From ad4f87831bcb7f1b0319b0112c3549b2913a6718 Mon Sep 17 00:00:00 2001
From: Emil Ernerfeldt <emilernerfeldt@gmail.com>
Date: Mon, 12 Oct 2020 03:22:41 +0200
Subject: [PATCH] [refactor] Make `Ui` lighter by using a clone-on-write
 `Arc<Style>`

---
 egui/src/context.rs | 11 +++++------
 egui/src/ui.rs      | 10 +++++-----
 2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/egui/src/context.rs b/egui/src/context.rs
index f23ad566..cd36d31c 100644
--- a/egui/src/context.rs
+++ b/egui/src/context.rs
@@ -26,7 +26,7 @@ struct PaintStats {
 #[derive(Default)]
 pub struct Context {
     /// The default style for new `Ui`:s
-    style: Mutex<Style>,
+    style: Mutex<Arc<Style>>,
     paint_options: Mutex<paint::PaintOptions>,
     /// None until first call to `begin_frame`.
     fonts: Option<Arc<Fonts>>,
@@ -123,13 +123,12 @@ impl Context {
         *self.font_definitions.lock() = font_definitions;
     }
 
-    // TODO: return MutexGuard
-    pub fn style(&self) -> Style {
+    pub fn style(&self) -> Arc<Style> {
         lock(&self.style, "style").clone()
     }
 
-    pub fn set_style(&self, style: Style) {
-        *lock(&self.style, "style") = style;
+    pub fn set_style(&self, style: impl Into<Arc<Style>>) {
+        *lock(&self.style, "style") = style.into();
     }
 
     pub fn pixels_per_point(&self) -> f32 {
@@ -605,7 +604,7 @@ impl Context {
 
 impl Context {
     pub fn style_ui(&self, ui: &mut Ui) {
-        let mut style = self.style();
+        let mut style: Style = (*self.style()).clone();
         style.ui(ui);
         self.set_style(style);
     }
diff --git a/egui/src/ui.rs b/egui/src/ui.rs
index 92db9283..703db922 100644
--- a/egui/src/ui.rs
+++ b/egui/src/ui.rs
@@ -39,7 +39,7 @@ pub struct Ui {
     max_rect: Rect,
 
     /// Override default style in this ui
-    style: Style,
+    style: Arc<Style>,
 
     layout: Layout,
 
@@ -92,7 +92,7 @@ impl Ui {
             painter: self.painter.clone(),
             min_rect,
             max_rect,
-            style: self.style().clone(),
+            style: self.style.clone(),
             layout,
             cursor,
             child_count: 0,
@@ -113,11 +113,11 @@ impl Ui {
     /// Mutably borrow internal `Style`.
     /// Changes apply to this `Ui` and its subsequent children.
     pub fn style_mut(&mut self) -> &mut Style {
-        &mut self.style
+        Arc::make_mut(&mut self.style) // clone-on-write
     }
 
-    pub fn set_style(&mut self, style: Style) {
-        self.style = style
+    pub fn set_style(&mut self, style: impl Into<Arc<Style>>) {
+        self.style = style.into();
     }
 
     pub fn ctx(&self) -> &Arc<Context> {