fix: 首次提交

SettingsLib/DisplayUtils/src/com/android/settingslib/display/BrightnessUtils.java

@@ -0,0 +1,142 @@
+/*
+ * Copyright (C) 2018 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.settingslib.display;
+
+import android.util.MathUtils;
+
+/** Utility methods for calculating the display brightness. */
+public class BrightnessUtils {
+
+    public static final int GAMMA_SPACE_MIN = 0;
+    public static final int GAMMA_SPACE_MAX = 65535;
+
+    // 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 that the slider works in to the
+     * linear space that the setting works in.
+     *
+     * The gamma space effectively provides us a way to make linear changes to the slider that
+     * result in linear changes in perception. If we made changes to the slider in the linear space
+     * then we'd see an approximately logarithmic change in perception (c.f. Fechner's Law).
+     *
+     * 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.
+     *
+     * @param val The slider value.
+     * @param min The minimum acceptable value for the setting.
+     * @param max The maximum acceptable value for the setting.
+     * @return The corresponding setting value.
+     */
+    public static final int convertGammaToLinear(int val, int min, int max) {
+        final float normalizedVal = MathUtils.norm(GAMMA_SPACE_MIN, GAMMA_SPACE_MAX, val);
+        final float ret;
+        if (normalizedVal <= R) {
+            ret = MathUtils.sq(normalizedVal / R);
+        } else {
+            ret = MathUtils.exp((normalizedVal - C) / A) + B;
+        }
+
+        // HLG is normalized to the range [0, 12], so we need to re-normalize to the range [0, 1]
+        // in order to derive the correct setting value.
+        return Math.round(MathUtils.lerp(min, max, ret / 12));
+    }
+
+    /**
+     * Version of {@link #convertGammaToLinear} that takes and returns float values.
+     * TODO(flc): refactor Android Auto to use float version
+     *
+     * @param val The slider value.
+     * @param min The minimum acceptable value for the setting.
+     * @param max The maximum acceptable value for the setting.
+     * @return The corresponding setting value.
+     */
+    public static final float convertGammaToLinearFloat(int val, float min, float max) {
+        final float normalizedVal = MathUtils.norm(GAMMA_SPACE_MIN, GAMMA_SPACE_MAX, val);
+        final float ret;
+        if (normalizedVal <= R) {
+            ret = MathUtils.sq(normalizedVal / R);
+        } else {
+            ret = MathUtils.exp((normalizedVal - 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 MathUtils.lerp(min, max, normalizedRet / 12);
+    }
+
+    /**
+     * A function for converting from the linear space that the setting works in to the
+     * gamma space that the slider works in.
+     *
+     * The gamma space effectively provides us a way to make linear changes to the slider that
+     * result in linear changes in perception. If we made changes to the slider in the linear space
+     * then we'd see an approximately logarithmic change in perception (c.f. Fechner's Law).
+     *
+     * Internally, this implements the Hybrid Log Gamma opto-electronic 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.
+     *
+     * @param val The brightness setting value.
+     * @param min The minimum acceptable value for the setting.
+     * @param max The maximum acceptable value for the setting.
+     * @return The corresponding slider value
+     */
+    public static final int convertLinearToGamma(int val, int min, int max) {
+        return convertLinearToGammaFloat((float) val, (float) min, (float) max);
+    }
+
+    /**
+     * Version of {@link #convertLinearToGamma} that takes float values.
+     * TODO: brightnessfloat merge with above method(?)
+     * @param val The brightness setting value.
+     * @param min The minimum acceptable value for the setting.
+     * @param max The maximum acceptable value for the setting.
+     * @return The corresponding slider value
+     */
+    public static final int convertLinearToGammaFloat(float val, float min, float max) {
+        // For some reason, HLG normalizes to the range [0, 12] rather than [0, 1]
+        final float normalizedVal = MathUtils.norm(min, max, val) * 12;
+        final float ret;
+        if (normalizedVal <= 1f) {
+            ret = MathUtils.sqrt(normalizedVal) * R;
+        } else {
+            ret = A * MathUtils.log(normalizedVal - B) + C;
+        }
+
+        return Math.round(MathUtils.lerp(GAMMA_SPACE_MIN, GAMMA_SPACE_MAX, ret));
+    }
+}