Implement growing logic for TextAtlas

The `TextAtlas` will have an initial size of `256` (we could make this
configurable) and `try_allocate` will keep track of the glyphs in use
in the current frame, returning `None` when the LRU glyph is in use.

In that case, `TextRenderer::prepare` will return
`PrepareError::AtlasFull` with the `ContentType` of the atlas that is
full. The user of the library can then call `TextAtlas::grow` with the
provided `ContentType` to obtain a bigger atlas (by `256`).

A `TextAtlas::grow` call clears the whole atlas and, as a result, all of
the `prepare` calls need to be repeated in a frame until they all
succeed. Overall, the atlas will rarely need to grow and so the calls
will not need to be repated often.

Finally, the user needs to call `TextAtlas::trim` at the end of the
frame. This allows us to clear the glyphs in use collection in the atlas. Maybe
there is a better way to model this in an API that forces the user to
trim the atlas (e.g. make `trim` return a new type and changing `prepare` and `render` to take that type instead).

examples/hello-world.rs

@@ -140,6 +140,8 @@ async fn run() {
 
                 queue.submit(Some(encoder.finish()));
                 frame.present();
+
+                atlas.trim();
             }
             Event::WindowEvent {
                 event: WindowEvent::CloseRequested,

src/error.rs

@@ -1,3 +1,4 @@
+use crate::ContentType;
 use std::{
     error::Error,
     fmt::{self, Display, Formatter},
@@ -6,7 +7,7 @@ use std::{
 /// An error that occurred while preparing text for rendering.
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum PrepareError {
-    AtlasFull,
+    AtlasFull(ContentType),
 }
 
 impl Display for PrepareError {

src/lib.rs

@@ -10,7 +10,7 @@ mod text_render;
 
 pub use error::{PrepareError, RenderError};
 pub use text_atlas::{ColorMode, TextAtlas};
-use text_render::ContentType;
+pub use text_render::ContentType;
 pub use text_render::TextRenderer;
 
 // Re-export all top-level types from `cosmic-text` for convenience.

src/text_atlas.rs

@@ -1,16 +1,16 @@
 use crate::{text_render::ContentType, CacheKey, GlyphDetails, GlyphToRender, Params, Resolution};
 use etagere::{size2, Allocation, BucketedAtlasAllocator};
 use lru::LruCache;
-use std::{borrow::Cow, mem::size_of, num::NonZeroU64, sync::Arc};
+use std::{borrow::Cow, collections::HashSet, mem::size_of, num::NonZeroU64, sync::Arc};
 use wgpu::{
-    BindGroup, BindGroupDescriptor, BindGroupEntry, BindGroupLayoutEntry, BindingResource,
-    BindingType, BlendState, Buffer, BufferBindingType, BufferDescriptor, BufferUsages,
-    ColorTargetState, ColorWrites, DepthStencilState, Device, Extent3d, FilterMode, FragmentState,
-    MultisampleState, PipelineLayout, PipelineLayoutDescriptor, PrimitiveState, Queue,
-    RenderPipeline, RenderPipelineDescriptor, SamplerBindingType, SamplerDescriptor, ShaderModule,
-    ShaderModuleDescriptor, ShaderSource, ShaderStages, Texture, TextureDescriptor,
-    TextureDimension, TextureFormat, TextureSampleType, TextureUsages, TextureView,
-    TextureViewDescriptor, TextureViewDimension, VertexFormat, VertexState,
+    BindGroup, BindGroupDescriptor, BindGroupEntry, BindGroupLayout, BindGroupLayoutEntry,
+    BindingResource, BindingType, BlendState, Buffer, BufferBindingType, BufferDescriptor,
+    BufferUsages, ColorTargetState, ColorWrites, DepthStencilState, Device, Extent3d, FilterMode,
+    FragmentState, MultisampleState, PipelineLayout, PipelineLayoutDescriptor, PrimitiveState,
+    Queue, RenderPipeline, RenderPipelineDescriptor, Sampler, SamplerBindingType,
+    SamplerDescriptor, ShaderModule, ShaderModuleDescriptor, ShaderSource, ShaderStages, Texture,
+    TextureDescriptor, TextureDimension, TextureFormat, TextureSampleType, TextureUsages,
+    TextureView, TextureViewDescriptor, TextureViewDimension, VertexFormat, VertexState,
 };
 
