Multi-Window

This adds the ability to have multiple windows by introducing new keybind actions `new_window`, `close_window`, and `quit`. These are bound on macOS by default to the standard `cmd+n`, `cmd+w`, and `cmd+q`, respectively.

The multi-window logic is absolutely minimal: we don't do any GPU data sharing between windows, so each window recreates a full font texture for example. We can continue to further optimize this in the future.

DevMode is also pretty limited (arguably broken) with multi-window: DevMode only works on the _first_ window opened. If you close the first window, DevMode is no longer available. This is due to complexities around multi-threading and imgui. It is possible to fix this but I deferred it since it was a bit of a mess!

pkg/imgui/context.zig

@@ -14,6 +14,10 @@ pub const Context = opaque {
         c.igDestroyContext(self.cval());
     }
 
+    pub fn setCurrent(self: *Context) void {
+        c.igSetCurrentContext(self.cval());
+    }
+
     pub inline fn cval(self: *Context) *c.ImGuiContext {
         return @ptrCast(
             *c.ImGuiContext,
@@ -25,4 +29,6 @@ pub const Context = opaque {
 test {
     var ctx = try Context.create();
     defer ctx.destroy();
+
+    ctx.setCurrent();
 }

src/App.zig

@@ -9,46 +9,138 @@ const glfw = @import("glfw");
 const Window = @import("Window.zig");
 const tracy = @import("tracy");
 const Config = @import("config.zig").Config;
+const BlockingQueue = @import("./blocking_queue.zig").BlockingQueue;
+const renderer = @import("renderer.zig");
 
 const log = std.log.scoped(.app);
 
+const WindowList = std.ArrayListUnmanaged(*Window);
+
+/// The type used for sending messages to the app thread.
+pub const Mailbox = BlockingQueue(Message, 64);
+
 /// General purpose allocator
 alloc: Allocator,
 
-/// The primary window for the application. We currently support only
-/// single window operations.
-window: *Window,
+/// The list of windows that are currently open
+windows: WindowList,
 
 // The configuration for the app.
 config: *const Config,
 
+/// The mailbox that can be used to send this thread messages. Note
+/// this is a blocking queue so if it is full you will get errors (or block).
+mailbox: *Mailbox,
+
+/// Set to true once we're quitting. This never goes false again.
+quit: bool,
+
 /// Initialize the main app instance. This creates the main window, sets
 /// up the renderer state, compiles the shaders, etc. This is the primary
 /// "startup" logic.
-pub fn init(alloc: Allocator, config: *const Config) !App {
-    // Create the window
-    var window = try Window.create(alloc, config);
-    errdefer window.destroy();
+pub fn create(alloc: Allocator, config: *const Config) !*App {
+    // The mailbox for messaging this thread
+    var mailbox = try Mailbox.create(alloc);
+    errdefer mailbox.destroy(alloc);
 
-    return App{
+    var app = try alloc.create(App);
+    errdefer alloc.destroy(app);
+    app.* = .{
         .alloc = alloc,
-        .window = window,
+        .windows = .{},
         .config = config,
+        .mailbox = mailbox,
+        .quit = false,
     };
+    errdefer app.windows.deinit(alloc);
+
+    // Create the first window
+    try app.newWindow();
+
+    return app;
 }
 
-pub fn deinit(self: *App) void {
-    self.window.destroy();
-    self.* = undefined;
+pub fn destroy(self: *App) void {
+    // Clean up all our windows
+    for (self.windows.items) |window| window.destroy();
+    self.windows.deinit(self.alloc);
+    self.mailbox.destroy(self.alloc);
+    self.alloc.destroy(self);
 }
 
-pub fn run(self: App) !void {
-    while (!self.window.shouldClose()) {
-        // Block for any glfw events. This may also be an "empty" event
-        // posted by the libuv watcher so that we trigger a libuv loop tick.
+/// Wake up the app event loop. This should be called after any messages
+/// are sent to the mailbox.
+pub fn wakeup(self: App) void {
+    _ = self;
+    glfw.postEmptyEvent() catch {};
+}
+
+/// Run the main event loop for the application. This blocks until the
+/// application quits or every window is closed.
+pub fn run(self: *App) !void {
+    while (!self.quit and self.windows.items.len > 0) {
+        // Block for any glfw events.
         try glfw.waitEvents();
 
