Track IsEffectivelyVisible state

[jmacato]

Previously, IsEffectivelyVisible was being calculated each time it was called. This was problematic for a couple of reasons:

1. It traversed the tree each time it was called
2. There is no way to track changes to IsEffectivelyVisible

This PR changes IsEffectivelyVisible to be tracked like IsEffectivelyEnabled which fixes 1). It doesn't add a way to track IsEffectivelyVisible changes yet though so doesn't address 2).

Regarding 2), making a IsEffectivelyVisible a DirectProperty may be problematic for performance reasons as the change notifications need to be fired even if there are no listeners. A CLR event may be acceptable, but the main reason we need to track changes to this is internally for the animation system (PR to follow which hooks into this) so there are currently no plans to expose an API for detecting changes to this.

[avaloniaui-bot]

You can test this PR using the following package version. 11.1.999-cibuild0042968-beta. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[jp2masa]

Some method names seem to be wrong: UpdateIsEffectivelyEnabled, SyncIsEffectivelyEnabledFromParent, it should be Visible, not Enabled.

Also, I may be reading it wrong, but not sure if the logic always works, e.g. does adding this to the test work?

child2.IsVisible = false;
root.IsVisible = true;

Assert.False(child2.IsEffectivelyEnabled);

Finally, I think there's room for optimization in UpdateIsEffectivelyEnabled, so that it only needs to do the recursive call when child.IsVisible.

[jmacato]

@jp2masa thanks for the advise!

child2.IsVisible = false;
root.IsVisible = true;
Assert.False(child2.IsEffectivelyEnabled);

Good catch on this one! I'm adding this to the test now!

Finally, I think there's room for optimization in UpdateIsEffectivelyEnabled, so that it only needs to do the recursive call when child.IsVisible.

Makes sense

[avaloniaui-bot]

You can test this PR using the following package version. 11.1.999-cibuild0043002-beta. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[workgroupengineering]

We could simplify the code this way by avoiding loops.

        /// <summary>
        /// Gets a value indicating whether this control and all its parents are visible.
        /// </summary>
        public bool IsEffectivelyVisible => 
            IsVisible && (VisualParent?.IsEffectivelyVisible ?? true);

[jmacato]

@workgroupengineering we intend to provide internal change notifications when IEV changes, so we can't do what you suggested there unfortunately.

[grokys]

A few nits, but also this doesn't seem to handle correctly setting the IsEffectivelyVisible state when adding a grandchild. Here is a failing test:

        [Fact]
        public void Added_Grandchild_Has_Correct_IsEffectivelyVisible()
        {
            var child = new Decorator();
            var grandchild = new Decorator();
            var root = new TestRoot 
            { 
                IsVisible = false,
                Child = child
            };

            child.Child = grandchild;
            Assert.False(grandchild.IsEffectivelyVisible);
        }

[grokys]

The VisualExtensions_GetVisualsAt.Should_Find_Control test seems to be flaky: I've seen it occur on macOS and now the Linux CI builds, but it passes locally. Not sure if it's caused by this PR or not.