[Impeller] Backdrop filters sometimes escape clips when drawn after platform views.

[bdero]

Adding clipped backdrop blurs to the Wondrous tab buttons reveals buggy behavior, including a clip escape.

bdfbug.mov

Wondrous diff:

diff --git a/lib/ui/screens/wonder_details/wonder_details_tab_menu.dart b/lib/ui/screens/wonder_details/wonder_details_tab_menu.dart
index d4ab611..3f41e85 100644
--- a/lib/ui/screens/wonder_details/wonder_details_tab_menu.dart
+++ b/lib/ui/screens/wonder_details/wonder_details_tab_menu.dart
@@ -1,3 +1,5 @@
+import 'dart:ui';
+
 import 'package:wonders/common_libs.dart';

 class WonderDetailsTabMenu extends StatelessWidget {
@@ -220,16 +222,23 @@ class _TabBtn extends StatelessWidget {
         selected: selected,
         label: tabLabel,
         child: ExcludeSemantics(
-          child: AppBtn.basic(
+          child: ElevatedButton(
             onPressed: () => onTap(index),
-            semanticLabel: label,
-            minimumSize: _isVertical ? Size(crossBtnSize, mainAxisSize) : Size(mainAxisSize, crossBtnSize),
-            // Image icon
-            child: Image.asset(
-              iconImgPath,
-              height: iconSize,
-              width: iconSize,
-              color: selected ? null : color,
+            clipBehavior: Clip.hardEdge,
+            child: BackdropFilter(
+              filter: ImageFilter.blur(sigmaX: 20, sigmaY: 20),
+              child: AppBtn.basic(
+                onPressed: () => onTap(index),
+                semanticLabel: label,
+                minimumSize: _isVertical ? Size(crossBtnSize, mainAxisSize) : Size(mainAxisSize, crossBtnSize),
+                // Image icon
+                child: Image.asset(
+                  iconImgPath,
+                  height: iconSize,
+                  width: iconSize,
+                  color: selected ? null : color,
+                ),
+              ),
             ),
           ),
         ),

[bdero]

@jonahwilliams found this to be a regression:

can repro on ToT but not a week ago so its probably something I changed when I did the switch to exp canvas that didn't get reverted

[bdero]

I bisected to this engine roll.

Reverting flutter/engine#54484 at ToT fixes the regression.
Revert: flutter/engine#54661

[flar]

Which hardware is this running on?

I cannot reproduce this on my iPhone 11. I poked around with various framework commits and engine commits before/after the 2 commits mentioned above and I never saw the BDF escape the buttons.

[bdero]

iPhone 12 mini.
Wondrous base commit is d5971af3c8ea0db5519236f656459e4c4bea0483.

This was my framework bisect:

73c9e4e57893c4a0156de3e30a406604fc74d209: Broken 
af815f0d9bd1241cb816c6240de40b30c8706a32
1633c47dda49e5470989d0518e65fe113adbfcda
ce63c029c5dda18734a5f148796915ab84bea3ef
70460854d1831990b5784c91f0982a95012f9722
ea87865364c60d482fb53f064f07c6ef172b214a
99f00a1309238338ef5a999fd86f85e200bbd044
108a355453c2ccb569fee1c1d02aa629fb5b3ecc
b4b8f07124da55f9ecda0650fa0442171b7bb3c6
4b60bb530f10ddd062368d8deed1ec6344775d3b
fafe3df40589a89fd89beb0a4d8bed948e218884
bd083887a475288f4f6ecd7730fadb509b4562ea
6289944ed68550439a58636fdc945d1cf717cd27
2a4e004bc0b6c2f81e9c625ddb66bc85883bfb89
f697d610259b2584060e660397100268a66110a7
5eca44a1c4f67ede29070eea2fdfedcfe166f834
51c640297f08cafaf5267e0a844119b175333531
ed40925bb1b7036422ee7e7d4dc1aaf68004b8b3
b5847d364a26d727af58ab885a6123e0e5304b2b
6ef1156f7e7b8f359285dda5eb7d1863cbd680d7
0e6c1d1015cec106a427bc7cf1a0d73a40d79315
354902f7ca9e24c8b6cd7a58170e46b6b4a12e4d: Broken
92c98e80ff3974a95c0cec44637e86fe1515f196: Broken ***
593729165d14f282e51bec381939c4b017bc43f4: Working
fb35123b38630d1427c2aada8e50b55f309cd4f6
85b3d97673360f4b0ecbee384074795b4dac8266
87abed2b23ea3c71855eafb3e616da8121a6ea27: Working
b32eaf6f751e0dae0f0bd23562abb356740c8c0d
5f99d5782a2cf3c9e333dabbf53144506a2dc48c
aba00947b6bf954e64258c4e8bdfaf4795f3c9fa
cc13cd1f11916857ec5adbe43ce4e747fb07a5d5
62003185862e05e80c48b29be552e5195d740c15
9feae10665b8669233c14c55279ec26f134a1dea: Working
f2ba2049174d28b08d7466946eb4362bbec6b821
bcbe3f81c92979fb1b941666dc924291dc5a5dac
e814afaa08818a34e49d01173181a9e6834574e1
2afc452d3a8eec9756d5936674d1269258299c4e
907df025e0b75666adacf69ee9f88acd8ed26fcf
289ba8dc25f6b34738ee8e62a6c53db83c7b45e7
e06738bba4fd5d76d93c274d6fc23fd1d1ce9c46
b6ef354cde766b2ff8bf084840028b89757a2e69
cc5d08bc793f54aad927e8369d373448b42b4329
fa1216761dcfac30dbdba3c4a68b67572311273f
97218291a05865581fc5beed6455624f5b67a792
5a04b4dda93d495de4cc0a8bff0a342b68bf663d: Working

[flar]

Notice the different test here where we determine if we need to emit a transform/clip op:
https://github.com/flutter/engine/blob/db034a514caf851cfe063a77f3b27a797316c740/display_list/display_list.cc#L145

And here where we determine whether we need a save/restore pair:
https://github.com/flutter/engine/blob/db034a514caf851cfe063a77f3b27a797316c740/display_list/display_list.cc#L159

They should be using the same test (save/saveLayer have more work to do so they need their own case statement, but their inclusion test should be identical).

Making the save/saveLayer condition the same as the transform/clip test fixes it. Time to make a unit test and submit a reland...