Simple script: Find and complete real ascender and descender values in all open fonts

Ramiro Espinoza · December 2016

Hi there,

This script will find the highest and lowest Y values in all open fonts (typically a family) and use them to fill the OpenType specific font metrics values. Works in Fontlab + Robofab (and probably Robofont too).

Image: https://us.v-cdn.net/5019405/uploads/editor/eg/7abbjtmssco0.png

#FLM: ReType Complete Real Asc/Desc V2.0
# Find and fill real asc and desc values in all open fonts 
from robofab.world import CurrentFont,AllFonts


max_Y_values = []
min_Y_values = []


for font in AllFonts():
	for x in font:
			max_Y_values.append(x.box[3])
			min_Y_values.append(x.box[1])

WinAscend = max(max_Y_values)
WinDescend = min(min_Y_values)
Ascender =	font.info.ascender 
Descender =	font.info.descender
Gap =  (Ascender + abs(Descender)) - (WinAscend + abs(WinDescend)) 

for font in AllFonts():
	font.info.openTypeOS2WinAscent = WinAscend
	font.info.openTypeOS2WinDescent = abs(WinDescend)
	font.info.openTypeOS2TypoAscender = Ascender
	font.info.openTypeOS2TypoDescender = Descender
	font.info.openTypeHheaAscender = WinAscend
	font.info.openTypeHheaDescender = -abs(WinDescend)
	font.info.openTypeHheaLineGap = 0
	font.info.openTypeOS2TypoLineGap = abs(Gap)

print
print "In all open fonts:"
print "The maximun Y value is: "+ str(max(max_Y_values))
print "The minimum Y value is: "+ str(min(min_Y_values))
print "TypoLineGap is: " + str(Gap)

Lukas Schneider · December 2016

Hi Ramiro, maybe it would be good to leave out certain glyphs (like aringacute/Aringacute for example)?
there is another script by @Jens Kutilek (based on Karsten Lücke’s Calculations) for calculating the vertical metrics as well:
https://github.com/jenskutilek/RoboFont/blob/master/scripts/SetVerticalMetrics.py

Ramiro Espinoza · December 2016

Hi Lukas,
I sort of forgot the 'Aringacute' issue because I don't include it anymore in my fonts.
But you are right, this situation should be addressed. Below is the same script but with a line that exclude 'Aringacute' from the list. IMO, 'aringacute' is not usually a problem. I will check later Jens' script (surely way much better than mine).

#FLM: ReType Complete Real Asc/Desc V2.1
# Find and fill real asc and desc values in all open fonts 
from robofab.world import CurrentFont,AllFonts


max_Y_values = []
min_Y_values = []

for font in AllFonts():
	for x in font:
		if x.name != 'Aringacute':
			max_Y_values.append(x.box[3])
			min_Y_values.append(x.box[1])

WinAscend = max(max_Y_values)
WinDescend = min(min_Y_values)
Ascender =	font.info.ascender 
Descender =	font.info.descender
Gap =  (Ascender + abs(Descender)) - (WinAscend + abs(WinDescend)) 

for font in AllFonts():
	font.info.openTypeOS2WinAscent = WinAscend
	font.info.openTypeOS2WinDescent = abs(WinDescend)
	font.info.openTypeOS2TypoAscender = Ascender
	font.info.openTypeOS2TypoDescender = Descender
	font.info.openTypeHheaAscender = WinAscend
	font.info.openTypeHheaDescender = -abs(WinDescend)
	font.info.openTypeHheaLineGap = 0
	font.info.openTypeOS2TypoLineGap = abs(Gap)

print
print "In all open fonts:"
print "The maximun Y value is: "+ str(max(max_Y_values))
print "The minimum Y value is: "+ str(min(min_Y_values))
print "TypoLineGap is: " + str(Gap)

PabloImpallari · December 2016

The script is useful, but instead of letting the design dictate those values I suggest planning those values from the very beginning of the design process and use it as a restrain. In particular if you are adding Vietnamese or multiscript typefaces.

