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A gradle plugin that generates Material Design 3 themes for Android projects.
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/*
 * Copyright 2021 Google LLC
 *
 * 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.
 */

// This file is automatically generated. Do not modify it.

package blend;

import hct.Cam16;
import hct.Hct;
import utils.ColorUtils;
import utils.MathUtils;

/** Functions for blending in HCT and CAM16. */
public class Blend {
  private Blend() {}

  /**
   * Blend the design color's HCT hue towards the key color's HCT hue, in a way that leaves the
   * original color recognizable and recognizably shifted towards the key color.
   *
   * @param designColor ARGB representation of an arbitrary color.
   * @param sourceColor ARGB representation of the main theme color.
   * @return The design color with a hue shifted towards the system's color, a slightly
   *     warmer/cooler variant of the design color's hue.
   */
  public static int harmonize(int designColor, int sourceColor) {
    Hct fromHct = Hct.fromInt(designColor);
    Hct toHct = Hct.fromInt(sourceColor);
    double differenceDegrees = MathUtils.differenceDegrees(fromHct.getHue(), toHct.getHue());
    double rotationDegrees = Math.min(differenceDegrees * 0.5, 15.0);
    double outputHue =
        MathUtils.sanitizeDegreesDouble(
            fromHct.getHue()
                + rotationDegrees * MathUtils.rotationDirection(fromHct.getHue(), toHct.getHue()));
    return Hct.from(outputHue, fromHct.getChroma(), fromHct.getTone()).toInt();
  }

  /**
   * Blends hue from one color into another. The chroma and tone of the original color are
   * maintained.
   *
   * @param from ARGB representation of color
   * @param to ARGB representation of color
   * @param amount how much blending to perform; 0.0 >= and <= 1.0
   * @return from, with a hue blended towards to. Chroma and tone are constant.
   */
  public static int hctHue(int from, int to, double amount) {
    int ucs = cam16Ucs(from, to, amount);
    Cam16 ucsCam = Cam16.fromInt(ucs);
    Cam16 fromCam = Cam16.fromInt(from);
    Hct blended = Hct.from(ucsCam.getHue(), fromCam.getChroma(), ColorUtils.lstarFromArgb(from));
    return blended.toInt();
  }

  /**
   * Blend in CAM16-UCS space.
   *
   * @param from ARGB representation of color
   * @param to ARGB representation of color
   * @param amount how much blending to perform; 0.0 >= and <= 1.0
   * @return from, blended towards to. Hue, chroma, and tone will change.
   */
  public static int cam16Ucs(int from, int to, double amount) {
    Cam16 fromCam = Cam16.fromInt(from);
    Cam16 toCam = Cam16.fromInt(to);
    double fromJ = fromCam.getJstar();
    double fromA = fromCam.getAstar();
    double fromB = fromCam.getBstar();
    double toJ = toCam.getJstar();
    double toA = toCam.getAstar();
    double toB = toCam.getBstar();
    double jstar = fromJ + (toJ - fromJ) * amount;
    double astar = fromA + (toA - fromA) * amount;
    double bstar = fromB + (toB - fromB) * amount;
    return Cam16.fromUcs(jstar, astar, bstar).toInt();
  }
}