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

["Clément Pit-Claudel" <clement.pitclaudel@live.com>]

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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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