ImageButton that accepts drawable as mask. Touch is only processed when touched on black pixel of mask.

attrs.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="MaskedImageButton">
        <attr name="maskDrawable" format="reference" />
    </declare-styleable>
</resources>

MaskedImageButton.java

package package_name;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Color;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.widget.ImageButton;

import package_name.R;

public class MaskedImageButton extends ImageButton {
    private Bitmap mask;
    private int slopOffset;

    public MaskedImageButton(Context context, AttributeSet attrs) {
        super(context, attrs);

        TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.MaskedImageButton, 0, 0);
        int maskDrawableResource = a.getResourceId(R.styleable.MaskedImageButton_maskDrawable, 0);
        if (maskDrawableResource != 0) {
            mask = BitmapFactory.decodeResource(getResources(), maskDrawableResource);
        }
        a.recycle();

        slopOffset = ViewConfiguration.get(getContext()).getScaledTouchSlop() + 1;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (mask == null) return super.onTouchEvent(event);

        int x = (int) event.getX();
        int y = (int) event.getY();
        if (x < 0 || x >= mask.getWidth() || y < 0 || y >= mask.getHeight())
            return super.onTouchEvent(event);

        int pixelColor = mask.getPixel(x, y);
        if (pixelColor == Color.BLACK)
            return super.onTouchEvent(event);

        if (event.getAction() == MotionEvent.ACTION_MOVE) {
            // simulating we're out of button borders
            event.setLocation(-slopOffset, -slopOffset);
            return super.onTouchEvent(event);
        }
        return false;
    }
}