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font(freetype): tolerate fonts without OS/2 tables
This is more common than anticipated, so proper fallback logic has been added. Why must fonts be like this? -.-
This commit is contained in:
Qwerasd
@ -600,7 +600,6 @@ pub const Face = struct {
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const CalcMetricsError = error{
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CopyTableError,
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MissingOS2Table,
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};
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/// Calculate the metrics associated with a face. This is not public because
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@ -629,70 +628,80 @@ pub const Face = struct {
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const post = face.getSfntTable(.post) orelse return error.CopyTableError;
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// Read the 'OS/2' table out of the font data.
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const os2 = face.getSfntTable(.os2) orelse return error.CopyTableError;
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const maybe_os2: ?*freetype.c.TT_OS2 = os2: {
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const os2 = face.getSfntTable(.os2) orelse break :os2 null;
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if (os2.version == 0xFFFF) break :os2 null;
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break :os2 os2;
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};
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// Read the 'hhea' table out of the font data.
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const hhea = face.getSfntTable(.hhea) orelse return error.CopyTableError;
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// Some fonts don't actually have an OS/2 table, which
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// we need in order to do the metrics calculations, in
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// such cases FreeType sets the version to 0xFFFF
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if (os2.version == 0xFFFF) return error.MissingOS2Table;
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const units_per_em = head.Units_Per_EM;
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const px_per_em: f64 = @floatFromInt(size_metrics.y_ppem);
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const px_per_unit = px_per_em / @as(f64, @floatFromInt(units_per_em));
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const ascent: f64, const descent: f64, const line_gap: f64 = vertical_metrics: {
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const os2_ascent: f64 = @floatFromInt(os2.sTypoAscender);
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const os2_descent: f64 = @floatFromInt(os2.sTypoDescender);
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const os2_line_gap: f64 = @floatFromInt(os2.sTypoLineGap);
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const hhea_ascent: f64 = @floatFromInt(hhea.Ascender);
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const hhea_descent: f64 = @floatFromInt(hhea.Descender);
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const hhea_line_gap: f64 = @floatFromInt(hhea.Line_Gap);
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// If the font says to use typo metrics, trust it.
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// (The USE_TYPO_METRICS bit is bit 7)
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if (os2.fsSelection & (1 << 7) != 0) {
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if (maybe_os2) |os2| {
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const os2_ascent: f64 = @floatFromInt(os2.sTypoAscender);
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const os2_descent: f64 = @floatFromInt(os2.sTypoDescender);
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const os2_line_gap: f64 = @floatFromInt(os2.sTypoLineGap);
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// If the font says to use typo metrics, trust it.
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// (The USE_TYPO_METRICS bit is bit 7)
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if (os2.fsSelection & (1 << 7) != 0) {
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break :vertical_metrics .{
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os2_ascent * px_per_unit,
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os2_descent * px_per_unit,
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os2_line_gap * px_per_unit,
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};
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}
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// Otherwise we prefer the height metrics from 'hhea' if they
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// are available, or else OS/2 sTypo* metrics, and if all else
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// fails then we use OS/2 usWin* metrics.
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//
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// This is not "standard" behavior, but it's our best bet to
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// account for fonts being... just weird. It's pretty much what
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// FreeType does to get its generic ascent and descent metrics.
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if (hhea.Ascender != 0 or hhea.Descender != 0) {
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break :vertical_metrics .{
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hhea_ascent * px_per_unit,
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hhea_descent * px_per_unit,
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hhea_line_gap * px_per_unit,
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};
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}
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if (os2_ascent != 0 or os2_descent != 0) {
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break :vertical_metrics .{
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os2_ascent * px_per_unit,
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os2_descent * px_per_unit,
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os2_line_gap * px_per_unit,
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};
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}
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const win_ascent: f64 = @floatFromInt(os2.usWinAscent);
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const win_descent: f64 = @floatFromInt(os2.usWinDescent);
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break :vertical_metrics .{
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os2_ascent * px_per_unit,
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os2_descent * px_per_unit,
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os2_line_gap * px_per_unit,
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win_ascent * px_per_unit,
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// usWinDescent is *positive* -> down unlike sTypoDescender
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// and hhea.Descender, so we flip its sign to fix this.
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-win_descent * px_per_unit,
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0.0,
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};
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}
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// Otherwise we prefer the height metrics from 'hhea' if they
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// are available, or else OS/2 sTypo* metrics, and if all else
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// fails then we use OS/2 usWin* metrics.
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//
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// This is not "standard" behavior, but it's our best bet to
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// account for fonts being... just weird. It's pretty much what
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// FreeType does to get its generic ascent and descent metrics.
