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font(fix): Extract and apply Nerd Font codepoint mapping table (#9142) 

Fixes #9076

**Before** 
<img width="128" height="57" alt="Screenshot 2025-10-11 at 00 07 09"
src="https://github.com/user-attachments/assets/a6b416d5-dae1-4cea-a836-00640ceaf39b"
/>

**After**
<img width="128" height="57" alt="Screenshot 2025-10-11 at 00 07 31"
src="https://github.com/user-attachments/assets/7d2df7b1-4767-4e2d-84d2-8301da5c6602"
/>

These screenshots show the chevrons mentioned in
https://github.com/ghostty-org/ghostty/discussions/7820#discussioncomment-14617170,
which should be scaled as a group but were not until this PR.

The added code downloads each individual symbol font file from the Nerd
Fonts github repo (making sure to get the version corresponding to the
vendored `font-patcher.py`) and iterates over all of them to build the
correct and complete codepoint mapping table. The table is saved to
`nerd_font_codepoint_tables.py`, which `nerd_font_codegen.py` will reuse
if possible instead of downloading the font files again.

I'm not going to utter any famous last words or anything, but... after
this, I don't think the number of remaining issues with icon
scaling/alignment is _large._
1.2.x
Daniel Wennberg 2025-10-11 13:12:13 -07:00 committed by Mitchell Hashimoto
parent 5ecb00fd48
commit 1658c86eba
No known key found for this signature in database
GPG Key ID: 523D5DC389D273BC
3 changed files with 10971 additions and 1436 deletions
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1730
src/font/nerd_font_attributes.zig
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228
src/font/nerd_font_codegen.py
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@ -15,13 +15,14 @@ SymbolsNerdFont (not Mono!) font is passed as the first argument to it.
import ast
import sys
import math
from fontTools.ttLib import TTFont
from fontTools.ttLib import TTFont, TTLibError
from fontTools.pens.boundsPen import BoundsPen
from collections import defaultdict
from contextlib import suppress
from pathlib import Path
from types import SimpleNamespace
from typing import Literal, TypedDict, cast
from urllib.request import urlretrieve
type PatchSetAttributes = dict[Literal["default"] | int, PatchSetAttributeEntry]
type AttributeHash = tuple[
@ -58,6 +59,8 @@ class PatchSetAttributeEntry(TypedDict):
class PatchSet(TypedDict):
Name: str
Filename: str
Exact: bool
SymStart: int
SymEnd: int
SrcStart: int | None
@ -69,6 +72,18 @@ class PatchSetExtractor(ast.NodeVisitor):
def __init__(self) -> None:
self.symbol_table: dict[str, ast.expr] = {}
self.patch_set_values: list[PatchSet] = []
self.nf_version: str = ""
def visit_Assign(self, node):
if (
node.col_offset == 0 # top-level assignment
and len(node.targets) == 1 # no funny destructuring business
and isinstance(node.targets[0], ast.Name) # no setitem et cetera
and node.targets[0].id == "version" # it's the version string!
):
self.nf_version = ast.literal_eval(node.value)
else:
return self.generic_visit(node)
def visit_ClassDef(self, node: ast.ClassDef) -> None:
if node.name != "font_patcher":
@ -140,12 +155,8 @@ class PatchSetExtractor(ast.NodeVisitor):
def process_patch_entry(self, dict_node: ast.Dict) -> None:
entry = {}
disallowed_key_nodes = frozenset({"Filename", "Exact"})
for key_node, value_node in zip(dict_node.keys, dict_node.values):
if (
isinstance(key_node, ast.Constant)
and key_node.value not in disallowed_key_nodes
):
if isinstance(key_node, ast.Constant):
if key_node.value == "Enabled":
if self.safe_literal_eval(value_node):
continue # This patch set is enabled, continue to next key
