ATTENUATION_LogReverse implementation is reversed

Development Rendering
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1

The implementation is backwards, as you get farther from the source the source gets louder and as you get closer it goes to 0.

This is the original implementation:

case ATTENUATION_LogReverse:
return FMath::Max( 0.5f * FMath::Loge( 1.0f / ( 1.0f - ( Distance / Falloff ) ) ), 0.0f );

Assume Distance = 1000 and Falloff = 20000 then this will evaluate to 0.5 * log(1 / (1 - 0.05)) = 0.5 * log(1.05) = 0.01
Assume Distance = 10000 and Falloff = 20000 then this will evaluate to 0.5 * log(1 / (1 - 0.5)) = 0.5 * log(2.00) = 0.15
Assume Distance = 19000 and Falloff = 20000 then this will evaluate to 0.5 * log(1 / (1 - 0.95)) = 0.5 * log(20) = 0.65

As you can see here, this is not the same as it is here:
Wolfram Alpha plot of the above function:
Wolfram Alpha
UE4 Documentation:
Epic/UE4 Documentation

I think this was the intended implementation: 0.5*log(1-x) + 1

case ATTENUATION_LogReverse:
return FMath::Min( 0.5f * FMath::Loge( 1.0f - ( Distance / Falloff ) ) + 1.0f, 1.0f );

Assume Distance = 1000 and Falloff = 20000 then this will evaluate to 0.5 * log(1 - 0.05) + 1 = 0.5 * log(0.95) + 1 = 0.99
Assume Distance = 10000 and Falloff = 20000 then this will evaluate to 0.5 * log(1 - 0.5) + 1 = 0.5 * log(0.5) + 1 = 0.85
Assume Distance = 19000 and Falloff = 20000 then this will evaluate to 0.5 * log(1 - 0.95) + 1 = 0.5 * log(0.05) + 1 = 0.35

This is much better: Corrected version on Wolfram Alpha

2

I had to retype that twice and submit it 3 times… That sucked that it never saved its state in Chrome. It is best from now on to write these outside of the browser and then copy them over.

3

It seems that I cannot add another pull request as I currently have one pending. I tried to create another branch with only this change in it but I’m still seeing all of the previous commits. Do I need to fork another repo or do I wait or what? I would prefer to just submit a patch file if possible.
Thanks ,

4

Hi ,

Thank you for bringing this to our attention. I was able to verify that it does look like we mixed this one up. I can submit a ticket to report this, but I wanted to check first to see if you preferred to submit a pull request on GitHub.

5

You should be able to create multiple pull requests by creating a separate branch for each one. You would create a branch from the Master branch and make the changes for your pull request, then repeat that process for your next pull request. Once a pull request is closed, you can delete the branch for that pull request.

6

Thanks , I messed up earlier by committing to my master on my fork. So it seems that I may have to fork once again. It is a learning process that I guess everyone has to go through once. I just wish it was a higher priority for me to take the time to learn it properly, but I have more important tasks to perform. Thanks for your help!

7

Submitted as new pull request #748