ScrimUtil.java

/*
 * Copyright 2014 Google Inc.
 *
 * 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 io.hefuyi.listener.util;

import android.graphics.Color;
import android.graphics.LinearGradient;
import android.graphics.Shader;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.PaintDrawable;
import android.graphics.drawable.ShapeDrawable;
import android.graphics.drawable.shapes.RectShape;
import android.util.LruCache;
import android.view.Gravity;

public class ScrimUtil {

    private static final LruCache<Integer, Drawable> cubicGradientScrimCache = new LruCache<>(10);

    private ScrimUtil() {
    }

    /**
     * Creates an approximated cubic gradient using a multi-stop linear gradient. See
     * <a href="https://plus.google.com/+RomanNurik/posts/2QvHVFWrHZf">this post</a> for more
     * details.
     */
    public static Drawable makeCubicGradientScrimDrawable(int baseColor, int numStops, final int gravity) {

        // Generate a cache key by hashing together the inputs, based on the method described in the Effective Java book
        int cacheKeyHash = baseColor;
        cacheKeyHash = 31 * cacheKeyHash + numStops;
        cacheKeyHash = 31 * cacheKeyHash + gravity;

        Drawable cachedGradient = cubicGradientScrimCache.get(cacheKeyHash);
        if (cachedGradient != null) {
            return cachedGradient;
        }

        numStops = Math.max(numStops, 2);

        PaintDrawable paintDrawable = new PaintDrawable();
        paintDrawable.setShape(new RectShape());

        final int[] stopColors = new int[numStops];

        int red = Color.red(baseColor);
        int green = Color.green(baseColor);
        int blue = Color.blue(baseColor);
        int alpha = Color.alpha(baseColor);

        for (int i = 0; i < numStops; i++) {
            float x = i * 1f / (numStops - 1);
            float opacity = MathUtil.constrain(0, 1, (float) Math.pow(x, 3));
            stopColors[i] = Color.argb((int) (alpha * opacity), red, green, blue);
        }

        final float x0, x1, y0, y1;
        switch (gravity & Gravity.HORIZONTAL_GRAVITY_MASK) {
            case Gravity.LEFT:  x0 = 1; x1 = 0; break;
            case Gravity.RIGHT: x0 = 0; x1 = 1; break;
            case Gravity.CENTER_HORIZONTAL:
            default:            x0 = 0; x1 = 0; break;
        }
        switch (gravity & Gravity.VERTICAL_GRAVITY_MASK) {
            case Gravity.TOP:    y0 = 1; y1 = 0; break;
            case Gravity.BOTTOM: y0 = 0; y1 = 1; break;
            case Gravity.CENTER_VERTICAL:
            default:             y0 = 0; y1 = 0; break;
        }



        paintDrawable.setShaderFactory(new ShapeDrawable.ShaderFactory() {
            @Override
            public Shader resize(int width, int height) {
                return new LinearGradient(
                        width * x0,
                        height * y0,
                        gravity == Gravity.CENTER_VERTICAL ? width : width * x1,
                        gravity == Gravity.CENTER_HORIZONTAL ? height : height * y1,
                        gravity == Gravity.CENTER_HORIZONTAL || gravity == Gravity.CENTER_VERTICAL ? makeDoubleStopColors(stopColors) : stopColors,
                        null,
                        Shader.TileMode.CLAMP);
            }
        });

        cubicGradientScrimCache.put(cacheKeyHash, paintDrawable);
        return paintDrawable;
    }

    public static int[] makeDoubleStopColors(int[] stopColors) {
        int length = stopColors.length;
        int[] doubleStopColors = new int[length * 2];

        for (int i=0;i<length;i++) {
            doubleStopColors[i] = stopColors[length - 1 - i];
        }
        for (int j=length;j<length*2;j++) {
            doubleStopColors[j] = stopColors[j - length];
        }

        return doubleStopColors;
    }

    public static class MathUtil {
        public static float constrain(float min, float max, float v) {
            return Math.max(min, Math.min(max, v));
        }
    }
}