@Nullable
  public static ScaleTypeDrawable getActiveScaleTypeDrawable(@Nullable Drawable drawable) {
    if (drawable == null) {
      return null;
    } else if (drawable instanceof ScaleTypeDrawable) {
      return (ScaleTypeDrawable) drawable;
    } else if (drawable instanceof DrawableParent) {
      final Drawable childDrawable = ((DrawableParent) drawable).getDrawable();
      return getActiveScaleTypeDrawable(childDrawable);
    } else if (drawable instanceof ArrayDrawable) {
      final ArrayDrawable fadeDrawable = (ArrayDrawable) drawable;
      final int numLayers = fadeDrawable.getNumberOfLayers();

      for (int i = 0; i < numLayers; i++) {
        final Drawable childDrawable = fadeDrawable.getDrawable(i);
        final ScaleTypeDrawable result = getActiveScaleTypeDrawable(childDrawable);
        if (result != null) {
          return result;
        }
      }
    }
    return null;
  }
updateDebugOverlay updates the debug overlay. Subclasses of {@link PipelineDraweeController}
can override this method (and call <code>super</code>) to provide additional debug information.
drawee-backends/drawee-pipeline/src/main/java/com/facebook/drawee/backends/pipeline/PipelineDraweeController.java