ScrimUtil.java 文件源码

/**
 * 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, 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;
        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);
        }
    });

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