Sky Ambient color no longer blends during day cycle

[Hecklezz]

Environment

Second Life Release 7.1.14.15192634334 (64bit)

Rest of Environment-

Release Notes

You are at 62.2, 104.0, 39.3 in LunaCy Retreat located at simhost-05fb7c2ef05c6ba6c.agni
SLURL: http://maps.secondlife.com/secondlife/LunaCy%20Retreat/62/104/39
(global coordinates 168,766.0, 306,280.0, 39.3)
Second Life RC LeTigre 2025-04-24.14648572313
Release Notes

CPU: Intel(R) Core(TM) i7-9700K CPU @ 3.60GHz (3600 MHz)
Memory: 16302 MB
OS Version: Microsoft Windows 10 64-bit (Build 19045.5854)
Graphics Card Vendor: NVIDIA Corporation
Graphics Card: NVIDIA GeForce RTX 2080/PCIe/SSE2

Windows Graphics Driver Version: 32.0.15.7652
OpenGL Version: 4.6.0 NVIDIA 576.52

Window size: 1710x999
Font Size Adjustment: 96pt
UI Scaling: 1
Draw distance: 128m
Bandwidth: 3000kbit/s
LOD factor: 1.375
Render quality: 3
Texture memory: 8192MB
Disk cache: Max size 1638.4 MB (81.6% used)

J2C Decoder Version: KDU v7.10.4
Audio Driver Version: OpenAL, version 1.1 ALSOFT 1.24.2 / OpenAL Community / OpenAL Soft: OpenAL Soft
Dullahan: 1.14.0.202408091639
CEF: 118.4.1+g3dd6078+chromium-118.0.5993.54
Chromium: 118.0.5993.54
LibVLC Version: 3.0.21
Voice Server Version: Vivox 4.10.0000.32327.5fc3fe7c.5942f08

Packets Lost: 136/9,884 (1.4%)
May 28 2025 12:49:15

Description

PR with potential fix-
#4186

At some point around 7.1.11 (FS 7.1.11 doesn't have the issue but SLViewer 7.1.11 might have), the ambient colour of skies no longer blends during the day cycle and instead only immediately change at each key interval. In FS 7.1.11 and earlier, it used to blend correctly.
If a region has aggressive ambient colour changes, this creates a problem where it will very obviously and suddenly switch instead of nicely blend. (See my second video below, it occurs at 55seconds)

The culprit commit was this one where the blend function was optimised, however it appears to have introduced this side effect. Reverting the change to just the blend function brings back the correct functionality-
dfff269

Video of the issue in the Day Cycle settings-

SecondLifeViewer_2025-05-29_05-48-34.mp4

Video of issue during actual gameplay with the environment applied (changes at 55seconds)-

SecondLifeViewer_2025-05-29_06-18-17.mp4

Reproduction steps

1. Create a new day cycle
2. Ensure two different intervals have different ambient colours
3. Play the day cycle and observe ambient colour not blending

[AtlasLinden]

Passed QA.
Verified on Second Life Project 7.1.14.15976006598 (GLTF Mesh Import) on Win11/MacOS