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font-patcher: Rewrite font height calculation
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[why]
The initial font-patcher used the WIN font metrics to determine the cell
height. What has been found was forced into HHEA metrics but without
observing the USE_TYPO_METRICS flag.
That has been changed to use the TYPO metric instead of the WIN metric
when the font wants that. For that the gap value becomes important.

This is the current code. It still has problems to detect the correct
cell height. A more rigorous approach seem to be needed.

[how]
The baseline to baseline distance is what we need as 'cell height', to
fill it completely with the powerline glyphs. This is a little bit
complicated and not really specified, each font rendering application or
engine can handle the font metrics differently. But there are some
common approaches.

So we try to come up with the correct and congruent height, comparing
different metrics and issuing a warning on problematic fonts.
Afterwards we make all metrics equal (even if they were not before),
because our goal is clear now and we impose it onto all platforms.

[note]
Useful resources:
* https://glyphsapp.com/learn/vertical-metrics
* https://github.com/source-foundry/font-line

Fixes: #1056

Signed-off-by: Fini Jastrow <[email protected]>
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@Finii
Finii committed Jan 20, 2023
1 parent ec38ad9 commit 9c2000b
Showing 1 changed file with 80 additions and 32 deletions.
112 changes: 80 additions & 32 deletions font-patcher
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@
from __future__ import absolute_import, print_function, unicode_literals

# Change the script version when you edit this script:
script_version = "3.4.4"
script_version = "3.5.0"

version = "2.3.0"
projectName = "Nerd Fonts"
Expand Down Expand Up @@ -259,8 +259,8 @@ class font_patcher:
self.assert_monospace()
self.remove_ligatures()
self.setup_patch_set()
self.improve_line_dimensions()
self.get_sourcefont_dimensions()
self.improve_line_dimensions()
self.sourceFont.encoding = 'UnicodeFull' # Update the font encoding to ensure that the Unicode glyphs are available
self.onlybitmaps = self.sourceFont.onlybitmaps # Fetch this property before adding outlines. NOTE self.onlybitmaps initialized and never used

Expand Down Expand Up @@ -892,6 +892,7 @@ class font_patcher:
# center more evenly.
if self.args.adjustLineHeight:
if (self.sourceFont.os2_winascent + self.sourceFont.os2_windescent) % 2 != 0:
# All three are equal before due to get_sourcefont_dimensions()
self.sourceFont.hhea_ascent += 1
self.sourceFont.os2_typoascent += 1
self.sourceFont.os2_winascent += 1
Expand All @@ -909,18 +910,56 @@ class font_patcher:
self.essential.add(self.sourceFont[r[0]].unicode)

def get_sourcefont_dimensions(self):
# Initial font dimensions
self.font_dim = {
'xmin' : 0,
'ymin' : -self.sourceFont.os2_windescent,
'xmax' : 0,
'ymax' : self.sourceFont.os2_winascent,
'width' : 0,
'height': 0,
}
if self.sourceFont.os2_use_typo_metrics:
self.font_dim['ymin'] = self.sourceFont.os2_typodescent
self.font_dim['ymax'] = self.sourceFont.os2_typoascent
""" This gets the font dimensions (cell width and height), and makes them equal on all platforms """
# Step 1
# There are three ways to discribe the baseline to baseline distance
# (a.k.a. line spacing) of a font. That is all a kuddelmuddel
# and we try to sort this out here
# See also https://glyphsapp.com/learn/vertical-metrics
# See also https://github.com/source-foundry/font-line
hhea_height = self.sourceFont.hhea_ascent - self.sourceFont.hhea_descent
typo_height = self.sourceFont.os2_typoascent - self.sourceFont.os2_typodescent
win_height = self.sourceFont.os2_winascent + self.sourceFont.os2_windescent
win_gap = max(0, self.sourceFont.hhea_linegap - win_height + hhea_height)
hhea_btb = hhea_height + self.sourceFont.hhea_linegap
typo_btb = typo_height + self.sourceFont.os2_typolinegap
win_btb = win_height + win_gap
use_typo = self.sourceFont.os2_use_typo_metrics != 0

# We use either TYPO (1) or WIN (2) and compare with HHEA
# and use HHEA (0) if the fonts seems broken
our_btb = typo_btb if use_typo else win_btb
if our_btb == hhea_btb:
metrics = 1 if use_typo else 2 # conforming font
elif abs(our_btb - hhea_btb) / our_btb < 0.03:
print("{}: Font vertical metrics slightly off ({:.1f}%)".format(projectName, (our_btb - hhea_btb) / our_btb * 100.0))
metrics = 1 if use_typo else 2
else:
# Try the other metric
our_btb = typo_btb if not use_typo else win_btb
if our_btb == hhea_btb:
print("{}: Font vertical metrics probably wrong USE TYPO METRICS, assume opposite (i.e. {})".format(projectName, not use_typo))
use_typo = not use_typo
self.sourceFont.os2_use_typo_metrics = 1 if use_typo else 0
metrics = 1 if use_typo else 2
else:
print("{}: WARNING Font vertical metrics inconsistent ({:.1f}%), using HHEA".format(projectName, (our_btb - hhea_btb) / our_btb * 100.0))
our_btb = hhea_btb
metrics = 0

