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fix(font): make face.getMetrics() infallible

Browse Source 
Before we had a bad day if we tried to get the metrics of a bitmap font,
which would happen if we ever used one as fallback because we started
doing it for all fonts when we added fallback font scaling. This is a
pretty easy fix and finally allows users to configure true bitmap fonts
as their primary font as long as FreeType/CoreText can handle it.
This commit is contained in:
Qwerasd
2025-09-03 20:04:29 -06:00
parent c3e7857a2c
commit 5c1d87fda6
3 changed files with 216 additions and 175 deletions
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23
src/font/Collection.zig
View File

@@ -92,7 +92,6 @@ pub const AddOptions = struct {
pub const AddError =
Allocator.Error ||
Face.GetMetricsError ||
error{
/// There's no more room in the collection.
CollectionFull,
@@ -127,7 +126,7 @@ pub fn add(
// Scale factor to adjust the size of the added face.
const scale_factor = self.scaleFactor(
try owned_face.getMetrics(),
owned_face.getMetrics(),
opts.size_adjustment,
);
@@ -225,7 +224,7 @@ fn getFaceFromEntry(
// entry now that we have a loaded face.
entry.scale_factor = .{
.scale = self.scaleFactor(
try face.getMetrics(),
face.getMetrics(),
entry.scale_factor.adjustment,
),
};
@@ -592,7 +591,7 @@ fn scaleFactor(
@branchHint(.unlikely);
// If we can't load the primary face, just use 1.0 as the scale factor.
const primary_face = self.getFace(.{ .idx = 0 }) catch return 1.0;
self.primary_face_metrics = primary_face.getMetrics() catch return 1.0;
self.primary_face_metrics = primary_face.getMetrics();
}
const primary_metrics = self.primary_face_metrics.?;
@@ -652,7 +651,7 @@ fn scaleFactor(
return primary_metric / face_metric;
}
const UpdateMetricsError = font.Face.GetMetricsError || error{
const UpdateMetricsError = error{
CannotLoadPrimaryFont,
};
@@ -663,7 +662,7 @@ const UpdateMetricsError = font.Face.GetMetricsError || error{
pub fn updateMetrics(self: *Collection) UpdateMetricsError!void {
const primary_face = self.getFace(.{ .idx = 0 }) catch return error.CannotLoadPrimaryFont;
self.primary_face_metrics = try primary_face.getMetrics();
self.primary_face_metrics = primary_face.getMetrics();
var metrics = Metrics.calc(self.primary_face_metrics.?);
@@ -1288,8 +1287,8 @@ test "adjusted sizes" {
// The chosen metric should match.
{
const primary_metrics = try (try c.getFace(.{ .idx = 0 })).getMetrics();
const fallback_metrics = try (try c.getFace(fallback_idx)).getMetrics();
const primary_metrics = (try c.getFace(.{ .idx = 0 })).getMetrics();
const fallback_metrics = (try c.getFace(fallback_idx)).getMetrics();
try std.testing.expectApproxEqAbs(
@field(primary_metrics, metric).?,
@@ -1302,8 +1301,8 @@ test "adjusted sizes" {
// Resize should keep that relationship.
try c.setSize(.{ .points = 37, .xdpi = 96, .ydpi = 96 });
{
const primary_metrics = try (try c.getFace(.{ .idx = 0 })).getMetrics();
const fallback_metrics = try (try c.getFace(fallback_idx)).getMetrics();
const primary_metrics = (try c.getFace(.{ .idx = 0 })).getMetrics();
const fallback_metrics = (try c.getFace(fallback_idx)).getMetrics();
try std.testing.expectApproxEqAbs(
@field(primary_metrics, metric).?,
@@ -1359,8 +1358,8 @@ test "adjusted sizes" {
// Test fallback to lineHeight() (ex_height and cap_height not defined in symbols font).
