diff --git a/src/App.zig b/src/App.zig
index 1154cf86d..683a70f47 100644
--- a/src/App.zig
+++ b/src/App.zig
@@ -128,6 +128,7 @@ fn drainMailbox(self: *App, rt_app: *apprt.App) !void {
             .close => |surface| try self.closeSurface(rt_app, surface),
             .quit => try self.setQuit(),
             .surface_message => |msg| try self.surfaceMessage(msg.surface, msg.message),
+            .redraw_surface => |surface| try self.redrawSurface(rt_app, surface),
         }
     }
 }
@@ -137,6 +138,11 @@ fn closeSurface(self: *App, rt_app: *apprt.App, surface: *Surface) !void {
     rt_app.closeSurface(surface.rt_surface);
 }
 
+fn redrawSurface(self: *App, rt_app: *apprt.App, surface: *apprt.Surface) !void {
+    if (!self.hasSurface(&surface.core_surface)) return;
+    rt_app.redrawSurface(surface);
+}
+
 /// Create a new window
 fn newWindow(self: *App, rt_app: *apprt.App, msg: Message.NewWindow) !void {
     if (!@hasDecl(apprt.App, "newWindow")) {
@@ -230,6 +236,12 @@ pub const Message = union(enum) {
         message: apprt.surface.Message,
     },
 
+    /// Redraw a surface. This only has an effect for runtimes that
+    /// use single-threaded draws. To redraw a surface for all runtimes,
+    /// wake up the renderer thread. The renderer thread will send this
+    /// message if it needs to.
+    redraw_surface: *apprt.Surface,
+
     const NewWindow = struct {
         /// The parent surface
         parent: ?*Surface = null,
diff --git a/src/Surface.zig b/src/Surface.zig
index 65740340e..b7ce3ede7 100644
--- a/src/Surface.zig
+++ b/src/Surface.zig
@@ -316,6 +316,7 @@ pub fn init(
         rt_surface,
         &self.renderer,
         &self.renderer_state,
+        app_mailbox,
     );
     errdefer render_thread.deinit();
 
diff --git a/src/apprt/glfw.zig b/src/apprt/glfw.zig
index 6ba10656d..dbdb925d3 100644
--- a/src/apprt/glfw.zig
+++ b/src/apprt/glfw.zig
@@ -137,6 +137,13 @@ pub const App = struct {
         self.app.alloc.destroy(surface);
     }
 
+    pub fn redrawSurface(self: *App, surface: *Surface) void {
+        _ = self;
+        _ = surface;
+
+        @panic("This should never be called for GLFW.");
+    }
+
     fn glfwErrorCallback(code: glfw.ErrorCode, desc: [:0]const u8) void {
         std.log.warn("glfw error={} message={s}", .{ code, desc });
 
diff --git a/src/apprt/gtk.zig b/src/apprt/gtk.zig
index 62020e4eb..4c4cb9429 100644
--- a/src/apprt/gtk.zig
+++ b/src/apprt/gtk.zig
@@ -115,6 +115,11 @@ pub const App = struct {
         @panic("This should not be called with GTK.");
     }
 
+    pub fn redrawSurface(self: *App, surface: *Surface) void {
+        _ = self;
+        surface.invalidate();
+    }
+
     pub fn newWindow(self: *App, parent_: ?*CoreSurface) !void {
         _ = parent_;
 
@@ -169,42 +174,30 @@ pub const Surface = struct {
     /// The app we're part of
     app: *App,
 
+    /// Our GTK area
+    gl_area: *c.GtkGLArea,
+
     /// The core surface backing this surface
     core_surface: CoreSurface,
 
+    /// Cached metrics about the surface from GTK callbacks.
+    size: apprt.SurfaceSize,
+
     pub fn init(self: *Surface, app: *App, opts: Options) !void {
         // Build our result
         self.* = .{
             .app = app,
+            .gl_area = opts.gl_area,
             .core_surface = undefined,
+            .size = .{ .width = 800, .height = 600 },
         };
         errdefer self.* = undefined;
 
