[cells-devel] Celtk/Cells: How to best do own new widgets...

[Ken Tilton]

Frank Goenninger wrote:

> Kenny, all:
>
> some status report on my endeavor to create a hobby app with Celtk  
> and also a few things to discuss:
>
> I have put together the GUI prototype for my app - using Tcl/Tk  directly.

Very nice!

> Purpose was to learn Tcl/Tk and see how well I could do  some advanced 
> things like building my own widgets / GUI elements  using only basic 
> commands as supported by Celtk.
>
> Now there's some GUI there that can be translated straightforward to  
> Celtk  except for a meter widget for displaying analog value like  
> voltage and current. 

I did not see anything (in a quick scan) that Celtk could not handle. 
Straightforward? Well, there is a /lot/ of code. :) And I think some of 
the code I saw begs for me to port more of my typical positioning logic 
to Celtk. These would replace Tk positioning productivity tricks pack 
and grid and rely on place (and parent-relative canvas coord scheme). 
Some of this has already been done for my commercial app.

> You can test the GUI by firing it up with
>
> wish psu-rc-gui.tcl

heh-heh. I double-clicked the file in my FireFox downloads list and up 
it came! had to get fancy to see the text. :)

>
> using the attached files. One is a font file that is needed to  
> display LCD type characters (font DS-Dgital, folder ds-digital).
>
> I used the voltmeter.tcl file by Marco Maggi  (http://wiki.tcl.tk/ 
> 9109) as a reference but decided to go without actually creating a Tk  
> widget.
>
> Now, I see the that I'd like to use some kind of new widget class  
> either by sub-classing Celtk:widget or by enhancing the Celtk:widget  
> class. I'd need some possibility to send over Tcl/Tk code to the wish  
> upon first instance creation in order to install the widget on the Tk  
> side. That's approach #1.
>
> #2 would be to do this all in Lisp and just send the drawing commands  
> to the wish...
>
> Hmmm!? Which one would you choose. Why ?

Do it all in Lisp. Why? Mainly because, looking at your code, Tk is not 
buying you anything over Celtk. all the calculations you do could be 
done as easily in Lisp. And then when you get beyond the GUI, Tk 
/really/ does not add value. I definitely want to write the hard part 
(there may not be a "hard part" to this controller, but as a rule...) in 
Lisp. So if my GUI is in Lisp and my model is in Lisp, they can easily 
talk to each other. People talk about separation of model and view, but 
they /do/ have to talk to each other, and when it is easy, developers 
tend to go further with GUIs than when it is painful. "Sure, gimme an 
hour then come back to test it" So I would as a rule rather be writing 
Lisp.

Almost as important, I think you would like the way it all turns out 
with Cells. Mind you, if your Tcl were stronger I think this would have 
been easier. I am looking at the way you positioned one button to the 
right of another by hardcoding an offset off the prior buttons position:

> set oper_lamp_x $hv_enable_lamp_x
> signal_lamp $oper_lamp_x $lamps1_y $lamps1_w $lamps1_h green 
> .oper_mode_lamp
>
> set oper_text_x $hv_enable_x
> .c create text $oper_text_x $status_text_y -text "OPER" -anchor center \
>    -font status_text_font
>
> set test_lamp_x [ expr { $oper_lamp_x + $button_distance } ]
> signal_lamp $test_lamp_x $lamps1_y $lamps1_w $lamps1_h gold  
> .test_mode_lamp
>
If you do that in a loop over  a vector of button specs, the spacing can 
be calculated relatively. then you could change the order of buttons 
without re-hardwiring all the depenedencies.

If you got stuck on Celtk, I suggest you narrow this example down to a 
few buttons, a voltage meter and a few decorations and maybe I can toss 
something off in a couple of hours to get you jumpstarted. Maybe check 
with me on what to leave in/take out before actually hacking the code to 
make sure we agree on the scope I will be able to make time for.

cheers, ken
-------------- next part --------------
A non-text attachment was scrubbed...
Name: kentilton.vcf
Type: text/x-vcard
Size: 171 bytes
Desc: not available
URL: <https://mailman.common-lisp.net/pipermail/cells-devel/attachments/20060420/c135dd2f/attachment.vcf>