Split text measurements cache from rendering cache

This speeds up layouting in the most common scenario considerably!
:tada:

9 files changed, 53 insertions, 24 deletions

diff --git a/core/src/widget/image.rs b/core/src/widget/image.rs
index 7e1b1085..996ab5e1 100644
--- a/core/src/widget/image.rs
+++ b/core/src/widget/image.rs
@@ -1,6 +1,6 @@
 //! Display images in your user interface.
 
-use crate::{Align, Length, Rectangle};
+use crate::{Length, Rectangle};
 
 /// A frame that displays an image while keeping aspect ratio.
 ///
diff --git a/examples/scroll.rs b/examples/scroll.rs
index 98206268..50701879 100644
--- a/examples/scroll.rs
+++ b/examples/scroll.rs
@@ -1,6 +1,6 @@
 use iced::{
-    button, scrollable, Align, Application, Button, Column, Container, Element,
-    Image, Length, Scrollable, Text,
+    button, scrollable, Align, Application, Button, Container, Element, Image,
+    Length, Scrollable, Text,
 };
 
 pub fn main() {
diff --git a/native/src/renderer.rs b/native/src/renderer.rs
index 5963d577..833de571 100644
--- a/native/src/renderer.rs
+++ b/native/src/renderer.rs
@@ -26,6 +26,15 @@ mod windowed;
 pub use debugger::Debugger;
 pub use windowed::{Target, Windowed};
 
-pub trait Renderer {
+use crate::{layout, Element};
+
+pub trait Renderer: Sized {
     type Output;
+
+    fn layout<'a, Message>(
+        &mut self,
+        element: &Element<'a, Message, Self>,
+    ) -> layout::Node {
+        element.layout(self, &layout::Limits::NONE)
+    }
 }
diff --git a/native/src/user_interface.rs b/native/src/user_interface.rs
index 4343086b..f031b090 100644
--- a/native/src/user_interface.rs
+++ b/native/src/user_interface.rs
@@ -97,7 +97,7 @@ where
     pub fn build<E: Into<Element<'a, Message, Renderer>>>(
         root: E,
         cache: Cache,
-        renderer: &Renderer,
+        renderer: &mut Renderer,
     ) -> Self {
         let root = root.into();
 
@@ -110,7 +110,7 @@ where
             cache.layout
         } else {
             let layout_start = std::time::Instant::now();
-            let layout = root.layout(renderer, &layout::Limits::NONE);
+            let layout = renderer.layout(&root);
             dbg!(std::time::Instant::now() - layout_start);
 
             layout
diff --git a/wgpu/Cargo.toml b/wgpu/Cargo.toml
index 032f4ae0..3ebfa7ea 100644
--- a/wgpu/Cargo.toml
+++ b/wgpu/Cargo.toml
@@ -10,6 +10,7 @@ repository = "https://github.com/hecrj/iced"
 [dependencies]
 iced_native = { version = "0.1.0-alpha", path = "../native" }
 wgpu = "0.4"
+glyph_brush = "0.6"
 wgpu_glyph = { version = "0.5", git = "https://github.com/hecrj/wgpu_glyph", branch = "feature/scissoring" }
 raw-window-handle = "0.3"
 image = "0.22"
diff --git a/wgpu/src/renderer.rs b/wgpu/src/renderer.rs
index 7f7b79a5..87e499e2 100644
--- a/wgpu/src/renderer.rs
+++ b/wgpu/src/renderer.rs
@@ -22,8 +22,8 @@ pub struct Renderer {
     queue: Queue,
     quad_pipeline: quad::Pipeline,
     image_pipeline: crate::image::Pipeline,
-
-    glyph_brush: RefCell<wgpu_glyph::GlyphBrush<'static, ()>>,
+    text_pipeline: wgpu_glyph::GlyphBrush<'static, ()>,
+    text_measurements: RefCell<glyph_brush::GlyphBrush<'static, ()>>,
 }
 
 pub struct Layer<'a> {
@@ -73,11 +73,14 @@ impl Renderer {
 
         let fonts = vec![default_font, mono_font];
 
-        let glyph_brush =
-            wgpu_glyph::GlyphBrushBuilder::using_fonts_bytes(fonts)
+        let text_pipeline =
+            wgpu_glyph::GlyphBrushBuilder::using_fonts_bytes(fonts.clone())
                 .initial_cache_size((2048, 2048))
                 .build(&mut device, TextureFormat::Bgra8UnormSrgb);
 
+        let text_measurements =
+            glyph_brush::GlyphBrushBuilder::using_fonts_bytes(fonts).build();
+
         let quad_pipeline = quad::Pipeline::new(&mut device);
         let image_pipeline = crate::image::Pipeline::new(&mut device);
 