 #[allow(dead_code)]
@@ -19,25 +19,27 @@ pub(crate) struct InnerAtlas {
     pub texture: Texture,
     pub texture_view: TextureView,
     pub packer: BucketedAtlasAllocator,
-    pub width: u32,
-    pub height: u32,
+    pub size: u32,
     pub glyph_cache: LruCache<CacheKey, GlyphDetails>,
+    pub glyphs_in_use: HashSet<CacheKey>,
+    pub max_texture_dimension_2d: u32,
 }
 
 impl InnerAtlas {
+    const INITIAL_SIZE: u32 = 256;
+
     fn new(device: &Device, _queue: &Queue, kind: Kind) -> Self {
         let max_texture_dimension_2d = device.limits().max_texture_dimension_2d;
-        let width = max_texture_dimension_2d;
-        let height = max_texture_dimension_2d;
+        let size = Self::INITIAL_SIZE.min(max_texture_dimension_2d);
 
-        let packer = BucketedAtlasAllocator::new(size2(width as i32, height as i32));
+        let packer = BucketedAtlasAllocator::new(size2(size as i32, size as i32));
 
         // Create a texture to use for our atlas
         let texture = device.create_texture(&TextureDescriptor {
             label: Some("glyphon atlas"),
             size: Extent3d {
-                width,
-                height,
+                width: size,
+                height: size,
                 depth_or_array_layers: 1,
             },
             mip_level_count: 1,
@@ -51,15 +53,17 @@ impl InnerAtlas {
         let texture_view = texture.create_view(&TextureViewDescriptor::default());
 
         let glyph_cache = LruCache::unbounded();
+        let glyphs_in_use = HashSet::new();
 
         Self {
             kind,
             texture,
             texture_view,
             packer,
-            width,
-            height,
+            size,
             glyph_cache,
+            glyphs_in_use,
+            max_texture_dimension_2d,
         }
     }
 
@@ -68,20 +72,82 @@ impl InnerAtlas {
 
         loop {
             let allocation = self.packer.allocate(size);
+
             if allocation.is_some() {
                 return allocation;
             }
 
             // Try to free least recently used allocation
-            let (_, value) = self.glyph_cache.pop_lru()?;
-            self.packer
-                .deallocate(value.atlas_id.expect("cache corrupt"));
+            let (_, mut value) = self.glyph_cache.peek_lru()?;
+
+            while value.atlas_id.is_none() {
+                let _ = self.glyph_cache.pop_lru();
+
+                (_, value) = self.glyph_cache.peek_lru()?;
+            }
+
+            let (key, value) = self.glyph_cache.pop_lru().unwrap();
+
+            if self.glyphs_in_use.contains(&key) {
+                return None;
+            }
+
+            self.packer.deallocate(value.atlas_id.unwrap());
         }
     }
 
