android-34/com/android/systemui/monet/palettes/TonalPalette.java

/*
 * Copyright (C) 2023 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.systemui.monet.palettes;

import com.android.systemui.monet.hct.Hct;

import java.util.HashMap;
import java.util.Map;

/**
 * A convenience class for retrieving colors that are constant in hue and chroma, but vary in tone.
 */
public final class TonalPalette {
    Map<Integer, Integer> cache;
    Hct keyColor;
    double hue;
    double chroma;

    /**
     * Create tones using the HCT hue and chroma from a color.
     *
     * @param argb ARGB representation of a color
     * @return Tones matching that color's hue and chroma.
     */
    public static TonalPalette fromInt(int argb) {
        return fromHct(Hct.fromInt(argb));
    }

    /**
     * Create tones using a HCT color.
     *
     * @param hct HCT representation of a color.
     * @return Tones matching that color's hue and chroma.
     */
    public static TonalPalette fromHct(Hct hct) {
        return new TonalPalette(hct.getHue(), hct.getChroma(), hct);
    }

    /**
     * Create tones from a defined HCT hue and chroma.
     *
     * @param hue    HCT hue
     * @param chroma HCT chroma
     * @return Tones matching hue and chroma.
     */
    public static TonalPalette fromHueAndChroma(double hue, double chroma) {
        return new TonalPalette(hue, chroma, createKeyColor(hue, chroma));
    }

    private TonalPalette(double hue, double chroma, Hct keyColor) {
        cache = new HashMap<>();
        this.hue = hue;
        this.chroma = chroma;
        this.keyColor = keyColor;
    }

    /** The key color is the first tone, starting from T50, matching the given hue and chroma. */
    private static Hct createKeyColor(double hue, double chroma) {
        double startTone = 50.0;
        Hct smallestDeltaHct = Hct.from(hue, chroma, startTone);
        double smallestDelta = Math.abs(smallestDeltaHct.getChroma() - chroma);
        // Starting from T50, check T+/-delta to see if they match the requested
        // chroma.
        //
        // Starts from T50 because T50 has the most chroma available, on
        // average. Thus it is most likely to have a direct answer and minimize
        // iteration.
        for (double delta = 1.0; delta < 50.0; delta += 1.0) {
            // Termination condition rounding instead of minimizing delta to avoid
            // case where requested chroma is 16.51, and the closest chroma is 16.49.
            // Error is minimized, but when rounded and displayed, requested chroma
            // is 17, key color's chroma is 16.
            if (Math.round(chroma) == Math.round(smallestDeltaHct.getChroma())) {
                return smallestDeltaHct;
            }

            final Hct hctAdd = Hct.from(hue, chroma, startTone + delta);
            final double hctAddDelta = Math.abs(hctAdd.getChroma() - chroma);
            if (hctAddDelta < smallestDelta) {
                smallestDelta = hctAddDelta;
                smallestDeltaHct = hctAdd;
            }

            final Hct hctSubtract = Hct.from(hue, chroma, startTone - delta);
            final double hctSubtractDelta = Math.abs(hctSubtract.getChroma() - chroma);
            if (hctSubtractDelta < smallestDelta) {
                smallestDelta = hctSubtractDelta;
                smallestDeltaHct = hctSubtract;
            }
        }

        return smallestDeltaHct;
    }

    /**
     * Create an ARGB color with HCT hue and chroma of this Tones instance, and the provided HCT
     * tone.
     *
     * @param tone HCT tone, measured from 0 to 100.
     * @return ARGB representation of a color with that tone.
     */
    // AndroidJdkLibsChecker is higher priority than ComputeIfAbsentUseValue (b/119581923)
    @SuppressWarnings("ComputeIfAbsentUseValue")
    public int tone(int tone) {
        Integer color = cache.get(tone);
        if (color == null) {
            color = Hct.from(this.hue, this.chroma, tone).toInt();
            cache.put(tone, color);
        }
        return color;
    }

    /** Given a tone, use hue and chroma of palette to create a color, and return it as HCT. */
    public Hct getHct(double tone) {
        return Hct.from(this.hue, this.chroma, tone);
    }

    /** The chroma of the Tonal Palette, in HCT. Ranges from 0 to ~130 (for sRGB gamut). */
    public double getChroma() {
        return this.chroma;
    }

    /** The hue of the Tonal Palette, in HCT. Ranges from 0 to 360. */
    public double getHue() {
        return this.hue;
    }

    /** The key color is the first tone, starting from T50, that matches the palette's chroma. */
    public Hct getKeyColor() {
        return this.keyColor;
    }
}