How do I draw this exact gradient on the iPhone?

Question

The gradient in question is Figure 8-5 from the Quartz 2D Programming Guide, "A radial gradient that varies between a point and a circle".

I'm trying to build a CGGradient object (not a CGShading object, which might be the problem) like so:

    CGColorSpaceRef rgb = CGColorSpaceCreateDeviceRGB();
    CGFloat colors[] =
    {
        0, 0, 0, 0.9,
        0, 0, 0, 0
    };
    CGGradientRef gradient = CGGradientCreateWithColorComponents(rgb, colors, NULL, sizeof(colors)/(sizeof(colors[0])*sizeof(CGFloat)));
    CGContextClipToRect(context, rect);
    CGContextDrawRadialGradient(context, gradient, startCenter, startRadius, endCenter, endRadius, gradientDrawingOptions);
    CGGradientRelease(gradient);
    CGColorSpaceRelease(rgb);

Of course, that isn't exactly right -- the centre points and radii are correct, but the actual gradient doesn't look the same. I just wish Apple had provided the source code for each example! >:(

Answer 1

UPDATE: These color values add the shading on top of other content (drawing from a point out to a circle):

CGFloat colors[] =
{
    0.0f, 0.0f, 0.0f, 0.0f,
    0.0f, 0.0f, 0.0f, 0.75f
};

Using these color values is pretty close (drawing from a point out to a circle):

CGFloat colors[] =
{
    0.0f, 1.0f, 1.0f, 1.0f,
    0.0f, 0.0f, 0.0f, 0.75f
};