ATUnclippedTextField.h

#import <Cocoa/Cocoa.h>

// NSTextField has alignmentRectInsets = {.left=.right=3, .top=.bottom=0}, so
// when autolayout aligns NSTextField to its container's side margin (e.g. to x=0),
// the actual x position is -3, and the label gets clipped.
//
// ATUnclippedTextField compensates for that by overriding drawRect to extend
// the clipping rect by alignmentRectInsets.
//
// Note that visual artifacts may occur in certain case; make sure that no other views
// are within a 3px area to both sides of the label. We take care of NSClipView,
// any other view interactions are up to you.
//
// Requires OS X 10.7.
//
@interface ATUnclippedTextField : NSTextField

@end

ATUnclippedTextField.m

#import "ATUnclippedTextField.h"


static NSView *ATFindViewAncestorByClass(NSView *view, Class ancestorClass) {
    NSView *contentView = view.window.contentView;

    while (view != nil) {
        if ([view isKindOfClass:ancestorClass])
            return view;
        if (view == contentView)
            break;
        view = view.superview;
    }

    return nil;
}


@implementation ATUnclippedTextField

// has no effect (for an unknown reason), but we set our own clipping rect anyway, so it cannot hurt either
- (BOOL)wantsDefaultClipping {
    return NO;
}

- (void)drawRect:(NSRect)dirtyRect {
    [NSGraphicsContext saveGraphicsState];

    NSRect clipRect = self.bounds;

    // compensate for alignment rect insets by extending the clip rect
    NSEdgeInsets insets = self.alignmentRectInsets;
    clipRect.origin.x   -= insets.left;
    clipRect.size.width += insets.left + insets.right;

    // force-clip by NSClipView to avoid the 3px overhang spilling out of NSScrollView
    NSView *clippingAncestor = ATFindViewAncestorByClass(self, [NSClipView class]);
    if (clippingAncestor) {
        NSRect ancestorRect = [self convertRect:clippingAncestor.bounds fromView:clippingAncestor];
        clipRect = NSIntersectionRect(clipRect, ancestorRect);
    }

    [[NSBezierPath bezierPathWithRect:clipRect] setClip];

    [super drawRect:dirtyRect];

    [NSGraphicsContext restoreGraphicsState];
}

@end