph, Rect, Vector};
    use linked_hash_map::LinkedHashMap;
    use rustc_hash::{FxHashMap, FxHasher};
    use std::collections::{HashMap, HashSet};
    use std::error;
    use std::fmt;
    use std::hash::BuildHasherDefault;

    type FxBuildHasher = BuildHasherDefault<FxHasher>;

    /// Texture coordinates (floating point) of the quad for a glyph in the cache,
    /// as well as the pixel-space (integer) coordinates that this region should be
    /// drawn at.
    pub type TextureCoords = (Rect<f32>, Rect<i32>);
    type FontId = usize;

    /// Indicates where a glyph texture is stored in the cache
    /// (row position, glyph index in row)
    type TextureRowGlyphIndex = (u32, u32);

    /// Texture lookup key that uses scale & offset as integers attained
    /// by dividing by the relevant tolerance.
    #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
    struct LossyGlyphInfo {
        font_id: FontId,
        glyph_id: GlyphId,
        /// x & y scales divided by `scale_tolerance` & rounded
        scale_over_tolerance: (u32, u32),
        /// Normalised subpixel positions divided by `position_tolerance` & rounded
        ///
        /// `u16` is enough as subpixel position `[-0.5, 0.5]` converted to `[0, 1]`
        ///  divided by the min `position_tolerance` (`0.001`) is small.
        offset_over_tolerance: (u16, u16),
    }

    #[derive(Debug, Clone, PartialEq, Eq)]
    struct ByteArray2d {
        inner_array: Vec<u8>,
        row: usize,
        col: usize,
    }

    impl ByteArray2d {
        #[inline]
        pub fn zeros(row: usize, col: usize) -> Self {
            ByteArray2d {
                inner_array: vec![0; row * col],
                row,
                col,
            }
        }

        #[inline]
        fn as_slice(&self) -> &[u8] {
            self.inner_array.as_slice()
        }

        #[inline]
        fn get_vec_index(&self, row: usize, col: usize) -> usize {
            debug_assert!(
                row < self.row,
                "row out of range: row={}, given={}",
                self.row,
                row
            );
            debug_assert!(
                col < self.col,
                "column out of range: col={}, given={}",
                self.col,
                col
            );
            row * self.col + col
        }
    }

    impl std::ops::Index<(usize, usize)> for ByteArray2d {
        type Output = u8;

        #[inline]
        fn index(&self, (row, col): (usize, usize)) -> &u8 {
            &self.inner_array[self.get_vec_index(row, col)]
        }
    }

    impl std::ops::IndexMut<(usize, usize)> for ByteArray2d {
        #[inline]
        fn index_mut(&mut self, (row, col): (usize, usize)) -> &mut u8 {
            let vec_index = self.get_vec_index(row, col);
            &mut self.inner_array[vec_index]
        }
    }

    /// Row of pixel data
    struct Row {
        /// Row pixel height
        height: u32,
        /// Pixel width current in use by glyphs
        width: u32,
        glyphs: Vec<GlyphTexInfo>,
    }

    struct GlyphTexInfo {
        glyph_info: LossyGlyphInfo,
        /// Actual (lossless) normalised subpixel offset of rasterized glyph
        offset: Vector<f32>,
        tex_coords: Rect<u32>,
    }

    trait PaddingAware {
        fn unpadded(self) -> Self;
    }

    impl PaddingAware for Rect<u32> {
        /// A padded texture has 1 extra pixel on all sides
        fn unpadded(mut self) -> Self {
            self.min.x += 1;
            self.min.y += 1;
            self.max.x -= 1;
            self.max.y -= 1;
            self
        }
    }

    /// An implementation of a dynamic GPU glyph cache. See the module documentation
    /// for more information.
    pub struct Cache<'font> {
        scale_tolerance: f32,
        position_tolerance: f32,
        width: u32,
        height: u32,
        rows: LinkedHashMap<u32, Row, FxBuildHasher>,
        /// Mapping of row gaps bottom -> top
        space_start_for_end: FxHashMap<u32, u32>,
        /// Mapping of row gaps top -> bottom
        space_end_for_start: FxHashMap<u32, u32>,
        queue: Vec<(FontId, PositionedGlyph<'font>)>,
        all_glyphs: FxHashMap<LossyGlyphInfo, TextureRowGlyphIndex>,
        pad_glyphs: bool,
        align_4x4: bool,
        multithread: bool,
    }

