Add dynamic exposure correction (#12959)

* Add uniform for frame delta time
* Adjust exposure in logarithmic (EV) space
* Add network support and LUA API
* Add testing mod

src/lighting.h

@@ -19,10 +19,38 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 
 #pragma once
 
+
+/**
+ * Parameters for automatic exposure compensation
+ *
+ * Automatic exposure compensation uses the following equation:
+ *
+ * wanted_exposure = 2^exposure_correction / clamp(observed_luminance, 2^luminance_min, 2^luminance_max)
+ *
+ */
+struct AutoExposure
+{
+    /// @brief Minimum boundary for computed luminance
+    float luminance_min;
+    /// @brief Maximum boundary for computed luminance
+    float luminance_max;
+    /// @brief Luminance bias. Higher values make the scene darker, can be negative.
+    float exposure_correction;
+    /// @brief Speed of transition from dark to bright scenes
+    float speed_dark_bright;
+    /// @brief Speed of transition from bright to dark scenes
+    float speed_bright_dark;
+    /// @brief Power value for center-weighted metering. Value of 1.0 measures entire screen uniformly
+    float center_weight_power;
+
+    AutoExposure();
+};
+
 /** Describes ambient light settings for a player
  */
 struct Lighting
 {
+    AutoExposure exposure;
     float shadow_intensity {0.0f};
     float saturation {1.0f};
 };