Vassil Kateliev · December 2016

Here is a slightly better and a little more complex, de-robofabed script.
It will also get dimensions of composite characters and utilizes a banList of omitted glyphs.

#FLM: Set Vertical Metrics 1.2 
#(based on ReType.com Complete Real Asc/Desc V2.1)
# ------------------------
# (C) Vassil Kateliev, 2016 (http://www.kateliev.com)

# No warranties. By using this you agree
# that you use it at your own risk!

from FL import *

# - Global configuration
banList = 'Aring Abreve'.split(' ') # List of omitted glyphs
workWithComponents = True # Process composite characters - non destructive

# - Functions
def getFontYBounds(font, banList, workWithComponents = False):
	'''
	Returns tuple(min_Y, max_Y) values for given [font] omitting glyph names (str) listed in [banList].
	'''

	def getYBounds(glyph):
		return (glyph.GetBoundingRect().y, glyph.GetBoundingRect().height + glyph.GetBoundingRect().y)

	fontMinY, fontMaxY = [], []

	for gID in range(len(font)):
		currGlyph = font[gID]
		if currGlyph.name not in banList and not len(currGlyph.components):
			yBounds = getYBounds(currGlyph)

		elif currGlyph.name not in banList and len(currGlyph.components) and workWithComponents:
			tempGlyph = Glyph(currGlyph)
			currGlyph.Decompose() 			# Workaround! tempGlyph is an orphan so it could not be decomposed
			yBounds = getYBounds(currGlyph)
			currGlyph.Assign(tempGlyph) 	# Repair that mess!
		
		fontMinY.append(int(yBounds[0])); fontMaxY.append(int(yBounds[1]))

	return (min(fontMinY), max(fontMaxY))

# - Run	-------------------
# - Get values
fontBounds = zip(*[getFontYBounds(fl[fID], banList, workWithComponents) for fID in range(len(fl))])
fontInfoBounds = zip(*[(fl[fID].descender[0], fl[fID].ascender[0]) for fID in range(len(fl))])

WinAscend, WinDescend = max(fontBounds[1]), min(fontBounds[0])
Ascender, Descender = max(fontInfoBounds[1]), min(fontInfoBounds[0])
Gap = abs((Ascender + abs(Descender)) - (WinAscend + abs(WinDescend)))

# - Process all open fonts
for fID in range(len(fl)):
	currentFont = fl[fID]

	# - Report
	print '\nProcessing:\t%s\n-----\nFont feature\tOLD\tNEW'  %currentFont.full_name
	print 'WIN Ascent:\t%s \t%s' %(currentFont.ttinfo.os2_us_win_ascent, WinAscend)
	print 'WIN Descent:\t%s \t%s' %(currentFont.ttinfo.os2_us_win_descent, abs(WinDescend))
	print 'Typo Ascent:\t%s \t%s' %(currentFont.ttinfo.os2_s_typo_ascender, Ascender)
	print 'Typo Descent:\t%s \t%s' %(currentFont.ttinfo.os2_s_typo_descender, Descender)
	print 'Typo Line Gap:\t%s \t%s' %(currentFont.ttinfo.os2_s_typo_line_gap,Gap)
	print 'HHEA Ascent\t%s \t%s' %(currentFont.ttinfo.hhea_ascender, WinAscend)
	print 'HHEA Descent:\t%s \t%s' %(currentFont.ttinfo.hhea_descender, -abs(WinDescend))
	print 'HHEA Line Gap:\t%s \t%s\n' %(currentFont.ttinfo.hhea_line_gap, 0)
	
	# - Process
	currentFont.ttinfo.os2_us_win_ascent = WinAscend
	currentFont.ttinfo.os2_us_win_descent = abs(WinDescend)

	currentFont.ttinfo.os2_s_typo_ascender = Ascender
	currentFont.ttinfo.os2_s_typo_descender = Descender
	
	currentFont.ttinfo.hhea_ascender = WinAscend
	currentFont.ttinfo.hhea_descender = -abs(WinDescend)
	
	currentFont.ttinfo.hhea_line_gap = 0
	currentFont.ttinfo.os2_s_typo_line_gap = Gap

print 'End.'

