font: a mess

src/font/Group.zig

@@ -16,7 +16,6 @@ const Allocator = std.mem.Allocator;
 const ziglyph = @import("ziglyph");
 
 const font = @import("main.zig");
-const Collection = @import("main.zig").Collection;
 const DeferredFace = @import("main.zig").DeferredFace;
 const Face = @import("main.zig").Face;
 const Library = @import("main.zig").Library;
@@ -28,6 +27,13 @@ const quirks = @import("../quirks.zig");
 
 const log = std.log.scoped(.font_group);
 
+/// Packed array to map our styles to a set of faces.
+// Note: this is not the most efficient way to store these, but there is
+// usually only one font group for the entire process so this isn't the
+// most important memory efficiency we can look for. This is totally opaque
+// to the user so we can change this later.
+const StyleArray = std.EnumArray(Style, std.ArrayListUnmanaged(GroupFace));
+
 /// Packed array of booleans to indicate if a style is enabled or not.
 pub const StyleStatus = std.EnumArray(Style, bool);
 
@@ -86,7 +92,7 @@ metric_modifiers: ?font.face.Metrics.ModifierSet = null,
 
 /// The available faces we have. This shouldn't be modified manually.
 /// Instead, use the functions available on Group.
-faces: Collection,
+faces: StyleArray,
 
 /// The set of statuses and whether they're enabled or not. This defaults
 /// to true. This can be changed at runtime with no ill effect. If you
@@ -113,25 +119,107 @@ descriptor_cache: DescriptorCache = .{},
 /// terminal rendering will look wrong.
 sprite: ?font.sprite.Face = null,
 
+/// A face in a group can be deferred or loaded. A deferred face
+/// is not yet fully loaded and only represents the font descriptor
+/// and usually uses less resources. A loaded face is fully parsed,
+/// ready to rasterize, and usually uses more resources than a
+/// deferred version.
+///
+/// A face can also be a "fallback" variant that is still either
+/// deferred or loaded. Today, there is only one different between
+/// fallback and non-fallback (or "explicit") faces: the handling
+/// of emoji presentation.
+///
+/// For explicit faces, when an explicit emoji presentation is
+/// not requested, we will use any glyph for that codepoint found
+/// even if the font presentation does not match the UCD
+/// (Unicode Character Database) value. When an explicit presentation
+/// is requested (via either VS15/V16), that is always honored.
+/// The reason we do this is because we assume that if a user
+/// explicitly chosen a font face (hence it is "explicit" and
+/// not "fallback"), they want to use any glyphs possible within that
+/// font face. Fallback fonts on the other hand are picked as a
+/// last resort, so we should prefer exactness if possible.
+pub const GroupFace = union(enum) {
+    deferred: DeferredFace, // Not loaded
+    loaded: Face, // Loaded, explicit use
+
+    // The same as deferred/loaded but fallback font semantics (see large
+    // comment above GroupFace).
+    fallback_deferred: DeferredFace,
+    fallback_loaded: Face,
+
+    pub fn deinit(self: *GroupFace) void {
+        switch (self.*) {
+            inline .deferred,
+            .loaded,
+            .fallback_deferred,
+            .fallback_loaded,
+            => |*v| v.deinit(),
+        }
+    }
+
+    /// True if this face satisfies the given codepoint and presentation.
+    fn hasCodepoint(self: GroupFace, cp: u32, p_mode: PresentationMode) bool {
+        return switch (self) {
+            // Non-fallback fonts require explicit presentation matching but
+            // otherwise don't care about presentation
+            .deferred => |v| switch (p_mode) {
+                .explicit => |p| v.hasCodepoint(cp, p),
+                .default, .any => v.hasCodepoint(cp, null),
+            },
+
+            .loaded => |face| switch (p_mode) {
+                .explicit => |p| face.presentation == p and face.glyphIndex(cp) != null,
+                .default, .any => face.glyphIndex(cp) != null,
+            },
+
+            // Fallback fonts require exact presentation matching.
+            .fallback_deferred => |v| switch (p_mode) {
+                .explicit, .default => |p| v.hasCodepoint(cp, p),
+                .any => v.hasCodepoint(cp, null),
+            },
+
+            .fallback_loaded => |face| switch (p_mode) {
+                .explicit,
+                .default,
+                => |p| face.presentation == p and face.glyphIndex(cp) != null,
+                .any => face.glyphIndex(cp) != null,
+            },
+        };
+    }
+};
+
 /// Initializes an empty group. This is not useful until faces are added
 /// and finalizeInit is called.
 pub fn init(
     alloc: Allocator,
     lib: Library,
     size: font.face.DesiredSize,
-    collection: Collection,
 ) !Group {
-    return .{
-        .alloc = alloc,
-        .lib = lib,
-        .size = size,
-        .faces = collection,
-    };
+    var result = Group{ .alloc = alloc, .lib = lib, .size = size, .faces = undefined };
+
+    // Initialize all our styles to initially sized lists.
+    var i: usize = 0;
+    while (i < StyleArray.len) : (i += 1) {
+        result.faces.values[i] = .{};
+        try result.faces.values[i].ensureTotalCapacityPrecise(alloc, 2);
+    }
+
+    return result;
 }
 
 pub fn deinit(self: *Group) void {
-    self.faces.deinit(self.alloc);
+    {
+        var it = self.faces.iterator();
+        while (it.next()) |entry| {
+            for (entry.value.items) |*item| item.deinit();
+            entry.value.deinit(self.alloc);
+        }
+    }
+
     if (self.metric_modifiers) |*v| v.deinit(self.alloc);
+
     self.descriptor_cache.deinit(self.alloc);
 }
 
@@ -144,6 +232,23 @@ pub fn faceOptions(self: *const Group) font.face.Options {
     };
 }
 
+/// Add a face to the list for the given style. This face will be added as
+/// next in priority if others exist already, i.e. it'll be the _last_ to be
+/// searched for a glyph in that list.
+///
+/// The group takes ownership of the face. The face will be deallocated when
+/// the group is deallocated.
+pub fn addFace(self: *Group, style: Style, face: GroupFace) !FontIndex {
+    const list = self.faces.getPtr(style);
+
+    // We have some special indexes so we must never pass those.
+    if (list.items.len >= FontIndex.Special.start - 1) return error.GroupFull;
+
+    const idx = list.items.len;
+    try list.append(self.alloc, face);
+    return .{ .style = style, .idx = @intCast(idx) };
+}
+
 /// This will automatically create an italicized font from the regular
 /// font face if we don't have any italicized fonts.
 pub fn italicize(self: *Group) !void {
@@ -369,9 +474,7 @@ pub fn indexForCodepoint(
                 // Discovery is supposed to only return faces that have our
                 // codepoint but we can't search presentation in discovery so
                 // we have to check it here.
-                const face: Collection.Entry = .{
-                    .fallback_deferred = deferred_face,
-                };
+                const face: GroupFace = .{ .fallback_deferred = deferred_face };
                 if (!face.hasCodepoint(cp, p_mode)) {
                     deferred_face.deinit();
                     continue;
@@ -794,6 +897,9 @@ test "face count limit" {
     const alloc = testing.allocator;
     const testFont = @import("test.zig").fontRegular;
 
+    var atlas_greyscale = try font.Atlas.init(alloc, 512, .greyscale);
+    defer atlas_greyscale.deinit(alloc);
+
     var lib = try Library.init();
     defer lib.deinit();