From 01ad20f8a3561a04e760164951c0e784a85bd849 Mon Sep 17 00:00:00 2001
From: Kamil Jarosz <kjarosh256@gmail.com>
Date: Sun, 7 Jul 2024 21:41:49 +0200
Subject: [PATCH] core: Hide focus highlight on invalid and empty bounds

---
 core/src/focus_tracker.rs  | 22 ++++++++++++++++++++++
 swf/src/types/rectangle.rs |  5 +++++
 2 files changed, 27 insertions(+)

diff --git a/core/src/focus_tracker.rs b/core/src/focus_tracker.rs
index e0d7f504e..c18868d47 100644
--- a/core/src/focus_tracker.rs
+++ b/core/src/focus_tracker.rs
@@ -241,6 +241,28 @@ impl<'gc> FocusTracker<'gc> {
             return Highlight::ActiveHidden;
         }
 
+        // KJ: Flash Player has a fairly complicated, implementation-dependent behavior
+        // related to degenerate bounds and bounds that change after being highlighted.
+        // It seems that the highlight is hidden when there's nothing to be rendered:
+        //   1. For a clip with untouched graphics, the highlight is hidden.
+        //   2. For a clip with moveTo(0,0) lineTo(0,0), the highlight is not hidden.
+        // Sometimes highlight is not updated after highlight bounds change,
+        // but this behavior is rare and inconsistent, it even differs depending on
+        // when the update happens.
+        //
+        // However, the most common case of depending on the behavior above is when
+        // the SWF creates a movie clip, focuses it, and then adds some content to it.
+        // In that case FP will not render the highlight (even if in theory it should).
+        // The following condition covers this case, but:
+        //   1. In some rare cases, it will hide the highlight when it shouldn't
+        //      (e.g. non-empty graphics degenerated into a point).
+        //   2. It does not take into account that sometimes FP does not update highlight bounds.
+        // However, I've never seen these cases in real SWFs, only during testing.
+        let bounds = focus.highlight_bounds();
+        if !bounds.is_valid() || bounds.is_point() {
+            return Highlight::ActiveHidden;
+        }
+
         Highlight::ActiveVisible
     }
 
diff --git a/swf/src/types/rectangle.rs b/swf/src/types/rectangle.rs
index f0b353939..f41db10b9 100644
--- a/swf/src/types/rectangle.rs
+++ b/swf/src/types/rectangle.rs
@@ -141,6 +141,11 @@ impl<T: Coordinate> Rectangle<T> {
         }
         self
     }
+
+    #[must_use]
+    pub fn is_point(&self) -> bool {
+        self.x_min == self.x_max && self.y_min == self.y_max
+    }
 }
 
 impl<T: Coordinate> Default for Rectangle<T> {