{
const primary_metrics = try (try c.getFace(.{ .idx = 0 })).getMetrics();
const symbol_metrics = try (try c.getFace(symbol_idx)).getMetrics();
const primary_metrics = (try c.getFace(.{ .idx = 0 })).getMetrics();
const symbol_metrics = (try c.getFace(symbol_idx)).getMetrics();
try std.testing.expectApproxEqAbs(
primary_metrics.lineHeight(),

178
src/font/face/coretext.zig
View File

@@ -574,19 +574,12 @@ pub const Face = struct {
};
}
pub const GetMetricsError = error{
CopyTableError,
InvalidHeadTable,
InvalidPostTable,
InvalidHheaTable,
};
/// Get the `FaceMetrics` for this face.
pub fn getMetrics(self: *Face) GetMetricsError!font.Metrics.FaceMetrics {
pub fn getMetrics(self: *Face) font.Metrics.FaceMetrics {
const ct_font = self.font;
// Read the 'head' table out of the font data.
const head: opentype.Head = head: {
const head_: ?opentype.Head = head: {
// macOS bitmap-only fonts use a 'bhed' tag rather than 'head', but
// the table format is byte-identical to the 'head' table, so if we
// can't find 'head' we try 'bhed' instead before failing.
@@ -597,29 +590,26 @@ pub const Face = struct {
const data =
ct_font.copyTable(head_tag) orelse
ct_font.copyTable(bhed_tag) orelse
return error.CopyTableError;
break :head null;
defer data.release();
const ptr = data.getPointer();
const len = data.getLength();
break :head opentype.Head.init(ptr[0..len]) catch |err| {
return switch (err) {
error.EndOfStream,
=> error.InvalidHeadTable,
};
log.warn("error parsing head table: {}", .{err});
break :head null;
};
};
// Read the 'post' table out of the font data.
const post: opentype.Post = post: {
const post_: ?opentype.Post = post: {
const tag = macos.text.FontTableTag.init("post");
const data = ct_font.copyTable(tag) orelse return error.CopyTableError;
const data = ct_font.copyTable(tag) orelse break :post null;
defer data.release();
const ptr = data.getPointer();
const len = data.getLength();
break :post opentype.Post.init(ptr[0..len]) catch |err| {
return switch (err) {
error.EndOfStream => error.InvalidPostTable,
};
log.warn("error parsing post table: {}", .{err});
break :post null;
};
};
@@ -637,96 +627,114 @@ pub const Face = struct {
};
// Read the 'hhea' table out of the font data.
const hhea: opentype.Hhea = hhea: {
const hhea_: ?opentype.Hhea = hhea: {
const tag = macos.text.FontTableTag.init("hhea");
const data = ct_font.copyTable(tag) orelse return error.CopyTableError;
const data = ct_font.copyTable(tag) orelse break :hhea null;
defer data.release();
const ptr = data.getPointer();
const len = data.getLength();
break :hhea opentype.Hhea.init(ptr[0..len]) catch |err| {
return switch (err) {
error.EndOfStream => error.InvalidHheaTable,
};
log.warn("error parsing hhea table: {}", .{err});
break :hhea null;
};
};
const units_per_em: f64 = @floatFromInt(head.unitsPerEm);
const units_per_em: f64 =
if (head_) |head|
@floatFromInt(head.unitsPerEm)
else
@floatFromInt(self.font.getUnitsPerEm());
const px_per_em: f64 = ct_font.getSize();
const px_per_unit: f64 = px_per_em / units_per_em;
const ascent: f64, const descent: f64, const line_gap: f64 = vertical_metrics: {
const hhea_ascent: f64 = @floatFromInt(hhea.ascender);
const hhea_descent: f64 = @floatFromInt(hhea.descender);
const hhea_line_gap: f64 = @floatFromInt(hhea.lineGap);
if (hhea_) |hhea| {
const hhea_ascent: f64 = @floatFromInt(hhea.ascender);
const hhea_descent: f64 = @floatFromInt(hhea.descender);
const hhea_line_gap: f64 = @floatFromInt(hhea.lineGap);
if (os2_) |os2| {
const os2_ascent: f64 = @floatFromInt(os2.sTypoAscender);
const os2_descent: f64 = @floatFromInt(os2.sTypoDescender);
const os2_line_gap: f64 = @floatFromInt(os2.sTypoLineGap);
if (os2_) |os2| {
const os2_ascent: f64 = @floatFromInt(os2.sTypoAscender);
const os2_descent: f64 = @floatFromInt(os2.sTypoDescender);
const os2_line_gap: f64 = @floatFromInt(os2.sTypoLineGap);
// If the font says to use typo metrics, trust it.
