refactor(font): move Metrics from Face to Collection (#4739)

This refactor enables two very significant improvements to our font
handling, which I will be implementing next:
1. Automatically adjust size of fallback faces to better align with the
primary face, a la CSS
[`font-size-adjust`](https://developer.mozilla.org/en-US/docs/Web/CSS/font-size-adjust).
[^1]
2. Move glyph resizing/positioning out of GPU-land and in to
`renderGlyph` and apply alignment/resizing rules from the nerd fonts
patcher[^2] to the glyphs at rasterization time, so that we can ensure
exact cell fits and swap out our embedded JB Mono with an unpatched
version with a separate dedicated symbols-only nerd font.

In addition to being necessary prep work for those two changes, this PR
is also a minor but real stand-alone improvement. By only computing the
cell metrics for our primary font, we avoid a *lot* of wasted work when
loading fallback fonts, and also avoid that being a source of load
errors, which we don't yet handle gracefully[^3].

To validate this PR I've run the full set of font backend tests locally
on my Mac with no failures, and did a sanity check of running Ghostty
with both renderers and with CoreText and FreeType font backends and
then `cat`ing a file that requires fallback fonts to render, and
everything looks correct.

[^1]: #3029

[^2]: The alignment and resizing rules for the nerd font symbols are
defined in the patcher
[here](6d0b8ba05a/font-patcher (L866-L1151))

[^3]: #2991

src/config/Config.zig

@@ -32,7 +32,7 @@ const url = @import("url.zig");
 const Key = @import("key.zig").Key;
 const KeyValue = @import("key.zig").Value;
 const ErrorList = @import("ErrorList.zig");
-const MetricModifier = fontpkg.face.Metrics.Modifier;
+const MetricModifier = fontpkg.Metrics.Modifier;
 const help_strings = @import("help_strings");
 
 const log = std.log.scoped(.config);

src/font/Collection.zig

@@ -25,7 +25,7 @@ const DeferredFace = font.DeferredFace;
 const DesiredSize = font.face.DesiredSize;
 const Face = font.Face;
 const Library = font.Library;
-const Metrics = font.face.Metrics;
+const Metrics = font.Metrics;
 const Presentation = font.Presentation;
 const Style = font.Style;
 
@@ -35,6 +35,17 @@ const log = std.log.scoped(.font_collection);
 /// Instead, use the functions available on Collection.
 faces: StyleArray,
 
+/// The metric modifiers to use for this collection. The memory
+/// for this is owned by the user and is not freed by the collection.
+///
+/// Call `Collection.updateMetrics` to recompute the
+/// collection's metrics after making changes to these.
+metric_modifiers: Metrics.ModifierSet = .{},
+
+/// Metrics for this collection. Call `Collection.updateMetrics` to (re)compute
+/// these after adding a primary font or making changes to `metric_modifiers`.
+metrics: ?Metrics = null,
+
 /// The load options for deferred faces in the face list. If this
 /// is not set, then deferred faces will not be loaded. Attempting to
 /// add a deferred face will result in an error.
@@ -421,6 +432,28 @@ pub fn setSize(self: *Collection, size: DesiredSize) !void {
             .alias => continue,
         };
     }
+
+    try self.updateMetrics();
+}
+
+const UpdateMetricsError = font.Face.GetMetricsError || error{
+    CannotLoadPrimaryFont,
+};
+
+/// Update the cell metrics for this collection, based on
+/// the primary font and the modifiers in `metric_modifiers`.
+///
+/// This requires a primary font (index `0`) to be present.
+pub fn updateMetrics(self: *Collection) UpdateMetricsError!void {
+    const primary_face = self.getFace(.{ .idx = 0 }) catch return error.CannotLoadPrimaryFont;
+
+    const face_metrics = try primary_face.getMetrics();
+
+    var metrics = Metrics.calc(face_metrics);
+
+    metrics.apply(self.metric_modifiers);
+
+    self.metrics = metrics;
 }
 
 /// Packed array of all Style enum cases mapped to a growable list of faces.
@@ -448,10 +481,6 @@ pub const LoadOptions = struct {
     /// The desired font size for all loaded faces.
     size: DesiredSize = .{ .points = 12 },
 
