From 8155bf04a84a738b68c5d2aa030ab1a6a5bcc1fb Mon Sep 17 00:00:00 2001
From: Pixelflinger <pixelflinger@gmail.com>
Date: Fri, 7 Aug 2020 22:05:07 -0700
Subject: [PATCH] Implement variance clamping

variance clamping further shrinks the min/max AABB
---
 .../filament-android/src/main/cpp/View.cpp    |  2 +-
 filament/src/materials/antiAliasing/taa.mat   | 36 ++++++++++++++++++-
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/android/filament-android/src/main/cpp/View.cpp b/android/filament-android/src/main/cpp/View.cpp
index 58ec085f13..6ed7190a02 100644
--- a/android/filament-android/src/main/cpp/View.cpp
+++ b/android/filament-android/src/main/cpp/View.cpp
@@ -275,5 +275,5 @@ Java_com_google_android_filament_View_nSetTemporalAntiAliasingOptions(JNIEnv *,
         jlong nativeView, jfloat feedback, jfloat filterWidth, jboolean enabled) {
     View* view = (View*) nativeView;
     view->setTemporalAntiAliasingOptions({
-        .feedback = feedback, .filterWidth = filterWidth, .enabled = (bool) enabled});
+            .filterWidth = filterWidth, .feedback = feedback, .enabled = (bool) enabled});
 }
diff --git a/filament/src/materials/antiAliasing/taa.mat b/filament/src/materials/antiAliasing/taa.mat
index 81199999f3..3c905b56ec 100644
--- a/filament/src/materials/antiAliasing/taa.mat
+++ b/filament/src/materials/antiAliasing/taa.mat
@@ -52,6 +52,18 @@ fragment {
 #define TEXTURE_SPACE_DN    -1
 #endif
 
+/* Clipping box type */
+
+// Neighborhood AABB
+#define BOX_TYPE_AABB           0
+// Further clip by Neighborhood Variance
+#define BOX_TYPE_VARIANCE       1
+
+// High VARIANCE_GAMMA [0.75, 1.25] increases ghosting artefact, lower values increases jittering
+#define VARIANCE_GAMMA          1.0
+
+/* Clipping algorithm */
+
 // accurate box clipping
 #define BOX_CLIPPING_ACCURATE   0
 // clamping instead of clipping
@@ -59,22 +71,28 @@ fragment {
 // no clipping (for debugging only)
 #define BOX_CLIPPING_NONE       2
 
+/* Configuration mobile/desktop */
+
 #if defined(TARGET_MOBILE)
 #define BOX_CLIPPING            BOX_CLIPPING_ACCURATE
+#define BOX_TYPE                BOX_TYPE_VARIANCE
 #define USE_YCoCg               0
 #define PREVENT_FLICKERING      0
 #define FILTER_HISTORY          0
 #else
 #define BOX_CLIPPING            BOX_CLIPPING_ACCURATE
+#define BOX_TYPE                BOX_TYPE_VARIANCE
 #define USE_YCoCg               1
 #define PREVENT_FLICKERING      0   // FIXME: thin lines disapear
 #define FILTER_HISTORY          1
 #endif
 
-// disable for debugging only
+/* debugging helper */
+
 #define HISTORY_REPROJECTION    1
 #define FILTER_INPUT            1
 
+
 float luma(const vec3 color) {
 #if USE_YCoCg
     return color.x;
@@ -253,6 +271,22 @@ void postProcess(inout PostProcessInputs postProcess) {
     vec3 boxmin = (box5min + box9min) * 0.5;
     vec3 boxmax = (box5max + box9max) * 0.5;
 
+#if BOX_TYPE == BOX_TYPE_VARIANCE
+    // "An Excursion in Temporal Supersampling" by Marco Salvi
+    vec3 m0 = s[4];
+    vec3 m1 = s[4] * s[4];
+    // we use only 5 samples instead of all 9
+    for (int i = 1 ; i < 9 ; i+=2) {
+        m0 += s[i];
+        m1 += s[i] * s[i];
+    }
+    vec3 a0 = m0 * (1.0 / 5.0);
+    vec3 a1 = m1 * (1.0 / 5.0);
+    vec3 sigma = sqrt(a1 - a0 * a0);
+    boxmin = min(boxmin, a0 - VARIANCE_GAMMA * sigma);
+    boxmax = max(boxmax, a0 + VARIANCE_GAMMA * sigma);
+#endif
+
     // history clamping
     history = clipToBox(BOX_CLIPPING, boxmin, boxmax, filtered, history);