if (os2.fsSelection.use_typo_metrics) break :vertical_metrics .{
os2_ascent * px_per_unit,
os2_descent * px_per_unit,
os2_line_gap * px_per_unit,
};
// If the font says to use typo metrics, trust it.
if (os2.fsSelection.use_typo_metrics) break :vertical_metrics .{
os2_ascent * px_per_unit,
os2_descent * px_per_unit,
os2_line_gap * px_per_unit,
};
// Otherwise we prefer the height metrics from 'hhea' if they
// are available, or else OS/2 sTypo* metrics, and if all else
// fails then we use OS/2 usWin* metrics.
//
// This is not "standard" behavior, but it's our best bet to
// account for fonts being... just weird. It's pretty much what
// FreeType does to get its generic ascent and descent metrics.
// Otherwise we prefer the height metrics from 'hhea' if they
// are available, or else OS/2 sTypo* metrics, and if all else
// fails then we use OS/2 usWin* metrics.
//
// This is not "standard" behavior, but it's our best bet to
// account for fonts being... just weird. It's pretty much what
// FreeType does to get its generic ascent and descent metrics.
if (hhea.ascender != 0 or hhea.descender != 0) break :vertical_metrics .{
if (hhea.ascender != 0 or hhea.descender != 0) break :vertical_metrics .{
hhea_ascent * px_per_unit,
hhea_descent * px_per_unit,
hhea_line_gap * px_per_unit,
};
if (os2_ascent != 0 or os2_descent != 0) break :vertical_metrics .{
os2_ascent * px_per_unit,
os2_descent * px_per_unit,
os2_line_gap * px_per_unit,
};
const win_ascent: f64 = @floatFromInt(os2.usWinAscent);
const win_descent: f64 = @floatFromInt(os2.usWinDescent);
break :vertical_metrics .{
win_ascent * px_per_unit,
// usWinDescent is *positive* -> down unlike sTypoDescender
// and hhea.Descender, so we flip its sign to fix this.
-win_descent * px_per_unit,
0.0,
};
}
// If our font has no OS/2 table, then we just
// blindly use the metrics from the hhea table.
break :vertical_metrics .{
hhea_ascent * px_per_unit,
hhea_descent * px_per_unit,
hhea_line_gap * px_per_unit,
};
if (os2_ascent != 0 or os2_descent != 0) break :vertical_metrics .{
os2_ascent * px_per_unit,
os2_descent * px_per_unit,
os2_line_gap * px_per_unit,
};
const win_ascent: f64 = @floatFromInt(os2.usWinAscent);
const win_descent: f64 = @floatFromInt(os2.usWinDescent);
break :vertical_metrics .{
win_ascent * px_per_unit,
// usWinDescent is *positive* -> down unlike sTypoDescender
// and hhea.Descender, so we flip its sign to fix this.
-win_descent * px_per_unit,
0.0,
};
}
// If our font has no OS/2 table, then we just
// blindly use the metrics from the hhea table.
// If we couldn't get the hhea table, rely on metrics from CoreText.
break :vertical_metrics .{
hhea_ascent * px_per_unit,
hhea_descent * px_per_unit,
hhea_line_gap * px_per_unit,
self.font.getAscent(),
-self.font.getDescent(),
self.font.getLeading(),
};
};
// Some fonts have degenerate 'post' tables where the underline
// thickness (and often position) are 0. We consider them null
// if this is the case and use our own fallbacks when we calculate.
const has_broken_underline = post.underlineThickness == 0;
const underline_position, const underline_thickness = ul: {
const post = post_ orelse break :ul .{ null, null };
// If the underline position isn't 0 then we do use it,
// even if the thickness is't properly specified.
const underline_position: ?f64 = if (has_broken_underline and post.underlinePosition == 0)
null
else
@as(f64, @floatFromInt(post.underlinePosition)) * px_per_unit;
// Some fonts have degenerate 'post' tables where the underline
// thickness (and often position) are 0. We consider them null
// if this is the case and use our own fallbacks when we calculate.