-    /// The metric modifiers to use for all loaded faces. The memory
-    /// for this is owned by the user and is not freed by the collection.
-    metric_modifiers: Metrics.ModifierSet = .{},
-
     /// Freetype Load Flags to use when loading glyphs. This is a list of
     /// bitfield constants that controls operations to perform during glyph
     /// loading. Only a subset is exposed for configuration, for the whole set
@@ -467,7 +496,6 @@ pub const LoadOptions = struct {
     pub fn faceOptions(self: *const LoadOptions) font.face.Options {
         return .{
             .size = self.size,
-            .metric_modifiers = &self.metric_modifiers,
             .freetype_load_flags = self.freetype_load_flags,
         };
     }
@@ -864,3 +892,66 @@ test "hasCodepoint emoji default graphical" {
     try testing.expect(c.hasCodepoint(idx, '🥸', .{ .any = {} }));
     // TODO(fontmem): test explicit/implicit
 }
+
+test "metrics" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+    const testFont = font.embedded.inconsolata;
+
+    var lib = try Library.init();
+    defer lib.deinit();
+
+    var c = init();
+    defer c.deinit(alloc);
+    c.load_options = .{ .library = lib };
+
+    _ = try c.add(alloc, .regular, .{ .loaded = try Face.init(
+        lib,
+        testFont,
+        .{ .size = .{ .points = 12, .xdpi = 96, .ydpi = 96 } },
+    ) });
+
+    try c.updateMetrics();
+
+    try std.testing.expectEqual(font.Metrics{
+        .cell_width = 8,
+        // The cell height is 17 px because the calculation is
+        //
+        //  ascender - descender + gap
+        //
+        // which, for inconsolata is
+        //
+        //  859 - -190 + 0
+        //
+        // font units, at 1000 units per em that works out to 1.049 em,
+        // and 1em should be the point size * dpi scale, so 12 * (96/72)
+        // which is 16, and 16 * 1.049 = 16.784, which finally is rounded
+        // to 17.
+        .cell_height = 17,
+        .cell_baseline = 3,
+        .underline_position = 17,
+        .underline_thickness = 1,
+        .strikethrough_position = 10,
+        .strikethrough_thickness = 1,
+        .overline_position = 0,
+        .overline_thickness = 1,
+        .box_thickness = 1,
+        .cursor_height = 17,
+    }, c.metrics);
+
+    // Resize should change metrics
+    try c.setSize(.{ .points = 24, .xdpi = 96, .ydpi = 96 });
+    try std.testing.expectEqual(font.Metrics{
+        .cell_width = 16,
+        .cell_height = 34,
+        .cell_baseline = 6,
+        .underline_position = 34,
+        .underline_thickness = 2,
+        .strikethrough_position = 19,
+        .strikethrough_thickness = 2,
+        .overline_position = 0,
+        .overline_thickness = 2,
+        .box_thickness = 2,
+        .cursor_height = 34,
+    }, c.metrics);
+}

src/font/Metrics.zig

@@ -52,7 +52,12 @@ const Minimums = struct {
     const cursor_height = 1;
 };
 
-const CalcOpts = struct {
+/// Metrics extracted from a font face, based on
+/// the metadata tables and glyph measurements.
+pub const FaceMetrics = struct {
+    /// The minimum cell width that can contain any glyph in the ASCII range.
+    ///
+    /// Determined by measuring all printable glyphs in the ASCII range.
     cell_width: f64,
 
     /// The typographic ascent metric from the font.
@@ -110,45 +115,45 @@ const CalcOpts = struct {
 /// do not round them before using them for this function.
 ///
 /// For any nullable options that are not provided, estimates will be used.
-pub fn calc(opts: CalcOpts) Metrics {
+pub fn calc(face: FaceMetrics) Metrics {
     // We use the ceiling of the provided cell width and height to ensure
     // that the cell is large enough for the provided size, since we cast
     // it to an integer later.
-    const cell_width = @ceil(opts.cell_width);
+    const cell_width = @ceil(face.cell_width);
-    const cell_height = @ceil(opts.ascent - opts.descent + opts.line_gap);
+    const cell_height = @ceil(face.ascent - face.descent + face.line_gap);
 
     // We split our line gap in two parts, and put half of it on the top
     // of the cell and the other half on the bottom, so that our text never
     // bumps up against either edge of the cell vertically.
-    const half_line_gap = opts.line_gap / 2;
+    const half_line_gap = face.line_gap / 2;
 
     // Unlike all our other metrics, `cell_baseline` is relative to the
     // BOTTOM of the cell.
-    const cell_baseline = @round(half_line_gap - opts.descent);
+    const cell_baseline = @round(half_line_gap - face.descent);
 
