NSTextView, appending text and smooth scrolling

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- (void)maybeAutoscrollForThumb:(ThumbImageView *)thumb {autoscrollDistance = 0;// only autoscroll if the thumb is overlapping the thumbScrollViewif (CGRectIntersectsRect([thumb frame], [thumbScrollView bounds])) {    CGPoint touchLocation = [thumb convertPoint:[thumb touchLocation] toView:thumbScrollView];    float distanceFromLeftEdge  = touchLocation.x - CGRectGetMinX([thumbScrollView bounds]);    float distanceFromRightEdge = CGRectGetMaxX([thumbScrollView bounds]) - touchLocation.x;    if (distanceFromLeftEdge < AUTOSCROLL_THRESHOLD) {        autoscrollDistance = [self autoscrollDistanceForProximityToEdge:distanceFromLeftEdge] * -1; // if scrolling left, distance is negative    } else if (distanceFromRightEdge < AUTOSCROLL_THRESHOLD) {        autoscrollDistance = [self autoscrollDistanceForProximityToEdge:distanceFromRightEdge];    }        }// if no autoscrolling, stop and clear timerif (autoscrollDistance == 0) {    [autoscrollTimer invalidate];    autoscrollTimer = nil;} // otherwise create and start timer (if we don't already have a timer going)else if (autoscrollTimer == nil) {    autoscrollTimer = [NSTimer scheduledTimerWithTimeInterval:(1.0 / 60.0)                                                       target:self                                                      selector:@selector(autoscrollTimerFired:)                                                      userInfo:thumb                                                       repeats:YES];} 

}