mach: finish splitting Core and Engine

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

src/engine.zig

@@ -0,0 +1,55 @@
+const Core = @import("core").Core;
+const gpu = @import("core").gpu;
+
+const std = @import("std");
+const ecs = @import("ecs");
+
+/// The Mach engine ECS module. This enables access to `engine.get(.mach, .core)` `*Core` APIs, as
+/// to for example `.setOptions(.{.title = "foobar"})`, or to access the GPU device via
+/// `engine.get(.mach, .device)`
+pub const module = ecs.Module(.{
+    .globals = struct {
+        core: *Core,
+        device: *gpu.Device,
+    },
+});
+
+var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+const allocator = gpa.allocator();
+
+pub fn App(
+    comptime modules: anytype,
+    comptime app_init: anytype, // fn (engine: *ecs.World(modules)) !void
+) type {
+    // TODO: validate modules.mach is the expected type.
+    // TODO: validate init has the right function signature
+
+    return struct {
+        engine: ecs.World(modules),
+        core: Core,
+
+        pub fn init(app: *@This()) !void {
+            try app.core.init(allocator, .{});
+            app.* = .{
+                .core = app.core,
+                .engine = try ecs.World(modules).init(allocator),
+            };
+            app.engine.set(.mach, .core, &app.core);
+            app.engine.set(.mach, .device, app.core.device());
+            try app_init(&app.engine);
+        }
+
+        pub fn deinit(app: *@This()) void {
+            const core = app.engine.get(.mach, .core);
+            core.deinit();
+            allocator.destroy(core);
+            app.engine.deinit();
+            _ = gpa.deinit();
+        }
+
+        pub fn update(app: *@This()) !bool {
+            app.engine.tick();
+            return false;
+        }
+    };
+}

src/main.zig

@@ -1,10 +1,14 @@
-pub usingnamespace @import("entry.zig");
-pub const Core = @import("Core.zig");
-pub const Timer = @import("Timer.zig");
-pub const gpu = @import("gpu");
+const core = @import("core");
+pub const GPUInterface = core.GPUInterface;
+pub const scope_levels = core.scope_levels;
+pub const log_level = core.log_level;
+pub const Core = core.Core;
+pub const Timer = core.Timer;
+pub const gpu = core.gpu;
+pub const sysjs = core.sysjs;
+
 pub const ecs = @import("ecs");
 pub const sysaudio = @import("sysaudio");
-pub const sysjs = @import("sysjs");
 pub const earcut = @import("earcut");
 pub const gfx = @import("gfx/util.zig");
 pub const ResourceManager = @import("resource/ResourceManager.zig");