     // We calculate a top_to_baseline to make following calculations simpler.
     const top_to_baseline = cell_height - cell_baseline;
 
     // If we don't have a provided cap height,
     // we estimate it as 75% of the ascent.
-    const cap_height = opts.cap_height orelse opts.ascent * 0.75;
+    const cap_height = face.cap_height orelse face.ascent * 0.75;
 
     // If we don't have a provided ex height,
     // we estimate it as 75% of the cap height.
-    const ex_height = opts.ex_height orelse cap_height * 0.75;
+    const ex_height = face.ex_height orelse cap_height * 0.75;
 
     // If we don't have a provided underline thickness,
     // we estimate it as 15% of the ex height.
-    const underline_thickness = @max(1, @ceil(opts.underline_thickness orelse 0.15 * ex_height));
+    const underline_thickness = @max(1, @ceil(face.underline_thickness orelse 0.15 * ex_height));
 
     // If we don't have a provided strikethrough thickness
     // then we just use the underline thickness for it.
-    const strikethrough_thickness = @max(1, @ceil(opts.strikethrough_thickness orelse underline_thickness));
+    const strikethrough_thickness = @max(1, @ceil(face.strikethrough_thickness orelse underline_thickness));
 
     // If we don't have a provided underline position then
     // we place it 1 underline-thickness below the baseline.
     const underline_position = @round(top_to_baseline -
-        (opts.underline_position orelse
+        (face.underline_position orelse
         -underline_thickness));
 
     // If we don't have a provided strikethrough position
@@ -156,7 +161,7 @@ pub fn calc(opts: CalcOpts) Metrics {
     // ex height, so that it's perfectly centered on lower
     // case text.
     const strikethrough_position = @round(top_to_baseline -
-        (opts.strikethrough_position orelse
+        (face.strikethrough_position orelse
         ex_height * 0.5 + strikethrough_thickness * 0.5));
 
     var result: Metrics = .{
@@ -355,7 +360,7 @@ pub const Modifier = union(enum) {
     }
 
     test "formatConfig percent" {
-        const configpkg = @import("../../config.zig");
+        const configpkg = @import("../config.zig");
         const testing = std.testing;
         var buf = std.ArrayList(u8).init(testing.allocator);
         defer buf.deinit();
@@ -366,7 +371,7 @@ pub const Modifier = union(enum) {
     }
 
     test "formatConfig absolute" {
-        const configpkg = @import("../../config.zig");
+        const configpkg = @import("../config.zig");
         const testing = std.testing;
         var buf = std.ArrayList(u8).init(testing.allocator);
         defer buf.deinit();

src/font/SharedGrid.zig

@@ -29,7 +29,7 @@ const Collection = font.Collection;
 const Face = font.Face;
 const Glyph = font.Glyph;
 const Library = font.Library;
-const Metrics = font.face.Metrics;
+const Metrics = font.Metrics;
 const Presentation = font.Presentation;
 const Style = font.Style;
 const RenderOptions = font.face.RenderOptions;
@@ -111,15 +111,10 @@ pub fn deinit(self: *SharedGrid, alloc: Allocator) void {
 }
 
 fn reloadMetrics(self: *SharedGrid) !void {
-    // Get our cell metrics based on a regular font ascii 'M'. Why 'M'?
-    // Doesn't matter, any normal ASCII will do we're just trying to make
-    // sure we use the regular font.
-    // We don't go through our caching layer because we want to minimize
-    // possible failures.
     const collection = &self.resolver.collection;
-    const index = collection.getIndex('M', .regular, .{ .any = {} }).?;
+    try collection.updateMetrics();
-    const face = try collection.getFace(index);
+
-    self.metrics = face.metrics;
+    self.metrics = collection.metrics.?;
 
     // Setup our sprite font.
     self.resolver.sprite = .{ .metrics = self.metrics };

src/font/SharedGridSet.zig

@@ -20,7 +20,7 @@ const Collection = font.Collection;
 const Discover = font.Discover;
 const Style = font.Style;
 const Library = font.Library;
-const Metrics = font.face.Metrics;
+const Metrics = font.Metrics;
 const CodepointMap = font.CodepointMap;
 const DesiredSize = font.face.DesiredSize;
 const Face = font.Face;
@@ -167,13 +167,13 @@ fn collection(
     const load_options: Collection.LoadOptions = .{
         .library = self.font_lib,
         .size = size,
-        .metric_modifiers = key.metric_modifiers,
         .freetype_load_flags = key.freetype_load_flags,
     };
 
     var c = Collection.init();
     errdefer c.deinit(self.alloc);
     c.load_options = load_options;
+    c.metric_modifiers = key.metric_modifiers;
 