         // Mark this so we're in a totally different "frame"
         tracy.frameMark();
+
+        // If any windows are closing, destroy them
+        var i: usize = 0;
+        while (i < self.windows.items.len) {
+            const window = self.windows.items[i];
+            if (window.shouldClose()) {
+                window.destroy();
+                _ = self.windows.swapRemove(i);
+                continue;
+            }
+
+            i += 1;
+        }
+
+        // Drain our mailbox only if we're not quitting.
+        if (!self.quit) try self.drainMailbox();
     }
 }
+
+/// Drain the mailbox.
+fn drainMailbox(self: *App) !void {
+    var drain = self.mailbox.drain();
+    defer drain.deinit();
+
+    while (drain.next()) |message| {
+        log.debug("mailbox message={}", .{message});
+        switch (message) {
+            .new_window => try self.newWindow(),
+            .quit => try self.setQuit(),
+        }
+    }
+}
+
+/// Create a new window
+fn newWindow(self: *App) !void {
+    var window = try Window.create(self.alloc, self, self.config);
+    errdefer window.destroy();
+    try self.windows.append(self.alloc, window);
+    errdefer _ = self.windows.pop();
+}
+
+/// Start quitting
+fn setQuit(self: *App) !void {
+    if (self.quit) return;
+    self.quit = true;
+
+    // Mark that all our windows should close
+    for (self.windows.items) |window| {
+        window.window.setShouldClose(true);
+    }
+}
+
+/// The message types that can be sent to the app thread.
+pub const Message = union(enum) {
+    /// Create a new terminal window.
+    new_window: void,
+
+    /// Quit
+    quit: void,
+};

src/Window.zig

@@ -22,6 +22,7 @@ const terminal = @import("terminal/main.zig");
 const Config = @import("config.zig").Config;
 const input = @import("input.zig");
 const DevMode = @import("DevMode.zig");
+const App = @import("App.zig");
 
 // Get native API access on certain platforms so we can do more customization.
 const glfwNative = glfw.Native(.{
@@ -36,6 +37,9 @@ const Renderer = renderer.Renderer;
 /// Allocator
 alloc: Allocator,
 
+/// The app that this window is a part of.
+app: *App,
+
 /// The font structures
 font_lib: font.Library,
 font_group: *font.GroupCache,
@@ -107,7 +111,7 @@ const Mouse = struct {
 /// Create a new window. This allocates and returns a pointer because we
 /// need a stable pointer for user data callbacks. Therefore, a stack-only
 /// initialization is not currently possible.
-pub fn create(alloc: Allocator, config: *const Config) !*Window {
+pub fn create(alloc: Allocator, app: *App, config: *const Config) !*Window {
     var self = try alloc.create(Window);
     errdefer alloc.destroy(self);
 
@@ -136,6 +140,10 @@ pub fn create(alloc: Allocator, config: *const Config) !*Window {
     };
 
     // Find all the fonts for this window
+    //
+    // Future: we can share the font group amongst all windows to save
+    // some new window init time and some memory. This will require making
+    // thread-safe changes to font structs.
     var font_lib = try font.Library.init();
     errdefer font_lib.deinit();
     var font_group = try alloc.create(font.GroupCache);
@@ -247,6 +255,7 @@ pub fn create(alloc: Allocator, config: *const Config) !*Window {
 
     // Create our terminal grid with the initial window size
     var renderer_impl = try Renderer.init(alloc, font_group);
+    errdefer renderer_impl.deinit();
     renderer_impl.background = .{
         .r = config.background.r,
         .g = config.background.g,
@@ -307,8 +316,14 @@ pub fn create(alloc: Allocator, config: *const Config) !*Window {
     var io_thread = try termio.Thread.init(alloc, &self.io);
     errdefer io_thread.deinit();
 
+    // True if this window is hosting devmode. We only host devmode on
+    // the first window since imgui is not threadsafe. We need to do some
+    // work to make DevMode work with multiple threads.
+    const host_devmode = DevMode.enabled and DevMode.instance.window == null;
+
     self.* = .{
         .alloc = alloc,
+        .app = app,
         .font_lib = font_lib,
         .font_group = font_group,
         .window = window,
@@ -323,7 +338,7 @@ pub fn create(alloc: Allocator, config: *const Config) !*Window {
                 .visible = true,
             },
             .terminal = &self.io.terminal,
-            .devmode = if (!DevMode.enabled) null else &DevMode.instance,
+            .devmode = if (!host_devmode) null else &DevMode.instance,
         },
         .renderer_thr = undefined,
         .mouse = .{},
@@ -333,7 +348,7 @@ pub fn create(alloc: Allocator, config: *const Config) !*Window {
         .grid_size = grid_size,
         .config = config,
 
