Using ClipDrawable to hide a part of and ImageView

Question

I am trying to hide a part of an image so that the user does not see it. Initially I copied the Bitmap pixels on another Bitmap, without copying only the pixels that I needed and making the second bitmap the correct size at creation. That worked, but I have many large images and that results in OOMs unfortunately. So instead of doing that I thought on using a ClipDrawable to draw the image, and making the pixels that I don't need invisible.

The code is as follows

ClipDrawable clipDrawable = new ClipDrawable(new BitmapDrawable(resources, bitmap), gravity, orientation);
clipDrawable.setLevel(level);

// Cannot use as the imageview source. Must use background or else we don't get anything on the screen.
picture.setBackground(clipDrawable);
// This is super important. Do not modify this! Without it you will not get the fullscreen image working and the ImageView will be deleted
// from the parent layout.
picture.setImageResource(android.R.color.transparent);

The idea is that I calculate the level based on the image size so that I hide the pixels that I don't need. And it's working. Except I don't understand why I need to use

picture.setBackground(clipDrawable);

picture.setImageResource(android.R.color.transparent);

instead of the more normal:

picture.setImageDrawable(clipDrawable);

If I do the second more normal example then I don't get anything in the ImageView, but if I set it as a background and put a transparent image over it, then it works. Since I want to further manipulate the ImageView using a zooming class that needs the picture set as the src and not as background, I cannot have both, either I get the ClipDrawable showing or I get to have zoom on the image.

Any help would be appreciated!

Answer 1

picture.setImageDrawable(new
    ClipDrawable(new BitmapDrawable(resources, bitmap), gravity, orientation
));

ClipDrawable clipDrawable = (ClipDrawable) picture.getDrawable();
clipDrawable.setLevel(level);