     // Search for fonts
     if (Discover != void) discover: {

src/font/face.zig

@@ -1,7 +1,7 @@
 const std = @import("std");
 const builtin = @import("builtin");
 const options = @import("main.zig").options;
-pub const Metrics = @import("face/Metrics.zig");
+const Metrics = @import("main.zig").Metrics;
 const config = @import("../config.zig");
 const freetype = @import("face/freetype.zig");
 const coretext = @import("face/coretext.zig");
@@ -38,7 +38,6 @@ pub const freetype_load_flags_default = if (FreetypeLoadFlags != void) .{} else
 /// Options for initializing a font face.
 pub const Options = struct {
     size: DesiredSize,
-    metric_modifiers: ?*const Metrics.ModifierSet = null,
     freetype_load_flags: FreetypeLoadFlags = freetype_load_flags_default,
 };
 
@@ -89,7 +88,7 @@ pub const RenderOptions = struct {
     /// the metrics of the primary font face. The grid metrics are used
     /// by the font face to better layout the glyph in situations where
     /// the font is not exactly the same size as the grid.
-    grid_metrics: ?Metrics = null,
+    grid_metrics: Metrics,
 
     /// The number of grid cells this glyph will take up. This can be used
     /// optionally by the rasterizer to better layout the glyph.

src/font/face/coretext.zig

@@ -18,9 +18,6 @@ pub const Face = struct {
     /// if we're using Harfbuzz.
     hb_font: if (harfbuzz_shaper) harfbuzz.Font else void,
 
-    /// Metrics for this font face. These are useful for renderers.
-    metrics: font.face.Metrics,
-
     /// Set quirks.disableDefaultFontFeatures
     quirks_disable_default_font_features: bool = false,
 
@@ -87,11 +84,6 @@ pub const Face = struct {
     /// the CTFont. This does NOT copy or retain the CTFont.
     pub fn initFont(ct_font: *macos.text.Font, opts: font.face.Options) !Face {
         const traits = ct_font.getSymbolicTraits();
-        const metrics = metrics: {
-            var metrics = try calcMetrics(ct_font);
-            if (opts.metric_modifiers) |v| metrics.apply(v.*);
-            break :metrics metrics;
-        };
 
         var hb_font = if (comptime harfbuzz_shaper) font: {
             var hb_font = try harfbuzz.coretext.createFont(ct_font);
@@ -109,7 +101,6 @@ pub const Face = struct {
         var result: Face = .{
             .font = ct_font,
             .hb_font = hb_font,
-            .metrics = metrics,
             .color = color,
         };
         result.quirks_disable_default_font_features = quirks.disableDefaultFontFeatures(&result);
@@ -463,7 +454,7 @@ pub const Face = struct {
         };
         atlas.set(region, buf);
 
-        const metrics = opts.grid_metrics orelse self.metrics;
+        const metrics = opts.grid_metrics;
 
         // This should be the distance from the bottom of
         // the cell to the top of the glyph's bounding box.
@@ -506,14 +497,17 @@ pub const Face = struct {
         };
     }
 
-    const CalcMetricsError = error{
+    pub const GetMetricsError = error{
         CopyTableError,
         InvalidHeadTable,
         InvalidPostTable,
         InvalidHheaTable,
     };
 
-    fn calcMetrics(ct_font: *macos.text.Font) CalcMetricsError!font.face.Metrics {
+    /// Get the `FaceMetrics` for this face.
+    pub fn getMetrics(self: *Face) GetMetricsError!font.Metrics.FaceMetrics {
+        const ct_font = self.font;
+
         // Read the 'head' table out of the font data.
         const head: opentype.Head = head: {
             // macOS bitmap-only fonts use a 'bhed' tag rather than 'head', but
@@ -731,7 +725,7 @@ pub const Face = struct {
             break :cell_width max;
         };
 
-        return font.face.Metrics.calc(.{
+        return .{
             .cell_width = cell_width,
             .ascent = ascent,
             .descent = descent,
@@ -742,7 +736,7 @@ pub const Face = struct {
             .strikethrough_thickness = strikethrough_thickness,
             .cap_height = cap_height,
             .ex_height = ex_height,
-        });
+        };
     }
 
