#3219 Revert default exposure thresholds to DeltaFPS values (#3228)

Author: RunitaiLinden

indra/newview/app_settings/settings.xml

@@ -9298,6 +9298,17 @@
     <key>Value</key>
     <real>4.0</real>
   </map>
+  <key>RenderUseExposureSkySettings</key>
+  <map>
+    <key>Comment</key>
+    <string>Use exposure sky settings instead of deriving from HDR scale.</string>
+    <key>Persist</key>
+    <integer>0</integer>
+    <key>Type</key>
+    <string>Boolean</string>
+    <key>Value</key>
+    <integer>0</integer>
+  </map>
   <key>RenderDynamicExposureCoefficient</key>
   <map>
     <key>Comment</key>

indra/newview/pipeline.cpp

@@ -7077,18 +7077,37 @@ void LLPipeline::generateExposure(LLRenderTarget* src, LLRenderTarget* dst, bool
         LLSettingsSky::ptr_t sky = LLEnvironment::instance().getCurrentSky();
 
         F32 probe_ambiance = LLEnvironment::instance().getCurrentSky()->getReflectionProbeAmbiance(should_auto_adjust);
-        F32 exp_min = sky->getHDRMin();
-        F32 exp_max = sky->getHDRMax();
 
-        if (dynamic_exposure_enabled)
+        F32 exp_min = 1.f;
+        F32 exp_max = 1.f;
+
+        static LLCachedControl<bool> use_exposure_sky_settings(gSavedSettings, "RenderUseExposureSkySettings", false);
+
+        if (use_exposure_sky_settings)
         {
-            exp_min = sky->getHDROffset() - exp_min;
-            exp_max = sky->getHDROffset() + exp_max;
+            if (dynamic_exposure_enabled)
+            {
+                exp_min = sky->getHDROffset() - sky->getHDRMin();
+                exp_max = sky->getHDROffset() + sky->getHDRMax();
+            }
+            else
+            {
+                exp_min = sky->getHDROffset();
+                exp_max = sky->getHDROffset();
+            }
         }
-        else
+        else if (dynamic_exposure_enabled)
         {
-            exp_min = sky->getHDROffset();
-            exp_max = sky->getHDROffset();
+            if (probe_ambiance > 0.f)
+            {
+                F32 hdr_scale = sqrtf(LLEnvironment::instance().getCurrentSky()->getGamma()) * 2.f;
+
+                if (hdr_scale > 1.f)
+                {
+                    exp_min = 1.f / hdr_scale;
+                    exp_max = hdr_scale;
+                }
+            }
         }
 
         shader->uniform1f(dt, gFrameIntervalSeconds);