From 69636098bdfc990805975a35ed55b6d143535323 Mon Sep 17 00:00:00 2001 From: Cosimo Lupo Date: Wed, 15 Nov 2023 13:56:22 +0000 Subject: [PATCH] [instancer] Ensure hhea vertical metrics stay in sync with OS/2 ones after instancing Fixes https://github.com/fonttools/fonttools/issues/3297 --- Lib/fontTools/varLib/instancer/__init__.py | 42 +++++++++++++++++++++- 1 file changed, 41 insertions(+), 1 deletion(-) diff --git a/Lib/fontTools/varLib/instancer/__init__.py b/Lib/fontTools/varLib/instancer/__init__.py index cde1d39f6..a887e5d38 100644 --- a/Lib/fontTools/varLib/instancer/__init__.py +++ b/Lib/fontTools/varLib/instancer/__init__.py @@ -105,6 +105,7 @@ from fontTools.misc.cliTools import makeOutputFileName from fontTools.varLib.instancer import solver import collections import dataclasses +from contextlib import contextmanager from copy import deepcopy from enum import IntEnum import logging @@ -694,6 +695,43 @@ def setMvarDeltas(varfont, deltas): ) +@contextmanager +def verticalMetricsKeptInSync(varfont): + """Ensure hhea vertical metrics stay in sync with OS/2 ones after instancing. + + When applying MVAR deltas to the OS/2 table, if the ascender, descender and + line gap change but they were the same as the respective hhea metrics in the + original font, this context manager ensures that hhea metrcs also get updated + accordingly. + The MVAR spec only has tags for the OS/2 metrics, but it is common in fonts + to have the hhea metrics be equal to those for compat reasons. + + https://learn.microsoft.com/en-us/typography/opentype/spec/mvar + https://googlefonts.github.io/gf-guide/metrics.html#7-hhea-and-typo-metrics-should-be-equal + https://github.com/fonttools/fonttools/issues/3297 + """ + current_os2_vmetrics = [ + getattr(varfont["OS/2"], attr) + for attr in ("sTypoAscender", "sTypoDescender", "sTypoLineGap") + ] + metrics_are_synced = current_os2_vmetrics == [ + getattr(varfont["hhea"], attr) for attr in ("ascender", "descender", "lineGap") + ] + + yield metrics_are_synced + + if metrics_are_synced: + new_os2_vmetrics = [ + getattr(varfont["OS/2"], attr) + for attr in ("sTypoAscender", "sTypoDescender", "sTypoLineGap") + ] + if current_os2_vmetrics != new_os2_vmetrics: + for attr, value in zip( + ("ascender", "descender", "lineGap"), new_os2_vmetrics + ): + setattr(varfont["hhea"], attr, value) + + def instantiateMVAR(varfont, axisLimits): log.info("Instantiating MVAR table") @@ -701,7 +739,9 @@ def instantiateMVAR(varfont, axisLimits): fvarAxes = varfont["fvar"].axes varStore = mvar.VarStore defaultDeltas = instantiateItemVariationStore(varStore, fvarAxes, axisLimits) - setMvarDeltas(varfont, defaultDeltas) + + with verticalMetricsKeptInSync(varfont): + setMvarDeltas(varfont, defaultDeltas) if varStore.VarRegionList.Region: varIndexMapping = varStore.optimize()