     /// Copy the font table data for the given tag.
@@ -866,7 +860,12 @@ test {
     var i: u8 = 32;
     while (i < 127) : (i += 1) {
         try testing.expect(face.glyphIndex(i) != null);
-        _ = try face.renderGlyph(alloc, &atlas, face.glyphIndex(i).?, .{});
+        _ = try face.renderGlyph(
+            alloc,
+            &atlas,
+            face.glyphIndex(i).?,
+            .{ .grid_metrics = font.Metrics.calc(try face.getMetrics()) },
+        );
     }
 }
 
@@ -926,7 +925,12 @@ test "in-memory" {
     var i: u8 = 32;
     while (i < 127) : (i += 1) {
         try testing.expect(face.glyphIndex(i) != null);
-        _ = try face.renderGlyph(alloc, &atlas, face.glyphIndex(i).?, .{});
+        _ = try face.renderGlyph(
+            alloc,
+            &atlas,
+            face.glyphIndex(i).?,
+            .{ .grid_metrics = font.Metrics.calc(try face.getMetrics()) },
+        );
     }
 }
 
@@ -948,7 +952,12 @@ test "variable" {
     var i: u8 = 32;
     while (i < 127) : (i += 1) {
         try testing.expect(face.glyphIndex(i) != null);
-        _ = try face.renderGlyph(alloc, &atlas, face.glyphIndex(i).?, .{});
+        _ = try face.renderGlyph(
+            alloc,
+            &atlas,
+            face.glyphIndex(i).?,
+            .{ .grid_metrics = font.Metrics.calc(try face.getMetrics()) },
+        );
     }
 }
 
@@ -974,7 +983,12 @@ test "variable set variation" {
     var i: u8 = 32;
     while (i < 127) : (i += 1) {
         try testing.expect(face.glyphIndex(i) != null);
-        _ = try face.renderGlyph(alloc, &atlas, face.glyphIndex(i).?, .{});
+        _ = try face.renderGlyph(
+            alloc,
+            &atlas,
+            face.glyphIndex(i).?,
+            .{ .grid_metrics = font.Metrics.calc(try face.getMetrics()) },
+        );
     }
 }
 
@@ -1017,60 +1031,3 @@ test "glyphIndex colored vs text" {
         try testing.expect(face.isColorGlyph(glyph));
     }
 }
-
-test "coretext: metrics" {
-    const testFont = font.embedded.inconsolata;
-    const alloc = std.testing.allocator;
-
-    var atlas = try font.Atlas.init(alloc, 512, .grayscale);
-    defer atlas.deinit(alloc);
-
-    var ct_font = try Face.init(
-        undefined,
-        testFont,
-        .{ .size = .{ .points = 12, .xdpi = 96, .ydpi = 96 } },
-    );
-    defer ct_font.deinit();
-
-    try std.testing.expectEqual(font.face.Metrics{
-        .cell_width = 8,
-        // The cell height is 17 px because the calculation is
-        //
-        //  ascender - descender + gap
-        //
-        // which, for inconsolata is
-        //
-        //  859 - -190 + 0
-        //
-        // font units, at 1000 units per em that works out to 1.049 em,
-        // and 1em should be the point size * dpi scale, so 12 * (96/72)
-        // which is 16, and 16 * 1.049 = 16.784, which finally is rounded
-        // to 17.
-        .cell_height = 17,
-        .cell_baseline = 3,
-        .underline_position = 17,
-        .underline_thickness = 1,
-        .strikethrough_position = 10,
-        .strikethrough_thickness = 1,
-        .overline_position = 0,
-        .overline_thickness = 1,
-        .box_thickness = 1,
-        .cursor_height = 17,
-    }, ct_font.metrics);
-
-    // Resize should change metrics
-    try ct_font.setSize(.{ .size = .{ .points = 24, .xdpi = 96, .ydpi = 96 } });
-    try std.testing.expectEqual(font.face.Metrics{
-        .cell_width = 16,
-        .cell_height = 34,
-        .cell_baseline = 6,
-        .underline_position = 34,
-        .underline_thickness = 2,
-        .strikethrough_position = 19,
-        .strikethrough_thickness = 2,
-        .overline_position = 0,
-        .overline_thickness = 2,
-        .box_thickness = 2,
-        .cursor_height = 34,
-    }, ct_font.metrics);
-}

src/font/face/freetype.zig

@@ -38,9 +38,6 @@ pub const Face = struct {
     /// Harfbuzz font corresponding to this face.
     hb_font: harfbuzz.Font,
 