-        .imgui_ctx = if (!DevMode.enabled) void else try imgui.Context.create(),
+        .imgui_ctx = if (!DevMode.enabled) {} else try imgui.Context.create(),
     };
     errdefer if (DevMode.enabled) self.imgui_ctx.destroy();
 
@@ -361,7 +376,7 @@ pub fn create(alloc: Allocator, config: *const Config) !*Window {
 
     // Load imgui. This must be done LAST because it has to be done after
     // all our GLFW setup is complete.
-    if (DevMode.enabled) {
+    if (DevMode.enabled and DevMode.instance.window == null) {
         const dev_io = try imgui.IO.get();
         dev_io.cval().IniFilename = "ghostty_dev_mode.ini";
 
@@ -376,13 +391,16 @@ pub fn create(alloc: Allocator, config: *const Config) !*Window {
         const style = try imgui.Style.get();
         style.colorsDark();
 
-        // Add our window to the instance
+        // Add our window to the instance if it isn't set.
         DevMode.instance.window = self;
+
+        // Let our renderer setup
+        try renderer_impl.initDevMode(window);
     }
 
     // Give the renderer one more opportunity to finalize any window
     // setup on the main thread prior to spinning up the rendering thread.
-    try renderer_impl.finalizeInit(window);
+    try renderer_impl.finalizeWindowInit(window);
 
     // Start our renderer thread
     self.renderer_thr = try std.Thread.spawn(
@@ -412,18 +430,22 @@ pub fn destroy(self: *Window) void {
         self.renderer.threadEnter(self.window) catch unreachable;
         self.renderer_thread.deinit();
 
+        // If we are devmode-owning, clean that up.
+        if (DevMode.enabled and DevMode.instance.window == self) {
+            // Let our renderer clean up
+            self.renderer.deinitDevMode();
+
+            // Clear the window
+            DevMode.instance.window = null;
+
+            // Uninitialize imgui
+            self.imgui_ctx.destroy();
+        }
+
         // Deinit our renderer
         self.renderer.deinit();
     }
 
-    if (DevMode.enabled) {
-        // Clear the window
-        DevMode.instance.window = null;
-
-        // Uninitialize imgui
-        self.imgui_ctx.destroy();
-    }
-
     {
         // Stop our IO thread
         self.io_thread.stop.send() catch |err|
@@ -748,6 +770,22 @@ fn keyCallback(
                     DevMode.instance.visible = !DevMode.instance.visible;
                     win.queueRender() catch unreachable;
                 } else log.warn("dev mode was not compiled into this binary", .{}),
+
+                .new_window => {
+                    _ = win.app.mailbox.push(.{
+                        .new_window = {},
+                    }, .{ .instant = {} });
+                    win.app.wakeup();
+                },
+
+                .close_window => win.window.setShouldClose(true),
+
+                .quit => {
+                    _ = win.app.mailbox.push(.{
+                        .quit = {},
+                    }, .{ .instant = {} });
+                    win.app.wakeup();
+                },
             }
 
             // Bindings always result in us ignoring the char if printable

src/config.zig

@@ -157,6 +157,25 @@ pub const Config = struct {
             .{ .toggle_dev_mode = {} },
         );
 
+        // Windowing
+        try result.keybind.set.put(
+            alloc,
+            .{ .key = .n, .mods = .{ .super = true } },
+            .{ .new_window = {} },
+        );
+        try result.keybind.set.put(
+            alloc,
+            .{ .key = .w, .mods = .{ .super = true } },
+            .{ .close_window = {} },
+        );
+        if (builtin.os.tag == .macos) {
+            try result.keybind.set.put(
+                alloc,
+                .{ .key = .q, .mods = .{ .super = true } },
+                .{ .quit = {} },
+            );
+        }
+
         return result;
     }
 

src/input/Binding.zig

@@ -133,6 +133,15 @@ pub const Action = union(enum) {
 
     /// Dev mode
     toggle_dev_mode: void,
+
+    /// Open a new window
+    new_window: void,
+
+    /// Close the current window
+    close_window: void,
+
+    /// Quit ghostty
+    quit: void,
 };
 
