private void resetDirtyRect(float eventX, float eventY) {

        // The mLastTouchX and mLastTouchY were set when the ACTION_DOWN motion event occurred.
        mDirtyRect.left = Math.min(mLastTouchX, eventX);
        mDirtyRect.right = Math.max(mLastTouchX, eventX);
        mDirtyRect.top = Math.min(mLastTouchY, eventY);
        mDirtyRect.bottom = Math.max(mLastTouchY, eventY);
    }
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