androidx/wear/widget/BezierSCurveInterpolator.java

/*
 * Copyright (C) 2017 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 androidx.wear.widget;

import android.animation.TimeInterpolator;

import androidx.annotation.RestrictTo;
import androidx.annotation.RestrictTo.Scope;

/**
 * Interpolator that uses a Bezier derived S shaped curve.
 *
 * @hide
 */
@RestrictTo(Scope.LIBRARY)
class BezierSCurveInterpolator implements TimeInterpolator {

    /**
     * An instance of {@link BezierSCurveInterpolator}.
     */
    public static final BezierSCurveInterpolator INSTANCE = new BezierSCurveInterpolator();
    /**
     * Lookup table values. Generated using a Bezier curve from (0,0) to (1,1) with control points:
     * P0 (0,0) P1 (0.4, 0) P2 (0.2, 1.0) P3 (1.0, 1.0)
     *
     * <p>Values sampled with x at regular intervals between 0 and 1.
     */
    private static final float[] VALUES = new float[]{
            0.0f, 0.0002f, 0.0009f, 0.0019f, 0.0036f, 0.0059f, 0.0086f, 0.0119f, 0.0157f, 0.0209f,
            0.0257f, 0.0321f, 0.0392f, 0.0469f, 0.0566f, 0.0656f, 0.0768f, 0.0887f, 0.1033f,
            0.1186f, 0.1349f, 0.1519f, 0.1696f, 0.1928f, 0.2121f, 0.237f, 0.2627f, 0.2892f, 0.3109f,
            0.3386f, 0.3667f, 0.3952f, 0.4241f, 0.4474f, 0.4766f, 0.5f, 0.5234f, 0.5468f, 0.5701f,
            0.5933f, 0.6134f, 0.6333f, 0.6531f, 0.6698f, 0.6891f, 0.7054f, 0.7214f, 0.7346f,
            0.7502f, 0.763f, 0.7756f, 0.7879f, 0.8f, 0.8107f, 0.8212f, 0.8326f, 0.8415f, 0.8503f,
            0.8588f, 0.8672f, 0.8754f, 0.8833f, 0.8911f, 0.8977f, 0.9041f, 0.9113f, 0.9165f,
            0.9232f, 0.9281f, 0.9328f, 0.9382f, 0.9434f, 0.9476f, 0.9518f, 0.9557f, 0.9596f,
            0.9632f, 0.9662f, 0.9695f, 0.9722f, 0.9753f, 0.9777f, 0.9805f, 0.9826f, 0.9847f,
            0.9866f, 0.9884f, 0.9901f, 0.9917f, 0.9931f, 0.9944f, 0.9955f, 0.9964f, 0.9973f,
            0.9981f, 0.9986f, 0.9992f, 0.9995f, 0.9998f, 1.0f, 1.0f
    };
    private static final float STEP_SIZE = 1.0f / (VALUES.length - 1);

    /**
     * To avoid users of this class creating multiple copies needlessly, the constructor is
     * private.
     */
    private BezierSCurveInterpolator() {
    }

    @Override
    public float getInterpolation(float input) {
        if (input >= 1.0f) {
            return 1.0f;
        }

        if (input <= 0f) {
            return 0f;
        }

        int position = Math.min((int) (input * (VALUES.length - 1)), VALUES.length - 2);

        float quantized = position * STEP_SIZE;
        float difference = input - quantized;
        float weight = difference / STEP_SIZE;

        return VALUES[position] + weight * (VALUES[position + 1] - VALUES[position]);
    }
}