Baseline SnapLines do not appear in DesignSurface

[jholcmanchyron]

.NET version

9.0.4

Did it work in .NET Framework?

Yes

Did it work in any of the earlier releases of .NET Core or .NET 5+?

8.0.15

Issue description

After updating the runtime version from net8 to net9, the Baseline snap line (the purple one in the attached gif) stops appearing in the designer surface of a winforms app.

This is true for all controls I tried - Label, Button, CheckBox, DateTimePicker. I assume it is a general issue, not an issue with a specific control(s).

The other snap lines (Top, Bottom,...) are still working.

net8:

net9:

Steps to reproduce

Snaplinetest.zip

1. Using the attached solution.
2. Run SnaplinetestNet8
   a. The console output contains Baseline snap lines for both labels.
   b. The Baseline snap line (purple) appears when dragging one of the labels next to the other.
3. Run SnaplinetestNet9
   a. The console output still contains Baseline snap lines for both labels, as it should...
   b. ... but the snap line does not appear when dragging the label.

[merriemcgaw]

@jholcmanchyron we appreciate the minimum repro you provided, that should be helpful! I am curious as to your specific use case for the design surface. Are you creating a custom designer? Does this run in VS or standalone? This is something we could likely address in .NET 10, but to service back to 9 we'd need to know more about the customer impact.

[jholcmanchyron]

@merriemcgaw We have a custom designer embedded in our application that allows our users to build custom panels containing a set of supported Winforms controls. They use the DesignSurface to drag these controls around, resize them and align them to their liking. Once they have that, they can "bind" those controls to certain functionality of the application (Button Clicks to execute some action, TextBox Text to appear somewhere, etc.). The final panel is then rendered in another part of the application to actually run the use case the user needs. I hope that clarifies it a bit, let me know if I can provide more to speed things up.

[merriemcgaw]

@LeafShi1 can you help us find where this regressed from 8 to 9 (and what is happening in 10)?