SL-11055 Add back pre-EEP fog burnthrough for fullbrights

1 files changed, 8 insertions, 1 deletions

diff --git a/indra/newview/app_settings/shaders/class2/windlight/transportF.glsl b/indra/newview/app_settings/shaders/class2/windlight/transportF.glsl
index d2d839ed05..a06f4f22ad 100644
--- a/indra/newview/app_settings/shaders/class2/windlight/transportF.glsl
+++ b/indra/newview/app_settings/shaders/class2/windlight/transportF.glsl
@@ -51,7 +51,14 @@ vec3 atmosTransport(vec3 light)
 vec3 fullbrightAtmosTransport(vec3 light)
 {
     float brightness = dot(light.rgb * 0.5, vec3(0.3333)) + 0.1;
-    return atmosTransportFrag(light * 0.5, getAdditiveColor() * brightness, getAtmosAttenuation());
+    vec3 attenColor = atmosTransportFrag(light * 0.5, getAdditiveColor() * brightness, getAtmosAttenuation());
+
+    // attenColor is an accurate fog-attenuated result for any brightness
+    // But, the pre-EEP shader included a brightness-indexed lerp to a non-attenuated version
+    // of the color - effectively a fog 'burn-through' for very bright pixels. To more closely
+    // match the pre-EEP behavior, we'll also lerp to the pre-EEP color, based on overall brightness
+    float preEepBright = dot(light.rgb, vec3(0.3333));
+    retun mix(attenColor, (light.rgb + getAdditiveColor().rgb) * (2.0 - preEepBright), preEepBright * preEepBright);
 }
 
 vec3 fullbrightShinyAtmosTransport(vec3 light)