 /// Trigger is the associated key state that can trigger an action.

src/main.zig

@@ -22,6 +22,9 @@ pub fn main() !void {
     }
     std.log.info("renderer={}", .{renderer.Renderer});
 
+    // First things first, we fix our file descriptors
+    fixMaxFiles();
+
     const GPA = std.heap.GeneralPurposeAllocator(.{});
     var gpa: ?GPA = gpa: {
         // Use the libc allocator if it is available beacuse it is WAY
@@ -128,8 +131,8 @@ pub fn main() !void {
     defer glfw.terminate();
 
     // Run our app
-    var app = try App.init(alloc, &config);
-    defer app.deinit();
+    var app = try App.create(alloc, &config);
+    defer app.destroy();
     try app.run();
 }
 
@@ -188,6 +191,54 @@ fn glfwErrorCallback(code: glfw.Error, desc: [:0]const u8) void {
     std.log.warn("glfw error={} message={s}", .{ code, desc });
 }
 
+/// This maximizes the number of file descriptors we can have open. We
+/// need to do this because each window consumes at least a handful of fds.
+/// This is extracted from the Zig compiler source code.
+fn fixMaxFiles() void {
+    if (!@hasDecl(std.os.system, "rlimit")) return;
+    const posix = std.os;
+
+    var lim = posix.getrlimit(.NOFILE) catch {
+        std.log.warn("failed to query file handle limit, may limit max windows", .{});
+        return; // Oh well; we tried.
+    };
+    if (comptime builtin.target.isDarwin()) {
+        // On Darwin, `NOFILE` is bounded by a hardcoded value `OPEN_MAX`.
+        // According to the man pages for setrlimit():
+        //   setrlimit() now returns with errno set to EINVAL in places that historically succeeded.
+        //   It no longer accepts "rlim_cur = RLIM.INFINITY" for RLIM.NOFILE.
+        //   Use "rlim_cur = min(OPEN_MAX, rlim_max)".
+        lim.max = std.math.min(std.os.darwin.OPEN_MAX, lim.max);
+    }
+
+    // If we're already at the max, we're done.
+    if (lim.cur >= lim.max) {
+        std.log.debug("file handle limit already maximized value={}", .{lim.cur});
+        return;
+    }
+
+    // Do a binary search for the limit.
+    var min: posix.rlim_t = lim.cur;
+    var max: posix.rlim_t = 1 << 20;
+    // But if there's a defined upper bound, don't search, just set it.
+    if (lim.max != posix.RLIM.INFINITY) {
+        min = lim.max;
+        max = lim.max;
+    }
+
+    while (true) {
+        lim.cur = min + @divTrunc(max - min, 2); // on freebsd rlim_t is signed
+        if (posix.setrlimit(.NOFILE, lim)) |_| {
+            min = lim.cur;
+        } else |_| {
+            max = lim.cur;
+        }
+        if (min + 1 >= max) break;
+    }
+
+    std.log.debug("file handle limit raised value={}", .{lim.cur});
+}
+
 test {
     _ = @import("Atlas.zig");
     _ = @import("Pty.zig");

src/renderer/Metal.zig

@@ -240,11 +240,6 @@ pub fn init(alloc: Allocator, font_group: *font.GroupCache) !Metal {
 }
 
 pub fn deinit(self: *Metal) void {
-    if (DevMode.enabled) {
-        imgui.ImplMetal.shutdown();
-        imgui.ImplGlfw.shutdown();
-    }
-
     self.cells.deinit(self.alloc);
 
     self.font_shaper.deinit();
@@ -255,7 +250,7 @@ pub fn deinit(self: *Metal) void {
 
