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bug#31666: Bad interaction between visual-line-mode and wrap-prefix on l


From: Clément Pit-Claudel
Subject: bug#31666: Bad interaction between visual-line-mode and wrap-prefix on long lines
Date: Sat, 9 Jun 2018 08:45:17 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0


On 2018-06-09 04:42, Eli Zaretskii wrote:
>> Would it help to restrict that property to spaces and tabs, since we only 
>> break lines on these at the moment?  Or is the cost of accessing text 
>> properties from IT_DISPLAYING_WHITESPACE too high in any case?
> 
> I didn't say it would be too expensive.  But it will definitely be
> more expensive than it is today, which is why I'm trying to suggest
> other solutions first.

Makes sense. Thanks.

>> I tried to see how often text properties were accessed after calling 
>> IT_DISPLAYING_WHITESPACE, but without too much success.  In one of the 4 
>> calls, it seems that a subsequent call to PRODUCE_GLYPHS will check 
>> specified-space properties like QCalign_to.  For the other three calls, I'm 
>> not sure.  Would these other three calls sufer from additional property 
>> checks?
> 
> The IT_DISPLAYING_WHITESPACE macro itself will have to lookup text
> properties at the location where it attempts to decide whether a space
> or a tab can be used as wrap point.
> 
>> (I can see how overlay properties would further complicate matters.  Maybe 
>> we could restrict support to char properties, at first)
> 
> That'd be most probably frowned upon by the community, since we
> generally handle them the same elsewhere in Emacs.

OK, that makes sense.

> Once again, the implementation shouldn't be hard, but if alternative
> solutions exist, I'd prefer not to make the display engine slower than
> it is already.

Understood.


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