- UPDATE 2015-06-12: See bottom of post for footage of the bug described.
- UPDATE 2015-06-13: This “sudden inexplicable forward collision component” issue also happens when moving directly downwards onto Basic Cylinder, but not under any other circumstances on the Cylinder or the Cube (even when pressing downwards onto one of its edges). Also, added a list of things that Do Not Work at the end of the post.
- UPDATE 2015-06-21: Tried using different Normals that UE4 offers me. Same issues.
Hello everyone,
I am having an issue with collision in my UE4 project. I am using the Flying template and while I have added things to it, the general sweeping behaviour remains. I added in “strafing” (ie, moving laterally without rotating the ship) and I am testing collision by grinding against walls (perpendicularly) using this strafing. The strafing relies on Sweeps, much like the default “thrust” motion, and on collisions the ship’s Hit Normal redirects the plane (ie, it bounces off of walls) and player input is disabled momentarily (to prevent players from sticking themselves to solid walls). My “bounce” calculation is from this page, and uses the Hit Normal returned from Event Hits: c# - How to calculate bounce angle? - Stack Overflow I am printing Hit Normals on collision to the screen to help me debug.
On collisions with UE4 “default” objects (ie, left side of the screen → Basic → Cube or Cylinder), collision works perfectly. I can increase my speed, decrease my speed, whatever, and the bounces I get from the collision I have written is visually acceptable and results in a sensible Hit Normal. (I have Physics disabled, as is default.)
However, on collisions with BSPs, BSPs-turned-Static-Meshes, or imported Static Meshes (with UCXs or with in-engine-generated collision meshes), things get wacky. The issue seems to be specifically with what the engine determines to be the Hit Normal; it’s less precise than with the “default” objects, and is inconsistent enough that it will deliver a Hit Normal of 0.14 or higher in X (the player’s direction of travel), when the Default objects all play nice and give me 0.001X at most. (Again, the impacts should be perpendicular, with no Hit Normal in the direction of the player’s travel; 0.001X is acceptable and probably just float imprecision.)
I suspect that my issue lies somewhere in the collision settings for the non-default objects, but there are simply too many different variables that could potentially be interacting with one another for me to simply sort this out through trial and error. (That doesn’t mean that I haven’t tried, of course; I’m also here because the IRC channel has no idea, either.) Some things I’ve tried:
- Colliding with a BSP (first time I noticed this issue)
- Colliding with a BSP turned into a static mesh (same issue, even if I then removed the generated Collision and generated my own collisions; same issue even if I made the player object’s collision mesh more or less simple)
- Making my own UCX for imported Blender meshes (UCX is recognized but the collision still behaves in the same, wrong way as the previous two attempts)
- A myriad of object settings that either made the issue worse or had no effect on collision behaviour
I will record some .webms and post screenshots of my code/physics settings if this is not enough information. I will respond to all questions asking me whether or not I have tried some given solution yet, and will list my responses in the Question itself as I answer these questions, if possible. (I am working in Blueprints, but I am almost certain that the issue here is not with the code I have made, but with the settings I am using for the collision objects in question.)
Thank you very much for your time and thank you again if you have any help to offer.
- Object 1: Engine/BasicShapes/Cube, stretched on one axis and rotated slightly. No issue with collision. Note how x, the direction of travel, is not at all part of the Hit Normal.
- Object 2: Engine/BasicShapes/Cylinder, also stretched. No issue with collision.
- Object 3: An imported Blender Static Mesh. Note how the collision randomly decides to be over .5 in the X direction. This also happens with BSPs, Static Meshes made from BSPs, and with Blender-made Static Meshes with UE4-made collision boxes.
Things that do not work:
Changing collision settings on the custom mesh (both Enabled and Disabled do not change the collision behaviour):
- changing the material to DefaultPhysicalMaterial
- changing Simulation Generates Collision
- changing Generate Overlap Events
- changing CollisionPresets from BlockAll to BlockAllDynamic
- changing Use CCD
- changing Always create Physics State
- changing Multi Body Overlap
- changing Check Async Scene on Move
- changing Trace Complex on Move
- changing Can Ever Effect Navigation
- Flipping the player model’s collision mesh does not change the collision problem at all. Moving downward onto the Cylinder still functions in the same (wrong) way.
Changing settings on the player Mesh:
- Changing Enable Collision
- Changing Recompute Normals
- Changing Use Full Precision UVs
- Collision Complexity settings: Default, Use Simple Collision as Complex, Use Complex Collision as Simple
- Modifying the collision mesh (all settings result in the same “randomly described as a non-parallel collision” behaviour)
- This includes going as simple as a Box Collision and as complex as a multi-Hull collision
- Giving the Player Mesh a Physical Material
- Going to Static Mesh Settings, with a complex collision box, and going “Use Simple Collision as Complex” seems to reduce the frequency of these erroneous Hit Normals, but they still happen
Changing which Normal I use:
- Using Break Hit Result’s Impact Normal still occasionally results in these in-travel-direction Normal spikes
- as does Break Hit Result’s Normal
