DrawableUtils.java

/*
 * Copyright (c) 2015 Zhang Hai <Dreaming.in.Code.ZH@Gmail.com>
 * All Rights Reserved.
 */

package me.zhanghai.android.douya.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.view.Gravity;

public class DrawableUtils {

    private DrawableUtils() {}

    // From Muzei, Copyright 2014 Google Inc.
    public static Drawable makeScrimDrawable(int baseColor, int numStops, int gravity) {

        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 = MathUtils.clamp((float) Math.pow(x, 3), 0, 1);
            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;
            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;
            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,
                        width * x1,
                        height * y1,
                        stopColors, null,
                        Shader.TileMode.CLAMP);
            }
        });

        paintDrawable.setAlpha(Math.round(0.4f * 255));

        return paintDrawable;
    }

    public static Drawable makeScrimDrawable(int gravity) {
        return makeScrimDrawable(Color.BLACK, 9, gravity);
    }

    public static Drawable makeScrimDrawable() {
        return makeScrimDrawable(Gravity.BOTTOM);
    }
}