Cocoa: How to draw inset text as in Mail.app?

Question

How can I draw this style of text in Cocoa (OS X)? It seems to be used in several Apple apps including Mail (as pictured above) and several places in Xcode sidebars. I've looked around but haven't been able to find any resources suggesting how to reproduce this specific style of text. It looks like an inset shadow and my first guess was to try using an NSShadow with the blur radius set to a negative value but apparently only positive values are allowed. Any ideas?

Answer 1

Please don't pick this as the answer I just implemented the above suggestions for fun and put it here because it will probably be useful to someone in the future!

https://github.com/danieljfarrell/InnerShadowTextFieldCell

Following from the advice of indragie and wil-shipley here is a subclass of NSTextFieldCell that draws the text with an inner shadow.

The header file,

// InnerShadowTextFieldCell.h
#import <Cocoa/Cocoa.h>
@interface InnerShadowTextFieldCell : NSTextFieldCell
@property (strong) NSShadow *innerShadow;
@end

Now the implementation file,

// InnerShadowTextFieldCell.m
#import "InnerShadowTextFieldCell.h"
// This class needs the NSString category -bezierWithFont: from,
// https://developer.apple.com/library/mac/samplecode/SpeedometerView/Listings/SpeedyCategories_m.html

@implementation InnerShadowTextFieldCell


- (void)drawInteriorWithFrame:(NSRect)cellFrame inView:(NSView *)controlView {

    //// Shadow Declarations
    if (_innerShadow == nil) {
        /* Inner shadow has not been set, override here with default shadow.
           You may or may not want this behaviour. */
        _innerShadow = [[NSShadow alloc] init];
        [_innerShadow setShadowColor: [NSColor darkGrayColor]];
        [_innerShadow setShadowOffset: NSMakeSize(0.1, 0.1)];
        /* Trying to find a default shadow radius which will look good for
           a label of any size, let's get a rough estimate based on the
           hypotenuse of the cell frame. */
        [_innerShadow setShadowBlurRadius: 0.0075 * hypot(NSWidth(cellFrame), NSHeight(cellFrame)) ];
    }

    /* Because we are using the -bezierWithFont: we get a slightly 
       different path than had we used the superclass to drawn the 
       text path. This means that the background colour and text 
       colour looks odd if we use call the superclass's,
            -drawInteriorWithFrame:inView: method let's do that 
       drawing here. Not making the call to super might cause 
       problems for general use (?) but for a simple label is seems 
       to work OK */
    [self.backgroundColor setFill];
    NSRectFill(cellFrame);

    NSBezierPath *bezierPath = [self.title bezierWithFont:self.font];
    [self.textColor setFill];
    [bezierPath fill];


    /* The following is inner shadow drawing method is taken from Paint Code */

    ////// Bezier Inner Shadow
    NSShadow *shadow = _innerShadow;
    NSRect bezierBorderRect = NSInsetRect([bezierPath bounds], -shadow.shadowBlurRadius, -shadow.shadowBlurRadius);
    bezierBorderRect = NSOffsetRect(bezierBorderRect, -shadow.shadowOffset.width, shadow.shadowOffset.height);
    bezierBorderRect = NSInsetRect(NSUnionRect(bezierBorderRect, [bezierPath bounds]), -1, -1);

    NSBezierPath* bezierNegativePath = [NSBezierPath bezierPathWithRect: bezierBorderRect];
    [bezierNegativePath appendBezierPath: bezierPath];
    [bezierNegativePath setWindingRule: NSEvenOddWindingRule];

    [NSGraphicsContext saveGraphicsState];
    {
        NSShadow* shadowWithOffset = [shadow copy];
        CGFloat xOffset = shadowWithOffset.shadowOffset.width + round(bezierBorderRect.size.width);
        CGFloat yOffset = shadowWithOffset.shadowOffset.height;
        shadowWithOffset.shadowOffset = NSMakeSize(xOffset + copysign(0.0, xOffset), yOffset + copysign(0.1, yOffset));
        [shadowWithOffset set];
        [[NSColor grayColor] setFill];
        [bezierPath addClip];
        NSAffineTransform* transform = [NSAffineTransform transform];
        [transform translateXBy: -round(bezierBorderRect.size.width) yBy: 0];
        [[transform transformBezierPath: bezierNegativePath] fill];
    }
    [NSGraphicsContext restoreGraphicsState];


}
@end

This could probably be made more robust but it seems fine for just drawing static labels.

