Implement explicit text caching in the widget state tree

2 files changed, 366 insertions, 0 deletions

diff --git a/graphics/src/text/cache.rs b/graphics/src/text/cache.rs
new file mode 100644
index 00000000..8aea6715
--- /dev/null
+++ b/graphics/src/text/cache.rs
@@ -0,0 +1,120 @@
+use crate::core::{Font, Size};
+use crate::text;
+
+use rustc_hash::{FxHashMap, FxHashSet};
+use std::collections::hash_map;
+use std::hash::{BuildHasher, Hash, Hasher};
+
+#[allow(missing_debug_implementations)]
+#[derive(Default)]
+pub struct Cache {
+    entries: FxHashMap<KeyHash, cosmic_text::Buffer>,
+    aliases: FxHashMap<KeyHash, KeyHash>,
+    recently_used: FxHashSet<KeyHash>,
+    hasher: HashBuilder,
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+type HashBuilder = twox_hash::RandomXxHashBuilder64;
+
+#[cfg(target_arch = "wasm32")]
+type HashBuilder = std::hash::BuildHasherDefault<twox_hash::XxHash64>;
+
+impl Cache {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    pub fn get(&self, key: &KeyHash) -> Option<&cosmic_text::Buffer> {
+        self.entries.get(key)
+    }
+
+    pub fn allocate(
+        &mut self,
+        font_system: &mut cosmic_text::FontSystem,
+        key: Key<'_>,
+    ) -> (KeyHash, &mut cosmic_text::Buffer) {
+        let hash = key.hash(self.hasher.build_hasher());
+
+        if let Some(hash) = self.aliases.get(&hash) {
+            let _ = self.recently_used.insert(*hash);
+
+            return (*hash, self.entries.get_mut(hash).unwrap());
+        }
+
+        if let hash_map::Entry::Vacant(entry) = self.entries.entry(hash) {
+            let metrics = cosmic_text::Metrics::new(key.size, key.line_height);
+            let mut buffer = cosmic_text::Buffer::new(font_system, metrics);
+
+            buffer.set_size(
+                font_system,
+                key.bounds.width,
+                key.bounds.height.max(key.line_height),
+            );
+            buffer.set_text(
+                font_system,
+                key.content,
+                text::to_attributes(key.font),
+                text::to_shaping(key.shaping),
+            );
+
+            let bounds = text::measure(&buffer);
+            let _ = entry.insert(buffer);
+
+            for bounds in [
+                bounds,
+                Size {
+                    width: key.bounds.width,
+                    ..bounds
+                },
+            ] {
+                if key.bounds != bounds {
+                    let _ = self.aliases.insert(
+                        Key { bounds, ..key }.hash(self.hasher.build_hasher()),
+                        hash,
+                    );
+                }
+            }
+        }
+
+        let _ = self.recently_used.insert(hash);
+
+        (hash, self.entries.get_mut(&hash).unwrap())
+    }
+
+    pub fn trim(&mut self) {
+        self.entries
+            .retain(|key, _| self.recently_used.contains(key));
+
+        self.aliases
+            .retain(|_, value| self.recently_used.contains(value));
+
+        self.recently_used.clear();
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Key<'a> {
+    pub content: &'a str,
+    pub size: f32,
+    pub line_height: f32,
+    pub font: Font,
+    pub bounds: Size,
+    pub shaping: text::Shaping,
+}
+
+impl Key<'_> {
+    fn hash<H: Hasher>(self, mut hasher: H) -> KeyHash {
+        self.content.hash(&mut hasher);
+        self.size.to_bits().hash(&mut hasher);
+        self.line_height.to_bits().hash(&mut hasher);
+        self.font.hash(&mut hasher);
+        self.bounds.width.to_bits().hash(&mut hasher);
+        self.bounds.height.to_bits().hash(&mut hasher);
+        self.shaping.hash(&mut hasher);
+
+        hasher.finish()
+    }
+}
+
+pub type KeyHash = u64;
diff --git a/graphics/src/text/paragraph.rs b/graphics/src/text/paragraph.rs
new file mode 100644
index 00000000..7b70376a
--- /dev/null
+++ b/graphics/src/text/paragraph.rs
@@ -0,0 +1,246 @@
+use crate::core;
+use crate::core::alignment;
+use crate::core::text::{Hit, LineHeight, Shaping, Text};
+use crate::core::{Font, Pixels, Point, Size};
+use crate::text::{self, FontSystem};
+
+use std::fmt;
+use std::sync::{self, Arc};
+
+#[derive(Clone, PartialEq, Default)]
+pub struct Paragraph(Arc<Internal>);
+
+struct Internal {
+    buffer: cosmic_text::Buffer,
+    content: String, // TODO: Reuse from `buffer` (?)
