{Core,examples}: set window title via component

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

src/Core.zig

@@ -15,6 +15,10 @@ pub const global_events = .{
 };
 
 pub const local_events = .{
+    .update = .{ .handler = update, .description = 
+    \\ Send this when window entities have been updated and you want the new values respected.
+    },
+
     .init = .{ .handler = init },
     .init_done = .{ .handler = fn () void },
 
@@ -26,10 +30,40 @@ pub const local_events = .{
     .exit = .{ .handler = exit },
 };
 
+pub const components = .{
+    .title = .{ .type = [:0]u8, .description = 
+    \\ Window title slice. Can be set with a format string and arguments via:
+    \\
+    \\ ```
+    \\ try mach.Core.printTitle(core_mod, core_mod.state().main_window, "Hello, {s}!", .{"Mach"});
+    \\ ```
+    \\
+    \\ If setting this component yourself, ensure the buffer is allocated using core.state().allocator
+    \\ as it will be freed for you as part of the .deinit event.
+    },
+};
+
+/// Prints into the window title buffer using a format string and arguments. e.g.
+///
+/// ```
+/// try mach.Core.printTitle(core_mod, core_mod.state().main_window, "Hello, {s}!", .{"Mach"});
+/// ```
+pub fn printTitle(
+    core: *mach.Core.Mod,
+    window_id: mach.EntityID,
+    comptime fmt: []const u8,
+    args: anytype,
+) !void {
+    const slice = try std.fmt.allocPrintZ(core.state().allocator, fmt, args);
+    try core.set(window_id, .title, slice);
+}
+
 var gpa = std.heap.GeneralPurposeAllocator(.{}){};
 
+allocator: std.mem.Allocator,
 device: *mach.gpu.Device,
 queue: *mach.gpu.Queue,
+main_window: mach.EntityID,
 should_exit: bool = false,
 
 fn init(core: *Mod) !void {
@@ -41,19 +75,52 @@ fn init(core: *Mod) !void {
     try mach.core.init(.{});
 
     core.init(.{
+        .allocator = mach.core.allocator,
         .device = mach.core.device,
         .queue = mach.core.device.getQueue(),
+        .main_window = try core.newEntity(),
     });
 
     core.sendGlobal(.init, .{});
     core.send(.init_done, .{});
 }
 
+fn update(core: *Mod) !void {
+    var archetypes_iter = core.entities.query(.{ .all = &.{
+        .{ .mach_core = &.{
+            .title,
+        } },
+    } });
+
+    var num_windows: usize = 0;
+    while (archetypes_iter.next()) |archetype| {
+        for (
+            archetype.slice(.entity, .id),
+            archetype.slice(.mach_core, .title),
+        ) |window_id, title| {
+            num_windows += 1;
+            _ = window_id;
+            try mach.core.printTitle("{s}", .{title});
+        }
+    }
+    if (num_windows > 1) @panic("mach: Core currently only supports a single window");
+}
+
 fn deinit(core: *Mod) void {
     core.state().queue.release();
     // TODO: this triggers a device loss error, which we should handle correctly
     // core.state().device.release();
     mach.core.deinit();
+
+    var archetypes_iter = core.entities.query(.{ .all = &.{
+        .{ .mach_core = &.{
+            .title,
+        } },
+    } });
+    while (archetypes_iter.next()) |archetype| {
+        for (archetype.slice(.mach_core, .title)) |title| core.state().allocator.free(title);
+    }
+
     _ = gpa.deinit();
 }