@@ -86,8 +89,8 @@ impl Renderer {
             queue,
             quad_pipeline,
             image_pipeline,
-
-            glyph_brush: RefCell::new(glyph_brush),
+            text_pipeline,
+            text_measurements: RefCell::new(text_measurements),
         }
     }
 
@@ -293,8 +296,7 @@ impl Renderer {
         let first = layers.first().unwrap();
         let mut overlay = Layer::new(first.bounds, Vector::new(0, 0));
 
-        let font_id =
-            wgpu_glyph::FontId(self.glyph_brush.borrow().fonts().len() - 1);
+        let font_id = wgpu_glyph::FontId(self.text_pipeline.fonts().len() - 1);
         let scale = wgpu_glyph::Scale { x: 20.0, y: 20.0 };
 
         for (i, line) in lines.iter().enumerate() {
@@ -361,8 +363,6 @@ impl Renderer {
         }
 
         if layer.text.len() > 0 {
-            let mut glyph_brush = self.glyph_brush.borrow_mut();
-
             for text in layer.text.iter() {
                 // Target physical coordinates directly to avoid blurry text
                 let text = wgpu_glyph::Section {
@@ -378,10 +378,10 @@ impl Renderer {
                     ..*text
                 };
 
-                glyph_brush.queue(text);
+                self.text_pipeline.queue(text);
             }
 
-            glyph_brush
+            self.text_pipeline
                 .draw_queued_with_transform_and_scissoring(
                     &mut self.device,
                     encoder,
@@ -401,6 +401,25 @@ impl Renderer {
 
 impl iced_native::Renderer for Renderer {
     type Output = (Primitive, MouseCursor);
+
+    fn layout<'a, Message>(
+        &mut self,
+        element: &iced_native::Element<'a, Message, Self>,
+    ) -> iced_native::layout::Node {
+        let node = element.layout(self, &iced_native::layout::Limits::NONE);
+
+        // Trim measurements cache
+        // TODO: We should probably use a `GlyphCalculator` for this. However,
+        // it uses a lifetimed `GlyphCalculatorGuard` with side-effects on drop.
+        // This makes stuff quite inconvenient. A manual method for trimming the
+        // cache would make our lives easier.
+        self.text_measurements
+            .borrow_mut()
+            .process_queued(|_, _| {}, |_| {})
+            .expect("Trim text measurements");
+
+        node
+    }
 }
 
 impl Windowed for Renderer {
diff --git a/wgpu/src/renderer/widget/text.rs b/wgpu/src/renderer/widget/text.rs
index 713b514f..b9ccd787 100644
--- a/wgpu/src/renderer/widget/text.rs
+++ b/wgpu/src/renderer/widget/text.rs
@@ -22,7 +22,7 @@ impl text::Renderer for Renderer {
         };
 
         let (width, height) = if let Some(bounds) =
-            self.glyph_brush.borrow_mut().glyph_bounds(&section)
+            self.text_measurements.borrow_mut().glyph_bounds(&section)
         {
             (bounds.width().ceil(), bounds.height().ceil())
         } else {
diff --git a/wgpu/src/renderer/widget/text_input.rs b/wgpu/src/renderer/widget/text_input.rs
index b5f6c5f6..75eb20f7 100644
--- a/wgpu/src/renderer/widget/text_input.rs
+++ b/wgpu/src/renderer/widget/text_input.rs
@@ -78,7 +78,7 @@ impl text_input::Renderer for Renderer {
                 .to_string();
 
             let mut text_value_width = self
-                .glyph_brush
+                .text_measurements
                 .borrow_mut()
                 .glyph_bounds(Section {
                     text: text_before_cursor,
@@ -94,7 +94,7 @@ impl text_input::Renderer for Renderer {
 
             if spaces_at_the_end > 0 {
                 let space_width = {
-                    let glyph_brush = self.glyph_brush.borrow();
+                    let glyph_brush = self.text_measurements.borrow();
 
                     // TODO: Select appropriate font
                     let font = &glyph_brush.fonts()[0];
diff --git a/winit/src/application.rs b/winit/src/application.rs
index fdd659d9..331bafa0 100644
--- a/winit/src/application.rs
+++ b/winit/src/application.rs
@@ -61,7 +61,7 @@ pub trait Application {
         let user_interface = UserInterface::build(
             document(&mut self, size, &mut debug),
             Cache::default(),
-            &renderer,
+            &mut renderer,
         );
         debug.layout_finished();
 
@@ -87,7 +87,7 @@ pub trait Application {
                 let mut user_interface = UserInterface::build(
                     document(&mut self, size, &mut debug),
                     cache.take().unwrap(),
-                    &renderer,
+                    &mut renderer,
                 );
                 debug.layout_finished();
 
@@ -130,7 +130,7 @@ pub trait Application {
                     let user_interface = UserInterface::build(
                         document(&mut self, size, &mut debug),
                         temp_cache,
-                        &renderer,
+                        &mut renderer,
                     );
                     debug.layout_finished();