Re: Button Cell Images

[Richard Frith-Macdonald]

On 24 Jun 2007, at 08:34, Christopher Armstrong wrote:

> Hi
>
> I think I've written on this before, but I don't remember getting a  
> reply so I'll try again. I want to put some images into a theme  
> bundle that are to be used as button images for radio buttons and  
> switch buttons. It appears the API for this is incomplete. Someone  
> has been working on it but I am trying to understand what they were  
> doing.

It's a long time since I had a chance to work on that ... I can  
hardly remember myself.  I think I stopped at the point where I  
realised I needed to do a lot of experimentation with Apple's code to  
make sure we matched it's behavior, and didn't have the time to do  
that experimentation.

> From what I can see, button images are currently loaded from the  
> Appkit bundle by using the +[NSImage imageNamed:] API when - 
> [NSButtonCell setButtonType:] is called. I believe the intention is  
> to replace the encoding and decoding of system button images with  
> instances of NSButtonImageSource; there appears to be some code to  
> do this in NSButtonCell.m but it doesn't make any sense.  
> NSButtonImageSource also seems incomplete and it isn't clear what  
> role GSTheme plays in this.
>
> My guess is that NSButtonImageSource instances are to be created  
> for each type of button (NSRadioButton and NSSwitch), and they are  
> to be put where -[NSButtonCell setImage:] is. NSButtonImageSource  
> appears to be a hidden class in Cocoa as both QuantumStep and  
> Cocotron have versions of it. I don't understand the part where it  
> only gets stored for the alternate image (not the main one as well).
>
> Would someone kindly explain what the intention of this is and how  
> it should work? I have the time to work on it at the moment but I  
> have no idea what should happen.

The basic idea is that buttons of the standard types have to have a  
default set of images to be automatically used when the button is in  
various states, but the programmer can override this behavior by  
setting their own image and alternate image.  Apple implemented this  
using a private NSButtonImageSource class to provide the images as  
long as the button didn't have the images overridden by the  
programmer.  Exactly what the circumstances are in which the use of  
the methods to set images will remove the NSButtonImageSource, and  
how you can get it set for a button, are not clear without  
experimentation.

Greg implemented a minimal NSButtonImageSource to handle decoding of  
nibs, but it doesn't really work the way Apples' implementation does,  
and doesn't support  theming.

What I wanted to do was produce an implementation which was  
consistent with Apple's implementation, but also worked with GSTheme  
to provide alternative sets of images for each default button type,  
so that a theme could change the default button types cleanly.  So  
when a button of the default type wants to draw itssself, it asks its  
imagesource for the image for the current state of the button, and  
the image source provides it from a cache which it populates from the  
current theme (and flushes when the theme changes).