Thomas Phinney · January 2017

PabloImpallari said:

The script is useful, but instead of letting the design dictate those values I suggest planning those values from the very beginning of the design process and use it as a restrain. In particular if you are adding Vietnamese or multiscript typefaces.

I agree—and when planning these values from the beginning, you should consider that you need to either allow for such things as Vietnamese stacked accents from the beginning (even if they aren't in your current plans), else be prepared that if you add such things later, you may have to break vertical metrics compatibility with the older version of the font.

Ramiro Espinoza · January 2017

The way I use this sort of scripts doesn't exclude the kind of planning Pablo and the rest are mentioning. It would be silly not to have an idea of the vertical boundaries of a family I have designed. But with a script you can quickly determined the highest and lowest points in the heaviest weights and see if everything is within the planned limits.
And I frequently work on fonts from other designers and therefore need to asses the family to enter the correct values. I am not producing Vietnamese fonts and I don't need to care much about stacked diacritics.

Stuart Sandler · January 2017

Thanks for this gang! Quick way to port this to Glyphs?

LeMo aka PatternMan aka Frank E Blokland · January 2017

[…] when planning these values from the beginning, you should consider that you need to either allow for such things as Vietnamese stacked accents from the beginning […]

I could be wrong, but wasn’t bit 7 (USE_TYPO_METRICS) in the in OS/2 table v.4 not speciﬁed to get rid of this problem, i.e., that one can use the largest WinAscent/Descent values to prevent clipping without inﬂuencing the line spacing?

Simon Cozens · January 2017

Stuart Sandler said:

Thanks for this gang! Quick way to port this to Glyphs?

Quickest way is to buy Simon beer.

Jens Kutilek · January 2017

Stuart Sandler said:

Thanks for this gang! Quick way to port this to Glyphs?

Robofab scripts should run in Glyphs without modifications.

Georg Seifert · January 2017

This script does not use RoboFab any more. I adapted it to run in Glyphs. I hope I didn't mess it up

#FLM: Set Vertical Metrics 1.2 
#(based on ReType.com Complete Real Asc/Desc V2.1)
# ------------------------
# (C) Vassil Kateliev, 2016 (http://www.kateliev.com)
# Adapted for Glyphs by Georg Seifert
# No warranties. By using this you agree
# that you use it at your own risk!

import GlyphsApp

# - Global configuration
banList = 'Aring Abreve'.split(' ') # List of omitted glyphs
workWithComponents = True # Process composite characters - non destructive

# - Functions
def getFontYBounds(font, banList, workWithComponents = False):
	'''
	Returns tuple(min_Y, max_Y) values for given [font] omitting glyph names (str) listed in [banList].
	'''

	def getYBounds(layer):
		bounds = layer.bounds
		return (NSMinY(bounds), NSMaxY(bounds))

	fontMinY, fontMaxY = [], []
	masterIDs = [m.id for m in font.masters]
	
	for currGlyph in font.glyphs:
		if currGlyph.name not in banList:
			for masterID in masterIDs:
				currLayer = currGlyph.layers[masterID]
				if not len(currLayer.components) or workWithComponents:
					yBounds = getYBounds(currLayer)
		
		fontMinY.append(int(yBounds[0])); fontMaxY.append(int(yBounds[1]))

	return (min(fontMinY), max(fontMaxY))

