gfx: font: begin adding text shaping via harfbuzz

Helps hexops/mach#877

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

src/gfx/font/native/Font.zig

@@ -0,0 +1,57 @@
+const std = @import("std");
+const ft = @import("mach-freetype");
+const harfbuzz = @import("mach-harfbuzz");
+const TextRun = @import("TextRun.zig");
+const px_per_pt = @import("../main.zig").px_per_pt;
+
+const Font = @This();
+
+var freetype_ready_mu: std.Thread.Mutex = .{};
+var freetype_ready: bool = false;
+var freetype: ft.Library = undefined;
+
+face: ft.Face,
+
+pub fn initFreetype() !void {
+    freetype_ready_mu.lock();
+    defer freetype_ready_mu.unlock();
+    if (!freetype_ready) {
+        freetype = try ft.Library.init();
+        freetype_ready = true;
+    }
+}
+
+pub fn initBytes(font_bytes: []const u8) anyerror!Font {
+    try initFreetype();
+    return .{
+        .face = try freetype.createFaceMemory(font_bytes, 0),
+    };
+}
+
+pub fn shape(f: *const Font, r: *TextRun) anyerror!void {
+    // Guess text segment properties.
+    r.buffer.guessSegmentProps();
+    // TODO: Optionally override specific text segment properties?
+    // buffer.setDirection(.ltr);
+    // buffer.setScript(.latin);
+    // buffer.setLanguage(harfbuzz.Language.fromString("en"));
+
+    const hb_face = harfbuzz.Face.fromFreetypeFace(f.face);
+    const hb_font = harfbuzz.Font.init(hb_face);
+    defer hb_font.deinit();
+
+    const font_size_pt = @as(f32, @floatFromInt(r.font_size_px)) / px_per_pt;
+    hb_font.setScale(@as(i32, @intFromFloat(font_size_pt)) * 256, @as(i32, @intFromFloat(font_size_pt)) * 256);
+    hb_font.setPTEM(font_size_pt);
+
+    // TODO: optionally pass shaping features?
+    hb_font.shape(r.buffer, null);
+
+    r.index = 0;
+    r.infos = r.buffer.getGlyphInfos();
+    r.positions = r.buffer.getGlyphPositions() orelse return error.OutOfMemory;
+}
+
+pub fn deinit(f: *const Font) void {
+    f.face.deinit();
+}