Re: [Adobe-source-devel] command system questions

[Sean P. <sea...@ma...>]

On Dec 5, 2005, at 9:22 PM, Ralph Thomas wrote:

> Hi adobe-source list,
>
>   I was looking at the new command system and was wondering how to
> command system will work with the current "action_fallback" in
> window_server_t. Currently I use the action fallback like this:
>
>   button( name: "Rotate Right", action: @rotate, value:
> ["file://image.jpg", 90] );
>   button( name: "Rotate Left", action: @rotate, value:
> ["file://image.jpg", 270] );
>
> I specify the target of the action by the value. This is very limited,
> because I can't do things like (say) disable the buttons if
> "file://image.jpg" is read-only. Is this the kind of problem that the
> new command_system could help solve?

This is the goal - certainly the details aren't worked out yet  
(Foster's getting a good start though - I haven't yet had a chance to  
fully review his work).

The idea with the button as with a menu is that the enabled state is  
controlled by some predicate representing the pre-condition of the  
command.

Normally with Adam and buttons this is driven from invariants on the  
Adam sheet (an Adam sheet is a model for relationships having to do  
with the parameters to some function, an invariant in Adam is a pre- 
condition of the function). So normally we would bind the button to a  
parameter and it's associated predicate (fire up the image size  
example and make the very large in pixels in either dimension). You  
example would be better described as:

// eve description
button (name "Rotate Left", action: @rotate, value: 270, bind: @file);

// adam description
   input:
	file_name: "file://image.jpg";
   output:
	file <== file_name;
   invariant:
	fa <== is_valid_file(file_name, @writeable);


This is not a particularly elegant solution - but hopefully conveys  
the idea. For commands I've asked Foster to simply provide an  
"enabled" flag which can be set to reflect if the preconditions are  
satisfied - there should be two ways to drive this flag:

Have a collection of predicate functions which are evaluated "when  
something has changed" - not particularly efficient but easy to  
represent.

Have an Adam (like) rule which is updated by tracking dependencies  
(Adam is currently brute force so it isn't any more efficient than  
the above solution - but the dependencies are available so it could  
do better).

The goal here is to start using the Adam modeling capabilities for  
describing functions to control the enabling of commands.

Sean

>
> Thanks,
>  Ralph
>
>
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