font discovery builds up a set of deferred faces

src/font/DeferredFace.zig

@@ -17,18 +17,23 @@ const Presentation = @import("main.zig").Presentation;
 face: ?Face = null,
 
 /// Fontconfig
-fc: if (options.fontconfig) Fontconfig else void = undefined,
+fc: if (options.fontconfig) ?Fontconfig else void = if (options.fontconfig) null else {},
 
 /// Fontconfig specific data. This is only present if building with fontconfig.
 pub const Fontconfig = struct {
     pattern: *fontconfig.Pattern,
-    charset: *fontconfig.CharSet,
-    langset: *fontconfig.LangSet,
+    charset: *const fontconfig.CharSet,
+    langset: *const fontconfig.LangSet,
+
+    pub fn deinit(self: *Fontconfig) void {
+        self.pattern.destroy();
+        self.* = undefined;
+    }
 };
 
 pub fn deinit(self: *DeferredFace) void {
     if (self.face) |*face| face.deinit();
-
+    if (options.fontconfig) if (self.fc) |*fc| fc.deinit();
     self.* = undefined;
 }
 
@@ -54,13 +59,14 @@ pub fn hasCodepoint(self: DeferredFace, cp: u32, p: ?Presentation) bool {
     // If we are using fontconfig, use the fontconfig metadata to
     // avoid loading the face.
     if (options.fontconfig) {
+        if (self.fc) |fc| {
             // Check if char exists
-        if (!self.fc.charset.hasChar(cp)) return false;
+            if (!fc.charset.hasChar(cp)) return false;
 
             // If we have a presentation, check it matches
             if (p) |desired| {
                 const emoji_lang = "und-zsye";
-            const actual: Presentation = if (self.fc.langset.hasLang(emoji_lang))
+                const actual: Presentation = if (fc.langset.hasLang(emoji_lang))
                     .emoji
                 else
                     .text;
@@ -70,6 +76,7 @@ pub fn hasCodepoint(self: DeferredFace, cp: u32, p: ?Presentation) bool {
 
             return true;
         }
+    }
 
     // This is unreachable because discovery mechanisms terminate, and
     // if we're not using a discovery mechanism, the face MUST be loaded.

src/font/discovery.zig

@@ -1,9 +1,14 @@
 const std = @import("std");
 const assert = std.debug.assert;
 const fontconfig = @import("fontconfig");
+const DeferredFace = @import("main.zig").DeferredFace;
 
 const log = std.log.named(.discovery);
 
+pub const Error = error{
+    FontConfigFailed,
+};
+
 /// Descriptor is used to search for fonts. The only required field
 /// is "family". The rest are ignored unless they're set to a non-zero value.
 pub const Descriptor = struct {
@@ -53,25 +58,78 @@ pub const Fontconfig = struct {
     pub fn init() Fontconfig {
         // safe to call multiple times and concurrently
         _ = fontconfig.init();
-        return .{ .fc_config = fontconfig.initLoadConfig() };
+        return .{ .fc_config = fontconfig.initLoadConfigAndFonts() };
     }
 
-    pub fn discover(self: *Fontconfig, desc: Descriptor) void {
+    /// Discover fonts from a descriptor. This returns an iterator that can
+    /// be used to build up the deferred fonts.
+    pub fn discover(self: *Fontconfig, desc: Descriptor) !DiscoverIterator {
         // Build our pattern that we'll search for
         const pat = desc.toFcPattern();
-        defer pat.destroy();
+        errdefer pat.destroy();
         assert(self.fc_config.substituteWithPat(pat, .pattern));
         pat.defaultSubstitute();
 
         // Search
         const res = self.fc_config.fontSort(pat, true, null);
-        defer res.fs.destroy();
+        if (res.result != .match) return Error.FontConfigFailed;
+        errdefer res.fs.destroy();
+
+        return DiscoverIterator{
+            .config = self.fc_config,
+            .pattern = pat,
+            .set = res.fs,
+            .fonts = res.fs.fonts(),
+            .i = 0,
+        };
     }
+
+    pub const DiscoverIterator = struct {
+        config: *fontconfig.Config,
+        pattern: *fontconfig.Pattern,
+        set: *fontconfig.FontSet,
+        fonts: []*fontconfig.Pattern,
+        i: usize,
+
+        pub fn deinit(self: *DiscoverIterator) void {
+            self.set.destroy();
+            self.pattern.destroy();
+            self.* = undefined;
+        }
+
+        pub fn next(self: *DiscoverIterator) fontconfig.Error!?DeferredFace {
+            if (self.i >= self.fonts.len) return null;
+
+            // Get the copied pattern from our fontset that has the
+            // attributes configured for rendering.
+            const font_pattern = try self.config.fontRenderPrepare(
+                self.pattern,
+                self.fonts[self.i],
+            );
+            errdefer font_pattern.destroy();
+
+            // Increment after we return
+            defer self.i += 1;
+
+            return DeferredFace{
+                .face = null,
+                .fc = .{
+                    .pattern = font_pattern,
+                    .charset = (try font_pattern.get(.charset, 0)).char_set,
+                    .langset = (try font_pattern.get(.lang, 0)).lang_set,
+                },
+            };
+        }
+    };
 };
 
 test {
-    defer fontconfig.fini();
-    var fc = Fontconfig.init();
+    const testing = std.testing;
 
-    fc.discover(.{ .family = "monospace" });
+    var fc = Fontconfig.init();
+    var it = try fc.discover(.{ .family = "monospace" });
+    defer it.deinit();
+    while (try it.next()) |face| {
+        try testing.expect(!face.loaded());
+    }
 }