 /// This is called just prior to spinning up the renderer thread for
 /// final main thread setup requirements.
-pub fn finalizeInit(self: *const Metal, window: glfw.Window) !void {
+pub fn finalizeWindowInit(self: *const Metal, window: glfw.Window) !void {
     // Set our window backing layer to be our swapchain
     const nswindow = objc.Object.fromId(glfwNative.getCocoaWindow(window).?);
     const contentView = objc.Object.fromId(nswindow.getProperty(?*anyopaque, "contentView").?);
@@ -268,7 +263,10 @@ pub fn finalizeInit(self: *const Metal, window: glfw.Window) !void {
     const layer = contentView.getProperty(objc.Object, "layer");
     const scaleFactor = nswindow.getProperty(macos.graphics.c.CGFloat, "backingScaleFactor");
     layer.setProperty("contentsScale", scaleFactor);
+}
 
+/// This is called if this renderer runs DevMode.
+pub fn initDevMode(self: *const Metal, window: glfw.Window) !void {
     if (DevMode.enabled) {
         // Initialize for our window
         assert(imgui.ImplGlfw.initForOther(
@@ -279,6 +277,16 @@ pub fn finalizeInit(self: *const Metal, window: glfw.Window) !void {
     }
 }
 
+/// This is called if this renderer runs DevMode.
+pub fn deinitDevMode(self: *const Metal) void {
+    _ = self;
+
+    if (DevMode.enabled) {
+        imgui.ImplMetal.shutdown();
+        imgui.ImplGlfw.shutdown();
+    }
+}
+
 /// Callback called by renderer.Thread when it begins.
 pub fn threadEnter(self: *const Metal, window: glfw.Window) !void {
     _ = self;

src/renderer/OpenGL.zig

@@ -300,11 +300,6 @@ pub fn init(alloc: Allocator, font_group: *font.GroupCache) !OpenGL {
 }
 
 pub fn deinit(self: *OpenGL) void {
-    if (DevMode.enabled) {
-        imgui.ImplOpenGL3.shutdown();
-        imgui.ImplGlfw.shutdown();
-    }
-
     self.font_shaper.deinit();
     self.alloc.free(self.font_shaper.cell_buf);
 
@@ -387,7 +382,15 @@ pub fn windowInit(window: glfw.Window) !void {
 
 /// This is called just prior to spinning up the renderer thread for
 /// final main thread setup requirements.
-pub fn finalizeInit(self: *const OpenGL, window: glfw.Window) !void {
+pub fn finalizeWindowInit(self: *const OpenGL, window: glfw.Window) !void {
+    _ = self;
+    _ = window;
+}
+
+/// This is called if this renderer runs DevMode.
+pub fn initDevMode(self: *const OpenGL, window: glfw.Window) !void {
+    _ = self;
+
     if (DevMode.enabled) {
         // Initialize for our window
         assert(imgui.ImplGlfw.initForOpenGL(
@@ -396,9 +399,16 @@ pub fn finalizeInit(self: *const OpenGL, window: glfw.Window) !void {
         ));
         assert(imgui.ImplOpenGL3.init("#version 330 core"));
     }
+}
 
-    // Call thread exit to clean up our context
-    self.threadExit();
+/// This is called if this renderer runs DevMode.
+pub fn deinitDevMode(self: *const OpenGL) void {
+    _ = self;
+
+    if (DevMode.enabled) {
+        imgui.ImplOpenGL3.shutdown();
+        imgui.ImplGlfw.shutdown();
+    }
 }
 
 /// Callback called by renderer.Thread when it begins.

src/renderer/Thread.zig

@@ -65,7 +65,11 @@ pub fn init(
 
     // Create our event loop.
     var loop = try libuv.Loop.init(alloc);
-    errdefer loop.deinit(alloc);
+    errdefer {
+        // Run the loop once to close any of our handles
+        _ = loop.run(.nowait) catch 0;
+        loop.deinit(alloc);
+    }
     loop.setData(allocPtr);
 
     // This async handle is used to "wake up" the renderer and force a render.

src/termio/Exec.zig

@@ -15,6 +15,12 @@ const renderer = @import("../renderer.zig");
 
 const log = std.log.scoped(.io_exec);
 
+const c = @cImport({
+    @cInclude("errno.h");
+    @cInclude("signal.h");
+    @cInclude("unistd.h");
+});
+
 /// Allocator
 alloc: Allocator,
 
