3301: Can't set hint.stem with negative value programatically

1 
for glyph in Glyphs.font.glyphs:
	for layer in glyph.layers:
		if layer.hints:
			for hint in layer.hints:
				if hint.isTrueType and hint.horizontal and hint.type == TTSTEM:
						hint.options = TTDONTROUND
						hint.stem = -1

gives me an error of:

Traceback (most recent call last):
  File "<macro panel>", line 409
  File "GlyphsApp/GlyphsApp/__init__.py", line 11956, in <lambda>
  File "GlyphsApp/GlyphsApp/__init__.py", line 11949, in GSHint__setStem__
ValueError: Wrong value. Stem values can be indices of TT stems ("TTFStems" master custom parameter) or -1 for no stem or -2 for automatic.

I believe this used to workā€¦ how long ago I donā€™t remember :sweat_smile:

2

in case anyone else runs into this, a workaround is hint.setStem_(-1) though it isnā€™t documented

3

The setter expects that you have added a ā€œTTFStemsā€ custom parameter in the master settings. But there was also an error in the setter code. That I finally fixed. So thanks for the reminder.

1 Like
4

aha, thank you. just to clarify - the TTFStems parameter is unnecessary if all the hints are set to ā€œno stemā€ and/or if your PS/TT hints arenā€™t different? I assume the master-level stems get used by default and the TTFStems parameter is only used if defined?

5

Side question: why do you like to change the stem in the first place? In almost all cases, you just leave it on ā€˜autoā€™.

6

I have been testing different strategies for variable fonts, no stem seems to work better in some apps. but I am starting to lean toward no hinting at all in variable fonts. outside VF, ā€œno stemā€ also seems to work better in some glyphs in terms of how it distorts the red-colored preview outline, but I donā€™t know that it affects the actual rendering much if at all

7

If you do not use stems, you can use align instructions, instead of stem instructions. Those are basically stems without stem == -1.