Invalidate existing paragraphs when new fonts are loaded

core/src/text.rs

@@ -172,18 +172,14 @@ pub trait Renderer: crate::Renderer {
         paragraph: &mut Self::Paragraph,
         text: Text<'_, Self::Font>,
     ) {
-        if paragraph.content() != text.content
-            || paragraph.text_size() != text.size
-            || paragraph.line_height().to_absolute(text.size)
-                != text.line_height.to_absolute(text.size)
-            || paragraph.font() != text.font
-            || paragraph.shaping() != text.shaping
-            || paragraph.horizontal_alignment() != text.horizontal_alignment
-            || paragraph.vertical_alignment() != text.vertical_alignment
-        {
-            *paragraph = self.create_paragraph(text);
-        } else if paragraph.bounds() != text.bounds {
-            self.resize_paragraph(paragraph, text.bounds);
+        match compare(paragraph, text) {
+            Difference::None => {}
+            Difference::Bounds => {
+                self.resize_paragraph(paragraph, text.bounds);
+            }
+            Difference::Shape => {
+                *paragraph = self.create_paragraph(text);
+            }
         }
     }
 
@@ -255,3 +251,51 @@ pub trait Paragraph: Default {
         self.min_bounds().height
     }
 }
+
+/// The difference detected in some text.
+///
+/// You will obtain a [`Difference`] when you [`compare`] a [`Paragraph`] with some
+/// [`Text`].
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Difference {
+    /// No difference.
+    ///
+    /// The text can be reused as it is!
+    None,
+
+    /// A bounds difference.
+    ///
+    /// This normally means a relayout is necessary, but the shape of the text can
+    /// be reused.
+    Bounds,
+
+    /// A shape difference.
+    ///
+    /// The contents, alignment, sizes, fonts, or any other essential attributes
+    /// of the shape of the text have changed. A complete reshape and relayout of
+    /// the text is necessary.
+    Shape,
+}
+
+/// Compares a [`Paragraph`] with some desired [`Text`] and returns the
+/// [`Difference`].
+pub fn compare<Font: PartialEq>(
+    paragraph: &impl Paragraph<Font = Font>,
+    text: Text<'_, Font>,
+) -> Difference {
+    if paragraph.content() != text.content
+        || paragraph.text_size() != text.size
+        || paragraph.line_height().to_absolute(text.size)
+            != text.line_height.to_absolute(text.size)
+        || paragraph.font() != text.font
+        || paragraph.shaping() != text.shaping
+        || paragraph.horizontal_alignment() != text.horizontal_alignment
+        || paragraph.vertical_alignment() != text.vertical_alignment
+    {
+        Difference::Shape
+    } else if paragraph.bounds() != text.bounds {
+        Difference::Bounds
+    } else {
+        Difference::None
+    }
+}

graphics/src/renderer.rs

@@ -162,6 +162,29 @@ where
         text::Paragraph::with_text(text, self.backend.font_system())
     }
 
+    fn update_paragraph(
+        &self,
+        paragraph: &mut Self::Paragraph,
+        text: Text<'_, Self::Font>,
+    ) {
+        let font_system = self.backend.font_system();
+
+        if paragraph.version() != font_system.version() {
+            // The font system has changed, paragraph fonts may be outdated
+            *paragraph = self.create_paragraph(text);
+        } else {
+            match core::text::compare(paragraph, text) {
+                core::text::Difference::None => {}
+                core::text::Difference::Bounds => {
+                    self.resize_paragraph(paragraph, text.bounds);
+                }
+                core::text::Difference::Shape => {
+                    *paragraph = self.create_paragraph(text);
+                }
+            }
+        }
+    }
+
     fn resize_paragraph(
         &self,
         paragraph: &mut Self::Paragraph,

graphics/src/text.rs

@@ -10,30 +10,54 @@ use crate::core::font::{self, Font};
 use crate::core::text::Shaping;
 use crate::core::Size;
 
+use std::borrow::Cow;
 use std::sync::{self, Arc, RwLock};
 
 #[allow(missing_debug_implementations)]
-pub struct FontSystem(RwLock<cosmic_text::FontSystem>);
+pub struct FontSystem {
+    raw: RwLock<cosmic_text::FontSystem>,
+    version: Version,
+}
 
 impl FontSystem {
     pub fn new() -> Self {
-        FontSystem(RwLock::new(cosmic_text::FontSystem::new_with_fonts(
-            [cosmic_text::fontdb::Source::Binary(Arc::new(
-                include_bytes!("../fonts/Iced-Icons.ttf").as_slice(),
-            ))]
-            .into_iter(),
-        )))
+        FontSystem {
+            raw: RwLock::new(cosmic_text::FontSystem::new_with_fonts(
+                [cosmic_text::fontdb::Source::Binary(Arc::new(
+                    include_bytes!("../fonts/Iced-Icons.ttf").as_slice(),
+                ))]
+                .into_iter(),
+            )),
+            version: Version::default(),
+        }
     }
 
     pub fn get_mut(&mut self) -> &mut cosmic_text::FontSystem {
-        self.0.get_mut().expect("Lock font system")
+        self.raw.get_mut().expect("Lock font system")
     }
 