-    /// Metrics for this font face. These are useful for renderers.
-    metrics: font.face.Metrics,
-
     /// Freetype load flags for this font face.
     load_flags: font.face.FreetypeLoadFlags,
 
@@ -86,7 +83,6 @@ pub const Face = struct {
             .lib = lib.lib,
             .face = face,
             .hb_font = hb_font,
-            .metrics = try calcMetrics(face, opts.metric_modifiers),
             .load_flags = opts.freetype_load_flags,
         };
         result.quirks_disable_default_font_features = quirks.disableDefaultFontFeatures(&result);
@@ -186,7 +182,6 @@ pub const Face = struct {
     /// for clearing any glyph caches, font atlas data, etc.
     pub fn setSize(self: *Face, opts: font.face.Options) !void {
         try setSize_(self.face, opts.size);
-        self.metrics = try calcMetrics(self.face, opts.metric_modifiers);
     }
 
     fn setSize_(face: freetype.Face, size: font.face.DesiredSize) !void {
@@ -224,6 +219,8 @@ pub const Face = struct {
         vs: []const font.face.Variation,
         opts: font.face.Options,
     ) !void {
+        _ = opts;
+
         // If this font doesn't support variations, we can't do anything.
         if (!self.face.hasMultipleMasters() or vs.len == 0) return;
 
@@ -257,9 +254,6 @@ pub const Face = struct {
 
         // Set them!
         try self.face.setVarDesignCoordinates(coords);
-
-        // We need to recalculate font metrics which may have changed.
-        self.metrics = try calcMetrics(self.face, opts.metric_modifiers);
     }
 
     /// Returns the glyph index for the given Unicode code point. If this
@@ -306,7 +300,7 @@ pub const Face = struct {
         glyph_index: u32,
         opts: font.face.RenderOptions,
     ) !Glyph {
-        const metrics = opts.grid_metrics orelse self.metrics;
+        const metrics = opts.grid_metrics;
 
         // If we have synthetic italic, then we apply a transformation matrix.
         // We have to undo this because synthetic italic works by increasing
@@ -589,23 +583,14 @@ pub const Face = struct {
         return @as(opentype.sfnt.F26Dot6, @bitCast(@as(u32, @intCast(v)))).to(f64);
     }
 
-    const CalcMetricsError = error{
+    pub const GetMetricsError = error{
         CopyTableError,
     };
 
-    /// Calculate the metrics associated with a face. This is not public because
+    /// Get the `FaceMetrics` for this face.
-    /// the metrics are calculated for every face and cached since they're
+    pub fn getMetrics(self: *Face) GetMetricsError!font.Metrics.FaceMetrics {
-    /// frequently required for renderers and take up next to little memory space
+        const face = self.face;
-    /// in the grand scheme of things.
+
-    ///
-    /// An aside: the proper way to limit memory usage due to faces is to limit
-    /// the faces with DeferredFaces and reload on demand. A Face can't be converted
-    /// into a DeferredFace but a Face that comes from a DeferredFace can be
-    /// deinitialized anytime and reloaded with the deferred face.
-    fn calcMetrics(
-        face: freetype.Face,
-        modifiers: ?*const font.face.Metrics.ModifierSet,
-    ) CalcMetricsError!font.face.Metrics {
         const size_metrics = face.handle.*.size.*.metrics;
 
         // This code relies on this assumption, and it should always be
@@ -793,7 +778,7 @@ pub const Face = struct {
             };
         };
 
-        var result = font.face.Metrics.calc(.{
+        return .{
             .cell_width = cell_width,
 
             .ascent = ascent,
@@ -808,13 +793,7 @@ pub const Face = struct {
 
             .cap_height = cap_height,
             .ex_height = ex_height,
-        });
+        };
-
-        if (modifiers) |m| result.apply(m.*);
-
-        // std.log.warn("font metrics={}", .{result});
-
-        return result;
     }
 
     /// Copy the font table data for the given tag.
@@ -843,16 +822,31 @@ test {
     // Generate all visible ASCII
     var i: u8 = 32;
     while (i < 127) : (i += 1) {
-        _ = try ft_font.renderGlyph(alloc, &atlas, ft_font.glyphIndex(i).?, .{});
+        _ = try ft_font.renderGlyph(
+            alloc,
+            &atlas,
+            ft_font.glyphIndex(i).?,
+            .{ .grid_metrics = font.Metrics.calc(try ft_font.getMetrics()) },
+        );
     }
 
