Why do some feature codes get altered when opening a font file with Glyphs?

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When you open a font file using the Glyphs application, some feature codes (OpenType feature code) might appear to have been changed 。

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With “font file”, do you mean an OTF/TTF file? Those are exported files which cannot be fully reconstructed into feature code and so the code looks different and might be missing some parts. Similar to how you cannot open a PDF in Word and expect to get an editable document that looks exactly like the PDF or open an image in Photoshop and expect that all of the layers are still there.

When working with source files like .glyphs, .glyphspackage, or .ufo, feature code will not be altered when opening the file again.

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But is there any room for improvement that would preserve more feature code?

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There is always room for improvement. Could you send me your file, I could have a look. But can’t promise anything.

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ichitenfont/I.Ming: I.Ming ( I.明體 / 一点明朝体 / 一點明體 ) (github.com)
about：˥˦˧˨˩꜒꜓꜔꜕꜖

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I have same problem. I open it in fontlab and see more feature codes. then save it for glyphs

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For the record, there is no feature code in a compiled font (.otf/.ttf). Therefore, no feature code can be ‘preserved’. Feature code is something you only see in the source formats (.glyphs/.ufo/.vfb). Different editors (Glyphs, Robofont, FontLab) use different kinds of code, and they are not 100% compatible with each other. So, if you want to preserve feature code, you need to get the original source file.

So the big question is: Why do you reverse engineer compiled fonts? Why do you not use the source files instead?

The quantity alone of reverse-engineered code does not say much yet. E.g. feature code in Glyphs can express some things more efficiently (with less code) than FontLab can.

Of course the results of reverse engineering feature code are different. Very unlikely to get the exact same thing. This by itself is to be expected and not a problem.

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Mainly for study and research.

There are different ways to achieve the same effect.

However, even open source fonts rarely provide source code.

FontCreator can read most of the source code, but there are still losses.

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What?

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Feature code

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The definition of open-source fonts is that they are open-source.

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I misunderstood, they are free fonts.