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if (hhea.Ascender != 0 or hhea.Descender != 0) {
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const hhea_ascent: f64 = @floatFromInt(hhea.Ascender);
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const hhea_descent: f64 = @floatFromInt(hhea.Descender);
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const hhea_line_gap: f64 = @floatFromInt(hhea.Line_Gap);
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break :vertical_metrics .{
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hhea_ascent * px_per_unit,
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hhea_descent * px_per_unit,
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hhea_line_gap * px_per_unit,
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};
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}
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if (os2_ascent != 0 or os2_descent != 0) {
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break :vertical_metrics .{
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os2_ascent * px_per_unit,
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os2_descent * px_per_unit,
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os2_line_gap * px_per_unit,
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};
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}
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const win_ascent: f64 = @floatFromInt(os2.usWinAscent);
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const win_descent: f64 = @floatFromInt(os2.usWinDescent);
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// If our font has no OS/2 table, then we just
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// blindly use the metrics from the hhea table.
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break :vertical_metrics .{
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win_ascent * px_per_unit,
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// usWinDescent is *positive* -> down unlike sTypoDescender
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// and hhea.Descender, so we flip its sign to fix this.
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-win_descent * px_per_unit,
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0.0,
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hhea_ascent * px_per_unit,
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hhea_descent * px_per_unit,
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hhea_line_gap * px_per_unit,
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};
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};
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@ -714,17 +723,25 @@ pub const Face = struct {
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@as(f64, @floatFromInt(post.underlineThickness)) * px_per_unit;
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// Similar logic to the underline above.
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const has_broken_strikethrough = os2.yStrikeoutSize == 0;
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const strikethrough_position, const strikethrough_thickness = st: {
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if (maybe_os2) |os2| {
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const has_broken_strikethrough = os2.yStrikeoutSize == 0;
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const strikethrough_position = if (has_broken_strikethrough and os2.yStrikeoutPosition == 0)
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null
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else
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@as(f64, @floatFromInt(os2.yStrikeoutPosition)) * px_per_unit;
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const pos: ?f64 = if (has_broken_strikethrough and os2.yStrikeoutPosition == 0)
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null
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else
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@as(f64, @floatFromInt(os2.yStrikeoutPosition)) * px_per_unit;
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const strikethrough_thickness = if (has_broken_strikethrough)
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null
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else
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@as(f64, @floatFromInt(os2.yStrikeoutSize)) * px_per_unit;
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const thick: ?f64 = if (has_broken_strikethrough)
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null
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else
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@as(f64, @floatFromInt(os2.yStrikeoutSize)) * px_per_unit;
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break :st .{ pos, thick };
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}
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break :st .{ null, null };
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};
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// Cell width is calculated by calculating the widest width of the
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// visible ASCII characters. Usually 'M' is widest but we just take
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@ -754,37 +771,33 @@ pub const Face = struct {
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break :cell_width max;
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};
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// The OS/2 table does not include sCapHeight or sxHeight in version 1.
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const has_os2_height_metrics = os2.version >= 2;
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// We use the cap height specified by the font if it's
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// available, otherwise we try to measure the `H` glyph.
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const cap_height: ?f64 = cap_height: {
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if (has_os2_height_metrics) {
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break :cap_height @as(f64, @floatFromInt(os2.sCapHeight)) * px_per_unit;
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// We use the cap and ex heights specified by the font if they're
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// available, otherwise we try to measure the `H` and `x` glyphs.
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const cap_height: ?f64, const ex_height: ?f64 = heights: {
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if (maybe_os2) |os2| {
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break :heights .{
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@as(f64, @floatFromInt(os2.sCapHeight)) * px_per_unit,
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@as(f64, @floatFromInt(os2.sxHeight)) * px_per_unit,
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};
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}
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if (face.getCharIndex('H')) |glyph_index| {
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if (face.loadGlyph(glyph_index, .{ .render = true })) {
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break :cap_height f26dot6ToF64(face.handle.*.glyph.*.metrics.height);
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} else |_| {}
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}
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break :cap_height null;
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};
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// We use the ex height specified by the font if it's
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// available, otherwise we try to measure the `x` glyph.
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const ex_height: ?f64 = ex_height: {
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if (has_os2_height_metrics) {
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break :ex_height @as(f64, @floatFromInt(os2.sxHeight)) * px_per_unit;
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}
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if (face.getCharIndex('x')) |glyph_index| {
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if (face.loadGlyph(glyph_index, .{ .render = true })) {
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break :ex_height f26dot6ToF64(face.handle.*.glyph.*.metrics.height);
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} else |_| {}
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}
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break :ex_height null;
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break :heights .{
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cap: {
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if (face.getCharIndex('H')) |glyph_index| {
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if (face.loadGlyph(glyph_index, .{ .render = true })) {
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break :cap f26dot6ToF64(face.handle.*.glyph.*.metrics.height);
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} else |_| {}
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}
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break :cap null;
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},
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ex: {
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if (face.getCharIndex('x')) |glyph_index| {
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if (face.loadGlyph(glyph_index, .{ .render = true })) {
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break :ex f26dot6ToF64(face.handle.*.glyph.*.metrics.height);
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} else |_| {}
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}
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break :ex null;
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},
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};
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};
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var result = font.face.Metrics.calc(.{
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