     pub fn num_channels(&self) -> usize {
         self.kind.num_channels()
     }
+
+    pub(crate) fn promote(&mut self, glyph: CacheKey) {
+        self.glyph_cache.promote(&glyph);
+        self.glyphs_in_use.insert(glyph);
+    }
+
+    pub(crate) fn put(&mut self, glyph: CacheKey, details: GlyphDetails) {
+        self.glyph_cache.put(glyph, details);
+        self.glyphs_in_use.insert(glyph);
+    }
+
+    pub(crate) fn grow(&mut self, device: &wgpu::Device) -> bool {
+        if self.size >= self.max_texture_dimension_2d {
+            return false;
+        }
+
+        // TODO: Better resizing logic (?)
+        let new_size = (self.size + Self::INITIAL_SIZE).min(self.max_texture_dimension_2d);
+
+        self.packer = BucketedAtlasAllocator::new(size2(new_size as i32, new_size as i32));
+
+        // Create a texture to use for our atlas
+        self.texture = device.create_texture(&TextureDescriptor {
+            label: Some("glyphon atlas"),
+            size: Extent3d {
+                width: new_size,
+                height: new_size,
+                depth_or_array_layers: 1,
+            },
+            mip_level_count: 1,
+            sample_count: 1,
+            dimension: TextureDimension::D2,
+            format: self.kind.texture_format(),
+            usage: TextureUsages::TEXTURE_BINDING | TextureUsages::COPY_DST,
+            view_formats: &[],
+        });
+
+        self.texture_view = self.texture.create_view(&TextureViewDescriptor::default());
+        self.size = new_size;
+
+        self.glyph_cache.clear();
+        self.glyphs_in_use.clear();
+
+        true
+    }
+
+    fn trim(&mut self) {
+        self.glyphs_in_use.clear();
+    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -145,6 +211,8 @@ pub struct TextAtlas {
         Arc<RenderPipeline>,
     )>,
     pub(crate) bind_group: Arc<BindGroup>,
+    pub(crate) bind_group_layout: BindGroupLayout,
+    pub(crate) sampler: Sampler,
     pub(crate) color_atlas: InnerAtlas,
     pub(crate) mask_atlas: InnerAtlas,
     pub(crate) pipeline_layout: PipelineLayout,
@@ -322,6 +390,8 @@ impl TextAtlas {
             params_buffer,
             cached_pipelines: Vec::new(),
             bind_group,
+            bind_group_layout,
+            sampler,
             color_atlas,
             mask_atlas,
             pipeline_layout,
@@ -331,8 +401,23 @@ impl TextAtlas {
         }
     }
 
-    pub(crate) fn contains_cached_glyph(&self, glyph: &CacheKey) -> bool {
-        self.mask_atlas.glyph_cache.contains(glyph) || self.color_atlas.glyph_cache.contains(glyph)
+    pub fn trim(&mut self) {
+        self.mask_atlas.trim();
+        self.color_atlas.trim();
+    }
+
+    pub fn grow(&mut self, device: &wgpu::Device, content_type: ContentType) -> bool {
+        let did_grow = match content_type {
+            ContentType::Mask => self.mask_atlas.grow(device),
+            ContentType::Color => self.color_atlas.grow(device),
+        };
+
+        if did_grow {
+            self.rebind(device);
+            true
+        } else {
+            false
+        }
     }
 
     pub(crate) fn glyph(&self, glyph: &CacheKey) -> Option<&GlyphDetails> {
@@ -388,4 +473,29 @@ impl TextAtlas {
                 pipeline
             })
     }
+
+    fn rebind(&mut self, device: &wgpu::Device) {
+        self.bind_group = Arc::new(device.create_bind_group(&BindGroupDescriptor {
+            layout: &self.bind_group_layout,
+            entries: &[
+                BindGroupEntry {
+                    binding: 0,
+                    resource: self.params_buffer.as_entire_binding(),
+                },
+                BindGroupEntry {
+                    binding: 1,
+                    resource: BindingResource::TextureView(&self.color_atlas.texture_view),
+                },
+                BindGroupEntry {
+                    binding: 2,
+                    resource: BindingResource::TextureView(&self.mask_atlas.texture_view),
+                },
+                BindGroupEntry {
+                    binding: 3,
+                    resource: BindingResource::Sampler(&self.sampler),
+                },
+            ],
+            label: Some("glyphon bind group"),
+        }));
+    }
 }