    /// Builder & rebuilder for `Cache`.
    ///
    /// # Example
    ///
    /// ```
    /// use rusttype::gpu_cache::Cache;
    ///
    /// // Create a cache with all default values set explicitly
    /// // equivalent to `Cache::builder().build()`
    /// let default_cache = Cache::builder()
    ///     .dimensions(256, 256)
    ///     .scale_tolerance(0.1)
    ///     .position_tolerance(0.1)
    ///     .pad_glyphs(true)
    ///     .align_4x4(false)
    ///     .multithread(true)
    ///     .build();
    ///
    /// // Create a cache with all default values, except with a dimension of 1024x1024
    /// let bigger_cache = Cache::builder().dimensions(1024, 1024).build();
    /// ```
    #[derive(Debug, Clone)]
    pub struct CacheBuilder {
        dimensions: (u32, u32),
        scale_tolerance: f32,
        position_tolerance: f32,
        pad_glyphs: bool,
        align_4x4: bool,
        multithread: bool,
    }

    impl Default for CacheBuilder {
        fn default() -> Self {
            Self {
                dimensions: (256, 256),
                scale_tolerance: 0.1,
                position_tolerance: 0.1,
                pad_glyphs: true,
                align_4x4: false,
                multithread: true,
            }
        }
    }

    impl CacheBuilder {
        /// `width` & `height` dimensions of the 2D texture that will hold the
        /// cache contents on the GPU.
        ///
        /// This must match the dimensions of the actual texture used, otherwise
        /// `cache_queued` will try to cache into coordinates outside the bounds of
        /// the texture.
        ///
        /// # Example (set to default value)
        ///
        /// ```
        /// # use rusttype::gpu_cache::Cache;
        /// let cache = Cache::builder().dimensions(256, 256).build();
        /// ```
        pub fn dimensions(mut self, width: u32, height: u32) -> Self {
            self.dimensions = (width, height);
            self
        }

        /// Specifies the tolerances (maximum allowed difference) for judging
        /// whether an existing glyph in the cache is close enough to the
        /// requested glyph in scale to be used in its place. Due to floating
        /// point inaccuracies a min value of `0.001` is enforced.
        ///
        /// Both `scale_tolerance` and `position_tolerance` are measured in pixels.
        ///
        /// Tolerances produce even steps for scale and subpixel position. Only a
        /// single glyph texture will be used within a single step. For example,
        /// `scale_tolerance = 0.1` will have a step `9.95-10.05` so similar glyphs
        /// with scale `9.98` & `10.04` will match.
        ///
        /// A typical application will produce results with no perceptible
        /// inaccuracies with `scale_tolerance` and `position_tolerance` set to
        /// 0.1. Depending on the target DPI higher tolerance may be acceptable.
        ///
        /// # Example (set to default value)
        ///
        /// ```
        /// # use rusttype::gpu_cache::Cache;
        /// let cache = Cache::builder().scale_tolerance(0.1).build();
        /// ```
        pub fn scale_tolerance<V: Into<f32>>(mut self, scale_tolerance: V) -> Self {
            self.scale_tolerance = scale_tolerance.into();
            self
        }
        /// Specifies the tolerances (maximum allowed difference) for judging
        /// whether an existing glyph in the cache is close enough to the requested
        /// glyph in subpixel offset to be used in its place. Due to floating
        /// point inaccuracies a min value of `0.001` is enforced.
        ///
        /// Both `scale_tolerance` and `position_tolerance` are measured in pixels.
        ///
        /// Tolerances produce even steps for scale and subpixel position. Only a
        /// single glyph texture will be used within a single step. For example,
        /// `scale_tolerance = 0.1` will have a step `9.95-10.05` so similar glyphs
        /// with scale `9.98` & `10.04` will match.
        ///
        /// Note that since `position_tolerance` is a tolerance of subpixel
        /// offsets, setting it to 1.0 or higher is effectively a "don't care"
        /// option.
        ///
        /// A typical application will produce results with no perceptible
        /// inaccuracies with `scale_tolerance` and `position_tolerance` set to
        /// 0.1. Depending on the target DPI higher tolerance may be acceptable.
        ///
        /// # Example (set to default value)
        ///
        /// ```
        /// # use rusttype::gpu_cache::Cache;
        /// let cache = Cache::builder().position_tolerance(0.1).build();
        /// ```
        pub fn position_tolerance<V: Into<f32>>(mut self, position_tolerance: V) -> Self {
            self.position_tolerance = position_tolerance.into();
            self
        }
        /// Pack glyphs in texture with a padding of a single zero alpha pixel to
        /// avoid bleeding from interpolated shader texture lookups near edges.
        ///
        /// If glyphs are never transformed this may be set to `false` to slightly
        /// improve the glyph packing.
        ///
        /// # Example (set to default value)
        ///
        /// ```
        /// # use rusttype::gpu_cache::Cache;
        /// let cache = Cache::builder().pad_glyphs(true).build();
        /// ```
        pub fn pad_glyphs(mut self, pad_glyphs: bool) -> Self {
            self.pad_glyphs = pad_glyphs;
            self
        }
        /// Align glyphs in texture to 4x4 texel boundaries.
        ///
        /// If your backend requires texture updates to be aligned to 4x4 texel
        /// boundaries (e.g. WebGL), this should be set to `true`.
        ///
        /// # Example (set to default value)
        ///
        /// ```
        /// # use rusttype::gpu_cache::Cache;
        /// let cache = Cache::builder().align_4x4(false).build();
        /// ```
        pub fn align_4x4(mut self, align_4x4: bool) -> Self {
            self.align_4x4 = align_4x4;
            self
        }
        /// When multiple CPU cores are available spread rasterization work across
        /// all cores.
        ///
        /// Significantly reduces worst case latency in multicore environments.
        ///
        /// # Platform-specific behaviour
        ///
        /// This option has no effect on wasm32.
        ///
        /// # Example (set to default value)
        ///
        /// ```
        /// # use rusttype::gpu_cache::Cache;
        /// let cache = Cache::builder().multithread(true).build();
        /// ```
        pub fn multithread(mut self, multithread: bool) -> Self {
            self.multithread = multithread;
            self
        }