const has_broken_underline = post.underlineThickness == 0;
const underline_thickness = if (has_broken_underline)
null
else
@as(f64, @floatFromInt(post.underlineThickness)) * px_per_unit;
// If the underline position isn't 0 then we do use it,
// even if the thickness is't properly specified.
const pos: ?f64 = if (has_broken_underline and post.underlinePosition == 0)
null
else
@as(f64, @floatFromInt(post.underlinePosition)) * px_per_unit;
const thick: ?f64 = if (has_broken_underline)
null
else
@as(f64, @floatFromInt(post.underlineThickness)) * px_per_unit;
break :ul .{ pos, thick };
};
// Similar logic to the underline above.
const strikethrough_position, const strikethrough_thickness = st: {
@@ -989,7 +997,7 @@ test {
alloc,
&atlas,
face.glyphIndex(i).?,
.{ .grid_metrics = font.Metrics.calc(try face.getMetrics()) },
.{ .grid_metrics = font.Metrics.calc(face.getMetrics()) },
);
}
}
@@ -1054,7 +1062,7 @@ test "in-memory" {
alloc,
&atlas,
face.glyphIndex(i).?,
.{ .grid_metrics = font.Metrics.calc(try face.getMetrics()) },
.{ .grid_metrics = font.Metrics.calc(face.getMetrics()) },
);
}
}
@@ -1081,7 +1089,7 @@ test "variable" {
alloc,
&atlas,
face.glyphIndex(i).?,
.{ .grid_metrics = font.Metrics.calc(try face.getMetrics()) },
.{ .grid_metrics = font.Metrics.calc(face.getMetrics()) },
);
}
}
@@ -1112,7 +1120,7 @@ test "variable set variation" {
alloc,
&atlas,
face.glyphIndex(i).?,
.{ .grid_metrics = font.Metrics.calc(try face.getMetrics()) },
.{ .grid_metrics = font.Metrics.calc(face.getMetrics()) },
);
}
}

190
src/font/face/freetype.zig
View File

@@ -784,12 +784,8 @@ pub const Face = struct {
return @as(F26Dot6, @bitCast(@as(i32, @intCast(v)))).to(f64);
}
pub const GetMetricsError = error{
CopyTableError,
};
/// Get the `FaceMetrics` for this face.
pub fn getMetrics(self: *Face) GetMetricsError!font.Metrics.FaceMetrics {
pub fn getMetrics(self: *Face) font.Metrics.FaceMetrics {
const face = self.face;
const size_metrics = face.handle.*.size.*.metrics;
@@ -799,10 +795,10 @@ pub const Face = struct {
assert(size_metrics.x_ppem == size_metrics.y_ppem);
// Read the 'head' table out of the font data.
const head = face.getSfntTable(.head) orelse return error.CopyTableError;
const head_ = face.getSfntTable(.head);
// Read the 'post' table out of the font data.
const post = face.getSfntTable(.post) orelse return error.CopyTableError;
const post_ = face.getSfntTable(.post);
// Read the 'OS/2' table out of the font data.
const os2_: ?*freetype.c.TT_OS2 = os2: {
@@ -812,92 +808,130 @@ pub const Face = struct {
};
// Read the 'hhea' table out of the font data.
const hhea = face.getSfntTable(.hhea) orelse return error.CopyTableError;
const hhea_ = face.getSfntTable(.hhea);
const units_per_em = head.Units_Per_EM;
// Whether the font is in a scalable format. We need to know this
// because many of the metrics provided by FreeType are invalid for
// non-scalable fonts.
const is_scalable = face.handle.*.face_flags & freetype.c.FT_FACE_FLAG_SCALABLE != 0;
// We get the UPM from the head table.
//
// If we have no head, but it is a scalable face, take the UPM from
// FreeType's units_per_EM, otherwise we'll assume that UPM == PPEM.