-    pub fn write(&self) -> sync::RwLockWriteGuard<'_, cosmic_text::FontSystem> {
-        self.0.write().expect("Write font system")
+    pub fn write(
+        &self,
+    ) -> (sync::RwLockWriteGuard<'_, cosmic_text::FontSystem>, Version) {
+        (self.raw.write().expect("Write font system"), self.version)
+    }
+
+    pub fn load_font(&mut self, bytes: Cow<'static, [u8]>) {
+        let _ = self.get_mut().db_mut().load_font_source(
+            cosmic_text::fontdb::Source::Binary(Arc::new(bytes.into_owned())),
+        );
+
+        self.version = Version(self.version.0 + 1);
+    }
+
+    pub fn version(&self) -> Version {
+        self.version
     }
 }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Default)]
+pub struct Version(u32);
+
 impl Default for FontSystem {
     fn default() -> Self {
         Self::new()

graphics/src/text/paragraph.rs

@@ -19,6 +19,7 @@ struct Internal {
     vertical_alignment: alignment::Vertical,
     bounds: Size,
     min_bounds: Size,
+    version: text::Version,
 }
 
 impl Paragraph {
@@ -27,9 +28,9 @@ impl Paragraph {
     }
 
     pub fn with_text(text: Text<'_, Font>, font_system: &FontSystem) -> Self {
-        log::trace!("\nAllocating paragraph: {}", text.content);
+        log::trace!("Allocating paragraph: {}", text.content);
 
-        let mut font_system = font_system.write();
+        let (mut font_system, version) = font_system.write();
 
         let mut buffer = cosmic_text::Buffer::new(
             &mut font_system,
@@ -63,6 +64,7 @@ impl Paragraph {
             shaping: text.shaping,
             bounds: text.bounds,
             min_bounds,
+            version,
         })))
     }
 
@@ -70,6 +72,10 @@ impl Paragraph {
         &self.internal().buffer
     }
 
+    pub fn version(&self) -> text::Version {
+        self.internal().version
+    }
+
     pub fn downgrade(&self) -> Weak {
         let paragraph = self.internal();
 
@@ -89,8 +95,10 @@ impl Paragraph {
 
         match Arc::try_unwrap(paragraph) {
             Ok(mut internal) => {
+                let (mut font_system, _) = font_system.write();
+
                 internal.buffer.set_size(
-                    &mut font_system.write(),
+                    &mut font_system,
                     new_bounds.width,
                     new_bounds.height,
                 );
@@ -246,6 +254,7 @@ impl Default for Internal {
             vertical_alignment: alignment::Vertical::Top,
             bounds: Size::ZERO,
             min_bounds: Size::ZERO,
+            version: text::Version::default(),
         }
     }
 }

tiny_skia/src/text.rs

@@ -9,7 +9,6 @@ use rustc_hash::{FxHashMap, FxHashSet};
 use std::borrow::Cow;
 use std::cell::RefCell;
 use std::collections::hash_map;
-use std::sync::Arc;
 
 #[allow(missing_debug_implementations)]
 pub struct Pipeline {
@@ -32,9 +31,7 @@ impl Pipeline {
     }
 
     pub fn load_font(&mut self, bytes: Cow<'static, [u8]>) {
-        self.font_system.get_mut().db_mut().load_font_source(
-            cosmic_text::fontdb::Source::Binary(Arc::new(bytes.into_owned())),
-        );
+        self.font_system.load_font(bytes);
 
         self.cache = RefCell::new(Cache::new());
     }

wgpu/src/text.rs

@@ -7,7 +7,6 @@ use crate::layer::Text;
 
 use std::borrow::Cow;
 use std::cell::RefCell;
-use std::sync::Arc;
 
 #[allow(missing_debug_implementations)]
 pub struct Pipeline {
@@ -47,9 +46,7 @@ impl Pipeline {
     }
 
     pub fn load_font(&mut self, bytes: Cow<'static, [u8]>) {
-        let _ = self.font_system.get_mut().db_mut().load_font_source(
-            glyphon::fontdb::Source::Binary(Arc::new(bytes.into_owned())),
-        );
+        self.font_system.load_font(bytes);
 
         self.cache = RefCell::new(Cache::new());
     }