Added feature switch to disable animations in TUI (#6870)

This PR adds support for a new feature flag `tui.animations`. By
default, the TUI uses animations in its welcome screen, "working"
spinners, and "shimmer" effects. This animations can interfere with
screen readers, so it's good to provide a way to disable them.

This change is inspired by [a
PR](https://github.com/openai/codex/pull/4014) contributed by @Orinks.
That PR has faltered a bit, but I think the core idea is sound. This
version incorporates feedback from @aibrahim-oai. In particular:
1. It uses a feature flag (`tui.animations`) rather than the unqualified
CLI key `no-animations`. Feature flags are the preferred way to expose
boolean switches. They are also exposed via CLI command switches.
2. It includes more complete documentation.
3. It disables a few animations that the other PR omitted.

codex-rs/tui/src/onboarding/auth.rs

@@ -155,6 +155,7 @@ pub(crate) struct AuthModeWidget {
     pub auth_manager: Arc<AuthManager>,
     pub forced_chatgpt_workspace_id: Option<String>,
     pub forced_login_method: Option<ForcedLoginMethod>,
+    pub animations_enabled: bool,
 }
 
 impl AuthModeWidget {
@@ -260,10 +261,14 @@ impl AuthModeWidget {
 
     fn render_continue_in_browser(&self, area: Rect, buf: &mut Buffer) {
         let mut spans = vec!["  ".into()];
-        // Schedule a follow-up frame to keep the shimmer animation going.
-        self.request_frame
-            .schedule_frame_in(std::time::Duration::from_millis(100));
-        spans.extend(shimmer_spans("Finish signing in via your browser"));
+        if self.animations_enabled {
+            // Schedule a follow-up frame to keep the shimmer animation going.
+            self.request_frame
+                .schedule_frame_in(std::time::Duration::from_millis(100));
+            spans.extend(shimmer_spans("Finish signing in via your browser"));
+        } else {
+            spans.push("Finish signing in via your browser".into());
+        }
         let mut lines = vec![spans.into(), "".into()];
 
         let sign_in_state = self.sign_in_state.read().unwrap();
@@ -670,6 +675,7 @@ mod tests {
             ),
             forced_chatgpt_workspace_id: None,
             forced_login_method: Some(ForcedLoginMethod::Chatgpt),
+            animations_enabled: true,
         };
         (widget, codex_home)
     }

codex-rs/tui/src/onboarding/onboarding_screen.rs

@@ -88,6 +88,7 @@ impl OnboardingScreen {
         steps.push(Step::Welcome(WelcomeWidget::new(
             !matches!(login_status, LoginStatus::NotAuthenticated),
             tui.frame_requester(),
+            config.animations,
         )));
         if show_login_screen {
             let highlighted_mode = match forced_login_method {
@@ -105,6 +106,7 @@ impl OnboardingScreen {
                 auth_manager,
                 forced_chatgpt_workspace_id,
                 forced_login_method,
+                animations_enabled: config.animations,
             }))
         }
         let is_git_repo = get_git_repo_root(&cwd).is_some();

codex-rs/tui/src/onboarding/welcome.rs

@@ -25,10 +25,14 @@ const MIN_ANIMATION_WIDTH: u16 = 60;
 pub(crate) struct WelcomeWidget {
     pub is_logged_in: bool,
     animation: AsciiAnimation,
+    animations_enabled: bool,
 }
 
 impl KeyboardHandler for WelcomeWidget {
     fn handle_key_event(&mut self, key_event: KeyEvent) {
+        if !self.animations_enabled {
+            return;
+        }
         if key_event.kind == KeyEventKind::Press
             && key_event.code == KeyCode::Char('.')
             && key_event.modifiers.contains(KeyModifiers::CONTROL)
@@ -40,10 +44,15 @@ impl KeyboardHandler for WelcomeWidget {
 }
 
 impl WelcomeWidget {
-    pub(crate) fn new(is_logged_in: bool, request_frame: FrameRequester) -> Self {
+    pub(crate) fn new(
+        is_logged_in: bool,
+        request_frame: FrameRequester,
+        animations_enabled: bool,
+    ) -> Self {
         Self {
             is_logged_in,
             animation: AsciiAnimation::new(request_frame),
+            animations_enabled,
         }
     }
 }
@@ -51,17 +60,17 @@ impl WelcomeWidget {
 impl WidgetRef for &WelcomeWidget {
     fn render_ref(&self, area: Rect, buf: &mut Buffer) {
         Clear.render(area, buf);
-        self.animation.schedule_next_frame();
+        if self.animations_enabled {
+            self.animation.schedule_next_frame();
+        }
 
         // Skip the animation entirely when the viewport is too small so we don't clip frames.
         let show_animation =
             area.height >= MIN_ANIMATION_HEIGHT && area.width >= MIN_ANIMATION_WIDTH;
 
         let mut lines: Vec<Line> = Vec::new();
-        if show_animation {
+        if show_animation && self.animations_enabled {
             let frame = self.animation.current_frame();
-            // let frame_line_count = frame.lines().count();
-            // lines.reserve(frame_line_count + 2);
             lines.extend(frame.lines().map(Into::into));
             lines.push("".into());
         }
@@ -99,7 +108,7 @@ mod tests {
 
     #[test]
     fn welcome_renders_animation_on_first_draw() {
-        let widget = WelcomeWidget::new(false, FrameRequester::test_dummy());
+        let widget = WelcomeWidget::new(false, FrameRequester::test_dummy(), true);
         let area = Rect::new(0, 0, MIN_ANIMATION_WIDTH, MIN_ANIMATION_HEIGHT);
         let mut buf = Buffer::empty(area);
         (&widget).render(area, &mut buf);
@@ -129,6 +138,7 @@ mod tests {
         let mut widget = WelcomeWidget {
             is_logged_in: false,
             animation: AsciiAnimation::with_variants(FrameRequester::test_dummy(), &VARIANTS, 0),
+            animations_enabled: true,
         };
 
         let before = widget.animation.current_frame();