@ -156,11 +167,11 @@ class PatchSetExtractor(ast.NodeVisitor):
self.patch_set_values.append(cast("PatchSet", entry))
def extract_patch_set_values(source_code: str) -> list[PatchSet]:
def extract_patch_set_values(source_code: str) -> tuple[list[PatchSet], str]:
tree = ast.parse(source_code)
extractor = PatchSetExtractor()
extractor.visit(tree)
return extractor.patch_set_values
return extractor.patch_set_values, extractor.nf_version
def parse_alignment(val: str) -> str | None:
@ -290,12 +301,127 @@ def emit_zig_entry_multikey(codepoints: list[int], attr: PatchSetAttributeEntry)
return s
def generate_codepoint_tables(
patch_sets: list[PatchSet],
nerd_font: TTFont,
nf_version: str,
) -> dict[str, dict[int, int]]:
# We may already have the table saved from a previous run.
if Path("nerd_font_codepoint_tables.py").exists():
import nerd_font_codepoint_tables
if nerd_font_codepoint_tables.version == nf_version:
return nerd_font_codepoint_tables.cp_tables
cp_tables: dict[str, dict[int, int]] = {}
cp_table_full: dict[int, int] = {}
cmap = nerd_font.getBestCmap()
for entry in patch_sets:
patch_set_name = entry["Name"]
print(f"Info: Extracting codepoint table from patch set '{patch_set_name}'")
# Extract codepoint map from original font file; download if needed
source_filename = entry["Filename"]
target_folder = Path("nerd_font_symbol_fonts")
target_folder.mkdir(exist_ok=True)
target_file = target_folder / Path(source_filename).name
if not target_file.exists():
print(f"Info: Downloading '{source_filename}'")
urlretrieve(
f"https://github.com/ryanoasis/nerd-fonts/raw/refs/tags/v{nf_version}/src/glyphs/{source_filename}",
target_file,
)
try:
with TTFont(target_file) as patchfont:
patch_cmap = patchfont.getBestCmap()
except TTLibError:
# Not a TTF/OTF font. This is OK if this patch set is exact, so we
# let if pass. If there's a problem, later checks will catch it.
patch_cmap = None
# A glyph's scale rules are specified using its codepoint in
# the original font, which is sometimes different from its
# Nerd Font codepoint. If entry["Exact"] is False, the codepoints are
# mapped according to the following rules:
# * entry["SymStart"] and entry["SymEnd"] denote the patch set's codepoint
# range in the original font.
# * entry["SrcStart"] is the starting point of the patch set's mapped
# codepoint range. It must not be None if entry["Exact"] is False.
# * The destination codepoint range is packed; that is, while there may be
# gaps without glyphs in the original font's codepoint range, there are
# none in the Nerd Font range. Hence there is no constant codepoint
# offset; instead we must iterate through the range and increment the
# destination codepoint every time we encounter a glyph in the original
# font.
# If entry["Exact"] is True, the origin and Nerd Font codepoints are the
# same, gaps included, and entry["SrcStart"] must be None.
if entry["Exact"]:
assert entry["SrcStart"] is None
cp_nerdfont = 0
else:
assert entry["SrcStart"]
assert patch_cmap is not None
cp_nerdfont = entry["SrcStart"] - 1
if patch_set_name not in cp_tables:
# There are several patch sets with the same name, representing
# different codepoint ranges within the same original font. Merging
# these into a single table is OK. However, we need to keep separate
# tables for the different fonts to correctly deal with cases where
# they fill in each other's gaps.
cp_tables[patch_set_name] = {}
for cp_original in range(entry["SymStart"], entry["SymEnd"] + 1):
if patch_cmap and cp_original not in patch_cmap:
continue
if not entry["Exact"]:
cp_nerdfont += 1
else:
cp_nerdfont = cp_original
