UIUtils.java 文件源码

/**
 * This helper method creates a 'nice' scrim or background protection for layering text over
 * an image. This non-linear scrim is less noticable than a linear or constant one.
 *
 * Borrowed from github.com/romannurik/muzei
 *
 * 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) {
    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++) {
        double x = i * 1f / (numStops - 1);
        double opacity = Math.max(0, Math.min(1, Math.pow(x, 3)));
        stopColors[i] = (baseColor & 0x00ffffff) | ((int) (alpha * opacity) << 24);
    }

    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;
}