+    font: Font,
+    shaping: Shaping,
+    horizontal_alignment: alignment::Horizontal,
+    vertical_alignment: alignment::Vertical,
+    bounds: Size,
+    min_bounds: Size,
+}
+
+impl Paragraph {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    pub fn with_text(text: Text<'_, Font>, font_system: &FontSystem) -> Self {
+        let mut font_system = font_system.write();
+
+        let mut buffer = cosmic_text::Buffer::new(
+            &mut font_system,
+            cosmic_text::Metrics::new(
+                text.size.into(),
+                text.line_height.to_absolute(text.size).into(),
+            ),
+        );
+
+        buffer.set_size(
+            &mut font_system,
+            text.bounds.width,
+            text.bounds.height,
+        );
+
+        buffer.set_text(
+            &mut font_system,
+            text.content,
+            text::to_attributes(text.font),
+            text::to_shaping(text.shaping),
+        );
+
+        let min_bounds = text::measure(&buffer);
+
+        Self(Arc::new(Internal {
+            buffer,
+            content: text.content.to_owned(),
+            font: text.font,
+            horizontal_alignment: text.horizontal_alignment,
+            vertical_alignment: text.vertical_alignment,
+            shaping: text.shaping,
+            bounds: text.bounds,
+            min_bounds,
+        }))
+    }
+
+    pub fn buffer(&self) -> &cosmic_text::Buffer {
+        &self.0.buffer
+    }
+
+    pub fn downgrade(&self) -> Weak {
+        Weak {
+            raw: Arc::downgrade(&self.0),
+            min_bounds: self.0.min_bounds,
+            horizontal_alignment: self.0.horizontal_alignment,
+            vertical_alignment: self.0.vertical_alignment,
+        }
+    }
+
+    pub fn resize(&mut self, new_bounds: Size, font_system: &FontSystem) {
+        if let Some(internal) = Arc::get_mut(&mut self.0) {
+            // If there is no strong reference holding on to the paragraph, we
+            // resize the buffer in-place
+            internal.buffer.set_size(
+                &mut font_system.write(),
+                new_bounds.width,
+                new_bounds.height,
+            );
+
+            internal.bounds = new_bounds;
+            internal.min_bounds = text::measure(&internal.buffer);
+        } else {
+            let metrics = self.0.buffer.metrics();
+
+            // If there is a strong reference somewhere, we recompute the buffer
+            // from scratch
+            *self = Self::with_text(
+                Text {
+                    content: &self.0.content,
+                    bounds: self.0.bounds,
+                    size: Pixels(metrics.font_size),
+                    line_height: LineHeight::Absolute(Pixels(
+                        metrics.line_height,
+                    )),
+                    font: self.0.font,
+                    horizontal_alignment: self.0.horizontal_alignment,
+                    vertical_alignment: self.0.vertical_alignment,
+                    shaping: self.0.shaping,
+                },
+                font_system,
+            );
+        }
+    }
+}
+
+impl core::text::Paragraph for Paragraph {
+    type Font = Font;
+
+    fn content(&self) -> &str {
+        &self.0.content
+    }
+
+    fn text_size(&self) -> Pixels {
+        Pixels(self.0.buffer.metrics().font_size)
+    }
+
+    fn line_height(&self) -> LineHeight {