src/text_render.rs

@@ -1,8 +1,8 @@
 use crate::{
-    CacheKey, FontSystem, GlyphDetails, GlyphToRender, GpuCacheStatus, Params, PrepareError,
-    RenderError, Resolution, SwashCache, SwashContent, TextArea, TextAtlas,
+    FontSystem, GlyphDetails, GlyphToRender, GpuCacheStatus, Params, PrepareError, RenderError,
+    Resolution, SwashCache, SwashContent, TextArea, TextAtlas,
 };
-use std::{collections::HashSet, iter, mem::size_of, slice, sync::Arc};
+use std::{iter, mem::size_of, slice, sync::Arc};
 use wgpu::{
     Buffer, BufferDescriptor, BufferUsages, DepthStencilState, Device, Extent3d, ImageCopyTexture,
     ImageDataLayout, IndexFormat, MultisampleState, Origin3d, Queue, RenderPass, RenderPipeline,
@@ -16,7 +16,6 @@ pub struct TextRenderer {
     index_buffer: Buffer,
     index_buffer_size: u64,
     vertices_to_render: u32,
-    glyphs_in_use: HashSet<CacheKey>,
     screen_resolution: Resolution,
     pipeline: Arc<RenderPipeline>,
 }
@@ -53,7 +52,6 @@ impl TextRenderer {
             index_buffer,
             index_buffer_size,
             vertices_to_render: 0,
-            glyphs_in_use: HashSet::new(),
             screen_resolution: Resolution {
                 width: 0,
                 height: 0,
@@ -88,20 +86,16 @@ impl TextRenderer {
             });
         }
 
-        self.glyphs_in_use.clear();
-
         for text_area in text_areas.iter() {
             for run in text_area.buffer.layout_runs() {
                 for glyph in run.glyphs.iter() {
-                    self.glyphs_in_use.insert(glyph.cache_key);
-
                     if atlas.mask_atlas.glyph_cache.contains(&glyph.cache_key) {
-                        atlas.mask_atlas.glyph_cache.promote(&glyph.cache_key);
+                        atlas.mask_atlas.promote(glyph.cache_key);
                         continue;
                     }
 
                     if atlas.color_atlas.glyph_cache.contains(&glyph.cache_key) {
-                        atlas.color_atlas.glyph_cache.promote(&glyph.cache_key);
+                        atlas.color_atlas.promote(glyph.cache_key);
                         continue;
                     }
 
@@ -129,7 +123,9 @@ impl TextRenderer {
                         // Find a position in the packer
                         let allocation = match inner.try_allocate(width, height) {
                             Some(a) => a,
-                            None => return Err(PrepareError::AtlasFull),
+                            None => {
+                                return Err(PrepareError::AtlasFull(content_type));
+                            }
                         };
                         let atlas_min = allocation.rectangle.min;
 
@@ -171,19 +167,17 @@ impl TextRenderer {
                         (GpuCacheStatus::SkipRasterization, None, inner)
                     };
 
-                    if !inner.glyph_cache.contains(&glyph.cache_key) {
-                        inner.glyph_cache.put(
-                            glyph.cache_key,
-                            GlyphDetails {
-                                width: width as u16,
-                                height: height as u16,
-                                gpu_cache,
-                                atlas_id,
-                                top: image.placement.top as i16,
-                                left: image.placement.left as i16,
-                            },
-                        );
-                    }
+                    inner.put(
+                        glyph.cache_key,
+                        GlyphDetails {
+                            width: width as u16,
+                            height: height as u16,
+                            gpu_cache,
+                            atlas_id,
+                            top: image.placement.top as i16,
+                            left: image.placement.left as i16,
+                        },
+                    );
                 }
             }
         }
@@ -383,13 +377,6 @@ impl TextRenderer {
         }
 
         {
-            // Validate that glyphs haven't been evicted from cache since `prepare`
-            for glyph in self.glyphs_in_use.iter() {
-                if !atlas.contains_cached_glyph(glyph) {
-                    return Err(RenderError::RemovedFromAtlas);
-                }
-            }
-
             // Validate that screen resolution hasn't changed since `prepare`
             if self.screen_resolution != atlas.params.screen_resolution {
                 return Err(RenderError::ScreenResolutionChanged);
@@ -407,8 +394,8 @@ impl TextRenderer {
 }
 
 #[repr(u32)]
-#[derive(Clone, Copy, Eq, PartialEq)]
-pub(crate) enum ContentType {
+#[derive(Debug, Clone, Copy, Eq, PartialEq)]
+pub enum ContentType {
     Color = 0,
     Mask = 1,
 }