From e03ea2e17d73b3597a8dae8c4d833d40b1413a0c Mon Sep 17 00:00:00 2001
From: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>
Date: Sat, 30 Mar 2024 18:38:59 +0100
Subject: [PATCH] eframe: Early-out from context switching the `glow` backend
 (#4284)

* Closes https://github.com/emilk/egui/issues/4173
---
 crates/eframe/src/native/glow_integration.rs | 31 +++++++-------------
 1 file changed, 10 insertions(+), 21 deletions(-)

diff --git a/crates/eframe/src/native/glow_integration.rs b/crates/eframe/src/native/glow_integration.rs
index 8dd0f05f6e2..ba0b4d8fbd2 100644
--- a/crates/eframe/src/native/glow_integration.rs
+++ b/crates/eframe/src/native/glow_integration.rs
@@ -836,6 +836,13 @@ fn change_gl_context(
 ) {
     crate::profile_function!();
 
+    if let Some(current_gl_context) = current_gl_context {
+        crate::profile_scope!("is_current");
+        if gl_surface.is_current(current_gl_context) {
+            return; // Early-out to save a lot of time.
+        }
+    }
+
     let not_current = {
         crate::profile_scope!("make_not_current");
         current_gl_context
@@ -844,6 +851,7 @@ fn change_gl_context(
             .make_not_current()
             .unwrap()
     };
+
     crate::profile_scope!("make_current");
     *current_gl_context = Some(not_current.make_current(gl_surface).unwrap());
 }
@@ -1178,15 +1186,7 @@ impl GlutinWindowContext {
 
         if let Some(viewport) = self.viewports.get(&viewport_id) {
             if let Some(gl_surface) = &viewport.gl_surface {
-                self.current_gl_context = Some(
-                    self.current_gl_context
-                        .take()
-                        .unwrap()
-                        .make_not_current()
-                        .unwrap()
-                        .make_current(gl_surface)
-                        .unwrap(),
-                );
+                change_gl_context(&mut self.current_gl_context, gl_surface);
                 gl_surface.resize(
                     self.current_gl_context
                         .as_ref()
@@ -1436,18 +1436,7 @@ fn render_immediate_viewport(
 
     let screen_size_in_pixels: [u32; 2] = window.inner_size().into();
 
-    {
-        crate::profile_function!("context-switch");
-        *current_gl_context = Some(
-            current_gl_context
-                .take()
-                .unwrap()
-                .make_not_current()
-                .unwrap()
-                .make_current(gl_surface)
-                .unwrap(),
-        );
-    }
+    change_gl_context(current_gl_context, gl_surface);
 
     let current_gl_context = current_gl_context.as_ref().unwrap();