private int convertDpToPx(float dp) {
        return Math.round(getContext().getResources().getDisplayMetrics().density * dp);
    }
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