[FFmpeg-devel] proposal for a minor change in the behavior of the drawtext filter

[Michael Niedermayer]

On Fri, Apr 22, 2022 at 12:01:31PM +0200, Francesco Carusi wrote:
> Hello ffmpeg team,
> 
> I'm working on an enhanced version of the drawtext filter and would like to
> discuss with you about a minor change in its behavior related to line
> spacing management.
> In the current implementation the space between two lines of text is set
> equal to the height of the highest glyph found in the text plus the optional
> user defined "line_spacing" parameter (which defaults to 0):
> 
> line_height = max_glyph_h + line_spacing
> 
> This has some drawbacks:
> 1) the line height depends on the text
>     See image "line_height-old.png" (the blue lines where added by me)
>     The filter is applied three times with tree slightly different texts:
> the line_spacing parameter was not specified,
>     but the actual line height changes due to the different heights of the
> glyphs
> 2) the line height is not consistent between the same text being rendered by
> the filter and by external tools
> 
> The proposed change is:
> 1) the default line height is set to the font-defined line height
> 2) the line_spacing parameter, if specified, sets the actual line height
> (line_height = line_spacing)
> 3) the default value of line_spacing is set to -1 (which means: use the
> default line height)
> 
> The image "line_height-new.png" shows the effect of the new behavior.
> 
> Which is the impact of the change?
> A) users using the line_spacing parameter would see less space between lines
> B) users not using the line_spacing parameter would see (in most cases) more
> space between lines
> 
> Can the impact be mitigated?
> Well, yes, we may add a new parameter named 'line_height' and deprecate
> 'line_spacing', in this way anyone using line_spacing explicitly would not
> see any change in the filter behavior. I don't like this solution but it may
> help reducing the impact of the change.

just looking at the pngs, the old looks bad, the new looks like it has alot
more space then reasonable.
If i just compare this to any GUI text editor theres not that much space
between lines and at the same time the spacing is constant.
why can that not be achieved ?

thx


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When the tyrant has disposed of foreign enemies by conquest or treaty, and
there is nothing more to fear from them, then he is always stirring up
some war or other, in order that the people may require a leader. -- Plato
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 195 bytes
Desc: not available
URL: <https://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20220422/f86215bc/attachment.sig>