private void setIsEmpty(boolean newValue) {
        mIsEmpty = newValue;
        if (mOnSignedListener != null) {
            if (mIsEmpty) {
                mOnSignedListener.onClear();
            } else {
                mOnSignedListener.onSigned();
            }
        }
    }
Resets the dirty region when the motion event occurs.

@param eventX the event x coordinate.
@param eventY the event y coordinate.
signature-pad/src/main/java/com/github/gcacace/signaturepad/views/SignaturePad.java