Only produce animation frames when requested

Restore the FTXUI 6 behavior: animation frames are produced only when
requested via animation::RequestAnimationFrame(), typically by an
animation::Animator which arms it on construction and re-arms it from
OnAnimation until the transition completes.

Handling an event no longer implicitly grants an animation tick. That
behavior was introduced accidentally by the v7 event loop rework
(33a40ee) and is what made the #1302 feedback loop possible in the
first place: internal terminal replies are events too.

Author: ArthurSonzogni

CHANGELOG.md

@@ -8,9 +8,10 @@ Next
 - Bugfix: Fix high CPU usage (app and terminal emulator, e.g. tmux) caused by a
   cursor position request/reply feedback loop redrawing the screen at ~60fps in
   the non-alternate-screen modes. See #1302.
-- Request the animation frame when an event is handled instead of when it is
-  received. All internal terminal replies (not only cursor position reports)
-  stop triggering animation frames.
+- Animation frames are now produced only when requested via
+  `animation::RequestAnimationFrame()` (e.g. by `animation::Animator`), as in
+  FTXUI 6. Receiving an event no longer implicitly triggers an animation
+  frame.
 
 ### Dom
 - Performance: `text` computes its requirement once and renders only the

src/ftxui/component/animation_test.cpp

@@ -52,6 +52,13 @@ class AnimationCounter : public ComponentBase {
  private:
   Element OnRender() override { return text(""); }
   void OnAnimation(animation::Params& /*params*/) override { count++; }
+  bool OnEvent(Event event) override {
+    if (event == Event::Character('a')) {
+      animation::RequestAnimationFrame();
+      return true;
+    }
+    return false;
+  }
 };
 
 // Give the recurring AnimationTask (reposted every 15ms) time to become due,
@@ -63,31 +70,34 @@ void RunAnimationTask(Loop& loop) {
 
 }  // namespace
 
-// OnAnimation must tick once per handled event, and not tick for the
-// terminal's replies to FTXUI's own internal requests. See #1302.
-TEST(AnimationTest, EventRequestsAnimationFrame) {
+// OnAnimation must tick only when a frame was requested with
+// animation::RequestAnimationFrame(), typically by an Animator. In particular,
+// handling an event must not implicitly produce a tick: internal terminal
+// replies are events too, and animating on them caused the #1302 feedback
+// loop.
+TEST(AnimationTest, TicksOnlyWhenRequested) {
   auto component = Make<AnimationCounter>();
   auto screen = App::FixedSize(10, 1);
   Loop loop(&screen, component);
   loop.RunOnce();
 
-  // No event: the recurring AnimationTask is a no-op.
+  // No request: the recurring AnimationTask is a no-op.
   RunAnimationTask(loop);
   EXPECT_EQ(component->count, 0);
 
-  // A handled event grants exactly one animation tick.
+  // An event alone doesn't produce a tick.
   screen.PostEvent(Event::Custom);
   loop.RunOnce();
   RunAnimationTask(loop);
-  EXPECT_EQ(component->count, 1);
-  RunAnimationTask(loop);
-  EXPECT_EQ(component->count, 1);
+  EXPECT_EQ(component->count, 0);
 
-  // An internal terminal reply must not grant one.
-  screen.PostEvent(Event::CursorPosition("", 1, 1));
+  // A component requesting a frame gets exactly one tick.
+  screen.PostEvent(Event::Character('a'));
   loop.RunOnce();
   RunAnimationTask(loop);
   EXPECT_EQ(component->count, 1);
+  RunAnimationTask(loop);
+  EXPECT_EQ(component->count, 1);
 }
 
 }  // namespace ftxui

src/ftxui/component/app.cpp

@@ -918,13 +918,6 @@ void App::Internal::HandleTask(Component component, Task& task) {
 #endif
 
       frame_valid_ = false;
-
-      // Give animated components one tick in response to the event. This must
-      // stay below the early-returns above: requesting a frame for the
-      // terminal's replies to our own requests creates a redraw -> request ->
-      // reply -> redraw feedback loop.
-      // See https://github.com/ArthurSonzogni/FTXUI/issues/1302.
-      public_->RequestAnimationFrame();
       return;
     }