        fn validated(self) -> Self {
            assert!(self.scale_tolerance >= 0.0);
            assert!(self.position_tolerance >= 0.0);
            let scale_tolerance = self.scale_tolerance.max(0.001);
            let position_tolerance = self.position_tolerance.max(0.001);
            #[cfg(not(target_arch = "wasm32"))]
            let multithread = self.multithread && num_cpus::get() > 1;
            Self {
                scale_tolerance,
                position_tolerance,
                #[cfg(not(target_arch = "wasm32"))]
                multithread,
                ..self
            }
        }

        /// Constructs a new cache. Note that this is just the CPU side of the
        /// cache. The GPU texture is managed by the user.
        ///
        /// # Panics
        ///
        /// `scale_tolerance` or `position_tolerance` are less than or equal to
        /// zero.
        ///
        /// # Example
        ///
        /// ```
        /// # use rusttype::gpu_cache::Cache;
        /// let cache = Cache::builder().build();
        /// ```
        pub fn build<'a>(self) -> Cache<'a> {
            let CacheBuilder {
                dimensions: (width, height),
                scale_tolerance,
                position_tolerance,
                pad_glyphs,
                align_4x4,
                multithread,
            } = self.validated();

            Cache {
                scale_tolerance,
                position_tolerance,
                width,
                height,
                rows: LinkedHashMap::default(),
                space_start_for_end: {
                    let mut m = HashMap::default();
                    m.insert(height, 0);
                    m
                },
                space_end_for_start: {
                    let mut m = HashMap::default();
                    m.insert(0, height);
                    m
                },
                queue: Vec::new(),
                all_glyphs: HashMap::default(),
                pad_glyphs,
                align_4x4,
                multithread,
            }
        }

        /// Rebuilds a cache with new attributes. Carries over the existing cache
        /// queue unmodified.
        ///
        /// # Panics
        ///
        /// `scale_tolerance` or `position_tolerance` are less than or equal to
        /// zero.
        ///
        /// # Example
        ///
        /// ```
        /// # use rusttype::gpu_cache::Cache;
        /// # let mut cache = Cache::builder().build();
        /// // Rebuild the cache with different dimensions
        /// cache.to_builder().dimensions(768, 768).rebuild(&mut cache);
        /// ```
        pub fn rebuild(self, cache: &mut Cache) {
            let CacheBuilder {
                dimensions: (width, height),
                scale_tolerance,
                position_tolerance,
                pad_glyphs,
                align_4x4,
                multithread,
            } = self.validated();

            cache.width = width;
            cache.height = height;
            cache.scale_tolerance = scale_tolerance;
            cache.position_tolerance = position_tolerance;
            cache.pad_glyphs = pad_glyphs;
            cache.align_4x4 = align_4x4;
            cache.multithread = multithread;
            cache.clear();
        }
    }

    /// Returned from `Cache::rect_for`.
    #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
    pub enum CacheReadErr {
        /// Indicates that the requested glyph is not present in the cache
        GlyphNotCached,
    }
    impl fmt::Display for CacheReadErr {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            write!(f, "{}", error::Error::description(self))
        }
    }
    impl error::Error for CacheReadErr {
        fn description(&self) -> &str {
            match *self {
                CacheReadErr::GlyphNotCached => "Glyph not cached",
            }
        }
    }

    /// Returned from `Cache::cache_queued`.
    #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
    pub enum CacheWriteErr {
        /// At least one of the queued glyphs is too big to fit into the cache, even
        /// if all other glyphs are removed.
        GlyphTooLarge,
        /// Not all of the requested glyphs can fit into the cache, even if the
        /// cache is completely cleared before the attempt.
        NoRoomForWholeQueue,
    }
    impl fmt::Display for CacheWriteErr {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            write!(f, "{}", error::Error::description(self))
        }
    }
    impl error::Error for CacheWriteErr {
        fn description(&self) -> &str {
            match *self {
                CacheWriteErr::GlyphTooLarge => "Glyph too large",
                CacheWriteErr::NoRoomForWholeQueue => "No room for whole queue",
            }
        }
    }

    /// Successful method of caching of the queue.
    #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
    pub enum CachedBy {
        /// Added any additional glyphs into the texture without affecting
        /// the position of any already cached glyphs in the latest queue.
        ///
        /// Glyphs not in the latest queue may have been removed.
        Adding,
        /// Fit the glyph queue by re-ordering all glyph texture positions.
        /// Previous texture positions are no longer valid.
        Reordering,
    }

    fn normalised_offset_from_position(position: Point<f32>) -> Vector<f32> {
        let mut offset = vector(position.x.fract(), position.y.fract());
        if offset.x > 0.5 {
            offset.x -= 1.0;
        } else if offset.x < -0.5 {
            offset.x += 1.0;
        }
        if offset.y > 0.5 {
            offset.y -= 1.0;
        } else if offset.y < -0.5 {
            offset.y += 1.0;
        }
        offset
    }

    impl<'font> Cache<'font> {
        /// Returns a default `CacheBuilder`.
        #[inline]
        pub fn builder() -> CacheBuilder {
            CacheBuilder::default()
        }