const units_per_em: freetype.c.FT_UShort =
if (head_) |head|
head.Units_Per_EM
else if (is_scalable)
face.handle.*.units_per_EM
else
size_metrics.y_ppem;
const px_per_em: f64 = @floatFromInt(size_metrics.y_ppem);
const px_per_unit = px_per_em / @as(f64, @floatFromInt(units_per_em));
const ascent: f64, const descent: f64, const line_gap: f64 = vertical_metrics: {
const hhea_ascent: f64 = @floatFromInt(hhea.Ascender);
const hhea_descent: f64 = @floatFromInt(hhea.Descender);
const hhea_line_gap: f64 = @floatFromInt(hhea.Line_Gap);
if (hhea_) |hhea| {
const hhea_ascent: f64 = @floatFromInt(hhea.Ascender);
const hhea_descent: f64 = @floatFromInt(hhea.Descender);
const hhea_line_gap: f64 = @floatFromInt(hhea.Line_Gap);
if (os2_) |os2| {
const os2_ascent: f64 = @floatFromInt(os2.sTypoAscender);
const os2_descent: f64 = @floatFromInt(os2.sTypoDescender);
const os2_line_gap: f64 = @floatFromInt(os2.sTypoLineGap);
if (os2_) |os2| {
const os2_ascent: f64 = @floatFromInt(os2.sTypoAscender);
const os2_descent: f64 = @floatFromInt(os2.sTypoDescender);
const os2_line_gap: f64 = @floatFromInt(os2.sTypoLineGap);
// If the font says to use typo metrics, trust it.
// (The USE_TYPO_METRICS bit is bit 7)
if (os2.fsSelection & (1 << 7) != 0) {
// If the font says to use typo metrics, trust it.
// (The USE_TYPO_METRICS bit is bit 7)
if (os2.fsSelection & (1 << 7) != 0) {
break :vertical_metrics .{
os2_ascent * px_per_unit,
os2_descent * px_per_unit,
os2_line_gap * px_per_unit,
};
}
// Otherwise we prefer the height metrics from 'hhea' if they
// are available, or else OS/2 sTypo* metrics, and if all else
// fails then we use OS/2 usWin* metrics.
//
// This is not "standard" behavior, but it's our best bet to
// account for fonts being... just weird. It's pretty much what
// FreeType does to get its generic ascent and descent metrics.
if (hhea.Ascender != 0 or hhea.Descender != 0) {
break :vertical_metrics .{
hhea_ascent * px_per_unit,
hhea_descent * px_per_unit,
hhea_line_gap * px_per_unit,
};
}
if (os2_ascent != 0 or os2_descent != 0) {
break :vertical_metrics .{
os2_ascent * px_per_unit,
os2_descent * px_per_unit,
os2_line_gap * px_per_unit,
};
}
const win_ascent: f64 = @floatFromInt(os2.usWinAscent);
const win_descent: f64 = @floatFromInt(os2.usWinDescent);
break :vertical_metrics .{
os2_ascent * px_per_unit,
os2_descent * px_per_unit,
os2_line_gap * px_per_unit,
win_ascent * px_per_unit,
// usWinDescent is *positive* -> down unlike sTypoDescender
// and hhea.Descender, so we flip its sign to fix this.
-win_descent * px_per_unit,
0.0,
};
}
// Otherwise we prefer the height metrics from 'hhea' if they
// are available, or else OS/2 sTypo* metrics, and if all else
// fails then we use OS/2 usWin* metrics.
//
// This is not "standard" behavior, but it's our best bet to
// account for fonts being... just weird. It's pretty much what
// FreeType does to get its generic ascent and descent metrics.
if (hhea.Ascender != 0 or hhea.Descender != 0) {
break :vertical_metrics .{
hhea_ascent * px_per_unit,
hhea_descent * px_per_unit,
hhea_line_gap * px_per_unit,
};
}
if (os2_ascent != 0 or os2_descent != 0) {
break :vertical_metrics .{
os2_ascent * px_per_unit,
os2_descent * px_per_unit,
os2_line_gap * px_per_unit,
};
}
const win_ascent: f64 = @floatFromInt(os2.usWinAscent);
const win_descent: f64 = @floatFromInt(os2.usWinDescent);
// If our font has no OS/2 table, then we just
// blindly use the metrics from the hhea table.
break :vertical_metrics .{
win_ascent * px_per_unit,
// usWinDescent is *positive* -> down unlike sTypoDescender
// and hhea.Descender, so we flip its sign to fix this.
-win_descent * px_per_unit,
0.0,
hhea_ascent * px_per_unit,
hhea_descent * px_per_unit,
hhea_line_gap * px_per_unit,
};
}
// If our font has no OS/2 table, then we just
// blindly use the metrics from the hhea table.
