Developer Notes

Not much interest and the fix would be too involved to be done any time soon.

Description

Weird behavior occurs when toggling Simulate Physics on physics actors by input instead of on BeginPlay. Multiple odd behaviors are present such as touching physics actors ignoring collision.

Test project: [Link Removed]

Steps to Reproduce

REPRO STEPS USING QAGAME CONTENT:

  1. Launch UE4Editor.exe QAGame.
  2. Open the level TM-Collision.
  3. Simulate in viewport.

RESULT:

With the "Box Has Collision Enabled" and the "Mesh Has Collision Enabled" examples, the actors that are either overlapping or on top of each other will pass through each other. The "Both Have Collision Enabled" example will behave correctly.

ORIGINAL REPRO:

1. Download the project linked in the description
2. Unzip the project and open the .uproject file
3. Press play and press Tab (toggles simulate physics)
Result: The three sets of boxes react in unexpected ways
Expected: The Overlapping boxes for all three sets should react as the one on the right does, with it being shot out. The touching boxes should stay on top of each other without ignoring collision.

This can be tested further by pressing Tab again twice and seeing the boxes with the gap, that are now touching, will mimic the boxes that were originally touching.

Have Comments or More Details?

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Won't Fix
ComponentUE - Simulation - Physics
Affects Versions4.9.1
CreatedSep 21, 2015
ResolvedJan 20, 2016
UpdatedJul 14, 2021