[TCLCORE] Re: Fwd: -underline patch [tcl gateway]

[Laurent D. <lau...@ne...>]

On 22 Aug, Scott Stanton wrote:
> 
> This is a great idea!  It's taking advantage of some features in Unicode 
> to finesse the whole underline issue.  The concept is quite elegant, 
> really.  I do have a few comments about the implementation though:
> 

Thanks to Jan for the idea. I didn't even know such a character existed.

> - If you are adding \_ to the Tcl backslash parser, you need to do the 
> same thing for the regexp backslash parser.
> 

Ok, I'll look at it as soon as I have the time. Maybe even tonight.

> - Rather than putting a constant like 0x332 directly in the code, it might 
> be better to add a #define for TCL_COMBINING_LOW_LINE (the official 
> Unicode character name).
> 

Ok. Does this go in tcl.h? I guess, if it's needed by Tk.

> - Don't assume that the \_ character actually takes 2 bytes.  This is only 
> true if the string is in canonical UTF form.  It's actually possible to 
> represent a \_ with 3 or more bytes in a non-canonical form.  Always use 
> the Tcl UTF functions to compute character offsets.
> 

Ok. I'll revise that.

> - Your algorithm ends up scanning the string twice.  It would be faster to 
> skip the call to Tcl_UtfFindFirst() and just do character by character 
> comparisons.
> 

Hmmm... Ok. I have to go thru the string anyway.

> - If you remove the \_ from the original text string, then a cget -text 
> won't return the correct value.  You need to make a separate copy of the 
> string for rendering purposes.
> 

Well, the whole idea of removing the string was so I wouldn't have to keep a
separate copy around. I didn't want to modify the structure of tkButton and
gobble up even more memory. As I said in the Enhancement request on clt, I
didn't really like it. ... So maybe I'll add another attribute to tkButton
which will be non-null only if the string contains a \_ in it. That way, you
only use up 4 bytes to store the pointer but nothing else if you're not using
the facility. This will change the way ConfigureButton() works.

> - If you were going to update the string in place, you should call 
> Tcl_SetObjLength to set the new length.
> 

Ok, didn't know thatg.

> 
> For illustrative purposes, here is a revised ButtonComputeUnderline 
> function.  It hasn't been tested (and so is probably wrong in some 
> places), and it assumes the addition of a butPtr->textDisplayPtr field to 
> hold the display string.  It does demonstrate the correct way to process 
> the UTF data, though.  Note the use of Tcl_GetStringFromObj to get the 
> length in bytes in addition to the string pointer.
> 

Thanks, I'll study it and I'll try to send a revised patch by week's end but I
make no promises.

L

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