     // Test resizing
     {
-        const g1 = try ft_font.renderGlyph(alloc, &atlas, ft_font.glyphIndex('A').?, .{});
+        const g1 = try ft_font.renderGlyph(
+            alloc,
+            &atlas,
+            ft_font.glyphIndex('A').?,
+            .{ .grid_metrics = font.Metrics.calc(try ft_font.getMetrics()) },
+        );
         try testing.expectEqual(@as(u32, 11), g1.height);
 
         try ft_font.setSize(.{ .size = .{ .points = 24, .xdpi = 96, .ydpi = 96 } });
-        const g2 = try ft_font.renderGlyph(alloc, &atlas, ft_font.glyphIndex('A').?, .{});
+        const g2 = try ft_font.renderGlyph(
+            alloc,
+            &atlas,
+            ft_font.glyphIndex('A').?,
+            .{ .grid_metrics = font.Metrics.calc(try ft_font.getMetrics()) },
+        );
         try testing.expectEqual(@as(u32, 20), g2.height);
     }
 }
@@ -874,7 +868,12 @@ test "color emoji" {
     );
     defer ft_font.deinit();
 
-    _ = try ft_font.renderGlyph(alloc, &atlas, ft_font.glyphIndex('🥸').?, .{});
+    _ = try ft_font.renderGlyph(
+        alloc,
+        &atlas,
+        ft_font.glyphIndex('🥸').?,
+        .{ .grid_metrics = font.Metrics.calc(try ft_font.getMetrics()) },
+    );
 
     // Make sure this glyph has color
     {
@@ -885,8 +884,11 @@ test "color emoji" {
 
     // resize
     {
-        const glyph = try ft_font.renderGlyph(alloc, &atlas, ft_font.glyphIndex('🥸').?, .{
+        const glyph = try ft_font.renderGlyph(
-            .grid_metrics = .{
+            alloc,
+            &atlas,
+            ft_font.glyphIndex('🥸').?,
+            .{ .grid_metrics = .{
                 .cell_width = 10,
                 .cell_height = 24,
                 .cell_baseline = 0,
@@ -898,72 +900,12 @@ test "color emoji" {
                 .overline_thickness = 0,
                 .box_thickness = 0,
                 .cursor_height = 0,
-            },
+            } },
-        });
+        );
         try testing.expectEqual(@as(u32, 24), glyph.height);
     }
 }
 
-test "metrics" {
-    const testFont = font.embedded.inconsolata;
-    const alloc = testing.allocator;
-
-    var lib = try Library.init();
-    defer lib.deinit();
-
-    var atlas = try font.Atlas.init(alloc, 512, .grayscale);
-    defer atlas.deinit(alloc);
-
-    var ft_font = try Face.init(
-        lib,
-        testFont,
-        .{ .size = .{ .points = 12, .xdpi = 96, .ydpi = 96 } },
-    );
-    defer ft_font.deinit();
-
-    try testing.expectEqual(font.face.Metrics{
-        .cell_width = 8,
-        // The cell height is 17 px because the calculation is
-        //
-        //  ascender - descender + gap
-        //
-        // which, for inconsolata is
-        //
-        //  859 - -190 + 0
-        //
-        // font units, at 1000 units per em that works out to 1.049 em,
-        // and 1em should be the point size * dpi scale, so 12 * (96/72)
-        // which is 16, and 16 * 1.049 = 16.784, which finally is rounded
-        // to 17.
-        .cell_height = 17,
-        .cell_baseline = 3,
-        .underline_position = 17,
-        .underline_thickness = 1,
-        .strikethrough_position = 10,
-        .strikethrough_thickness = 1,
-        .overline_position = 0,
-        .overline_thickness = 1,
-        .box_thickness = 1,
-        .cursor_height = 17,
-    }, ft_font.metrics);
-
-    // Resize should change metrics
-    try ft_font.setSize(.{ .size = .{ .points = 24, .xdpi = 96, .ydpi = 96 } });
-    try testing.expectEqual(font.face.Metrics{
-        .cell_width = 16,
-        .cell_height = 34,
-        .cell_baseline = 6,
-        .underline_position = 34,
-        .underline_thickness = 2,
-        .strikethrough_position = 19,
-        .strikethrough_thickness = 2,
-        .overline_position = 0,
-        .overline_thickness = 2,
-        .box_thickness = 2,
-        .cursor_height = 34,
-    }, ft_font.metrics);
-}
-
 test "mono to rgba" {
     const alloc = testing.allocator;
     const testFont = font.embedded.emoji;
@@ -974,11 +916,16 @@ test "mono to rgba" {
     var atlas = try font.Atlas.init(alloc, 512, .rgba);
     defer atlas.deinit(alloc);
 