@@ -78,8 +84,8 @@ pub fn init(alloc: Allocator, opts: termio.Options) !Exec {
         .env = &env,
         .cwd = opts.config.@"working-directory",
         .pre_exec = (struct {
-            fn callback(c: *Command) void {
-                const p = c.getData(Pty) orelse unreachable;
+            fn callback(cmd: *Command) void {
+                const p = cmd.getData(Pty) orelse unreachable;
                 p.childPreExec() catch |err|
                     log.err("error initializing child: {}", .{err});
             }
@@ -113,9 +119,9 @@ pub fn init(alloc: Allocator, opts: termio.Options) !Exec {
 }
 
 pub fn deinit(self: *Exec) void {
-    // Deinitialize the pty. This closes the pty handles. This should
-    // cause a close in the our subprocess so just wait for that.
-    self.pty.deinit();
+    // Kill our command
+    self.killCommand() catch |err|
+        log.err("error sending SIGHUP to command, may hang: {}", .{err});
     _ = self.command.wait() catch |err|
         log.err("error waiting for command to exit: {}", .{err});
 
@@ -123,6 +129,42 @@ pub fn deinit(self: *Exec) void {
     self.terminal.deinit(self.alloc);
 }
 
+/// Kill the underlying subprocess. This closes the pty file handle and
+/// sends a SIGHUP to the child process. This doesn't wait for the child
+/// process to be exited.
+fn killCommand(self: *Exec) !void {
+    // Close our PTY
+    self.pty.deinit();
+
+    // We need to get our process group ID and send a SIGHUP to it.
+    if (self.command.pid) |pid| {
+        const pgid_: ?c.pid_t = pgid: {
+            const pgid = c.getpgid(pid);
+
+            // Don't know why it would be zero but its not a valid pid
+            if (pgid == 0) break :pgid null;
+
+            // If the pid doesn't exist then... okay.
+            if (pgid == c.ESRCH) break :pgid null;
+
+            // If we have an error...
+            if (pgid < 0) {
+                log.warn("error getting pgid for kill", .{});
+                break :pgid null;
+            }
+
+            break :pgid pgid;
+        };
+
+        if (pgid_) |pgid| {
+            if (c.killpg(pgid, c.SIGHUP) < 0) {
+                log.warn("error killing process group pgid={}", .{pgid});
+                return error.KillFailed;
+            }
+        }
+    }
+}
+
 pub fn threadEnter(self: *Exec, loop: libuv.Loop) !ThreadData {
     assert(self.data == null);
 
@@ -367,15 +409,15 @@ fn ttyRead(t: *libuv.Tty, n: isize, buf: []const u8) void {
     var i: usize = 0;
     const end = @intCast(usize, n);
     if (ev.terminal_stream.parser.state == .ground) {
-        for (buf[i..end]) |c| {
-            switch (terminal.parse_table.table[c][@enumToInt(terminal.Parser.State.ground)].action) {
+        for (buf[i..end]) |ch| {
+            switch (terminal.parse_table.table[ch][@enumToInt(terminal.Parser.State.ground)].action) {
                 // Print, call directly.
-                .print => ev.terminal_stream.handler.print(@intCast(u21, c)) catch |err|
+                .print => ev.terminal_stream.handler.print(@intCast(u21, ch)) catch |err|
                     log.err("error processing terminal data: {}", .{err}),
 
                 // C0 execute, let our stream handle this one but otherwise
                 // continue since we're guaranteed to be back in ground.
-                .execute => ev.terminal_stream.execute(c) catch |err|
+                .execute => ev.terminal_stream.execute(ch) catch |err|
                     log.err("error processing terminal data: {}", .{err}),
 
                 // Otherwise, break out and go the slow path until we're
@@ -413,8 +455,8 @@ const StreamHandler = struct {
         try self.ev.queueWrite(data);
     }
 
-    pub fn print(self: *StreamHandler, c: u21) !void {
-        try self.terminal.print(c);
+    pub fn print(self: *StreamHandler, ch: u21) !void {
+        try self.terminal.print(ch);
     }
 
     pub fn bell(self: StreamHandler) !void {

src/termio/Thread.zig

@@ -49,7 +49,11 @@ pub fn init(
 
     // Create our event loop.
     var loop = try libuv.Loop.init(alloc);
-    errdefer loop.deinit(alloc);
+    errdefer {
+        // Run the loop once to close any of our handles
+        _ = loop.run(.nowait) catch 0;
+        loop.deinit(alloc);
+    }
     loop.setData(allocPtr);
 
     // This async handle is used to "wake up" the renderer and force a render.