ScrimUtil.java

/*
 * Copyright 2015 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.plaidapp.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.support.annotation.ColorInt;
import android.view.Gravity;

/**
 * * Borrowed from github.com/romannurik/muzei
 */
public class ScrimUtil {

    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(@ColorInt 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 alpha = Color.alpha(baseColor);

        for (int i = 0; i < numStops; i++) {
            float x = i * 1f / (numStops - 1);
            float opacity = MathUtils.constrain(0, 1, (float) Math.pow(x, 3));
            stopColors[i] = ColorUtils.modifyAlpha(baseColor, (int) (alpha * opacity));
        }

        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) {
                LinearGradient linearGradient = new LinearGradient(
                        width * x0,
                        height * y0,
                        width * x1,
                        height * y1,
                        stopColors, null,
                        Shader.TileMode.CLAMP);
                return linearGradient;
            }
        });

        return paintDrawable;
    }
}