Add .otf back in for KDE users who want gamma-corrected rendering

[taprobane99]

KDE qt5 does gamma-corrected rendering of fonts, but only .otf.

On my system I have font hinting turned off completely.

Can you add .otf back in to the release, so that I can have proper gamma-corrected Fira Code on my desktop?

More info:

TTF (e.g. Noto Sans, Ubuntu)

No stem darkening and no gamma corrected alpha blending

Fonts appear too thin on dark backgrounds (e.g. dark themes, terminal applications)

Fonts appear too bold on light backgrounds

Prone to color fringing when using subpixel antialiasing

OTF (e.g. Cantarell)

Stem darkening and gamma corrected alpha blending (this is how it is done on macOS and Windows)

Fonts look nice on both light and dark backgrounds

Color fringing is not an issue.

[tonsky]

Interesting! Do you have any docs that confirm that the file extension is the primary cause of this?

[taprobane99]

This is the doc from the qt foundation confirming that only otf's are treated this way

"Enabled stem-darkening and gamma-correction on OpenType fonts on platforms that use FreeType, if supported."

https://doc.qt.io/qt-5/whatsnew59.html

I am not an expert, but my understanding is that a .otf file can contain .ttf or .otf, but not the reverse. It's not the extension that's important, but that the font has to be OpenType in the first place. Is Fira Code an otf font?

[taprobane99]

Also "The correct way of rendering a glyph image on a surface is to alpha blend it onto the surface in linear space and then apply gamma correction to translate the linear coverage map to something that is correct for our screens.1 No toolkit in the Linux ecosystem does it by default, even though Qt5 and Skia can and will do it on other platforms. Windows and Mac OS X do it natively. "

https://www.freetype.org/freetype2/docs/text-rendering-general.html

I think it is turned on in more recent versions of KDE Plasma.

[tonsky]

I am confused as well, but according to this: #939 (comment) yes, .ttf has opentype font, but truetype outlines and truetype container.

Can you confirm that when you switch between otf/ttf from e.g. https://github.com/tonsky/FiraCode/releases/tag/4 it turns gamma correction on/off? Maybe attach some screenshots?

[taprobane99]

Hi. Yes a definite difference. Tested with v4. Look how much darker the .ttf is [2nd image]!

I think you will need to download these and zoom in

Also, this is on a white background. On a coloured or black background the problems with .ttf will be even greater, which is why alpha blending and gamma correction are important.

[taprobane99]

zoomed in. ttf second

[tonsky]

Interesting! Can you try it on the latest version too, please (attached)? Just to confirm that file extension is the trick

Fira Code v6.zip

[taprobane99]

ttf 2nd. same thing. blacker/harsher blending with .ttf

[kenmcd]

FiraCode OTF-TT files have extensive hinting.
Of course they look darker than some Freetype canned rendering for OTF-PS files.
There is no "defect" in FiraCode fonts which needs to be fixed here.
It is just different. Just like the rendering on the Mac is just different.
Your personal preference for the minor differences resulting from a different rendering engine is not a reason to resurrect the OTF-PS files - and all of the other baggage that comes with it.

[taprobane99]

I have hinting turned off so there is no auto-hinting above. It is darker because it is incorrectly blended to the background.

Alpha blended and gamma corrected rendering is the correct method. It is used in Windows and OS X for both .ttf and .otf. Especially if you have a non-white background, or non-black text, then you just end up with an uneven mess without it. Unfortunately Linux support is limited to .otf

Screenshots are a poor way of showing what I am talking about, but there is a definite difference switching between the two formats. I attach photos of my 4K screen with a solarised background theme. It will be even worse on a 1080p screen.

I'm sure many Linux users will be using Fira Code with coloured or black background, in which case they are currently experiencing an inferior rendering of it. Look at the details lost in the letters i , r, and g in the ttf.

(ttf second)

Also I have noticed that some Linux apps when needing bold, apply a false-bold to the regular .ttf version instead of using the bold version, even though it is available. With .otf the bold version is used.

It will be shame if you cannot fix this.

[tonsky]

Ok, (hopefully) last thing so that we get to bottom of this. Can you compare these two for me? I turned off hinting in both, so that we can make sure it’s the file format and not anything else

Fira Code v6 unhinted.zip

P.S. is your primary problem with TTF its width? Have you tried Retina weight? Does it work better for you?

[taprobane99]

Photos of unhinted font (ttf second). Again the .ttf is generally less evenly rendered and there is a loss of small details. It's hard to convey this in photos, but it is obvious when viewing directly. It doesn't get better with other weights.

None of this is surprising. It's just that Freetype currently uses Adobe's CFF high quality rendering engine for .otf which includes the features mentioned earlier, and a less sophisticated engine for .ttf.

[HanabishiRecca]

so that we can make sure it’s the file format and not anything else

This is called Stem Darkening, a FreeType feature which work only with OpenType/CFF (.otf) fonts.
https://freetype.org/freetype2/docs/hinting/text-rendering-general.html

One of the reasons why otf is preferred on Linux.

[AchillesBoi]

This is called Stem Darkening, a FreeType feature which work only with OpenType/CFF (.otf) fonts.
https://freetype.org/freetype2/docs/hinting/text-rendering-general.html

One of the reasons why otf is preferred on Linux.

Hi there @HanabishiRecca, stranger passing by. I believe stem darkening is also available for TTF through AutoFitter. I have an environment variable that enables stem darkening system-wide for all fonts including OTF and TTF and it works:

FREETYPE_PROPERTIES="cff:no-stem-darkening=0 autofitter:no-stem-darkening=0"

Add this to /etc/environment and restart the computer.

[HanabishiRecca]

I believe stem darkening is also available for TTF through AutoFitter.

Unfortunately it does not work for me.
With the variable set, difference is still very noticable:

- TTF
- OTF