        /// Returns the current scale tolerance for the cache.
        pub fn scale_tolerance(&self) -> f32 {
            self.scale_tolerance
        }

        /// Returns the current subpixel position tolerance for the cache.
        pub fn position_tolerance(&self) -> f32 {
            self.position_tolerance
        }

        /// Returns the cache texture dimensions assumed by the cache. For proper
        /// operation this should match the dimensions of the used GPU texture.
        pub fn dimensions(&self) -> (u32, u32) {
            (self.width, self.height)
        }

        /// Queue a glyph for caching by the next call to `cache_queued`. `font_id`
        /// is used to disambiguate glyphs from different fonts. The user should
        /// ensure that `font_id` is unique to the font the glyph is from.
        pub fn queue_glyph(&mut self, font_id: usize, glyph: PositionedGlyph<'font>) {
            if glyph.pixel_bounding_box().is_some() {
                self.queue.push((font_id, glyph));
            }
        }

        /// Clears the cache. Does not affect the glyph queue.
        pub fn clear(&mut self) {
            self.rows.clear();
            self.space_end_for_start.clear();
            self.space_end_for_start.insert(0, self.height);
            self.space_start_for_end.clear();
            self.space_start_for_end.insert(self.height, 0);
            self.all_glyphs.clear();
        }

        /// Clears the glyph queue.
        pub fn clear_queue(&mut self) {
            self.queue.clear();
        }

        /// Returns a `CacheBuilder` with this cache's attributes.
        pub fn to_builder(&self) -> CacheBuilder {
            CacheBuilder {
                dimensions: (self.width, self.height),
                position_tolerance: self.position_tolerance,
                scale_tolerance: self.scale_tolerance,
                pad_glyphs: self.pad_glyphs,
                align_4x4: self.align_4x4,
                multithread: self.multithread,
            }
        }

        /// Returns glyph info with accuracy according to the set tolerances.
        fn lossy_info_for(&self, font_id: FontId, glyph: &PositionedGlyph<'font>) -> LossyGlyphInfo {
            let scale = glyph.scale();
            let offset = normalised_offset_from_position(glyph.position());

            LossyGlyphInfo {
                font_id,
                glyph_id: glyph.id(),
                scale_over_tolerance: (
                    (scale.x / self.scale_tolerance + 0.5) as u32,
                    (scale.y / self.scale_tolerance + 0.5) as u32,
                ),
                // convert [-0.5, 0.5] -> [0, 1] then divide
                offset_over_tolerance: (
                    ((offset.x + 0.5) / self.position_tolerance + 0.5) as u16,
                    ((offset.y + 0.5) / self.position_tolerance + 0.5) as u16,
                ),
            }
        }

        /// Caches the queued glyphs. If this is unsuccessful, the queue is
        /// untouched. Any glyphs cached by previous calls to this function may be
        /// removed from the cache to make room for the newly queued glyphs. Thus if
        /// you want to ensure that a glyph is in the cache, the most recently
        /// cached queue must have contained that glyph.
        ///
        /// `uploader` is the user-provided function that should perform the texture
        /// uploads to the GPU. The information provided is the rectangular region
        /// to insert the pixel data into, and the pixel data itself. This data is
        /// provided in horizontal scanline format (row major), with stride equal to
        /// the rectangle width.
        ///
        /// If successful returns a `CachedBy` that can indicate the validity of
        /// previously cached glyph textures.
        pub fn cache_queued<F: FnMut(Rect<u32>, &[u8])>(
            &mut self,
            mut uploader: F,
        ) -> Result<CachedBy, CacheWriteErr> {
            let mut queue_success = true;
            let from_empty = self.all_glyphs.is_empty();

            {
                let (mut in_use_rows, mut uncached_glyphs) = {
                    let mut in_use_rows =
                        HashSet::with_capacity_and_hasher(self.rows.len(), FxBuildHasher::default());
                    let mut uncached_glyphs = Vec::with_capacity(self.queue.len());

                    // divide glyphs into texture rows where a matching glyph texture
                    // already exists & glyphs where new textures must be cached
                    for (font_id, ref glyph) in &self.queue {
                        let glyph_info = self.lossy_info_for(*font_id, glyph);
                        if let Some((row, ..)) = self.all_glyphs.get(&glyph_info) {
                            in_use_rows.insert(*row);
                        } else {
                            uncached_glyphs.push((glyph, glyph_info));
                        }
                    }

                    (in_use_rows, uncached_glyphs)
                };

                for row in &in_use_rows {
                    self.rows.get_refresh(row);
                }

