[HarfBuzz] Backspace and Delete behaviours

[pravin.d.s at gmail.com]

On 21 July 2011 11:27, Harshula <harshula at gmail.com> wrote:

> Hi Shriramana,
>
> On Thu, 2011-07-21 at 09:27 +0530, Shriramana Sharma wrote:
> > On 07/21/2011 09:04 AM, Pravin Satpute wrote:
>
> > > 1) In pango we have faced problem of backspace due to decomposition.
> > > i.e. U+0958  was getting decomposed into U+0915 and U+093C, so for
> > > entered character was required 2 backspaces to delete.
> >
> > That doesn't sound right. The backspace should erase the last character
> > that was input. Rendering engines should only take care of rendering
> > whatever sequence of characters has been input and not change the
> > sequence of characters right?
>
> That's a bit simplistic. When a smart input method engine (IME) is
> activated, it can make sure that a backspace erases only the part of the
> glyph that the last keystroke inserted. e.g. It takes four keystrokes to
> generate කෝ (Sinhala syllable) with a particular IM. Another IM requires
> only two keystrokes. Each of these IMs controls how the backspace key
> operates and only deletes the part of the glyph inserted by the last
> keystroke.
>
> However, when the smart IME is deactivated, backspace then becomes
> someone else's responsibility. Here we see behaviour differences. e.g.
> For කෝ , Pango/gedit deletes in decomposed form (press backspace 4
> times) and ICU/OpenOffice deletes in composed form (press backspace 2
> times).
>
> Perhaps, there should be a separate discussion on which behaviour should
> be the default?
>
> Also, IIRC, Pango had a separate module that handled the cursor
> movement. I remember having to modify it for Sinhala.
>
>
Looks like we are going off topic little bit so changed subject line, but i
would like to ask one thing
is there any standard define for Backspace and Delete keys behaviour? I
think Unicode has given this but i have not find it yet
anyone knows anything?

Regards,
Pravin S
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