feat(unrealengine): better tonemap by luminance

src/games/unrealengine/addon.cpp

@@ -209,7 +209,7 @@ renodx::utils::settings::Settings settings = {
         .key = "ToneMapPerChannel",
         .binding = &shader_injection.toneMapPerChannel,
         .value_type = renodx::utils::settings::SettingValueType::INTEGER,
-        .default_value = 1.f,
+        .default_value = 0.f,
         .label = "Per Channel",
         .section = "Tone Mapping",
         .tooltip = "Applies tonemapping per-channel instead of by luminance",

src/games/unrealengine/common.hlsl

@@ -19,18 +19,18 @@ float3 PostToneMapScale(float3 color) {
   return color;
 }
 
-float UpgradeToneMapRatio(float ap1_color_hdr, float ap1_color_sdr, float ap1_post_process_color) {
-  if (ap1_color_hdr < ap1_color_sdr) {
+float UpgradeToneMapRatio(float color_hdr, float color_sdr, float post_process_color) {
+  if (color_hdr < color_sdr) {
     // If substracting (user contrast or paperwhite) scale down instead
     // Should only apply on mismatched HDR
-    return ap1_color_hdr / ap1_color_sdr;
+    return color_hdr / color_sdr;
   } else {
-    float ap1_delta = ap1_color_hdr - ap1_color_sdr;
-    ap1_delta = max(0, ap1_delta);  // Cleans up NaN
-    const float ap1_new = ap1_post_process_color + ap1_delta;
+    float delta = color_hdr - color_sdr;
+    delta = max(0, delta);  // Cleans up NaN
+    const float new_value = post_process_color + delta;
 
-    const bool ap1_valid = (ap1_post_process_color > 0);  // Cleans up NaN and ignore black
-    return ap1_valid ? (ap1_new / ap1_post_process_color) : 0;
+    const bool valid = (post_process_color > 0);  // Cleans up NaN and ignore black
+    return valid ? (new_value / post_process_color) : 0;
   }
 }
 float3 UpgradeToneMapPerChannel(float3 color_hdr, float3 color_sdr, float3 post_process_color, float post_process_strength) {
@@ -52,6 +52,25 @@ float3 UpgradeToneMapPerChannel(float3 color_hdr, float3 color_sdr, float3 post_
   return lerp(color_hdr, color_scaled, post_process_strength);
 }
 
+float3 UpgradeToneMapByLuminance(float3 color_hdr, float3 color_sdr, float3 post_process_color, float post_process_strength) {
+  // float ratio = 1.f;
+
+  float3 bt2020_hdr = max(0, renodx::color::bt2020::from::BT709(color_hdr));
+  float3 bt2020_sdr = max(0, renodx::color::bt2020::from::BT709(color_sdr));
+  float3 bt2020_post_process = max(0, renodx::color::bt2020::from::BT709(post_process_color));
+
+  float ratio = UpgradeToneMapRatio(
+      renodx::color::y::from::BT2020(bt2020_hdr),
+      renodx::color::y::from::BT2020(bt2020_sdr),
+      renodx::color::y::from::BT2020(bt2020_post_process));
+
+  float3 color_scaled = max(0, bt2020_post_process * ratio);
+  color_scaled = renodx::color::bt709::from::BT2020(color_scaled);
+  float peak_correction = saturate(1.f - renodx::color::y::from::BT2020(bt2020_post_process));
+  color_scaled = renodx::color::correct::Hue(color_scaled, post_process_color, peak_correction);
+  return lerp(color_hdr, color_scaled, post_process_strength);
+}
+
 float3 FinalizeOutput(float3 color) {
   if (injectedData.toneMapGammaCorrection == 2.f) {
     color = renodx::color::gamma::DecodeSafe(color, 2.4f);
@@ -162,12 +181,20 @@ float3 UpgradeToneMapAP1(float3 untonemapped_ap1, float3 tonemapped_bt709) {
 
   float3 neutral_sdr_color = RenoDRTSmoothClamp(untonemapped_bt709);
 
-  float3 untonemapped_graded = UpgradeToneMapPerChannel(
-      untonemapped_bt709,
-      neutral_sdr_color,
-      tonemapped_bt709,
-      1);
-
+  float3 untonemapped_graded;
+  if (injectedData.toneMapPerChannel == 1) {
+    untonemapped_graded = UpgradeToneMapPerChannel(
+        untonemapped_bt709,
+        neutral_sdr_color,
+        tonemapped_bt709,
+        1);
+  } else {
+    untonemapped_graded = UpgradeToneMapByLuminance(
+        untonemapped_bt709,
+        neutral_sdr_color,
+        tonemapped_bt709,
+        1);
+  }
   return ToneMap(untonemapped_graded);
 }