(Case 970882) Editor gets slow when using UnityEditor.IMGUI.Controls

The namespace UnityEditor.IMGUI.Controls provides a TreeView Control. Using this TreeView makes Unity slower over time. Or at least I noticed it when I was using the TreeView.

In the provided test project, the TreeView contains 10000 items. Moving the editor window where the TreeView is rendered into, is fast and responsive first. However, scrolling the TreeView adds a persistent performance penalty to the window, where persistent means to get rid of the performance issue, I need to close the window. The more you scroll, the slower it gets.

I recorded a video that shows in the Profiler that it gets slower over time. The interesting bit is that it does not seem the TreeView itself which is slow, but "GUI.ProcessEvents".

Reproduce

• Open user attached project
• Open Mainmenu > BugReport > Open TestCode window
• Move the window around and notice it's fast
• Scroll to the bottom of the TreeView and then to the top again, do this 10 times.
• Move the window around

Observe that moving the window is very laggy. Scrolling the TreeView is also not as fast as it was at the beginning.

Expected
The editor should not get slower after using the TreeView Control.

 

It's been added to the public Issue Tracker:
https://issuetracker.unity3d.com/is...vided-from-unityeditor-dot-imgui-dot-controls

 

Good news as we found a fix for this issue and it will be available in RC1. Thanks for your help identifying the issue!

 

That's awesome, great job!