Re: Drawing partially transparent gradient

On Sep 7, 2009, at 2:03, Scott Stevenson wrote:

>
> On Sep 6, 2009, at 4:39 PM, Christiaan Hofman wrote:
>
>> I am trying to draw an NSGradient starting from a light gray  
>> (though that's irrelevant) to clearColor over a (light) background.  
>> However, for some reason the gradient becomes dark in the middle,  
>> while near the ends it looks as I expected. I already tried setting  
>> the compositeOperation explicitly to NSCompositeSourceOver, but  
>> that did not help (other operations are certainly wrong). Also  
>> playing with the CG blend mode got me nowhere.
>
> Without actually trying this out myself, here's my hunch: [NSColor  
> clearColor] is defined as 0.0 alpha of black, not white:
>
>  NSLog(@"clearColor: %@", [NSColor clearColor]);
>
>  clearColor: NSCalibratedWhiteColorSpace 0 0
>
> The first '0' means it's 0.0 for the white value. So the gradient is  
> not transitioning just the alpha value, but the white value as well.  
> The effect you're seeing is probably the same as what you'd see in  
> Photoshop.
>
> My guess is that creating an NSColor with 0.0 for alpha and the same  
> white value as your start color will produce the result you want.
>
>     - Scott

Yes, that's it! Thanks!

Christiaan