                // tallest first gives better packing
                // can use 'sort_unstable' as order of equal elements is unimportant
                uncached_glyphs
                    .sort_unstable_by_key(|(glyph, ..)| -glyph.pixel_bounding_box().unwrap().height());

                self.all_glyphs.reserve(uncached_glyphs.len());
                let mut draw_and_upload = Vec::with_capacity(uncached_glyphs.len());

                'per_glyph: for (glyph, glyph_info) in uncached_glyphs {
                    // glyph may match a texture cached by a previous iteration
                    if self.all_glyphs.contains_key(&glyph_info) {
                        continue;
                    }

                    // Not cached, so add it:
                    let (unaligned_width, unaligned_height) = {
                        let bb = glyph.pixel_bounding_box().unwrap();
                        if self.pad_glyphs {
                            (bb.width() as u32 + 2, bb.height() as u32 + 2)
                        } else {
                            (bb.width() as u32, bb.height() as u32)
                        }
                    };
                    let (aligned_width, aligned_height) = if self.align_4x4 {
                        // align to the next 4x4 texel boundary
                        (unaligned_width + 3 & !3, unaligned_height + 3 & !3)
                    } else {
                        (unaligned_width, unaligned_height)
                    };
                    if aligned_width >= self.width || aligned_height >= self.height {
                        return Result::Err(CacheWriteErr::GlyphTooLarge);
                    }
                    // find row to put the glyph in, most used rows first
                    let mut row_top = None;
                    for (top, row) in self.rows.iter().rev() {
                        if row.height >= aligned_height && self.width - row.width >= aligned_width {
                            // found a spot on an existing row
                            row_top = Some(*top);
                            break;
                        }
                    }

                    if row_top.is_none() {
                        let mut gap = None;
                        // See if there is space for a new row
                        for (start, end) in &self.space_end_for_start {
                            if end - start >= aligned_height {
                                gap = Some((*start, *end));
                                break;
                            }
                        }
                        if gap.is_none() {
                            // Remove old rows until room is available
                            while !self.rows.is_empty() {
                                // check that the oldest row isn't also in use
                                if !in_use_rows.contains(self.rows.front().unwrap().0) {
                                    // Remove row
                                    let (top, row) = self.rows.pop_front().unwrap();

                                    for g in row.glyphs {
                                        self.all_glyphs.remove(&g.glyph_info);
                                    }

                                    let (mut new_start, mut new_end) = (top, top + row.height);
                                    // Update the free space maps
                                    // Combine with neighbouring free space if possible
                                    if let Some(end) = self.space_end_for_start.remove(&new_end) {
                                        new_end = end;
                                    }
                                    if let Some(start) = self.space_start_for_end.remove(&new_start) {
                                        new_start = start;
                                    }
                                    self.space_start_for_end.insert(new_end, new_start);
                                    self.space_end_for_start.insert(new_start, new_end);
                                    if new_end - new_start >= aligned_height {
                                        // The newly formed gap is big enough
                                        gap = Some((new_start, new_end));
                                        break;
                                    }
                                }
                                // all rows left are in use
                                // try a clean insert of all needed glyphs
                                // if that doesn't work, fail
                                else if from_empty {
                                    // already trying a clean insert, don't do it again
                                    return Err(CacheWriteErr::NoRoomForWholeQueue);
                                } else {
                                    // signal that a retry is needed
                                    queue_success = false;
                                    break 'per_glyph;
                                }
                            }
                        }
                        let (gap_start, gap_end) = gap.unwrap();
                        // fill space for new row
                        let new_space_start = gap_start + aligned_height;
                        self.space_end_for_start.remove(&gap_start);
                        if new_space_start == gap_end {
                            self.space_start_for_end.remove(&gap_end);
                        } else {
                            self.space_end_for_start.insert(new_space_start, gap_end);
                            self.space_start_for_end.insert(gap_end, new_space_start);
                        }
                        // add the row
                        self.rows.insert(
                            gap_start,
                            Row {
                                width: 0,
                                height: aligned_height,
                                glyphs: Vec::new(),
                            },
                        );
                        row_top = Some(gap_start);
                    }
                    let row_top = row_top.unwrap();
                    // calculate the target rect
                    let row = self.rows.get_refresh(&row_top).unwrap();
                    let aligned_tex_coords = Rect {
                        min: point(row.width, row_top),
                        max: point(row.width + aligned_width, row_top + aligned_height),
                    };
                    let unaligned_tex_coords = Rect {
                        min: point(row.width, row_top),
                        max: point(row.width + unaligned_width, row_top + unaligned_height),
                    };

                    draw_and_upload.push((aligned_tex_coords, glyph));

                    // add the glyph to the row
                    row.glyphs.push(GlyphTexInfo {
                        glyph_info,
                        offset: normalised_offset_from_position(glyph.position()),
                        tex_coords: unaligned_tex_coords,
                    });
                    row.width += aligned_width;
                    in_use_rows.insert(row_top);

                    self.all_glyphs
                        .insert(glyph_info, (row_top, row.glyphs.len() as u32 - 1));
                }

                if queue_success {
                    #[cfg(not(target_arch = "wasm32"))] {
                        let glyph_count = draw_and_upload.len();