if cp_nerdfont not in cmap:
raise ValueError(
f"Missing codepoint in Symbols Only Font: {hex(cp_nerdfont)} in patch set '{patch_set_name}'"
)
elif cp_nerdfont in cp_table_full.values():
raise ValueError(
f"Overlap for codepoint {hex(cp_nerdfont)} in patch set '{patch_set_name}'"
)
cp_tables[patch_set_name][cp_original] = cp_nerdfont
cp_table_full |= cp_tables[patch_set_name]
# Store the table and corresponding Nerd Fonts version together in a module.
with open("nerd_font_codepoint_tables.py", "w") as f:
print(
"""#! This is a generated file, produced by nerd_font_codegen.py
#! DO NOT EDIT BY HAND!
#!
#! This file specifies the mapping of codepoints in the original symbol
#! fonts to codepoints in a patched Nerd Font. This is extracted from
#! the nerd fonts patcher script and the symbol font files.""",
file=f,
)
print(f'version = "{nf_version}"', file=f)
print("cp_tables = {", file=f)
for name, table in cp_tables.items():
print(f' "{name}": {{', file=f)
for key, value in table.items():
print(f" {hex(key)}: {hex(value)},", file=f)
print(" },", file=f)
print("}", file=f)
return cp_tables
def generate_zig_switch_arms(
patch_sets: list[PatchSet],
nerd_font: TTFont,
nf_version: str,
) -> str:
cmap = nerd_font.getBestCmap()
glyphs = nerd_font.getGlyphSet()
cp_tables = generate_codepoint_tables(patch_sets, nerd_font, nf_version)
cp_table_full: dict[int, int] = {}
for cp_table in cp_tables.values():
cp_table_full |= cp_table
entries: dict[int, PatchSetAttributeEntry] = {}
for entry in patch_sets:
@ -305,47 +431,21 @@ def generate_zig_switch_arms(
attributes = entry["Attributes"]
patch_set_entries: dict[int, PatchSetAttributeEntry] = {}
# A glyph's scale rules are specified using its codepoint in
# the original font, which is sometimes different from its
# Nerd Font codepoint. In font_patcher, the font to be patched
# (including the Symbols Only font embedded in Ghostty) is
# termed the sourceFont, while the original font is the
# symbolFont. Thus, the offset that maps the scale rule
# codepoint to the Nerd Font codepoint is SrcStart - SymStart.
cp_offset = entry["SrcStart"] - entry["SymStart"] if entry["SrcStart"] else 0
for cp_rule in range(entry["SymStart"], entry["SymEnd"] + 1):
cp_font = cp_rule + cp_offset
if cp_font not in cmap:
print(f"Info: Skipping missing codepoint {hex(cp_font)}")
cp_table = cp_tables[patch_set_name]
for cp_original in range(entry["SymStart"], entry["SymEnd"] + 1):
if cp_original not in cp_table:
continue
elif cp_font in entries:
# Patch sets sometimes have overlapping codepoint ranges.
# Sometimes a later set is a smaller set filling in a gap
# in the range of a larger, preceding set. Sometimes it's
# the other way around. The best thing we can do is hardcode
# each case.
if patch_set_name == "Font Awesome":
# The Font Awesome range has a gap matching the
# prededing Progress Indicators range.
print(f"Info: Not overwriting existing codepoint {hex(cp_font)}")
continue
elif patch_set_name == "Octicons":
# The fourth Octicons range overlaps with the first.
print(f"Info: Overwriting existing codepoint {hex(cp_font)}")
else:
raise ValueError(
f"Unknown case of overlap for codepoint {hex(cp_font)} in patch set '{patch_set_name}'"
)
if cp_rule in attributes:
patch_set_entries[cp_font] = attributes[cp_rule].copy()
cp_nerdfont = cp_table[cp_original]
if cp_nerdfont in entries:
raise ValueError(
f"Overlap for codepoint {hex(cp_nerdfont)} in patch set '{patch_set_name}'"
)
if cp_original in attributes:
patch_set_entries[cp_nerdfont] = attributes[cp_original].copy()
else:
patch_set_entries[cp_font] = attributes["default"].copy()
