[konsole] [Bug 451716] Hindi font display issues: halant cut too short, horizontal line break

[bugzilla_noreply at kde.org]

https://bugs.kde.org/show_bug.cgi?id=451716

--- Comment #2 from ninjalj at gmail.com ---
Which font are you using? Using what I think is Noto Sans Devanagari, I get the
result in the attachment above. If you are using fontconfig (typical on Linux),
a way to get a list of fonts containing a given codepoint is:

fc-list :charset=928

> 1. The halant seems to be cut too short, perhaps because it's exceeding the terminal's line height.

While konsole has some special case code for rendering glyphs which exceed its
cell to the right (particularly when followed by a space), it has no provisions
for rendering glyphs exceeding the cell's height.

OT: it seems like the usual way to write namaste is with a half-consonant SA,
instead of with SA+halant.

> 2. The horizontal line between the n and m has a tiny break, which it shouldn't. 

This depends on font, font size and a konsole profile setting in
"Advanced→Bi-directional text rendering" (which should be really called
something along the lines of "complex text layout").

When enabled, the profile setting makes konsole send whole runs of text of the
same script and attributes (instead of isolated characters) to Qt's renderer,
to make sure it can render right-to-left text and complex scripts. With this
you shouldn't see the gaps, but the width of runs of text with not perfectly
monospaced fonts may be quite off, causing issues.

In the absence of perfectly monospaced fonts, there appears an inherent
trade-off between proper rendering (e.g. with no gaps in Indic scripts) and
correct cell-aligned width. mlterm has a -V option which enables variable width
columns, but I haven't had much success trying it (I still see gaps, and in any
case mlterm seems to put the halant and the vowel E about one cell before they
should be, at least on my system with my mlterm configuration). 

You can compare the screenshots below: namaste-80-ctl.png (on, no gaps, width
off) and namaste-80-no-ctl.png (off, gaps visible between instances of
"namaste", width ok).

As for font and font size, YMMV. e.g. Noto Sans Devanagari seems to combine
well with about one of every two sizes of Hack on my system.

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