                        if self.multithread && glyph_count > 1 {
                            // multithread rasterization
                            use crossbeam_deque::Steal;
                            use std::{
                                mem,
                                sync::mpsc::{self, TryRecvError},
                            };

                            let rasterize_queue = crossbeam_deque::Injector::new();
                            let (to_main, from_stealers) = mpsc::channel();
                            let pad_glyphs = self.pad_glyphs;

                            for el in draw_and_upload {
                                rasterize_queue.push(el);
                            }
                            crossbeam_utils::thread::scope(|scope| {
                                for _ in 0..num_cpus::get().min(glyph_count).saturating_sub(1) {
                                    let rasterize_queue = &rasterize_queue;
                                    let to_main = to_main.clone();
                                    scope.spawn(move |_| loop {
                                        match rasterize_queue.steal() {
                                            Steal::Success((tex_coords, glyph)) => {
                                                let pixels = draw_glyph(tex_coords, glyph, pad_glyphs);
                                                to_main.send((tex_coords, pixels)).unwrap();
                                            }
                                            Steal::Empty => break,
                                            Steal::Retry => {}
                                        }
                                    });
                                }
                                mem::drop(to_main);

                                let mut workers_finished = false;
                                loop {
                                    match rasterize_queue.steal() {
                                        Steal::Success((tex_coords, glyph)) => {
                                            let pixels = draw_glyph(tex_coords, glyph, pad_glyphs);
                                            uploader(tex_coords, pixels.as_slice());
                                        }
                                        Steal::Empty if workers_finished => break,
                                        Steal::Empty | Steal::Retry => {}
                                    }

                                    while !workers_finished {
                                        match from_stealers.try_recv() {
                                            Ok((tex_coords, pixels)) => {
                                                uploader(tex_coords, pixels.as_slice())
                                            }
                                            Err(TryRecvError::Disconnected) => workers_finished = true,
                                            Err(TryRecvError::Empty) => break,
                                        }
                                    }
                                }
                            })
                            .unwrap();
                        } else {
                            // single thread rasterization
                            for (tex_coords, glyph) in draw_and_upload {
                                let pixels = draw_glyph(tex_coords, glyph, self.pad_glyphs);
                                uploader(tex_coords, pixels.as_slice());
                            }
                        }
                    }
                    #[cfg(target_arch = "wasm32")] {
                        for (tex_coords, glyph) in draw_and_upload {
                            let pixels = draw_glyph(tex_coords, glyph, self.pad_glyphs);
                            uploader(tex_coords, pixels.as_slice());
                        }
                    }
                }
            }

            if queue_success {
                self.queue.clear();
                Ok(CachedBy::Adding)
            } else {
                // clear the cache then try again with optimal packing
                self.clear();
                self.cache_queued(uploader).map(|_| CachedBy::Reordering)
            }
        }

        /// Retrieves the (floating point) texture coordinates of the quad for a
        /// glyph in the cache, as well as the pixel-space (integer) coordinates
        /// that this region should be drawn at. These pixel-space coordinates
        /// assume an origin at the top left of the quad. In the majority of cases
        /// these pixel-space coordinates should be identical to the bounding box of
        /// the input glyph. They only differ if the cache has returned a substitute
        /// glyph that is deemed close enough to the requested glyph as specified by
        /// the cache tolerance parameters.
        ///
        /// A sucessful result is `Some` if the glyph is not an empty glyph (no
        /// shape, and thus no rect to return).
        ///
        /// Ensure that `font_id` matches the `font_id` that was passed to
        /// `queue_glyph` with this `glyph`.
        pub fn rect_for(
            &self,
            font_id: usize,
            glyph: &PositionedGlyph,
        ) -> Result<Option<TextureCoords>, CacheReadErr> {
            if glyph.pixel_bounding_box().is_none() {
                return Ok(None);
            }

            let (row, index) = self
                .all_glyphs
                .get(&self.lossy_info_for(font_id, glyph))
                .ok_or(CacheReadErr::GlyphNotCached)?;

            let (tex_width, tex_height) = (self.width as f32, self.height as f32);

            let GlyphTexInfo {
                tex_coords: mut tex_rect,
                offset: tex_offset,
                ..
            } = self.rows[&row].glyphs[*index as usize];
            if self.pad_glyphs {
                tex_rect = tex_rect.unpadded();
            }
            let uv_rect = Rect {
                min: point(
                    tex_rect.min.x as f32 / tex_width,
                    tex_rect.min.y as f32 / tex_height,
                ),
                max: point(
                    tex_rect.max.x as f32 / tex_width,
                    tex_rect.max.y as f32 / tex_height,
                ),
            };

            let local_bb = glyph
                .unpositioned()
                .clone()
                .positioned(point(0.0, 0.0) + tex_offset)
                .pixel_bounding_box()
                .unwrap();
            let min_from_origin =
                point(local_bb.min.x as f32, local_bb.min.y as f32) - (point(0.0, 0.0) + tex_offset);
            let ideal_min = min_from_origin + glyph.position();
            let min = point(ideal_min.x.round() as i32, ideal_min.y.round() as i32);
            let bb_offset = min - local_bb.min;
            let bb = Rect {
                min,
                max: local_bb.max + bb_offset,
            };
            Ok(Some((uv_rect, bb)))
        }
    }