         // Create the GL area that will contain our surface
-        _ = c.g_signal_connect_data(
-            opts.gl_area,
-            "realize",
-            c.G_CALLBACK(&gtkRealize),
-            self,
-            null,
-            c.G_CONNECT_DEFAULT,
-        );
-        _ = c.g_signal_connect_data(
-            opts.gl_area,
-            "render",
-            c.G_CALLBACK(&gtkRender),
-            null,
-            null,
-            c.G_CONNECT_DEFAULT,
-        );
-        _ = c.g_signal_connect_data(
-            opts.gl_area,
-            "destroy",
-            c.G_CALLBACK(&gtkDestroy),
-            self,
-            null,
-            c.G_CONNECT_DEFAULT,
-        );
+        _ = c.g_signal_connect_data(opts.gl_area, "realize", c.G_CALLBACK(&gtkRealize), self, null, c.G_CONNECT_DEFAULT);
+        _ = c.g_signal_connect_data(opts.gl_area, "destroy", c.G_CALLBACK(&gtkDestroy), self, null, c.G_CONNECT_DEFAULT);
+        _ = c.g_signal_connect_data(opts.gl_area, "render", c.G_CALLBACK(&gtkRender), self, null, c.G_CONNECT_DEFAULT);
+        _ = c.g_signal_connect_data(opts.gl_area, "resize", c.G_CALLBACK(&gtkResize), self, null, c.G_CONNECT_DEFAULT);
     }
 
     fn realize(self: *Surface) !void {
@@ -220,16 +213,33 @@ pub const Surface = struct {
             self,
         );
         errdefer self.core_surface.deinit();
+
+        // Note we're realized
+        self.realized = true;
+    }
+
+    fn render(self: *Surface) !void {
+        try self.core_surface.renderer.draw();
+    }
+
+    /// Invalidate the surface so that it forces a redraw on the next tick.
+    fn invalidate(self: *Surface) void {
+        c.gtk_gl_area_queue_render(self.gl_area);
     }
 
     fn gtkRealize(area: *c.GtkGLArea, ud: ?*anyopaque) callconv(.C) void {
-        _ = area;
-
         log.debug("gl surface realized", .{});
 
+        // We need to make the context current so we can call GL functions.
+        c.gtk_gl_area_make_current(area);
+        if (c.gtk_gl_area_get_error(area)) |err| {
+            log.err("surface failed to realize: {s}", .{err.*.message});
+            return;
+        }
+
         // realize means that our OpenGL context is ready, so we can now
         // initialize the core surface which will setup the renderer.
-        const self = userdataSelf(ud orelse return);
+        const self = userdataSelf(ud.?);
         self.realize() catch |err| {
             // TODO: we need to destroy the GL area here.
             log.err("surface failed to realize: {}", .{err});
@@ -237,24 +247,45 @@ pub const Surface = struct {
         };
     }
 
+    /// render singal
     fn gtkRender(area: *c.GtkGLArea, ctx: *c.GdkGLContext, ud: ?*anyopaque) callconv(.C) c.gboolean {
         _ = area;
         _ = ctx;
-        _ = ud;
-        log.debug("gl render", .{});
 
-        const opengl = @import("../renderer/opengl/main.zig");
-        opengl.clearColor(0, 0.5, 1, 1);
-        opengl.clear(opengl.c.GL_COLOR_BUFFER_BIT);
+        const self = userdataSelf(ud.?);
+        self.render() catch |err| {
+            log.err("surface failed to render: {}", .{err});
+            return 0;
+        };
 
         return 1;
     }
 
+    /// render singal
+    fn gtkResize(area: *c.GtkGLArea, width: c.gint, height: c.gint, ud: ?*anyopaque) callconv(.C) void {
+        _ = area;
+        log.debug("gl resize {} {}", .{ width, height });
+
+        const self = userdataSelf(ud.?);
+        self.size = .{
+            .width = @intCast(u32, width),
+            .height = @intCast(u32, height),
+        };
+
+        // Call the primary callback.
+        if (self.realized) {
+            self.core_surface.sizeCallback(self.size) catch |err| {
+                log.err("error in size callback err={}", .{err});
+                return;
+            };
+        }
+    }
+
     /// "destroy" signal for surface
     fn gtkDestroy(v: *c.GtkWidget, ud: ?*anyopaque) callconv(.C) void {
         _ = v;
 
-        const self = userdataSelf(ud orelse return);
+        const self = userdataSelf(ud.?);
         const alloc = self.app.core_app.alloc;
         self.deinit();
         alloc.destroy(self);
@@ -283,8 +314,7 @@ pub const Surface = struct {
     }
 
     pub fn getSize(self: *const Surface) !apprt.SurfaceSize {
-        _ = self;
-        return .{ .width = 800, .height = 600 };
+        return self.size;
     }
 