# - Run	-------------------
# - Get values
fontBounds = []
fontInfoBounds = []
for currFont in Glyphs.fonts:
	fontBounds.append(getFontYBounds(currFont, banList, workWithComponents))
	for currMaster in currFont.masters:
		fontInfoBounds.append((currMaster.descender, currMaster.ascender))
fontBounds = zip(*fontBounds)
fontInfoBounds = zip(*fontInfoBounds)

WinAscend, WinDescend = max(fontBounds[1]), min(fontBounds[0])
Ascender, Descender = max(fontInfoBounds[1]), min(fontInfoBounds[0])
Gap = abs((Ascender + abs(Descender)) - (WinAscend + abs(WinDescend)))

# - Process all open fonts
for currFont in Glyphs.fonts:
	
	# - Report
	print '\nProcessing:\t%s\n-----\nFont feature\tOLD\tNEW' % currFont.familyName
	for currMaster in currFont.masters:
		print 'Master:\t%s' % currMaster.name
		if currMaster.customParameters["winAscent"]:
			print '  WIN Ascent:\t%s \t%s' % (currMaster.customParameters["winAscent"], WinAscend)
		if currMaster.customParameters["winDescent"]:
			print '  WIN Descent:\t%s \t%s' % (currMaster.customParameters["winDescent"], WinDescend)

		if currMaster.customParameters["typoAscender"]:
			print '  Typo Ascent:\t%s \t%s' % (currMaster.customParameters["typoAscender"], Ascender)
		else:
			print '  Typo Ascent:\t%s \t%s' % (currMaster.ascender, Ascender)
		if currMaster.customParameters["typoDescender"]:
			print '  Typo Descent:\t%s \t%s' % (currMaster.customParameters["typoDescender"], Descender)
		else:
			print '  Typo Descent:\t%s \t%s' % (currMaster.descender, Descender)
		if currMaster.customParameters["typoLineGap"]:
			print '  Typo Line Gap:\t%s \t%s' % (currMaster.customParameters["typoLineGap"], Gap)
		else:
			print '  Typo Line Gap:\t%s \t%s' % (currFont.upm * 1.2 - (currMaster.ascender + currMaster.descender), Gap)
		
		if currMaster.customParameters["hheaAscender"]:
			print '  HHEA Ascent\t%s \t%s' % (currMaster.customParameters["hheaAscender"], WinAscend)
		if currMaster.customParameters["hheaDescender"]:
			print '  HHEA Descent:\t%s \t%s' % (currMaster.customParameters["hheaDescender"], -abs(WinDescend))
		if currMaster.customParameters["hheaLineGap"]:
			print '  HHEA Line Gap:\t%s \t%s\n' % (currMaster.customParameters["hheaLineGap"], 0)
	
			# - Process
		currMaster.customParameters["winAscent"] = WinAscend
		currMaster.customParameters["winDescent"] = -abs(WinDescend)
	
		if abs(currMaster.ascender - Ascender) &gt; 0.5:
			currMaster.customParameters["typoAscender"] = Ascender
		if abs(currMaster.descender - Descender) &gt; 0.5:
			currMaster.customParameters["typoDescender"] = Descender
		if abs((currFont.upm * 1.2 - (currMaster.ascender + currMaster.descender)) - Gap) &gt; 0.5:
			currMaster.customParameters["typoLineGap"] = Gap
		
		currMaster.customParameters["hheaAscender"] = WinAscend
		currMaster.customParameters["hheaDescender"] = -abs(WinDescend)
		#currentFont.ttinfo.hhea_line_gap = 0
		

print 'End.'

Vassil Kateliev · January 2017

Great work @Georg Seifert ! Love the tolerance check and adding MM functionality is a nice touch! (... makes me think about reworking my FL script to add MM)

Ramiro Espinoza · January 2017

I've made some changes in my original script so it can store more information about the highest and lowest Y values. Now the info is stored in dictionaries and I can retrieve the value's glyph and font name.
Example:

The maximun Y value is: 993 from Otilde in Guyot Text Black

The minimum Y value is: -274 from Q in Guyot Text Black

You surely can improve it but it works for me.

