src/com/android/phone/common/compat/PathInterpolatorCompat.java

/*
 * Copyright (C) 2015 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.phone.common.compat;

import android.graphics.Path;
import android.graphics.PathMeasure;
import android.os.Build;
import android.view.animation.Interpolator;
import android.view.animation.PathInterpolator;

public class PathInterpolatorCompat {
    public static Interpolator create(float controlX1, float controlY1,
            float controlX2, float controlY2) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            return new PathInterpolator(controlX1, controlY1, controlX2, controlY2);
        }
        return new PathInterpolatorBase(controlX1, controlY1, controlX2, controlY2);
    }

    private static class PathInterpolatorBase implements Interpolator {
        /**
         * Governs the accuracy of the approximation of the {@link Path}.
         */
        private static final float PRECISION = 0.002f;

        private final float[] mX;
        private final float[] mY;

        public PathInterpolatorBase(Path path) {
            final PathMeasure pathMeasure = new PathMeasure(path, false /* forceClosed */);

            final float pathLength = pathMeasure.getLength();
            final int numPoints = (int) (pathLength / PRECISION) + 1;

            mX = new float[numPoints];
            mY = new float[numPoints];

            final float[] position = new float[2];
            for (int i = 0; i < numPoints; ++i) {
                final float distance = (i * pathLength) / (numPoints - 1);
                pathMeasure.getPosTan(distance, position, null /* tangent */);

                mX[i] = position[0];
                mY[i] = position[1];
            }
        }

        public PathInterpolatorBase(float controlX, float controlY) {
            this(createQuad(controlX, controlY));
        }

        public PathInterpolatorBase(float controlX1, float controlY1,
                                    float controlX2, float controlY2) {
            this(createCubic(controlX1, controlY1, controlX2, controlY2));
        }

        @Override
        public float getInterpolation(float t) {
            if (t <= 0.0f) {
                return 0.0f;
            } else if (t >= 1.0f) {
                return 1.0f;
            }

            // Do a binary search for the correct x to interpolate between.
            int startIndex = 0;
            int endIndex = mX.length - 1;
            while (endIndex - startIndex > 1) {
                int midIndex = (startIndex + endIndex) / 2;
                if (t < mX[midIndex]) {
                    endIndex = midIndex;
                } else {
                    startIndex = midIndex;
                }
            }

            final float xRange = mX[endIndex] - mX[startIndex];
            if (xRange == 0) {
                return mY[startIndex];
            }

            final float tInRange = t - mX[startIndex];
            final float fraction = tInRange / xRange;

            final float startY = mY[startIndex];
            final float endY = mY[endIndex];

            return startY + (fraction * (endY - startY));
        }

        private static Path createQuad(float controlX, float controlY) {
            final Path path = new Path();
            path.moveTo(0.0f, 0.0f);
            path.quadTo(controlX, controlY, 1.0f, 1.0f);
            return path;
        }

        private static Path createCubic(float controlX1, float controlY1,
                                        float controlX2, float controlY2) {
            final Path path = new Path();
            path.moveTo(0.0f, 0.0f);
            path.cubicTo(controlX1, controlY1, controlX2, controlY2, 1.0f, 1.0f);
            return path;
        }
    }

}