    #[inline]
    fn draw_glyph(tex_coords: Rect<u32>, glyph: &PositionedGlyph<'_>, pad_glyphs: bool) -> ByteArray2d {
        let mut pixels = ByteArray2d::zeros(tex_coords.height() as usize, tex_coords.width() as usize);
        if pad_glyphs {
            glyph.draw(|x, y, v| {
                let v = (v * 255.0).round().max(0.0).min(255.0) as u8;
                // `+ 1` accounts for top/left glyph padding
                pixels[(y as usize + 1, x as usize + 1)] = v;
            });
        } else {
            glyph.draw(|x, y, v| {
                let v = (v * 255.0).round().max(0.0).min(255.0) as u8;
                pixels[(y as usize, x as usize)] = v;
            });
        }
        pixels
    }

    #[cfg(test)]
    mod test {
        use super::*;
        use crate::{Font, FontCollection, Scale};
        use approx::*;

        #[test]
        fn cache_test() {
            let font_data = include_bytes!("../fonts/wqy-microhei/WenQuanYiMicroHei.ttf");
            let font = FontCollection::from_bytes(font_data as &[u8])
                .unwrap()
                .into_font()
                .unwrap();

            let mut cache = Cache::builder()
                .dimensions(32, 32)
                .scale_tolerance(0.1)
                .position_tolerance(0.1)
                .pad_glyphs(false)
                .build();
            let strings = [
                ("Hello World!", 15.0),
                ("Hello World!", 14.0),
                ("Hello World!", 10.0),
                ("Hello World!", 15.0),
                ("Hello World!", 14.0),
                ("Hello World!", 10.0),
            ];
            for &(string, scale) in &strings {
                println!("Caching {:?}", (string, scale));
                for glyph in font.layout(string, Scale::uniform(scale), point(0.0, 0.0)) {
                    cache.queue_glyph(0, glyph);
                }
                cache.cache_queued(|_, _| {}).unwrap();
            }
        }

        #[test]
        fn need_to_check_whole_cache() {
            let font_data = include_bytes!("../fonts/wqy-microhei/WenQuanYiMicroHei.ttf");
            let font = Font::from_bytes(font_data as &[u8]).unwrap();

            let glyph = font.glyph('l');

            let small = glyph.clone().scaled(Scale::uniform(10.0));
            let large = glyph.clone().scaled(Scale::uniform(10.05));

            let small_left = small.clone().positioned(point(0.0, 0.0));
            let large_left = large.clone().positioned(point(0.0, 0.0));
            let large_right = large.clone().positioned(point(-0.2, 0.0));

            let mut cache = Cache::builder()
                .dimensions(32, 32)
                .scale_tolerance(0.1)
                .position_tolerance(0.1)
                .pad_glyphs(false)
                .build();

            cache.queue_glyph(0, small_left.clone());
            // Next line is noop since it's within the scale tolerance of small_left:
            cache.queue_glyph(0, large_left.clone());
            cache.queue_glyph(0, large_right.clone());

            cache.cache_queued(|_, _| {}).unwrap();

            cache.rect_for(0, &small_left).unwrap();
            cache.rect_for(0, &large_left).unwrap();
            cache.rect_for(0, &large_right).unwrap();
        }

        #[test]
        fn lossy_info() {
            let font_data = include_bytes!("../fonts/wqy-microhei/WenQuanYiMicroHei.ttf");
            let font = Font::from_bytes(font_data as &[u8]).unwrap();
            let glyph = font.glyph('l');

            let small = glyph.clone().scaled(Scale::uniform(9.91));
            let near = glyph.clone().scaled(Scale::uniform(10.09));
            let far = glyph.clone().scaled(Scale::uniform(10.11));
            let really_far = glyph.clone().scaled(Scale::uniform(12.0));

            let small_pos = small.clone().positioned(point(0.0, 0.0));
            let match_1 = near.clone().positioned(point(-10.0, -0.1));
            let match_2 = near.clone().positioned(point(5.1, 0.24));
            let match_3 = small.clone().positioned(point(-100.2, 50.1));

            let miss_1 = far.clone().positioned(point(0.0, 0.0));
            let miss_2 = really_far.clone().positioned(point(0.0, 0.0));
            let miss_3 = small.clone().positioned(point(0.3, 0.0));

            let cache = Cache::builder()
                .scale_tolerance(0.2)
                .position_tolerance(0.5)
                .build();

            let small_info = cache.lossy_info_for(0, &small_pos);

            assert_eq!(small_info, cache.lossy_info_for(0, &match_1));
            assert_eq!(small_info, cache.lossy_info_for(0, &match_2));
            assert_eq!(small_info, cache.lossy_info_for(0, &match_3));

            assert_ne!(small_info, cache.lossy_info_for(0, &miss_1));
            assert_ne!(small_info, cache.lossy_info_for(0, &miss_2));
            assert_ne!(small_info, cache.lossy_info_for(0, &miss_3));
        }

