From 6aa82309c3ea31293db48fd7d0400e86a6d2e3f5 Mon Sep 17 00:00:00 2001
From: Euclid Ye <yezhizhenjiakang@gmail.com>
Date: Sat, 27 Sep 2025 21:29:44 +0800
Subject: [PATCH] webdriver: Wait animation frame callbacks before taking
 (element) screenshot (#39539)

According to spec, we should wait animation frame callbacks before
taking (element) screenshot. As "element screenshot" would automatically
scroll into view, this solves intermittency.

Testing: Manually tested on pages, and
`take_element_screenshot/scroll_into_view.py` passes stably now.
Fixes: #39306

---------

Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>
---
 components/compositing/compositor.rs                         | 2 +-
 components/servo/lib.rs                                      | 1 +
 components/webdriver_server/lib.rs                           | 5 +++++
 .../classic/take_element_screenshot/scroll_into_view.py.ini  | 3 ---
 4 files changed, 7 insertions(+), 4 deletions(-)
 delete mode 100644 tests/wpt/meta/webdriver/tests/classic/take_element_screenshot/scroll_into_view.py.ini

diff --git a/components/compositing/compositor.rs b/components/compositing/compositor.rs
index fe7ef0d9878..93d99358320 100644
--- a/components/compositing/compositor.rs
+++ b/components/compositing/compositor.rs
@@ -1223,7 +1223,7 @@ impl IOCompositor {
     }
 
     /// Render the WebRender scene to the active `RenderingContext`. If successful, trigger
-    /// the next round of animations.
+    /// the next round of animations. Return false if unable to render.
     pub fn render(&mut self) -> bool {
         self.global
             .borrow()
diff --git a/components/servo/lib.rs b/components/servo/lib.rs
index dd2b3965ac5..9bbe6f53ec7 100644
--- a/components/servo/lib.rs
+++ b/components/servo/lib.rs
@@ -1065,6 +1065,7 @@ impl Servo {
                     if let Err(e) = response_sender.send(Err(())) {
                         error!("Sending reply to create png failed {e:?}");
                     }
+                    return;
                 }
             }
 
diff --git a/components/webdriver_server/lib.rs b/components/webdriver_server/lib.rs
index 4dbfe5bd325..7e882fd1b73 100644
--- a/components/webdriver_server/lib.rs
+++ b/components/webdriver_server/lib.rs
@@ -2312,6 +2312,11 @@ impl Handler {
     }
 
     fn take_screenshot(&self, rect: Option<Rect<f32, CSSPixel>>) -> WebDriverResult<String> {
+        // Spec: Take screenshot after running the animation frame callbacks.
+        let _ = self.handle_execute_async_script(JavascriptCommandParameters {
+            script: "requestAnimationFrame(() => arguments[0]());".to_string(),
+            args: None,
+        });
         let webview_id = self.webview_id()?;
         let mut img = None;
 
diff --git a/tests/wpt/meta/webdriver/tests/classic/take_element_screenshot/scroll_into_view.py.ini b/tests/wpt/meta/webdriver/tests/classic/take_element_screenshot/scroll_into_view.py.ini
deleted file mode 100644
index 3c21fb97f05..00000000000
--- a/tests/wpt/meta/webdriver/tests/classic/take_element_screenshot/scroll_into_view.py.ini
+++ /dev/null
@@ -1,3 +0,0 @@
-[scroll_into_view.py]
-  [test_scroll_into_view]
-    expected: FAIL