rotate option of pango producer seems not working

[myme5261314]

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OSX 13.6.9 MLT v7.24.0

following shell will produce non-rotated text rendering in the video.

melt color:red out=250 -track -producer pango rotate=-90 text="Hello.你好" out=250 -transition composite -consumer avformat:pango.mp4

pango.mp4

Please take a look at some examples of pango text.

pango-view --text "Hello" --rotate -90  -o pango.png

pango-view --text "你好" --rotate -90 --gravity=east  -o pango.png

gravity sets to auto will have same visualization.

I notice two things:

• gravity property in pango markup text have no effects.

pango-view --markup --text "<span gravity='east'>你好</span>" --rotate -90  -o pango.png

• currently, gravity is set to auto in mlt, seems no place to adjust it.
  

  mlt/src/modules/gdk/producer_pango.c

  Line 897 in 460fde2

  pango_context_set_base_gravity(context, PANGO_GRAVITY_AUTO);

What I want to implement is the Microsoft Office's vertical text in the bounding box. Visualization like below.

But with the pango markup shell, it seems there is no way to adjust gravity only for Chinese characters (the gravity property in the span tag makes no effects).

pango-view --markup --text "<span>Hello,</span><span gravity='east'>你好</span>" --rotate -90  -o pango.png

With melt shell, it seems there is no way to implement vertical text from pango producer since the rotate parameter makes no effects in the first described video.

[bmatherly]

following shell will produce non-rotated text rendering in the video.

Rotated text is not supported when the pixel aspect ratio is not 1.0.

You can work around this by specifying a profile with square pixels.

For example, try this:
melt -profile atsc_720p_30 color:red out=250 -track -producer pango rotate=-90 text="Hello2" out=250 -transition composite

Result:

Your comments about the gravity are true, but not a bug. Just not implemented. We would welcome a patch to improve it. Also, just so you know, the pango producer is pretty old and has fallen out of favor for the qtext producer. I don't think that producer will support your rotation needs either. But if you are thinking about submitting code improvements, you might want to focus on qtext instead of pango.

[myme5261314]

Thanks for your help. It's good to know the rotate option of pango producer works with square pixel only.

I assume pango project still have some activities (https://gitlab.gnome.org/GNOME/pango/) and had already implemented the vertical text many years ago. (https://mces.blogspot.com/2007/05/advanced-opentype-features-in-pango.html)

Actually I can't find a proper way to implement vertical orientation text via qtext.
Even though qtext seems to support subset of html tags (https://doc.qt.io/qt-6/richtext-html-subset.html), but the most relevant feature lies in not included css property (https://developer.mozilla.org/en-US/docs/Web/CSS/text-orientation).