+        LineHeight::Absolute(Pixels(self.0.buffer.metrics().line_height))
+    }
+
+    fn font(&self) -> Font {
+        self.0.font
+    }
+
+    fn shaping(&self) -> Shaping {
+        self.0.shaping
+    }
+
+    fn horizontal_alignment(&self) -> alignment::Horizontal {
+        self.0.horizontal_alignment
+    }
+
+    fn vertical_alignment(&self) -> alignment::Vertical {
+        self.0.vertical_alignment
+    }
+
+    fn bounds(&self) -> Size {
+        self.0.bounds
+    }
+
+    fn min_bounds(&self) -> Size {
+        self.0.min_bounds
+    }
+
+    fn hit_test(&self, point: Point) -> Option<Hit> {
+        let cursor = self.0.buffer.hit(point.x, point.y)?;
+
+        Some(Hit::CharOffset(cursor.index))
+    }
+
+    fn grapheme_position(&self, line: usize, index: usize) -> Option<Point> {
+        let run = self.0.buffer.layout_runs().nth(line)?;
+
+        // TODO: Index represents a grapheme, not a glyph
+        let glyph = run.glyphs.get(index).or_else(|| run.glyphs.last())?;
+
+        let advance_last = if index == run.glyphs.len() {
+            glyph.w
+        } else {
+            0.0
+        };
+
+        Some(Point::new(
+            glyph.x + glyph.x_offset * glyph.font_size + advance_last,
+            glyph.y - glyph.y_offset * glyph.font_size,
+        ))
+    }
+}
+
+impl PartialEq for Internal {
+    fn eq(&self, other: &Self) -> bool {
+        self.content == other.content
+            && self.font == other.font
+            && self.shaping == other.shaping
+            && self.horizontal_alignment == other.horizontal_alignment
+            && self.vertical_alignment == other.vertical_alignment
+            && self.bounds == other.bounds
+            && self.min_bounds == other.min_bounds
+            && self.buffer.metrics() == other.buffer.metrics()
+    }
+}
+
+impl Default for Internal {
+    fn default() -> Self {
+        Self {
+            buffer: cosmic_text::Buffer::new_empty(cosmic_text::Metrics {
+                font_size: 1.0,
+                line_height: 1.0,
+            }),
+            content: String::new(),
+            font: Font::default(),
+            shaping: Shaping::default(),
+            horizontal_alignment: alignment::Horizontal::Left,
+            vertical_alignment: alignment::Vertical::Top,
+            bounds: Size::ZERO,
+            min_bounds: Size::ZERO,
+        }
+    }
+}
+
+impl fmt::Debug for Paragraph {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Paragraph")
+            .field("content", &self.0.content)
+            .field("font", &self.0.font)
+            .field("shaping", &self.0.shaping)
+            .field("horizontal_alignment", &self.0.horizontal_alignment)
+            .field("vertical_alignment", &self.0.vertical_alignment)
+            .field("bounds", &self.0.bounds)
+            .field("min_bounds", &self.0.min_bounds)
+            .finish()
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct Weak {
+    raw: sync::Weak<Internal>,
+    pub min_bounds: Size,
+    pub horizontal_alignment: alignment::Horizontal,
+    pub vertical_alignment: alignment::Vertical,
+}
+
+impl Weak {
+    pub fn upgrade(&self) -> Option<Paragraph> {
+        self.raw.upgrade().map(Paragraph)
+    }
+}
+
+impl PartialEq for Weak {
+    fn eq(&self, other: &Self) -> bool {
+        match (self.raw.upgrade(), other.raw.upgrade()) {
+            (Some(p1), Some(p2)) => p1 == p2,
+            _ => false,
+        }
+    }
+}