        #[test]
        fn cache_to_builder() {
            let cache = CacheBuilder {
                dimensions: (32, 64),
                scale_tolerance: 0.2,
                position_tolerance: 0.3,
                pad_glyphs: false,
                align_4x4: false,
                multithread: false,
            }
            .build();

            let to_builder: CacheBuilder = cache.to_builder();

            assert_eq!(to_builder.dimensions, (32, 64));
            assert_relative_eq!(to_builder.scale_tolerance, 0.2);
            assert_relative_eq!(to_builder.position_tolerance, 0.3);
            assert_eq!(to_builder.pad_glyphs, false);
            assert_eq!(to_builder.align_4x4, false);
            assert_eq!(to_builder.multithread, false);
        }

        #[test]
        fn builder_rebuild() {
            let mut cache = Cache::builder()
                .dimensions(32, 64)
                .scale_tolerance(0.2)
                .position_tolerance(0.3)
                .pad_glyphs(false)
                .align_4x4(true)
                .multithread(true)
                .build();

            let font = Font::from_bytes(
                include_bytes!("../fonts/wqy-microhei/WenQuanYiMicroHei.ttf") as &[u8],
            )
            .unwrap();
            cache.queue_glyph(
                0,
                font.glyph('l')
                    .scaled(Scale::uniform(25.0))
                    .positioned(point(0.0, 0.0)),
            );
            cache.cache_queued(|_, _| {}).unwrap();

            cache.queue_glyph(
                0,
                font.glyph('a')
                    .scaled(Scale::uniform(25.0))
                    .positioned(point(0.0, 0.0)),
            );

            Cache::builder()
                .dimensions(64, 128)
                .scale_tolerance(0.05)
                .position_tolerance(0.15)
                .pad_glyphs(true)
                .align_4x4(false)
                .multithread(false)
                .rebuild(&mut cache);

            assert_eq!(cache.width, 64);
            assert_eq!(cache.height, 128);
            assert_relative_eq!(cache.scale_tolerance, 0.05);
            assert_relative_eq!(cache.position_tolerance, 0.15);
            assert_eq!(cache.pad_glyphs, true);
            assert_eq!(cache.align_4x4, false);
            assert_eq!(cache.multithread, false);

            assert!(
                cache.all_glyphs.is_empty(),
                "cache should have been cleared"
            );

            assert_eq!(cache.queue.len(), 1, "cache should have an unchanged queue");
        }

        /// Provide to caller that the cache was re-ordered to fit the latest queue
        #[test]
        fn return_cache_by_reordering() {
            let font_data = include_bytes!("../fonts/wqy-microhei/WenQuanYiMicroHei.ttf");
            let font = FontCollection::from_bytes(font_data as &[u8])
                .unwrap()
                .into_font()
                .unwrap();

            let mut cache = Cache::builder()
                .dimensions(36, 27)
                .scale_tolerance(0.1)
                .position_tolerance(0.1)
                .build();

            for glyph in font.layout("ABCDEFG", Scale::uniform(16.0), point(0.0, 0.0)) {
                cache.queue_glyph(0, glyph);
            }
            assert_eq!(cache.cache_queued(|_, _| {}), Ok(CachedBy::Adding));

            for glyph in font.layout("DEFGHIJK", Scale::uniform(16.0), point(0.0, 0.0)) {
                cache.queue_glyph(0, glyph);
            }
            assert_eq!(cache.cache_queued(|_, _| {}), Ok(CachedBy::Reordering));
        }

        #[test]
        fn align_4x4() {
            // First, test align_4x4 disabled, to confirm non-4x4 alignment
            align_4x4_helper(false, 5, 19);
            // Now, test with align_4x4 enabled, to confirm 4x4 alignment
            align_4x4_helper(true, 8, 20);
        }

        fn align_4x4_helper(align_4x4: bool, expected_width: u32, expected_height: u32) {
            let mut cache = Cache::builder()
                .dimensions(64, 64)
                .align_4x4(align_4x4)
                .build();
            let font = Font::from_bytes(
                include_bytes!("../fonts/wqy-microhei/WenQuanYiMicroHei.ttf") as &[u8],
            )
            .unwrap();
            let glyph = font
                .glyph('l')
                .scaled(Scale::uniform(25.0))
                .positioned(point(0.0, 0.0));
            cache.queue_glyph(0, glyph.clone());
            cache
                .cache_queued(|rect, _| {
                    assert_eq!(rect.width(), expected_width);
                    assert_eq!(rect.height(), expected_height);
                })
                .unwrap();
            let (uv_rect, _screen_rect) = cache.rect_for(0, &glyph).unwrap().unwrap();
            assert_eq!(
                uv_rect,
                crate::Rect {
                    min: crate::point(0.015625, 0.015625),
                    max: crate::point(0.0625, 0.28125),
                }
            );
        }
    }

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