Summary

Negative repeats on a normal map inverts how light hits it.

Steps to reproduce

Just set the normal map to a texture to a negative value on the repeats and shine some light on it. The texture on the picture is at -10 horizontal scale.

Environment

Alchemy 6.3.4 (124) (64 bit) Nov 13 2019 00:11:46 (Alchemy Project FluffyFox) (B)
Release Notes

You are at 124.0, 150.8, 22.7 in Puff located at sim10614.agni.lindenlab.com (216.82.52.176:13010)
SLURL: http://maps.secondlife.com/secondlife/Puff/124/151/23
(global coordinates 183676.0, 305047.0, 22.7)
Second Life Server 2019-11-01T18:02:37.532376
Release Notes

CPU: Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz (3408 MHz)
Memory: 16349 MB
OS Version: Microsoft Windows 10 64-bit (Build 18362)
Graphics Card Vendor: NVIDIA Corporation
Graphics Card: GeForce GTX 1070/PCIe/SSE2

Windows Graphics Driver Version: 26.21.14.3064
OpenGL Version: 4.6.0 NVIDIA 430.64

Window size: 1920x1017
Font Size Adjustment: 96pt
UI Scaling: 1
Draw distance: 256m
Bandwidth: 1500kbit/s
LOD factor: 2
Render quality: 5
Advanced Lighting Model: Enabled
Texture memory: 2048MB
VFS (cache) creation time: August 07 2019 12:09:59

RestrainedLove API: RLV v3.2.1 / RLVa v2.2.2.124
libcurl Version: libcurl/7.66.0 OpenSSL/1.1.1d zlib/1.2.11 WinIDN nghttp2/1.39.2
J2C Decoder Version: OpenJPEG: 1.5.1, Runtime: 1.5.1
Audio Driver Version: FMOD Studio 2.00.03
Font Decoder Version: FreeType 2.10.1
Dullahan: 1.3.201910090921 / CEF: 77.1.7+gc7dbc2f+chromium-77.0.3865.90 / Chromium: 77.0.3865.90
LibVLC Version: 2.2.8
Voice Server Version: Vivox 4.10.0000.32327

Built with MSVC version 192328106
Packets Lost: 106/92086 (0.0%)
November 18 2019 15:43:41

Relevant logs and/or screenshots