Godot 4.4 3D physics interpolation causes gridmap flickering

[aldocd4]

Tested versions

Godot 4.4 beta 1 mono version
Godot 4.4 beta 3 mono version
Godot 4.4 mono version
Godot 4.4 RC1 mono version

System information

Godot v4.4.1.rc1.mono - Windows 11 (build 22631) - Multi-window, 1 monitor - Vulkan (Forward+) - dedicated Radeon RX Vega (Advanced Micro Devices, Inc.; 31.0.21921.1000) - AMD Ryzen 9 3900X 12-Core Processor (24 threads)

Issue description

I'm using GridMap in my 3D isometric turn-based game for some part of the gameplay, like for example the fights. I display a basic grid map with cells and I use the GridMap function set_cell_type to change cell color/effect during the fight. When 3D physics interpolation is disabled, everything works correctly.

When I enable 3D physics interpolation, i have some weird issues:

Note: this bug only happen when grid map is not positioned at 0, 0, 0. When its at the center of the map, it works. But my fight maps in my game are not at 0, 0, 0 unfortunately. That was working well with Godot 4.3 and with Godot 4.4 when 3D physics interpolation is disabled.

Steps to reproduce

• Open the project
• Run main scene
• Move mouse around white cells, they are supposed to become red using SetCellType
• You should see weird flickering

Then:

• Disable 3D physics interpolation
• Redo steps above
• No flickering

Minimal reproduction project (MRP)

DebugGridMap.zip

[akien-mga]

CC @lawnjelly @rburing

[lawnjelly]

MRPs should be in gdscript rather than C# unless they are C# specific - I can't run your MRP.

But it's likely you just need to call reset_physics_interpolation() on the gridmap.

https://docs.godotengine.org/en/stable/tutorials/physics/interpolation/using_physics_interpolation.html#call-reset-physics-interpolation-when-teleporting-objects

You need to call this on teleporting, but in your particular case of GridMap you may also need to call it after editing the gridmap to ensure the xforms are up to date in the server, I can't tell which is your problem as I say I can't run the MRP.

UPDATE:
Actually on looking I hadn't changed anything in gridmap for FTI (I was getting confused with tilemap), and it can use multimesh under the hood so there may be some small fixes to do in terms of responding to NOTIFICATION_RESET_PHYSICS_INTERPOLATION or setting these to be non-interpolated in the server.

UPDATE2:
As the multimeshes are not handled specially in gridmap, they look like they default to non-interpolated in the server, so there may be no problem there.

So likely the problem you are seeing are regular instances in gridmap, these should work fine as is after #104269 (as there is no longer interpolation in the server).

But yes if you can create MRP in gdscript that would be super helpful so I can check this is fixed.

[aldocd4]

Sorry for the delay. Here is the GDScript version:

DebugGridMapGD.zip

[lawnjelly]

Yes, I can confirm this is fixed by #104269 .

[aldocd4]

Do you know a way to fix it on my side before 4.5 is out? I tried turning off physics interpolation for the grid but it doesn't seems to fix it. I also tried the reset_physics_interpolation call but I have the same issue.

Or maybe I need to completely disable 3D interpolation on 4.4 for this exact scenario and wait for 4.5 before re-enabling it?

Thanks

[lawnjelly]

Do you know a way to fix it on my side before 4.5 is out? I tried turning off physics interpolation for the grid but it doesn't seems to fix it. I also tried the reset_physics_interpolation call but I have the same issue.

Or maybe I need to completely disable 3D interpolation on 4.4 for this exact scenario and wait for 4.5 before re-enabling it?

I'm not super familiar with GridMap and especially in 4.x. I had a little look and tried a few things like visibility and translate but no joy so far. It is possible there's something that would do the trick but I haven't time to look this evening.

I don't know the 4.4 release schedule but I would push for the new 3D FTI to be included asap as there's no point to continue working on the broken server-based version (imo), and it fixes a large number of bugs / design flaws. It's possible it will be in 4.4.1 or 4.4.2, that depends on reviewers and production team.

Until then I would disable it and be patient (or test it on other parts of your game / app). To some extent physics interpolation is experimental as it hasn't had a lot of testing in the wild, so it shouldn't be expected to be "production ready" from day 1, especially the more esoteric cases like this.

The other option is for you to simply download the artifact build for #104269 and work with that in the meantime.
https://docs.godotengine.org/en/stable/contributing/workflow/testing_pull_requests.html