Make sure your change the text color and text background color properties in Interface Builder otherwise you will not be able to see the shadow.

Answer 2

From your screenshot, that looks like text drawn with an inner shadow. Hence, the standard NSShadow method of using a blur radius of 0 won't work because that only draws the shadow under/above the text.

There are two steps to drawing text with an inner shadow.

1. Get the drawing path of the text

To be able to draw a shadow inside the text glyphs, you need to create a bezier path from the string. The Apple sample code SpeedometerView has a category that adds the method -bezierWithFont: to NSString. Run the project to see how this method is used.

2. Fill the path with an inner shadow

Drawing shadows under bezier paths is easy, but drawing a shadow inside one is not trivial. Fortunately, the NSBezierPath+MCAdditions category adds the -[NSBezierPath fillWithInnerShadow:] method to make this easy.

Answer 3

I have some code that draws an embossed cell (originally written Jonathon Mah, I believe). It might not do exactly what you want but it'll give you a place to start:

@implementation DMEmbossedTextFieldCell

#pragma mark NSCell

- (void)drawInteriorWithFrame:(NSRect)cellFrame inView:(NSView *)controlView;
{
    /* This method copies the three-layer method used by Safari's error page. That's accessible by forcing an
     * error (e.g. visiting <foo://>) and opening the web inspector. */

    // I tried to use NSBaselineOffsetAttributeName instead of shifting the frame, but that didn't seem to work
    const NSRect onePixelUpFrame = NSOffsetRect(cellFrame, 0.0, [NSGraphicsContext currentContext].isFlipped ? -1.0 : 1.0);
    const NSRange fullRange = NSMakeRange(0, self.attributedStringValue.length);

    NSMutableAttributedString *scratchString = [self.attributedStringValue mutableCopy];

    BOOL overDark = (self.backgroundStyle == NSBackgroundStyleDark);
    CGFloat (^whenLight)(CGFloat) = ^(CGFloat b) { return overDark ? 1.0 - b : b; };

    // Layer 1
    [scratchString addAttribute:NSForegroundColorAttributeName value:[NSColor colorWithCalibratedWhite:whenLight(1.0) alpha:1.0] range:fullRange];
    [scratchString drawInRect:cellFrame];

    // Layer 2
    BOOL useGradient = NO; // Safari 5.2 preview has switched to a lighter, solid color look for the detail text. Since we use the same class, use bold-ness to decide
    if (self.attributedStringValue.length > 0) {
        NSFont *font = [self.attributedStringValue attribute:NSFontAttributeName atIndex:0 effectiveRange:NULL];
        if ([[NSFontManager sharedFontManager] traitsOfFont:font] & NSBoldFontMask)
            useGradient = YES;
    }

    NSColor *solidShade = [NSColor colorWithCalibratedHue:200/360.0 saturation:0.03 brightness:whenLight(0.41) alpha:1.0];
    [scratchString addAttribute:NSForegroundColorAttributeName value:solidShade range:fullRange];
    [scratchString drawInRect:onePixelUpFrame];

    // Layer 3 (Safari uses alpha of 0.25)
    [scratchString addAttribute:NSForegroundColorAttributeName value:[NSColor colorWithCalibratedWhite:whenLight(1.0) alpha:0.25] range:fullRange];
    [scratchString drawInRect:cellFrame];
}

@end