Mirror: fix: ambient music fade in (#25874) (#137)

## Mirror of PR #25969: [fix: ambient music fade in
(#25874)](space-wizards/space-station-14#25969)
from <img src="https://avatars.githubusercontent.com/u/10567778?v=4"
alt="space-wizards" width="22"/>
[space-wizards](https://github.com/space-wizards)/[space-station-14](https://github.com/space-wizards/space-station-14)

###### `e47f84568eec53efd66fca6e79d8c594a508cf3c`

PR opened by <img
src="https://avatars.githubusercontent.com/u/82627200?v=4"
width="16"/><a href="https://github.com/Kokoc9n"> Kokoc9n</a> at
2024-03-10 16:26:28 UTC
PR merged by <img
src="https://avatars.githubusercontent.com/u/19864447?v=4"
width="16"/><a href="https://github.com/web-flow"> web-flow</a> at
2024-03-10 17:08:05 UTC

---

PR changed 1 files with 3 additions and 3 deletions.

The PR had the following labels:


---

<details open="true"><summary><h1>Original Body</h1></summary>

> <!-- Please read these guidelines before opening your PR:
https://docs.spacestation14.io/en/getting-started/pr-guideline -->
> <!-- The text between the arrows are comments - they will not be
visible on your PR. -->
> 
> ## About the PR
> <!-- What did you change in this PR? -->
> Ambient music  volume now set to ambient music volume slider.
> ## Why / Balance
> <!-- Why was it changed? Link any discussions or issues here. Please
discuss how this would affect game balance. -->
> Space ambience tracks being super loud #25874.
> ## Technical details
> <!-- If this is a code change, summarize at high level how your new
code works. This makes it easier to review. -->
> FadeIn and UpdateFades now get correct values instead of blasting
music on maximum volume.
> ## Media
> <!-- 
> PRs which make ingame changes (adding clothing, items, new features,
etc) are required to have media attached that showcase the changes.
> Small fixes/refactors are exempt.
> Any media may be used in SS14 progress reports, with clear credit
given.
> 
> If you're unsure whether your PR will require media, ask a maintainer.
> 
> Check the box below to confirm that you have in fact seen this (put an
X in the brackets, like [X]):
> -->
> 
> - [X] I have added screenshots/videos to this PR showcasing its
changes ingame, **or** this PR does not require an ingame showcase
> Before:
>
https://github.com/space-wizards/space-station-14/assets/82627200/8a2ab0c5-d3ae-4cb5-85d8-97703ecdb52a
> After:
>
https://github.com/space-wizards/space-station-14/assets/82627200/2b364261-b267-4bad-ab3e-10d389df6eb4


</details>

Co-authored-by: Gregg <82627200+Kokoc9n@users.noreply.github.com>

Content.Client/Audio/ContentAudioSystem.cs

@@ -107,7 +107,7 @@ public void FadeIn(EntityUid? stream, AudioComponent? component = null, float du
 
         _fadingOut.Remove(stream.Value);
         var curVolume = component.Volume;
-        var change = (curVolume - MinVolume) / duration;
+        var change = (MinVolume - curVolume) / duration;
         _fadingIn.Add(stream.Value, (change, component.Volume));
         component.Volume = MinVolume;
     }
@@ -151,8 +151,8 @@ private void UpdateFades(float frameTime)
                 continue;
             }
 
-            var volume = component.Volume + change * frameTime;
-            volume = MathF.Max(target, volume);
+            var volume = component.Volume - change * frameTime;
+            volume = MathF.Min(target, volume);
             _audio.SetVolume(stream, volume, component);
 
             if (component.Volume.Equals(target))