#FLM: ReType Complete Real Asc/Desc V 2.0
# Find and fill real asc and desc values in all open fonts
import operator
from robofab.world import AllFonts


max_Y_values = {}
min_Y_values = {}


for font in AllFonts():
    for x in font:
        if x.name != 'Aringacute':
			max_Y_values[x.name + " in " +  font.info.postscriptFullName] = x.box[3]
			min_Y_values[x.name+ " in " +  font.info.postscriptFullName] = x.box[1]
					

WinAscend = max(max_Y_values.iteritems(), key=operator.itemgetter(1))[1]
WinDescend = min(min_Y_values.iteritems(), key=operator.itemgetter(1))[1]
Ascender = font.info.ascender
Descender = font.info.descender
Gap = (Ascender + abs(Descender)) - (WinAscend + abs(WinDescend))

for font in AllFonts():
    font.info.openTypeOS2WinAscent = WinAscend
    font.info.openTypeOS2WinDescent = abs(WinDescend)
    font.info.openTypeOS2TypoAscender = Ascender
    font.info.openTypeOS2TypoDescender = Descender
    font.info.openTypeHheaAscender = WinAscend
    font.info.openTypeHheaDescender = -abs(WinDescend)
    font.info.openTypeHheaLineGap = 0
    font.info.openTypeOS2TypoLineGap = abs(Gap)

print
print "In all open fonts:"
print
print "The maximun Y value is: " + str(WinAscend) + " from " + max(max_Y_values.iteritems(), key=operator.itemgetter(1))[0]
print "The minimum Y value is: " + str(WinDescend) + " from " + min(min_Y_values.iteritems(), key=operator.itemgetter(1))[0]
print "TypoLineGap is: " + str(abs(Gap))

Kristof Bastiaensen · January 2017

which of the strategies from https://www.glyphsapp.com/tutorials/vertical-metrics does this use? Can it be made to work with the webfont strategy?

Ramiro Espinoza · January 2017

@Kristof Bastiaensen The strategy followed by my script is the 'Microsoft Strategy' described in your link but mine was taken from Karsten Lüecke's paper on font metrics: http://www.kltf.de/downloads/FontMetrics-kltf.pdf

Image: https://us.v-cdn.net/5019405/uploads/editor/31/s5l5ubr86j5l.png

Regarding a webfont font metrics strategy, it is quite simple to implement in the script but I am not sure which should be the most advisable policy. I used to follow the recommendation I found on a Google's page at: https://code.google.com/archive/p/googlefontdirectory/wikis/HowToGenerateWebNativeFonts.wiki but it's not available anymore and the recommendations were different to the one in the Glyphs' page.

For my web fonts I usually follow the following strategy:

First, calculate the winAscent and winDescent values, then:

TypoAscender = winAscent

TypoDescender = winDescent

hheaAscender = winAscent

hheaDescender = winDescent

hheaLineGap = 0

typoLineGap = 0

So, question to everybody, what is currently the best font metric policy for web fonts?

Simon Cozens · January 2017

Have a look at this thread: http://typedrawers.com/discussion/1705

Ramiro Espinoza · January 2017

Thanks! For what I see there is no consensus yet. Kristof, tell me what strategy you prefer and I will tweak the script to reproduce it (as soon as I have a little time).

Kristof Bastiaensen · January 2017

Ramiro, I have no idea, that's why I am asking

I am trying to find the best strategy for a project that I am writing, so any info or algorithm is very useful! I find there isn't much information about these metrics in the opentype spec, and the info that I found on the internet is often contradictory.
EDIT: thanks for the links, they were what I wanted to know!

Ramiro Espinoza · January 2017

@Kristof Bastiaensen I would say: read the entries at http://typedrawers.com/discussion/1705 and pick the option that suit you best.

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Simple script: Find and complete real ascender and descender values in all open fonts

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