Revert "[RESTRICT AUTOMERGE]DisplayManager: Switch RampAnimator to ramp in HLG space."

This reverts commit 682f01c6a92053a622bfb9acd3e78bf4690d3427.

Revert reason: Check if this causes AOC regression

Bug: 223124178
Change-Id: Ia410597785e9d0b636c69450ffb5ff6712253bd2
(cherry picked from commit 9b752ff2d972b2defec34fdeeb801533975e7262)
Merged-In: Ia410597785e9d0b636c69450ffb5ff6712253bd2

2 files changed, 7 insertions, 96 deletions

diff --git a/services/core/java/com/android/server/display/BrightnessUtils.java b/services/core/java/com/android/server/display/BrightnessUtils.java
deleted file mode 100644
index 84fa0cccbd10..000000000000
--- a/services/core/java/com/android/server/display/BrightnessUtils.java
+++ /dev/null
@@ -1,83 +0,0 @@
-/*
- * Copyright (C) 2022 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package com.android.server.display;
-
-import android.util.MathUtils;
-
-/**
- * Utility class providing functions to convert between linear and perceptual gamma space.
- *
- * Internally, this implements the Hybrid Log Gamma electro-optical transfer function, which is a
- * slight improvement to the typical gamma transfer function for displays whose max brightness
- * exceeds the 120 nit reference point, but doesn't set a specific reference brightness like the PQ
- * function does.
- *
- * Note that this transfer function is only valid if the display's backlight value is a linear
- * control. If it's calibrated to be something non-linear, then a different transfer function
- * should be used.
- *
- * Note: This code is based on the same class in the com.android.settingslib.display package.
- */
-public class BrightnessUtils {
-
-    // Hybrid Log Gamma constant values
-    private static final float R = 0.5f;
-    private static final float A = 0.17883277f;
-    private static final float B = 0.28466892f;
-    private static final float C = 0.55991073f;
-
-    /**
-     * A function for converting from the gamma space into the linear space.
-     *
-     * @param val The value in the gamma space [0 .. 1.0]
-     * @return The corresponding value in the linear space [0 .. 1.0].
-     */
-    public static final float convertGammaToLinear(float val) {
-        final float ret;
-        if (val <= R) {
-            ret = MathUtils.sq(val / R);
-        } else {
-            ret = MathUtils.exp((val - C) / A) + B;
-        }
-
-        // HLG is normalized to the range [0, 12], ensure that value is within that range,
-        // it shouldn't be out of bounds.
-        final float normalizedRet = MathUtils.constrain(ret, 0, 12);
-
-        // Re-normalize to the range [0, 1]
-        // in order to derive the correct setting value.
-        return normalizedRet / 12;
-    }
-
-    /**
-     * A function for converting from the linear space into the gamma space.
-     *
-     * @param val The value in linear space [0 .. 1.0]
-     * @return The corresponding value in gamma space [0 .. 1.0]
-     */
-    public static final float convertLinearToGamma(float val) {
-        // For some reason, HLG normalizes to the range [0, 12] rather than [0, 1]
-        final float normalizedVal = val * 12;
-        final float ret;
-        if (normalizedVal <= 1f) {
-            ret = MathUtils.sqrt(normalizedVal) * R;
-        } else {
-            ret = A * MathUtils.log(normalizedVal - B) + C;
-        }
-        return ret;
-    }
-}
diff --git a/services/core/java/com/android/server/display/RampAnimator.java b/services/core/java/com/android/server/display/RampAnimator.java
index 1ebd1f5a535c..ed3b15fb2661 100644
--- a/services/core/java/com/android/server/display/RampAnimator.java
+++ b/services/core/java/com/android/server/display/RampAnimator.java
@@ -23,8 +23,6 @@ import android.view.Choreographer;
 /**
  * A custom animator that progressively updates a property value at
  * a given variable rate until it reaches a particular target value.
- * The ramping at the given rate is done in the perceptual space using
- * the HLG transfer functions.
  */
 class RampAnimator<T> {
     private final T mObject;
@@ -59,9 +57,7 @@ class RampAnimator<T> {
      * @param rate The convergence rate in units per second, or 0 to set the value immediately.
      * @return True if the target differs from the previous target.
      */
-    public boolean animateTo(float targetLinear, float rate) {
-        // Convert the target from the linear into the HLG space.
-        final float target = BrightnessUtils.convertLinearToGamma(targetLinear);
+    public boolean animateTo(float target, float rate) {
 
         // Immediately jump to the target the first time.
         if (mFirstTime || rate <= 0) {
@@ -160,9 +156,7 @@ class RampAnimator<T> {
             final float oldCurrentValue = mCurrentValue;
             mCurrentValue = mAnimatedValue;
             if (oldCurrentValue != mCurrentValue) {
-                // Convert value from HLG into linear space for the property.
-                final float linearCurrentVal = BrightnessUtils.convertGammaToLinear(mCurrentValue);
-                mProperty.setValue(mObject, linearCurrentVal);
+                mProperty.setValue(mObject, mCurrentValue);
             }
             if (mTargetValue != mCurrentValue) {
                 postAnimationCallback();
@@ -207,14 +201,14 @@ class RampAnimator<T> {
          * If this is the first time the property is being set or if the rate is 0,
          * the value jumps directly to the target.
          *
-         * @param linearFirstTarget The first target value in linear space.
-         * @param linearSecondTarget The second target value in linear space.
+         * @param firstTarget The first target value.
+         * @param secondTarget The second target value.
          * @param rate The convergence rate in units per second, or 0 to set the value immediately.
          * @return True if either target differs from the previous target.
          */
-        public boolean animateTo(float linearFirstTarget, float linearSecondTarget, float rate) {
-            final boolean firstRetval = mFirst.animateTo(linearFirstTarget, rate);
-            final boolean secondRetval = mSecond.animateTo(linearSecondTarget, rate);
+        public boolean animateTo(float firstTarget, float secondTarget, float rate) {
+            final boolean firstRetval = mFirst.animateTo(firstTarget, rate);
+            final boolean secondRetval = mSecond.animateTo(secondTarget, rate);
             return firstRetval && secondRetval;
         }