Account for inverted tangents on normal-mapped objects (bug #3733)

CHANGELOG.md

@@ -3,6 +3,7 @@
 
     Bug #2987: Editor: some chance and AI data fields can overflow
     Bug #3623: Fix HiDPI on Windows
+    Bug #3733: Normal maps are inverted on mirrored UVs
     Bug #4329: Removed birthsign abilities are restored after reloading the save
     Bug #4383: Bow model obscures crosshair when arrow is drawn
     Bug #4411: Reloading a saved game while falling prevents damage in some cases

files/shaders/objects_fragment.glsl

@@ -68,7 +68,7 @@ void main()
 
     vec3 normalizedNormal = normalize(passNormal);
     vec3 normalizedTangent = normalize(passTangent.xyz);
-    vec3 binormal = cross(normalizedTangent, normalizedNormal);
+    vec3 binormal = cross(normalizedTangent, normalizedNormal) * passTangent.w;
     mat3 tbnTranspose = mat3(normalizedTangent, binormal, normalizedNormal);
 
     vec3 viewNormal = gl_NormalMatrix * normalize(tbnTranspose * (normalTex.xyz * 2.0 - 1.0));