Some View-centering code for a Canvas in an NSScrollView

CanvasCenter.m

BOOL TDSizeContainsSize(CGSize s1, CGSize s2) {
    return s1.width >= s2.width && s1.height >= s2.height;
}

CGRect TDSquareAroundPoint(CGPoint p, CGFloat side) {
    CGRect r = CGRectMake(p.x - side*0.5, p.y - side*0.5, side, side);
    return r;
}


CGPoint TDRectGetCenter(CGRect r) {
    return CGPointMake(NSMidX(r), NSMidY(r));
}

@implementation CanvasView
…

- (void)setFrame:(CGRect)newFrame {
    // center composition in scrollview
    NSClipView *cv = (NSClipView *)[self superview];
    TDAssert([cv isKindOfClass:[NSClipView class]]);
    
    CGRect compFrame = [self scaledCompositionFrame];

    // calc desired frame
    {
        CGSize superSize = cv.frame.size;
        CGSize scrollSize = compFrame.size;
        CGFloat margin = 0.0;
        
        if (TDSizeContainsSize(compFrame.size, scrollSize)) {
            margin = (CANVAS_MARGIN * 2.0)*[self currentZoomScale];
        }

        scrollSize.width += margin;
        scrollSize.height += margin;
        
        newFrame.size.width = MAX(scrollSize.width, superSize.width);
        newFrame.size.height = MAX(scrollSize.height, superSize.height);
    }

    [super setFrame:newFrame];
    
    [[self horizontalRulerView] setOriginOffset:compFrame.origin.x];
    [[self verticalRulerView] setOriginOffset:compFrame.origin.y];

    [self scrollToCenter];
}


- (void)scrollToCenter {    
    CGPoint centerPoint;
    
    if (_manipulator) {
        // if there's a selection, center around that
        centerPoint = [self convertPointFromComposition:_manipulator.center];
    } else {
        // else center around center of comp
        centerPoint = [self convertPointFromComposition:_composition.center];
    }
    
    //CGRect vizRect = [self visibleRect];
    //if (!CGRectContainsRect(vizRect, centerRect)) {
        [self scrollPointToCenter:centerPoint];
        [[[self window] windowController] invalidateRestorableState];
    //}
}


- (void)scrollRectToCenter:(CGRect)r {
    CGRect vizRect = [self visibleRect];
    if (TDSizeContainsSize(vizRect.size, r.size)) {
        CGPoint p = TDRectGetCenter(r);
        r = CGRectMake(p.x - vizRect.size.width*0.5, p.y - vizRect.size.height*0.5, vizRect.size.width, vizRect.size.height);
    }
    
    [self scrollRectToVisible:r];
}


- (void)scrollPointToCenter:(CGPoint)p {
    [self scrollRectToCenter:TDSquareAroundPoint(p, 2.0)];
}

…
@end