GradientUtil.java 文件源码

/**
 * Create a cubic gradient by using a compound gradient composed of a series of linear
 * gradients with intermediate color values.
 * adapted from: https://github.com/romannurik/muzei/blob/master/main/src/main/java/com/google/android/apps/muzei/util/ScrimUtil.java
 * @param baseColor The color from which the gradient starts (the ending color is transparent).
 * @param gravity Where the gradient should start from. Note: when making horizontal gradients,
 *                remember to use START/END, instead of LEFT/RIGHT.
 */
public static void setCubicGradient(PaintDrawable drawable, int baseColor, int gravity) {
    final int[] stopColors = new int[GRADIENT_NUM_STOPS];

    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 < GRADIENT_NUM_STOPS; i++) {
        float x = i * 1f / (GRADIENT_NUM_STOPS - 1);
        float opacity = MathUtil.constrain((float) Math.pow(x, GRADIENT_POWER), 0.0f, 1.0f);
        stopColors[i] = Color.argb((int) (alpha * opacity), red, green, blue);
    }

    final float x0, x1, y0, y1;
    switch (gravity & Gravity.HORIZONTAL_GRAVITY_MASK) {
        case Gravity.START:
            x0 = 1;
            x1 = 0;
            break;
        case Gravity.END:
            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;
    }

    drawable.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);
        }
    });
}