# print("FINI hhea {} typo {} win {} use {} {} {}".format(hhea_btb, typo_btb, win_btb, use_typo, our_btb != hhea_btb, self.sourceFont.fontname))

self.font_dim = {'xmin': 0, 'ymin': 0, 'xmax': 0, 'ymax': 0, 'width' : 0, 'height': 0}

if metrics == 0:
self.font_dim['ymin'] = self.sourceFont.hhea_descent + half_gap(self.sourceFont.hhea_linegap, False)
self.font_dim['ymax'] = self.sourceFont.hhea_ascent + half_gap(self.sourceFont.hhea_linegap, True)
elif metrics == 1:
self.font_dim['ymin'] = self.sourceFont.os2_typodescent + half_gap(self.sourceFont.os2_typolinegap, False)
self.font_dim['ymax'] = self.sourceFont.os2_typoascent + half_gap(self.sourceFont.os2_typolinegap, True)
else:
self.font_dim['ymin'] = -self.sourceFont.os2_windescent + half_gap(win_gap, False)
self.font_dim['ymax'] = self.sourceFont.os2_winascent + half_gap(win_gap, True)

# Calculate font height
self.font_dim['height'] = -self.font_dim['ymin'] + self.font_dim['ymax']
Expand All @@ -935,26 +974,21 @@ class font_patcher:
'width' : self.sourceFont.em,
'height': self.sourceFont.descent + self.sourceFont.ascent,
}
elif self.font_dim['height'] < 0:
sys.exit("{}: Can not detect sane font height".format(projectName))

# Line gap add extra space on the bottom of the line which
# doesn't allow the powerline glyphs to fill the entire line.
# Put half of the gap into the 'cell', each top and bottom
gap = max(self.sourceFont.hhea_linegap, self.sourceFont.os2_typolinegap) # TODO probably wrong
if self.sourceFont.os2_use_typo_metrics:
gap = self.sourceFont.os2_typolinegap
self.sourceFont.hhea_linegap = 0
# Make all metrics equal
self.sourceFont.os2_typolinegap = 0
if gap > 0:
gap_top = int(gap / 2)
gap_bottom = gap - gap_top
print("Redistributing line gap of {} ({} top and {} bottom)".format(gap, gap_top, gap_bottom))
self.font_dim['ymin'] -= gap_bottom
self.font_dim['ymax'] += gap_top
self.font_dim['height'] = -self.font_dim['ymin'] + self.font_dim['ymax']
self.sourceFont.os2_typoascent = self.sourceFont.os2_typoascent + gap_top
self.sourceFont.os2_typodescent = self.sourceFont.os2_typodescent - gap_bottom
# TODO Check what to do with win and hhea values

self.sourceFont.os2_typoascent = self.font_dim['ymax']
self.sourceFont.os2_typodescent = self.font_dim['ymin']
self.sourceFont.os2_winascent = self.sourceFont.os2_typoascent
self.sourceFont.os2_windescent = -self.sourceFont.os2_typodescent
self.sourceFont.hhea_ascent = self.sourceFont.os2_typoascent
self.sourceFont.hhea_descent = self.sourceFont.os2_typodescent
self.sourceFont.hhea_linegap = self.sourceFont.os2_typolinegap
self.sourceFont.os2_use_typo_metrics = 1

# Step 2
# Find the biggest char width
# Ignore the y-values, os2_winXXXXX values set above are used for line height
#
Expand Down Expand Up @@ -1364,6 +1398,20 @@ class font_patcher:
return None


def half_gap(gap, top):
""" Divides integer value into two new integers """
# Line gap add extra space on the bottom of the line which
# doesn't allow the powerline glyphs to fill the entire line.
# Put half of the gap into the 'cell', each top and bottom
if gap <= 0:
return 0
gap_top = int(gap / 2)
gap_bottom = gap - gap_top
if top:
print("Redistributing line gap of {} ({} top and {} bottom)".format(gap, gap_top, gap_bottom))
return gap_top
return gap_bottom

def replace_font_name(font_name, replacement_dict):
""" Replaces all keys with vals from replacement_dict in font_name. """
for key, val in replacement_dict.items():
Expand Down

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