     pub fn setSizeLimits(self: *Surface, min: apprt.SurfaceSize, max_: ?apprt.SurfaceSize) !void {
diff --git a/src/renderer/OpenGL.zig b/src/renderer/OpenGL.zig
index 9a2a2fc47..b041f8d2f 100644
--- a/src/renderer/OpenGL.zig
+++ b/src/renderer/OpenGL.zig
@@ -34,7 +34,7 @@ const CellsLRU = lru.AutoHashMap(struct {
 /// The runtime can request a single-threaded draw by setting this boolean
 /// to true. In this case, the renderer.draw() call is expected to be called
 /// from the runtime.
-const single_threaded_draw = if (@hasDecl(apprt.Surface, "opengl_single_threaded_draw"))
+pub const single_threaded_draw = if (@hasDecl(apprt.Surface, "opengl_single_threaded_draw"))
     apprt.Surface.opengl_single_threaded_draw
 else
     false;
diff --git a/src/renderer/Thread.zig b/src/renderer/Thread.zig
index 2ffd0a1df..12424272d 100644
--- a/src/renderer/Thread.zig
+++ b/src/renderer/Thread.zig
@@ -10,6 +10,7 @@ const apprt = @import("../apprt.zig");
 const BlockingQueue = @import("../blocking_queue.zig").BlockingQueue;
 const tracy = @import("tracy");
 const trace = tracy.trace;
+const App = @import("../App.zig");
 
 const Allocator = std.mem.Allocator;
 const log = std.log.scoped(.renderer_thread);
@@ -60,6 +61,9 @@ state: *renderer.State,
 /// this is a blocking queue so if it is full you will get errors (or block).
 mailbox: *Mailbox,
 
+/// Mailbox to send messages to the app thread
+app_mailbox: App.Mailbox,
+
 /// Initialize the thread. This does not START the thread. This only sets
 /// up all the internal state necessary prior to starting the thread. It
 /// is up to the caller to start the thread with the threadMain entrypoint.
@@ -68,6 +72,7 @@ pub fn init(
     surface: *apprt.Surface,
     renderer_impl: *renderer.Renderer,
     state: *renderer.State,
+    app_mailbox: App.Mailbox,
 ) !Thread {
     // Create our event loop.
     var loop = try xev.Loop.init(.{});
@@ -104,6 +109,7 @@ pub fn init(
         .renderer = renderer_impl,
         .state = state,
         .mailbox = mailbox,
+        .app_mailbox = app_mailbox,
     };
 }
 
@@ -307,6 +313,15 @@ fn renderCallback(
 
     t.renderer.render(t.surface, t.state) catch |err|
         log.warn("error rendering err={}", .{err});
+
+    // If we're doing single-threaded GPU calls then we also wake up the
+    // app thread to redraw at this point.
+    if (renderer.Renderer == renderer.OpenGL and
+        renderer.OpenGL.single_threaded_draw)
+    {
+        _ = t.app_mailbox.push(.{ .redraw_surface = t.surface }, .{ .instant = {} });
+    }
+
     return .disarm;
 }
 
diff --git a/src/renderer/opengl/Program.zig b/src/renderer/opengl/Program.zig
index 5140b7517..2e2978363 100644
--- a/src/renderer/opengl/Program.zig
+++ b/src/renderer/opengl/Program.zig
@@ -69,6 +69,7 @@ pub inline fn link(p: Program) !void {
 
 pub inline fn use(p: Program) !Binding {
     glad.context.UseProgram.?(p.id);
+    try errors.getError();
     return Binding{};
 }
 
diff --git a/src/renderer/opengl/Texture.zig b/src/renderer/opengl/Texture.zig
index 446f0a9ad..f52d12859 100644
--- a/src/renderer/opengl/Texture.zig
+++ b/src/renderer/opengl/Texture.zig
@@ -9,6 +9,7 @@ id: c.GLuint,
 
 pub inline fn active(target: c.GLenum) !void {
     glad.context.ActiveTexture.?(target);
+    try errors.getError();
 }
 
 /// Enun for possible texture binding targets.
@@ -153,6 +154,7 @@ pub inline fn create() !Texture {
 /// glBindTexture
 pub inline fn bind(v: Texture, target: Target) !Binding {
     glad.context.BindTexture.?(@enumToInt(target), v.id);
+    try errors.getError();
     return Binding{ .target = target };
 }
 
diff --git a/src/renderer/opengl/VertexArray.zig b/src/renderer/opengl/VertexArray.zig
index 6222a2b68..b86794042 100644
--- a/src/renderer/opengl/VertexArray.zig
+++ b/src/renderer/opengl/VertexArray.zig
@@ -2,6 +2,7 @@ const VertexArray = @This();
 
 const c = @import("c.zig");
 const glad = @import("glad.zig");
+const errors = @import("errors.zig");
 
 id: c.GLuint,
 
@@ -20,6 +21,7 @@ pub inline fn unbind() !void {
 /// glBindVertexArray
 pub inline fn bind(v: VertexArray) !void {
     glad.context.BindVertexArray.?(v.id);
+    try errors.getError();
 }
 
 pub inline fn destroy(v: VertexArray) void {