From 4f8ddffdf7723eea4651aa002e61e4de5578b0b5 Mon Sep 17 00:00:00 2001
From: Par Winzell <zell@fb.com>
Date: Mon, 6 Nov 2017 14:48:16 -0800
Subject: [PATCH] Better calculation of glTF opacity.

At the glTF level, transparency is a scalar; we just throw away any
color information in FBX TransparentColor. We still need to calculate
our total opacity from it, however. This is the right formula, which
additionally matches the deprecated (but still populated, by the Maya
exporter) 'Opacity' property.
---
 src/Fbx2Raw.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/Fbx2Raw.cpp b/src/Fbx2Raw.cpp
index fb33485..5593829 100644
--- a/src/Fbx2Raw.cpp
+++ b/src/Fbx2Raw.cpp
@@ -168,8 +168,8 @@ public:
         if (facTex) {
             fmt::printf("Warning: Mat [%s]: Can't handle texture for %s; discarding.\n", name, FbxSurfaceMaterial::sTransparencyFactor);
         }
-        // FBX color is RGB, so we supply the A channel from TransparencyFactor
-        res.colDiffuse[3] = 1.0 - transparency[3];
+        // FBX color is RGB, so we calculate the A channel as the average of the FBX transparency color vector
+        res.colDiffuse[3] = 1.0 - (transparency[0] + transparency[1] + transparency[2])/3.0;
 
         return res;
     }