// If we couldn't get the hhea table, rely on metrics from FreeType.
const ascender = f26dot6ToF64(size_metrics.ascender);
const descender = f26dot6ToF64(size_metrics.descender);
const height = f26dot6ToF64(size_metrics.height);
break :vertical_metrics .{
hhea_ascent * px_per_unit,
hhea_descent * px_per_unit,
hhea_line_gap * px_per_unit,
ascender,
descender,
// We compute the line gap by adding the (negative) descender
// and subtracting the (positive) ascender from the line height
// to get the remaining gap size.
//
// NOTE: This might always be 0... but it doesn't hurt to do.
height + descender - ascender,
};
};
// Some fonts have degenerate 'post' tables where the underline
// thickness (and often position) are 0. We consider them null
// if this is the case and use our own fallbacks when we calculate.
const has_broken_underline = post.underlineThickness == 0;
const underline_position: ?f64, const underline_thickness: ?f64 = ul: {
const post = post_ orelse break :ul .{ null, null };
// If the underline position isn't 0 then we do use it,
// even if the thickness is't properly specified.
const underline_position = if (has_broken_underline and post.underlinePosition == 0)
null
else
@as(f64, @floatFromInt(post.underlinePosition)) * px_per_unit;
// Some fonts have degenerate 'post' tables where the underline
// thickness (and often position) are 0. We consider them null
// if this is the case and use our own fallbacks when we calculate.
const has_broken_underline = post.underlineThickness == 0;
const underline_thickness = if (has_broken_underline)
null
else
@as(f64, @floatFromInt(post.underlineThickness)) * px_per_unit;
// If the underline position isn't 0 then we do use it,
// even if the thickness is't properly specified.
const pos: ?f64 = if (has_broken_underline and post.underlinePosition == 0)
null
else
@as(f64, @floatFromInt(post.underlinePosition)) * px_per_unit;
const thick: ?f64 = if (has_broken_underline)
null
else
@as(f64, @floatFromInt(post.underlineThickness)) * px_per_unit;
break :ul .{ pos, thick };
};
// Similar logic to the underline above.
const strikethrough_position, const strikethrough_thickness = st: {
@@ -1085,7 +1119,7 @@ test {
alloc,
&atlas,
ft_font.glyphIndex(i).?,
.{ .grid_metrics = font.Metrics.calc(try ft_font.getMetrics()) },
.{ .grid_metrics = font.Metrics.calc(ft_font.getMetrics()) },
);
}
@@ -1095,7 +1129,7 @@ test {
alloc,
&atlas,
ft_font.glyphIndex('A').?,
.{ .grid_metrics = font.Metrics.calc(try ft_font.getMetrics()) },
.{ .grid_metrics = font.Metrics.calc(ft_font.getMetrics()) },
);
try testing.expectEqual(@as(u32, 11), g1.height);
@@ -1104,7 +1138,7 @@ test {
alloc,
&atlas,
ft_font.glyphIndex('A').?,
.{ .grid_metrics = font.Metrics.calc(try ft_font.getMetrics()) },
.{ .grid_metrics = font.Metrics.calc(ft_font.getMetrics()) },
);
try testing.expectEqual(@as(u32, 20), g2.height);
}
@@ -1131,7 +1165,7 @@ test "color emoji" {
alloc,
&atlas,
ft_font.glyphIndex('🥸').?,
.{ .grid_metrics = font.Metrics.calc(try ft_font.getMetrics()) },
.{ .grid_metrics = font.Metrics.calc(ft_font.getMetrics()) },
);
// Make sure this glyph has color
@@ -1191,7 +1225,7 @@ test "mono to bgra" {
alloc,
&atlas,
3,
.{ .grid_metrics = font.Metrics.calc(try ft_font.getMetrics()) },
.{ .grid_metrics = font.Metrics.calc(ft_font.getMetrics()) },
);
}
@@ -1255,7 +1289,7 @@ test "bitmap glyph" {
alloc,
&atlas,
77,
.{ .grid_metrics = font.Metrics.calc(try ft_font.getMetrics()) },
.{ .grid_metrics = font.Metrics.calc(ft_font.getMetrics()) },
);
// should render crisp