diff --git a/src/font/SharedGrid.zig b/src/font/SharedGrid.zig
index bfb8f411f..f69a474fb 100644
--- a/src/font/SharedGrid.zig
+++ b/src/font/SharedGrid.zig
@@ -9,6 +9,13 @@
 //! reads well. Going even further, the font subsystem should be very rarely
 //! read at all since it should only be necessary when the grid actively
 //! changes.
+//!
+//! SharedGrid does NOT support resizing, font-family changes, font removals
+//! in collections, etc. Because the Grid is shared this would cause a
+//! major disruption in the rendering of multiple surfaces (i.e. increasing
+//! the font size in one would increase it in all). In many cases this isn't
+//! desirable so to implement configuration changes the grid should be
+//! reinitialized and all surfaces should switch over to using that one.
 const SharedGrid = @This();
 
 // TODO(fontmem):
@@ -21,7 +28,9 @@ const font = @import("main.zig");
 const Atlas = font.Atlas;
 const CodepointResolver = font.CodepointResolver;
 const Collection = font.Collection;
+const Face = font.Face;
 const Glyph = font.Glyph;
+const Library = font.Library;
 const Metrics = font.face.Metrics;
 const Presentation = font.Presentation;
 const Style = font.Style;
@@ -48,6 +57,18 @@ resolver: CodepointResolver,
 /// This is calculated based on the resolver and current fonts.
 metrics: Metrics,
 
+/// The RwLock used to protect the shared grid.
+lock: std.Thread.RwLock,
+
+/// Initialize the grid.
+///
+/// The resolver must have a collection that supports deferred loading
+/// (collection.load_options != null). This is because we need the load
+/// options data to determine grid metrics and setup our sprite font.
+///
+/// SharedGrid always configures the sprite font. This struct is expected to be
+/// used with a terminal grid and therefore the sprite font is always
+/// necessary for correct rendering.
 pub fn init(
     alloc: Allocator,
     resolver: CodepointResolver,
@@ -65,6 +86,8 @@ pub fn init(
         .resolver = resolver,
         .atlas_greyscale = atlas_greyscale,
         .atlas_color = atlas_color,
+        .lock = .{},
+        .metrics = undefined, // Loaded below
     };
 
     // We set an initial capacity that can fit a good number of characters.
@@ -78,6 +101,7 @@ pub fn init(
     return result;
 }
 
+/// Deinit. Assumes no concurrent access so no lock is taken.
 pub fn deinit(self: *SharedGrid, alloc: Allocator) void {
     self.codepoints.deinit(alloc);
     self.glyphs.deinit(alloc);
@@ -118,3 +142,57 @@ const GlyphKey = struct {
     glyph: u32,
     opts: RenderOptions,
 };
+
+const TestMode = enum { normal };
+
+fn testGrid(mode: TestMode, alloc: Allocator, lib: Library) !SharedGrid {
+    const testFont = @import("test.zig").fontRegular;
+
+    var c = try Collection.init(alloc);
+    c.load_options = .{ .library = lib };
+
+    switch (mode) {
+        .normal => {
+            _ = try c.add(alloc, .regular, .{ .loaded = try Face.init(
+                lib,
+                testFont,
+                .{ .size = .{ .points = 12, .xdpi = 96, .ydpi = 96 } },
+            ) });
+        },
+    }
+
+    var r: CodepointResolver = .{ .collection = c };
+    errdefer r.deinit(alloc);
+
+    return try init(alloc, r, false);
+}
+
+test "SharedGrid inits metrics" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+    // const testEmoji = @import("test.zig").fontEmoji;
+
+    var lib = try Library.init();
+    defer lib.deinit();
+
+    var grid = try testGrid(.normal, alloc, lib);
+    defer grid.deinit(alloc);
+
+    // Visible ASCII. Do it twice to verify cache is used.
+    // var i: u32 = 32;
+    // while (i < 127) : (i += 1) {
+    //     const idx = (try cache.indexForCodepoint(alloc, i, .regular, null)).?;
+    //     try testing.expectEqual(Style.regular, idx.style);
+    //     try testing.expectEqual(@as(Group.FontIndex.IndexInt, 0), idx.idx);
+    //
+    //     // Render
+    //     const face = try cache.group.faceFromIndex(idx);
+    //     const glyph_index = face.glyphIndex(i).?;
+    //     _ = try cache.renderGlyph(
+    //         alloc,
+    //         idx,
+    //         glyph_index,
+    //         .{},
+    //     );
+    // }
+}