-    var ft_font = try Face.init(lib, testFont, .{ .size = .{ .points = 12 } });
+    var ft_font = try Face.init(lib, testFont, .{ .size = .{ .points = 12, .xdpi = 72, .ydpi = 72 } });
     defer ft_font.deinit();
 
     // glyph 3 is mono in Noto
-    _ = try ft_font.renderGlyph(alloc, &atlas, 3, .{});
+    _ = try ft_font.renderGlyph(
+        alloc,
+        &atlas,
+        3,
+        .{ .grid_metrics = font.Metrics.calc(try ft_font.getMetrics()) },
+    );
 }
 
 test "svg font table" {
@@ -988,7 +935,7 @@ test "svg font table" {
     var lib = try font.Library.init();
     defer lib.deinit();
 
-    var face = try Face.init(lib, testFont, .{ .size = .{ .points = 12 } });
+    var face = try Face.init(lib, testFont, .{ .size = .{ .points = 12, .xdpi = 72, .ydpi = 72 } });
     defer face.deinit();
 
     const table = (try face.copyTable(alloc, "SVG ")).?;
@@ -1037,7 +984,12 @@ test "bitmap glyph" {
     defer ft_font.deinit();
 
     // glyph 77 = 'i'
-    const glyph = try ft_font.renderGlyph(alloc, &atlas, 77, .{});
+    const glyph = try ft_font.renderGlyph(
+        alloc,
+        &atlas,
+        77,
+        .{ .grid_metrics = font.Metrics.calc(try ft_font.getMetrics()) },
+    );
 
     // should render crisp
     try testing.expectEqual(8, glyph.width);

src/font/face/web_canvas.zig

@@ -27,7 +27,7 @@ pub const Face = struct {
     presentation: font.Presentation,
 
     /// Metrics for this font face. These are useful for renderers.
-    metrics: font.face.Metrics,
+    metrics: font.Metrics,
 
     /// The canvas element that we will reuse to render glyphs
     canvas: js.Object,
@@ -273,7 +273,7 @@ pub const Face = struct {
         const underline_position = cell_height - 1;
         const underline_thickness: f32 = 1;
 
-        const result = font.face.Metrics{
+        const result = font.Metrics{
             .cell_width = @intFromFloat(cell_width),
             .cell_height = @intFromFloat(cell_height),
             .cell_baseline = @intFromFloat(cell_baseline),

src/font/main.zig

@@ -14,7 +14,7 @@ pub const Collection = @import("Collection.zig");
 pub const DeferredFace = @import("DeferredFace.zig");
 pub const Face = face.Face;
 pub const Glyph = @import("Glyph.zig");
-pub const Metrics = face.Metrics;
+pub const Metrics = @import("Metrics.zig");
 pub const opentype = @import("opentype.zig");
 pub const shape = @import("shape.zig");
 pub const Shaper = shape.Shaper;

src/font/sprite/Face.zig

@@ -52,7 +52,7 @@ pub fn renderGlyph(
         }
     }
 
-    const metrics = opts.grid_metrics orelse self.metrics;
+    const metrics = self.metrics;
 
     // We adjust our sprite width based on the cell width.
     const width = switch (opts.cell_width orelse 1) {

src/renderer/Metal.zig

@@ -68,7 +68,7 @@ config: DerivedConfig,
 surface_mailbox: apprt.surface.Mailbox,
 
 /// Current font metrics defining our grid.
-grid_metrics: font.face.Metrics,
+grid_metrics: font.Metrics,
 
 /// The size of everything.
 size: renderer.Size,

src/renderer/OpenGL.zig

@@ -49,7 +49,7 @@ alloc: std.mem.Allocator,
 config: DerivedConfig,
 
 /// Current font metrics defining our grid.
-grid_metrics: font.face.Metrics,
+grid_metrics: font.Metrics,
 
 /// The size of everything.
 size: renderer.Size,
@@ -231,7 +231,7 @@ const SetScreenSize = struct {
 };
 
 const SetFontSize = struct {
-    metrics: font.face.Metrics,
+    metrics: font.Metrics,
 
     fn apply(self: SetFontSize, r: *const OpenGL) !void {
         const gl_state = r.gl_state orelse return error.OpenGLUninitialized;