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CHAPTER 7: User Interfaces: The Application Kit 215Listing 7-7. Drawing Gradients// Create a gradient and use it to fill our boundsNSGradient * gradient = [[NSGradient alloc] initWithStartingColor: [NSColor whiteColor]endingColor: [NSColor lightGrayColor]];if ( self.linear )[gradient drawInRect: [self bounds] angle: 0.0];else[gradient drawInRect: [self bounds] relativeCenterPosition: NSMakePoint(0, 0)];With a little persistence and a few coordinates, it’s possible to create even more interestinggradients. You can supply an array of colors that will be spaced out evenly for you or an array ofcolors with one-dimensional coordinates for each in order to space them out for you. One usefulexample of this is to easily draw a drop shadow below something like a title bar, as shown inListing 7-8; this produces the gradient seen in Figure 7-14.Listing 7-8. A Shadow GradientNSRect r = [self bounds];// fill the background[[NSColor whiteColor] setFill];NSRectFill([self bounds]);// the top 40 pixels will be a bar: no border, just a drop shadow in the 40 pixels below itr.origin.y = NSMaxY(r) - 80.0;r.size.height = 40.0;// the nice shadow gradient—this is grayscale, so use a grayscale color spaceNSArray * colors = @[[NSColor colorWithCalibratedWhite:0.0 alpha:0.0],[NSColor colorWithCalibratedWhite:0.0 alpha:0.1],[NSColor colorWithCalibratedWhite:0.0 alpha:0.3]];const CGFloat locations[3] = {0.0, 0.8, 1.0};gradient = [[NSGradient alloc] initWithColors: colors atLocations: locations colorSpace:[NSColorSpace genericGrayColorSpace]];// now draw it flowing bottom to top (clear to dark)[gradient drawInRect: r angle: 90.0];Figure 7-14. A simple shadow gradientwww.it-ebooks.info