fix(text): don't reload cache every redraw

I have >1000 fonts installed. COSMIC has always been somewhat laggy for me, but I had assumed it was just like that for everyone, or was the fault of my T480s. Eventually, when trying to diagnose some hitching, I ended up discovering that cosmic-launcher was consuming on average ~5% total CPU over time, which led me to discover that it was fetching all the fonts from disk and software rendering the fonts, every redraw, causing the high cpu usage *and* the stutters (as a result of hammering disk I/O). Oops.

The fix is simple: just persist the cache across redraws.

tiny_skia/src/text.rs

@@ -15,6 +15,7 @@ use std::collections::hash_map;
 pub struct Pipeline {
     glyph_cache: GlyphCache,
     cache: RefCell<Cache>,
+    swash_cache: cosmic_text::SwashCache,
 }
 
 impl Pipeline {
@@ -22,6 +23,7 @@ impl Pipeline {
         Pipeline {
             glyph_cache: GlyphCache::new(),
             cache: RefCell::new(Cache::new()),
+            swash_cache: cosmic_text::SwashCache::new(),
         }
     }
 
@@ -54,6 +56,7 @@ impl Pipeline {
         draw(
             font_system.raw(),
             &mut self.glyph_cache,
+            &mut self.swash_cache,
             paragraph.buffer(),
             position,
             color,
@@ -81,6 +84,7 @@ impl Pipeline {
         draw(
             font_system.raw(),
             &mut self.glyph_cache,
+            &mut self.swash_cache,
             editor.buffer(),
             position,
             color,
@@ -142,6 +146,7 @@ impl Pipeline {
         draw(
             font_system,
             &mut self.glyph_cache,
+            &mut self.swash_cache,
             &entry.buffer,
             Point::new(x, y),
             color,
@@ -165,6 +170,7 @@ impl Pipeline {
         draw(
             font_system.raw(),
             &mut self.glyph_cache,
+            &mut self.swash_cache,
             buffer,
             position,
             color,
@@ -183,6 +189,7 @@ impl Pipeline {
 fn draw(
     font_system: &mut cosmic_text::FontSystem,
     glyph_cache: &mut GlyphCache,
+    swash_cache: &mut cosmic_text::SwashCache,
     buffer: &cosmic_text::Buffer,
     position: Point,
     color: Color,
@@ -192,8 +199,6 @@ fn draw(
 ) {
     let position = position * transformation;
 
-    let mut swash = cosmic_text::SwashCache::new();
-
     for run in buffer.layout_runs() {
         for glyph in run.glyphs {
             let physical_glyph = glyph.physical(
@@ -205,7 +210,7 @@ fn draw(
                 physical_glyph.cache_key,
                 glyph.color_opt.map(from_color).unwrap_or(color),
                 font_system,
-                &mut swash,
+                swash_cache,
             ) {
                 let pixmap = tiny_skia::PixmapRef::from_bytes(
                     buffer,

wgpu/src/text.rs

@@ -308,6 +308,7 @@ pub struct State {
     prepare_layer: usize,
     cache: BufferCache,
     storage: Storage,
+    swash_cache: cryoglyph::SwashCache,
 }
 
 impl State {
@@ -352,6 +353,7 @@ impl State {
                         renderer,
                         &mut atlas,
                         &mut self.cache,
+                        &mut self.swash_cache,
                         text,
                         layer_bounds * layer_transformation,
                         layer_transformation * *transformation,
@@ -448,6 +450,7 @@ fn prepare(
     renderer: &mut cryoglyph::TextRenderer,
     atlas: &mut cryoglyph::TextAtlas,
     buffer_cache: &mut BufferCache,
+    swash_cache: &mut cryoglyph::SwashCache,
     sections: &[Text],
     layer_bounds: Rectangle,
     layer_transformation: Transformation,
@@ -643,6 +646,6 @@ fn prepare(
         atlas,
         viewport,
         text_areas,
-        &mut cryoglyph::SwashCache::new(),
+        swash_cache,
     )
 }