BUG: Impact normal for mobile and stand alone game reversed

I have found a bug in version 4.2. In the physics on collision hit the impact normal is not consistent from the mobile previewer to the play in new window . When I correct it for mobile previewer the play in new window breaks and vice versa. This is very frustrating when trying to play test. And when I finally build to a mobile device it sometimes breaks. Its very inconsistent on the mobile device though. Hard to predict.

This bug only started to happen when version 4.2 was released.

Hi ,

I have been assigned to look into this potential bug for you. Can you show me a copy of the blueprint you are working with so I can try to reproduce this on my end? Thank you!

Sure no problem… But can I request that we do this privately? Its for a project that I intend to release when it is ready and I don’t want anybody else seeing it.

Hi ,

Can you give me repro steps to recreate the bug you are describing? I certainly don’t want you to feel that your work must be shared, so if you can give me accurate steps to recreate the bug I can try to produce it on my end.

I have tried recreating my situation and it seems more complex then I originally thought. I have been debugging my blueprints structure and I have deduced that it has something to do with spawning custom blueprints In a game manager blueprint. Or how many items I spawn with the game manager. It seems to become a problem after about 3 items spawned. I will try and send you a exact plan soon.

Alright I have created a project that sometimes recreates the problem. it seems like it is not only spawning objects with a blueprint but any kind of change. I have experienced the bug when changing objects in the scene making changes to the blueprint and changing the player mode.

Below is a link to the project…

BUG_ImpactNormal - Project

In this project there is a moving object that collides with another object. When the object collides the impact normal will be drawn as a red line.

Recreating the problem takes persistence. I’m not sure exactly what triggers it. But if I find it I will let you know.

I’m sorry in advanced this bug is hard to recreate. But I would appreciate if you could help me out.

Hi ,

Thus far I have been unable to reproduce this effect. What is the specific action that is not working correctly. There is a possibility I have overlooked it, but currently I do not see any discernible difference or break between the two preview options.

It is actually a very hard bug to reproduce I have experienced is in so many ways. Spawning one is just one of them. Below is another containing two projects… one is broken and the other is fixed.

BUG_ImpactNormal_2 - Fixed and Broken Projects

I really can’t pinpoint the reason why it breaks. But it usually has to do with some kind of change, This could be a blueprint change, scene change, or even player change. But if I find a consistent reason why I will let you know.

I am not sure what I am looking for. The only thing I’ve seen so far is that the debug line faces a different direction between the two examples you have sent me, is this what you are looking for? If so I can try to see why this is happening and if it is a bug place a bug report for it. Otherwise I may need more information to fully understand what I should be looking for and what you are seeing.

Yes I am looking at the debug line. It is drawing the normal impulse of the collision hit. The two examples should be exactly the same but they are not. I’m sorry for the confusion.

Hi ,

It looks like the problem is with the specific setup. How do you want the debug lines drawn? For instance, if you are looking for a line to show you what actor hit the box, you can do a break hit result at impact location and lead it to the location of the other actor. See the image below.

Oh nice!!! This is supper useful. So Normal impulse is “The force that the Actors collided with”. Not the impact normal. Cool Ill try using this instead.

I’m happy to help. I will mark this question as answered for tracking purposes. Have a great day!

Yeah worked like a charm :slight_smile: Thank you so much.