[Seaside] Brushes and state

James Foster Smalltalk at JGFoster.net
Mon Jun 22 22:44:17 UTC 2009


I've gotten things going with GoogleMap as something other than a  
Brush or Component (see GoogleMaps-jgf.22.mcz in http://seaside.gemstone.com/ss/GoogleMaps.html) 
. As an exercise in rendering a generic object, it was certainly  
useful (I knew of the capability, but hadn't ever done it). My  
immediate reaction is that it is cleaner in that it _uses_ a brush  
rather than _is_ a brush. On the other hand, there are some  

With the Brush implementation, there are a number of inherited  
"features" that just come along. Specifically, I now need to cache any  
tag-related attributes that the programmer might want to set (such as  
ID, CLASS, etc.) and put them out. If there were a need for a full  
implementation, then this could get awkward (for example, I didn't do  
STYLE, and I don't support generic attributes).

Also, when I create my own canvas in #'renderOn:' (as suggested by  
your code just below), callbacks fail because the implementation of  
#'children' is incomplete. My work-around was to just use the passed- 
in Renderer, assuming that it supports HTML.

If the design philosophy is that Brushes represent only things defined  
in the official HTML spec (which seems reasonable), then the new  
approach is good enough. I do like this better than making a full  
Component (which seems heavy-weight).



On Jun 19, 2009, at 7:51 PM, Julian Fitzell wrote:

> That should provide a good comparison.
> Looking at the 2.9 code now I realize it may be hard for you to  
> simply lift the code because of the refactoring in the way walking  
> the component tree happens.
> As a starting point for 2.8, try making GoogleMap subclass Object  
> and implement something like:
> renderOn: aRenderer
>   |html|
>   html := WAHtmlCanvas
>     context: aRenderer context
>     callbacks: (aRenderer context callbacksFor: self).
>   self renderContentOn: html.
> I think you should then be able to implement #renderContentOn: to  
> output your content and allow a GoogleMap to be passed to the  
> #render: method.
> That code is untested, just typed into gmail, but it should be  
> something like that. :)
> Julian
> On Fri, Jun 19, 2009 at 4:43 PM, James Foster  
> <Smalltalk at jgfoster.net> wrote:
> Julian,
> I think the only think I'm equipped to give even a weak opinion on  
> is that as I was doing this some months ago I found a Brush to be  
> more natural to use (as a client) than a Canvas. As to the relative  
> merits of Painter and Renderer, I'm just not sufficiently informed  
> to venture an educated opinion (though that isn't usually an  
> impediment ;-).
> I like your point that a Brush can be embedded in another Brush and  
> this is a feature that the GoogleMap does not need. Given that  
> sending #with: to a GoogleMap does not make sense, I'll agree that  
> making it a Brush is a bit awkward. Also, there is a sense in which  
> subclassing from WADivTag comes back to the question of delegation  
> vs. inheritance, and in principal I'd prefer delegation.
> In an effort to contribute more intelligently to this discussion,  
> I'd like to try refactoring my library using a Painter. I'll fire up  
> a Seaside 2.9 environment and look at WAPainter with an eye toward  
> what would be required to refactor my GoogleMap in a Seaside 2.8  
> environment.
> James
> On Jun 19, 2009, at 12:20 PM, Julian Fitzell wrote:
>> On Fri, Jun 19, 2009 at 10:50 AM, James Foster <Smalltalk at jgfoster.net 
>> > wrote:
>> Julian,
>> As you were going through this my thought was eventually expressed  
>> when you said that the painter approach "works essentially the same  
>> as the brush" approach. And Yes, my updateRoot: code was simply an  
>> extension to WAComponent that adds some JavaScript. Switching it to  
>> a class-side method on GoogleMaps as you describe would be  
>> equivalent and perhaps more obvious and less intrusive.
>> The part I'm not yet following or seeing much value in is the idea  
>> that using a different renderer would be desirable. I don't see  
>> much point of rendering a GoogleMap on anything other than an HTML  
>> canvas. Or are you envisioning two renderers (HTML for the  
>> GoogleMap thing and something else for the rest)? At the moment, my  
>> understanding of the alternate renderers is so shallow that I don't  
>> see the use/value. For my purposes, at least, I'll probably leave  
>> my implementation as a Brush subclass since it seems to work for  
>> all use cases I understand. Which is not to say that I mind the  
>> discussion!
>> James,
>> The discussion is clarifying for me as well so let's carry on... :)
>> First, I do think your design would be improved slightly by putting  
>> that method on the class side of GoogleMap.
>> The idea of having different Renderers is that, for example,  
>> somebody might eventually decide they'd really like to have  
>> templates in Seaside and that would probably be implemented as a  
>> different Renderer. Or maybe they want to embed a google map in a  
>> Component that is using the RSS Renderer (actually, that Renderer  
>> still uses Brushes, so it may not be the best example). As I said,  
>> this is relatively theoretical at the moment given the lack of  
>> other Renderers but I'm interested in it from the architectural  
>> angle.
>> I believe (and this is where I may be wrong) that an implementation  
>> using Brushes is (slightly) less flexible and, while there are  
>> things that would be easier using Brushes, I don't see that this  
>> problem does any of those things.
>> Or to look at it another way, just as you say that GoogleMap  
>> doesn't need to *be* a Component but can be rather *used by* a  
>> Component, I don't think it needs to *be* a Brush but can instead  
>> *use* a Brush; there's nothing you need to output to the Document  
>> that can't easily be done with the existing Brushes.
>> So you might end up with
>> MyComponent
>>   (uses)
>> any Renderer
>>   (to render a)
>> GoogleMap (a Painter)
>>   (which uses its)
>> HtmlCanvas (a Renderer)
>>   (to get a)
>> DivTag (a Brush)
>>   (which writes to)
>> HtmlDocument (a Document)
>>   (which writes to)
>> Stream
>> When I say it "works essentially the same as the brush", what I  
>> mean is, the Painter implementation is equally convenient to use  
>> and no harder to implement but provides added flexibility. It also  
>> requires no class method extensions and means you can leverage  
>> WAScriptTag instead of duplicating stuff to make sure the CDATA is  
>> added and so on. Since I can't (yet) see an advantage to the Brush  
>> implementation, my suggestion is that the Painter implementation is  
>> "more correct" architecturally.
>> I still think "uses a Brush" (actually two) is a clearer  
>> relationship for this than "is a Brush" even in 2.8, but without  
>> Painter there's really no added benefit (though you could easily  
>> duplicate the very limited amount of functionality Painter has in  
>> its #renderOn: method and you'd be in the same shape as 2.9).
>> So the architectural question for me comes down to (sorry for the  
>> long message), is there an additional benefit to doing it as a  
>> Brush over a Painter that I'm missing?
>> Julian
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