ctrlcctrlv · August 18, 2019 10:47
diff --git a/#inkscape-devel_20190818.log b/#inkscape-devel_20190818.log
 06:06:35 copypaste this is a stretch, but maybe someone here knows the answer to this question we have about variable font interpolation? and could comment ? https://github.com/fontforge/fontforge/issues/3803#issuecomment-522224005
 06:07:01 copypaste basically we just want to know how it's done and whether inkscape's interpolator is the same method
 06:08:39 Mc afaik, variable fonts are rendered by harfbuzz or pango
 06:12:00 Mc http://wiki.inkscape.org/wiki/index.php/Variable_Fonts_support
 06:12:19 Mc Pango >= 1.41.1; FreeType >= 2.8
 06:12:35 Mc Harfbuzz >= 1.4.2
 06:13:59 copypaste ok but
 06:14:08 copypaste how do we implement it
 06:14:12 copypaste what kind of interpolation is in use
 06:15:11 copypaste we (fontforge) also use pango. are you telling me we ought to just make pango do it and not implement the interpolation in fontforge?
 06:17:18 Mc I'm not familiar enough with the font rendering code to answer that (ping @Tav )
 06:17:23 Mc Tav_: ^
 06:19:44 copypaste yeah we want to make it possible for people to *create* Variable Fonts in FontForge
 06:20:10 copypaste so like, maybe we don't need an implementation, idk, for some things we already just create a font _on the fly_ and have freetype help us out
 06:20:15 copypaste mostly for hinting related stuff we do that
 06:20:53 Mc my guess is that would also work for variable fonts
 06:21:02 Mc but don't take my word for it
 06:21:25 Mc in Inkscape we just "use" variable fonts so that's probably simpler
 06:21:56 inkchatbot <Tav> As Mc said, we rely on pango and harfbuzz. We get the path outline data and then fill or stroke the glyphs ourselves without making any adjustments.
 06:24:12 copypaste thanks. im talking about the interpolation extension. do you know if VFs use the same type of interpolation inkscape does
 06:24:31 copypaste tbh though, im looking through the harfbuzz API and you've definitely got my attention
 06:24:48 copypaste we might be able to just use harfbuzz and not write our own implementation
 06:25:40 copypaste like obviously VFs work via interpolation right, across multiple so-called "axes". so my Q is just, what kind of interpolation is it, at implementation level. *if* you know :-)
 06:26:18 inkchatbot <Tav> No idea....
 06:26:20 Mc ah like "linear per node or control point" ?
 06:26:59 copypaste yea i used the interpolation extension to make my example images
 06:27:22 copypaste no font stuff was used. i converted to paths and then used interpolaiton extension letter by letter
 06:27:40 copypaste im trying to figure out how this works at a more fundamental level because, well, im a developer of a font editor
 06:27:43 copypaste so it matters to me :-)
 06:27:47 Mc ah, the extension in inkscape !
 06:28:03 copypaste yea :-D
 06:28:13 Mc https://gitlab.com/inkscape/extensions/blob/master/interp.py
 06:28:16 copypaste im wondering just if you guys know if OpenType variable fonts use the same interpolator as you
 06:28:27 copypaste yes that's it
 06:28:30 copypaste at like a maths level
 06:28:46 copypaste because the results i got were stunning tbh
 06:29:53 copypaste if you don't know i understand. im trying to unravel this mystery. we don't have Google or Adobe or MS helping us. we didn't write the standard and our opinion wasnt sought
 06:30:28 copypaste we weren't even given drafts of it and now a lot of people are asking for it so im exploring the possibility of getting first-party support of variable fonts in fontforge
 06:31:39 Mc afaiu, interpolation looks linear per point/handle in the standard
 06:31:54 Mc ( https://docs.microsoft.com/en-us/typography/opentype/spec/otvaroverview#algorithm-for-interpolation-of-instance-values )
 06:33:48 Mc so for interpolating paths that have the same number and type of nodes, my guess is that the extension should work the same when set to linear ?
 06:34:18 copypaste now we're cooking with gas. the letter that didn't interpolate right, "a", had one too many points
 06:34:34 copypaste when i added another point to the other "a", it interpolated perfectly
 06:34:52 copypaste so i guess i should try to make an OT var font and see if the same thing happens to "a"!
 06:35:02 copypaste then i will know whether or not the same interpolator is being used :-)
 06:35:34 Mc yeah I think most of the complicated things we do in that extension is to accomodate difference in number of nodes
 06:35:51 copypaste that doesn't work well :~)
 06:36:06 copypaste sorry, honest truth. like maybe some people would find the effect "cool"
 06:36:08 Mc I don't think that's allowed for fonts :p
 06:36:13 copypaste but it doesn't look good hehe
 06:36:16 copypaste FOR FONTS
 06:39:47 inkchatbot <Tav> BTW, SVG allows paths to be animated by interpolation but the paths must have the exact same structure. (Discussions on relaxing this requirement have never gone anywhere.)
