diff --git a/src/App.zig b/src/App.zig
index 95a830a..cf4d0b7 100644
--- a/src/App.zig
+++ b/src/App.zig
@@ -1,8 +1,24 @@
 const std = @import("std");
 const nu = @import("nu.zig");
 
+const Bus = @import("nu/Bus.zig");
+const Render = @import("nu/Render.zig");
+const ImGui = @import("nu/ImGui.zig");
+
 pub fn init(alloc: std.mem.Allocator) !void {
     _ = alloc;
 }
 
 pub fn deinit() void {}
+
+pub fn nu_frame() void {}
+
+// pub fn nu_events(events: []const Bus.Event) void {
+//     std.debug.print("{any}\n", .{events});
+// }
+
+// pub fn nu_render_present(_: Render.au.CommandBufferProxy) void {}
+
+pub fn nu_imgui_frame() void {
+    ImGui.igShowMetricsWindow(null);
+}
diff --git a/src/main.zig b/src/main.zig
index 21cff7a..b8848d5 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -11,8 +11,17 @@ pub const nu_options: nu.Options = .{
     },
 };
 
-pub const nu_driver = nu.Window;
+// todo declare or infer module dependencies, topological sort for init order. clean up "init" lines in main.
+//
+// problem: where should gpa go? probably some "Engine" structure in nu.zig
+//
+// don't necessarily need to declare topological sort - depth-first traversal
+// of each module's dependencies without repeats would do.
+//
+// idea - use a structure like std.Build.Step where the polymorphic part is a
+// component of the larger structure.
 
+pub const nu_driver = nu.Window;
 pub const nu_modules = .{
     App,
     nu.ImGui,
@@ -24,15 +33,6 @@ pub fn main() !void {
     defer _ = gpa.detectLeaks();
     const alloc = gpa.allocator();
 
-    // todo declare or infer module dependencies, topological sort for init order
-    // problem: where should gpa go? probably some "Engine" structure in nu.zig
-
-    // don't necessarily need to declare topological sort - depth-first traversal
-    // of each module's dependencies without repeats would do.
-
-    // idea - use a structure like std.Build.Step where the polymorphic part is a
-    // component of the larger structure.
-
     try nu.Window.init(alloc);
     defer nu.Window.deinit();
 
diff --git a/src/nu.zig b/src/nu.zig
index 6ceccb9..887515b 100644
--- a/src/nu.zig
+++ b/src/nu.zig
@@ -8,13 +8,30 @@ pub const ImGui = @import("nu/ImGui.zig");
 pub const Options = struct {
     window: Window.Options = .{},
     render: Render.Options = .{},
-    // imgui: ImGui.Options = .{},
+    imgui: ImGui.Options = .{},
 };
 
 pub const options: Options = if (@hasDecl(root, "nu_options")) root.nu_options else .{};
 pub const modules = root.nu_modules;
 pub const driver = root.nu_driver;
 
+pub fn run() !void {
+    try invoke_hook("nu_enter", .{});
+
+    while (driver.next()) |events| {
+        if (events.len > 0) {
+            try invoke_hook("nu_events", .{events});
+        }
+
+        // todo frame timer
+        try invoke_hook("nu_frame", .{});
+
+        // todo fixed timestep
+    }
+
+    try invoke_hook("nu_close", .{});
+}
+
 fn invoke(func: anytype, args: anytype) !void {
     if (@typeInfo(@TypeOf(func)).Fn.return_type) |R| {
         switch (@typeInfo(R)) {
@@ -28,6 +45,10 @@ fn invoke(func: anytype, args: anytype) !void {
     }
 }
 
+// todo specify hook type.
+//  - special handling for error unions
+//  - allow per-hook state somehow declared in the handler
+
 pub fn invoke_hook(comptime name: []const u8, args: anytype) !void {
     inline for (modules) |module| {
         if (@hasDecl(module, name)) {
@@ -35,14 +56,3 @@ pub fn invoke_hook(comptime name: []const u8, args: anytype) !void {
         }
     }
 }
-
-pub fn run() !void {
-    while (driver.next()) |events| {
-        // todo event handler
-        _ = events;
-
-        try invoke_hook("frame", .{});
-
-        // todo fixed timestep
-    }
-}
diff --git a/src/nu/ImGui.zig b/src/nu/ImGui.zig
index ee9bfa0..ed69fb1 100644
--- a/src/nu/ImGui.zig
+++ b/src/nu/ImGui.zig
@@ -12,6 +12,8 @@ const Window = @import("Window.zig");
 const im = @import("cimgui");
 pub usingnamespace im;
 