patch_set_entries[cp_nerdfont] = attributes["default"].copy()
if entry["ScaleRules"] is not None:
if "ScaleGroups" not in entry["ScaleRules"]:
raise ValueError(
f"Scale rule format {entry['ScaleRules']} not implemented."
)
for group in entry["ScaleRules"]["ScaleGroups"]:
xMin = math.inf
yMin = math.inf
@ -353,15 +453,15 @@ def generate_zig_switch_arms(
yMax = -math.inf
individual_bounds: dict[int, tuple[int, int, int, int]] = {}
individual_advances: set[float] = set()
for cp_rule in group:
cp_font = cp_rule + cp_offset
if cp_font not in cmap:
continue
glyph = glyphs[cmap[cp_font]]
for cp_original in group:
# Scale groups may cut across patch sets, so we need to use
# the full lookup table here
cp_nerdfont = cp_table_full[cp_original]
glyph = glyphs[cmap[cp_nerdfont]]
individual_advances.add(glyph.width)
bounds = BoundsPen(glyphSet=glyphs)
glyph.draw(bounds)
individual_bounds[cp_font] = bounds.bounds
individual_bounds[cp_nerdfont] = bounds.bounds
xMin = min(bounds.bounds[0], xMin)
yMin = min(bounds.bounds[1], yMin)
xMax = max(bounds.bounds[2], xMax)
@ -371,34 +471,36 @@ def generate_zig_switch_arms(
group_is_monospace = (len(individual_bounds) > 1) and (
len(individual_advances) == 1
)
for cp_rule in group:
cp_font = cp_rule + cp_offset
for cp_original in group:
cp_nerdfont = cp_table_full[cp_original]
if (
cp_font not in cmap
or cp_font not in patch_set_entries
# Scale groups may cut across patch sets, but we're only
# updating a single patch set at a time, so we skip
# codepoints not in it.
cp_nerdfont not in patch_set_entries
# Codepoints may contribute to the bounding box of multiple groups,
# but should be scaled according to the first group they are found
# in. Hence, to avoid overwriting, we need to skip codepoints that
# have already been assigned a scale group.
or "relative_height" in patch_set_entries[cp_font]
or "relative_height" in patch_set_entries[cp_nerdfont]
):
continue
this_bounds = individual_bounds[cp_font]
this_bounds = individual_bounds[cp_nerdfont]
this_height = this_bounds[3] - this_bounds[1]
patch_set_entries[cp_font]["relative_height"] = (
patch_set_entries[cp_nerdfont]["relative_height"] = (
this_height / group_height
)
patch_set_entries[cp_font]["relative_y"] = (
patch_set_entries[cp_nerdfont]["relative_y"] = (
this_bounds[1] - yMin
) / group_height
# Horizontal alignment should only be grouped if the group is monospace,
# that is, if all glyphs in the group have the same advance width.
if group_is_monospace:
this_width = this_bounds[2] - this_bounds[0]
patch_set_entries[cp_font]["relative_width"] = (
patch_set_entries[cp_nerdfont]["relative_width"] = (
this_width / group_width
)
patch_set_entries[cp_font]["relative_x"] = (
patch_set_entries[cp_nerdfont]["relative_x"] = (
this_bounds[0] - xMin
) / group_width
entries |= patch_set_entries
@ -427,7 +529,7 @@ if __name__ == "__main__":
patcher_path = project_root / "vendor" / "nerd-fonts" / "font-patcher.py"
source = patcher_path.read_text(encoding="utf-8")
patch_set = extract_patch_set_values(source)
patch_set, nf_version = extract_patch_set_values(source)
out_path = project_root / "src" / "font" / "nerd_font_attributes.zig"
@ -444,5 +546,5 @@ const Constraint = @import("face.zig").RenderOptions.Constraint;
pub fn getConstraint(cp: u21) ?Constraint {
return switch (cp) {
""")
f.write(generate_zig_switch_arms(patch_set, nerd_font))
f.write(generate_zig_switch_arms(patch_set, nerd_font, nf_version))
f.write("\n else => null,\n };\n}\n")

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src/font/nerd_font_codepoint_tables.py Normal file
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