[Adium-devl] Improving BiDi support

[Evan Schoenberg]

On Sep 3, 2008, at 7:03 PM, Ofri wrote:

> The problem begins when sending/receiving messages made up of only
> weak characters and/or emoticons. If the message contains only weak
> characters, the algorithm uses NSWritingDirectionNatural as the
> direction, which aligns the message however defined in the message
> style (which left unless someone uses an RTL style). The problem with
> emoticons is that the direction algorithm is scanning the message as a
> simple string without knowing anything about them, so if for example I
> send the message ":-P" I'll be aligned left because "P" is a strong
> LTR character.
>
> Based on the above, my improved BiDi algorithm goes like this:
> 1. Remember the direction of the last sent and the last received
> messages.
> 2. When a new message is written/received, scan it for emoticons and
> remove them. Keep the stripped string.

Rather than stripping emoticons in a separate processing step  
(expensive and cumbersome), an RTL determination filter should run  
after emoticonification occurs.  It then will be able to neatly skip  
over emoticons with ease.  If it skips over all characters in a  
string, the string doesn't have a direction.  Then proceed with your  
proposal as below:

> 3. Try to determine the direction of the stripped message, using the
> algorithm described above (implemented as an NSString category in the
> FriBiDi framework).
>   3.1 If the string has a direction, remember it and display the
> complete message with that direction.
>   3.2 If the string doesn't have a direction, assume it's a
> continuation of the previous message and use the stored direction.
>   3.3 The string doesn't have a direction, and there's no previous
> direction.
>     3.3.1 If the message is outgoing, use the input field's  
> direction .
>     3.3.2 If the message is incoming, use the previous outgoing
> direction if available, and if not leave it up to the message style.
> This assumes that if I initiated a conversation in one language, the
> other side will usually answer in the same language.
>
> In addition, I also suggest a behavior change to the writing direction
> contextual menu, which will disable it when we know the direction and
> enable it when we don't. This will allow the user to override our
> algorithm for some edge cases. This will also make the input of the
> user consistent with the way it's displayed in the message view.

"When we know the direction?"  If this is the user's input field, can  
we know what the user is about to type?

Cheers,
Evan

> This solution seems rather complex for something that's not critical
> for the client to work, and that most users won't even notice (RTL
> users are a minority AFAIK. BTW, why not to include this info with
> Sparkle?). In addition, I don't know how easy it will be to strip
> emoticons from a string (never touched that code), and if it'll slow
> things down. Finally, I doubt I'll have the time to implement what I
> described above anytime soon.
>
> What do other people think? Sure it'd be nice to be able to say that
> Adium is the only IM client on all platforms that properly supports
> BiDi conversations, but does it worth the effort?

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