 06:45:26 copypaste is it ok for me to put the log of this chat in our github issue?
 06:46:08 Mc sure
	06:06:35 copypaste this is a stretch, but maybe someone here knows the answer to this question we have about variable font interpolation? and could comment ? https://github.com/fontforge/fontforge/issues/3803#issuecomment-522224005
	06:07:01 copypaste basically we just want to know how it's done and whether inkscape's interpolator is the same method
	06:08:39 Mc afaik, variable fonts are rendered by harfbuzz or pango
	06:12:00 Mc http://wiki.inkscape.org/wiki/index.php/Variable_Fonts_support
	06:12:19 Mc Pango >= 1.41.1; FreeType >= 2.8
	06:12:35 Mc Harfbuzz >= 1.4.2
	06:13:59 copypaste ok but
	06:14:08 copypaste how do we implement it
	06:14:12 copypaste what kind of interpolation is in use
	06:15:11 copypaste we (fontforge) also use pango. are you telling me we ought to just make pango do it and not implement the interpolation in fontforge?
	06:17:18 Mc I'm not familiar enough with the font rendering code to answer that (ping @Tav )
	06:17:23 Mc Tav_: ^
	06:19:44 copypaste yeah we want to make it possible for people to create Variable Fonts in FontForge
	06:20:10 copypaste so like, maybe we don't need an implementation, idk, for some things we already just create a font _on the fly_ and have freetype help us out
	06:20:15 copypaste mostly for hinting related stuff we do that
	06:20:53 Mc my guess is that would also work for variable fonts
	06:21:02 Mc but don't take my word for it
	06:21:25 Mc in Inkscape we just "use" variable fonts so that's probably simpler
	06:21:56 inkchatbot <Tav> As Mc said, we rely on pango and harfbuzz. We get the path outline data and then fill or stroke the glyphs ourselves without making any adjustments.
	06:24:12 copypaste thanks. im talking about the interpolation extension. do you know if VFs use the same type of interpolation inkscape does
	06:24:31 copypaste tbh though, im looking through the harfbuzz API and you've definitely got my attention
	06:24:48 copypaste we might be able to just use harfbuzz and not write our own implementation
	06:25:40 copypaste like obviously VFs work via interpolation right, across multiple so-called "axes". so my Q is just, what kind of interpolation is it, at implementation level. if you know :-)
	06:26:18 inkchatbot <Tav> No idea....
	06:26:20 Mc ah like "linear per node or control point" ?
	06:26:59 copypaste yea i used the interpolation extension to make my example images
	06:27:22 copypaste no font stuff was used. i converted to paths and then used interpolaiton extension letter by letter
	06:27:40 copypaste im trying to figure out how this works at a more fundamental level because, well, im a developer of a font editor
	06:27:43 copypaste so it matters to me :-)
	06:27:47 Mc ah, the extension in inkscape !
	06:28:03 copypaste yea :-D
	06:28:13 Mc https://gitlab.com/inkscape/extensions/blob/master/interp.py
	06:28:16 copypaste im wondering just if you guys know if OpenType variable fonts use the same interpolator as you
	06:28:27 copypaste yes that's it
	06:28:30 copypaste at like a maths level
	06:28:46 copypaste because the results i got were stunning tbh
	06:29:53 copypaste if you don't know i understand. im trying to unravel this mystery. we don't have Google or Adobe or MS helping us. we didn't write the standard and our opinion wasnt sought
	06:30:28 copypaste we weren't even given drafts of it and now a lot of people are asking for it so im exploring the possibility of getting first-party support of variable fonts in fontforge
	06:31:39 Mc afaiu, interpolation looks linear per point/handle in the standard
	06:31:54 Mc ( https://docs.microsoft.com/en-us/typography/opentype/spec/otvaroverview#algorithm-for-interpolation-of-instance-values )
	06:33:48 Mc so for interpolating paths that have the same number and type of nodes, my guess is that the extension should work the same when set to linear ?
	06:34:18 copypaste now we're cooking with gas. the letter that didn't interpolate right, "a", had one too many points
	06:34:34 copypaste when i added another point to the other "a", it interpolated perfectly
	06:34:52 copypaste so i guess i should try to make an OT var font and see if the same thing happens to "a"!
	06:35:02 copypaste then i will know whether or not the same interpolator is being used :-)
	06:35:34 Mc yeah I think most of the complicated things we do in that extension is to accomodate difference in number of nodes
	06:35:51 copypaste that doesn't work well :~)
	06:36:06 copypaste sorry, honest truth. like maybe some people would find the effect "cool"
	06:36:08 Mc I don't think that's allowed for fonts :p
	06:36:13 copypaste but it doesn't look good hehe
	06:36:16 copypaste FOR FONTS
	06:39:47 inkchatbot <Tav> BTW, SVG allows paths to be animated by interpolation but the paths must have the exact same structure. (Discussions on relaxing this requirement have never gone anywhere.)
	06:45:26 copypaste is it ok for me to put the log of this chat in our github issue?
	06:46:08 Mc sure
No results found