From 0dd80595dbc0a31079997f2e71c53ce6ec9a84da Mon Sep 17 00:00:00 2001
From: Jonathan Stone <jstone@lucasfilm.com>
Date: Thu, 28 Dec 2023 16:55:18 -0800
Subject: [PATCH] Fix off-by-one error

---
 libraries/pbrlib/genglsl/lib/mx_microfacet_specular.glsl | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libraries/pbrlib/genglsl/lib/mx_microfacet_specular.glsl b/libraries/pbrlib/genglsl/lib/mx_microfacet_specular.glsl
index 62b18310e6..85430c00ca 100644
--- a/libraries/pbrlib/genglsl/lib/mx_microfacet_specular.glsl
+++ b/libraries/pbrlib/genglsl/lib/mx_microfacet_specular.glsl
@@ -608,12 +608,12 @@ float mx_latlong_alpha_to_lod(float alpha)
 {
     // Return the mip level associated with the given alpha in a prefiltered environment.
     float lodBias = (alpha < 0.25) ? sqrt(alpha) : 0.5 * alpha + 0.375;
-    return lodBias * float($envRadianceMips);
+    return lodBias * float($envRadianceMips - 1);
 }
 
 float mx_latlong_lod_to_alpha(float lod)
 {
     // Return the alpha associated with the given mip level in a prefiltered environment.
-    float lodBias = lod / float($envRadianceMips);
+    float lodBias = lod / float($envRadianceMips - 1);
     return (lodBias < 0.5) ? mx_square(lodBias) : 2.0 * (lodBias - 0.375);
 }