+pub const Options = struct {};
+
 pub fn loader_wrapper(procname: [*c]const u8, _: ?*anyopaque) callconv(.C) vk.PfnVoidFunction {
     return au.glfwGetInstanceProcAddress(au.I.handle, procname);
 }
@@ -75,34 +77,30 @@ pub fn init() !void {
     if (!im.impl.ImGui_ImplVulkan_CreateFontsTexture()) {
         return error.igVulkanFontTextureFailed;
     }
-
-    try Render.add_present_callback(present);
-    errdefer Render.remove_present_callback(present);
 }
 
-pub fn frame() void {
+pub fn nu_frame() !void {
     im.impl.ImGui_ImplGlfw_NewFrame();
     im.impl.ImGui_ImplVulkan_NewFrame();
     im.igNewFrame();
 
-    im.igShowDemoWindow(null);
+    try nu.invoke_hook("nu_imgui_frame", .{});
 
     im.igEndFrame();
     im.igRender();
 }
 
-pub fn deinit() void {
-    Render.remove_present_callback(present);
-    im.impl.ImGui_ImplVulkan_Shutdown();
-    au.D.destroyDescriptorPool(descriptor_pool, null);
-    im.impl.ImGui_ImplGlfw_Shutdown();
-    im.igDestroyContext(ctx);
-}
-
-pub fn present(cmd: au.CommandBufferProxy) void {
+pub fn nu_render_present(cmd: au.CommandBufferProxy) void {
     im.impl.ImGui_ImplVulkan_RenderDrawData(
         @ptrCast(im.igGetDrawData()),
         @ptrFromInt(@intFromEnum(cmd.handle)),
         null,
     );
 }
+
+pub fn deinit() void {
+    im.impl.ImGui_ImplVulkan_Shutdown();
+    au.D.destroyDescriptorPool(descriptor_pool, null);
+    im.impl.ImGui_ImplGlfw_Shutdown();
+    im.igDestroyContext(ctx);
+}
diff --git a/src/nu/Render.zig b/src/nu/Render.zig
index 9dcd518..0d4d843 100644
--- a/src/nu/Render.zig
+++ b/src/nu/Render.zig
@@ -30,33 +30,11 @@ pub const Options = struct {
 var sc: au.SwapChain = undefined;
 var flights: au.Flights = undefined;
 
-const PresentCallback = *const fn (au.CommandBufferProxy) void;
-var present_callbacks: std.ArrayList(PresentCallback) = undefined;
-
-pub fn add_present_callback(cb: PresentCallback) !void {
-    if (std.mem.indexOfScalar(PresentCallback, present_callbacks.items, cb)) |_| {
-        return;
-    } else {
-        try present_callbacks.append(cb);
-    }
-}
-
-pub fn remove_present_callback(cb: PresentCallback) void {
-    if (std.mem.indexOfScalar(PresentCallback, present_callbacks.items, cb)) |idx| {
-        _ = present_callbacks.orderedRemove(idx);
-    } else {
-        return;
-    }
-}
-
 pub fn init(alloc: std.mem.Allocator) !void {
     // todo pick apart au into helpers; not a sub-module filled with its own globals.
     try au.init(alloc);
     errdefer au.deinit();
 
-    present_callbacks = std.ArrayList(PresentCallback).init(alloc);
-    errdefer present_callbacks.deinit();
-
     sc = try au.SwapChain.init(alloc);
     errdefer sc.deinit();
 
@@ -64,7 +42,7 @@ pub fn init(alloc: std.mem.Allocator) !void {
     errdefer flights.deinit();
 }
 
-pub fn frame() !void {
+pub fn nu_frame() !void {
     const flight: au.Flights.Flight = flights.next();
     try flight.wait();
 
@@ -89,14 +67,11 @@ pub fn frame() !void {
 
         try cmd.beginCommandBuffer(&.{ .flags = .{ .one_time_submit_bit = true } });
         target.begin_rendering(cmd, render_area);
-        for (present_callbacks.items) |cb| {
-            cb(cmd);
-        }
 
-        // todo really don't like this.
-        // there should be some comptime means for a module to invoke hooks on other modules. eg there should be some
-        // "record" hook that for each module that gets called here; but if the render module is never added then that
-        // hook never gets called
+        // todo manage frame in flight state for each hook; pass the current flight in as context.
+        // will need some comptime -> anytype mapping.
+        try nu.invoke_hook("nu_render_present", .{cmd});
+
         target.end_rendering(cmd);
         try cmd.endCommandBuffer();
 
@@ -127,9 +102,11 @@ pub fn frame() !void {
     }
 }
 
+pub fn nu_close() !void {
+    try au.D.deviceWaitIdle();
+}
+
 pub fn deinit() void {
-    present_callbacks.deinit();
-    au.D.deviceWaitIdle() catch {};
     flights.deinit();
     sc.deinit();
     au.deinit();