A todo example, and its picture in the Readme

run-app takes #:screenshot, a path: the window saves a PNG of itself there
once it is shown and laid out, at twice its size, and closes. It defaults to
the environment variable BJOGUI_SCREENSHOT, so any program can be pictured
with no change. docs/todo.png is examples/todo.bjo, taken that way.

🤖 Generated with [ECA](https://eca.dev) (anthropic/claude-opus-4-8)

Co-Authored-By: eca-agent <git@eca.dev>

examples/todo.bjo

@@ -0,0 +1,103 @@
+;; This Source Code Form is subject to the terms of the Mozilla Public
+;; License, v. 2.0. If a copy of the MPL was not distributed with this
+;; file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+;; bjogui/examples/todo.bjo — a todo list.
+;;
+;;     bjo run examples/todo.bjo
+;;
+;; The picture in the Readme is this program, taken with
+;;
+;;     BJOGUI_SCREENSHOT=docs/todo.png bjo run examples/todo.bjo
+
+(import (std prelude))
+(import (bjogui view))
+(import (bjogui app))
+
+(type (: Todo (Record (: id int) (: title string) (: done bool))))
+
+(type (: Msg (Union (: Typed string) Add (: Toggle int bool) (: Chose int)
+                    ClearDone (: Tab int) (: Size double))))
+
+(type (: Model (Record (: todos (List Todo)) (: draft string) (: next-id int)
+                       (: chosen int) (: tab int) (: size double))))
+
+(: gui-update (-> Msg Model (Tuple Model (List (Event Msg)))))
+(defun (gui-update msg m)
+  (next
+    (match msg
+      ((Typed s) (record-set m (draft s)))
+      (Add
+       (if (string-empty? (.draft m))
+           m
+           (record-set m (todos (list-append (.todos m)
+                                             (list (Todo (id (.next-id m)) (title (.draft m))
+                                                         (done #f)))))
+                         (draft "")
+                         (next-id (+ (.next-id m) 1)))))
+      ((Toggle id done)
+       (record-set m (todos (list-map (fun (t) (if (= (.id t) id) (record-set t (done done)) t))
+                                      (.todos m)))))
+      ((Chose i) (record-set m (chosen i)))
+      (ClearDone (record-set m (todos (list-filter (fun (t) (not (.done t))) (.todos m)))
+                               (chosen -1)))
+      ((Tab i) (record-set m (tab i)))
+      ((Size d) (record-set m (size d))))))
+
+(: (-> Model int))
+(defun (done-count m)
+  (length (list-filter (fun (t) (.done t)) (.todos m))))
+
+(: (-> Model double Todo (View Msg)))
+(defun (todo-row m size t)
+  (keyed (int->string (.id t))
+         (row #:spacing 8.0
+           (checkbox "" (.done t) (fun (b) (Toggle (.id t) b)))
+           (if (.done t)
+               (paint (text (.title t) #:size size) #:colour "#7f8c8d")
+               (text (.title t) #:size size)))))
+
+(: (-> Model (View Msg)))
+(defun (todo-tab m)
+  (def total (length (.todos m)))
+  (column #:spacing 10.0 #:margin 12.0
+    (grid #:columns "*,Auto" #:spacing 8.0
+      (at 0 0 (text-input (.draft m) Typed #:placeholder "What needs doing?"))
+      (at 0 1 (paint (button "Add" Add #:enabled (not (string-empty? (.draft m))))
+                     #:background "#27ae60" #:colour "white")))
+    (list-box (vec-map (fun (t) (todo-row m (.size m) t)) (list->vec (.todos m)))
+              (.chosen m) Chose #:height 218.0)
+    (grid #:columns "*,Auto" #:spacing 8.0
+      (at 0 0 (column #:spacing 4.0
+                (text #"${(done-count m)} of ${total} done")
+                (progress-bar (if (= total 0) 0.0
+                                  (/ (cast System.Double (done-count m)) (cast System.Double total))))))
+      (at 0 1 (button "Clear done" ClearDone #:enabled (> (done-count m) 0))))))
+
+(: (-> Model (View Msg)))
+(defun (settings-tab m)
+  (column #:spacing 10.0 #:margin 12.0
+    (text "Text size")
+    (slider (.size m) 10.0 24.0 Size)
+    (border (text "Written in Bjolang, drawn by Avalonia." #:wrap #t)
+            #:colour "#2980b9" #:radius 6.0 #:background "#ecf0f1" #:padding 10.0)))
+
+(: (-> Model (View Msg)))
+(defun (view m)
+  (column #:margin 8.0
+    (paint (text "Things to do" #:size 22.0 #:margin 6.0) #:colour "#2c3e50")
+    (tabs (.tab m) Tab
+      (tab "List" (todo-tab m))
+      (tab "Settings" (settings-tab m)))))
+
+(: (-> string bool int Todo))
+(defun (todo title done id) (Todo (id id) (title title) (done done)))
+
+(defun (main)
+  (run-app (Model (todos (list (todo "Buy milk" #t 1)
+                               (todo "Write the bjogui Readme" #t 2)
+                               (todo "Add menus and dialogs" #f 3)
+                               (todo "Walk the dog" #f 4)))
+                  (draft "Water the plants") (next-id 5) (chosen 2) (tab 0) (size 14.0))
+           gui-update view
+           #:title "bjogui todo" #:width 420.0 #:height 450.0))

src/app.bjo

@@ -81,6 +81,13 @@
   (ItemCollection    (: Avalonia.Controls.ItemCollection))
   (IList             (: System.Collections.IList))
   (ICollection       (: System.Collections.ICollection))
+  (Timer             (: Avalonia.Threading.DispatcherTimer (-> Timer)))
+  (TimeSpan          (: System.TimeSpan))
+  (EventArgs         (: System.EventArgs))
+  (PixelSize         (: Avalonia.PixelSize (-> int int PixelSize)))
+  (Vector            (: Avalonia.Vector (-> double double Vector)))
+  (Visual            (: Avalonia.Visual))
+  (RenderBitmap      (: Avalonia.Media.Imaging.RenderTargetBitmap (-> PixelSize Vector RenderBitmap)))
   (Controls          (: Avalonia.Controls.Controls))
   (Panel             (: Avalonia.Controls.Panel))
   (StackPanel        (: Avalonia.Controls.StackPanel (-> StackPanel)))
@@ -221,6 +228,16 @@
   (start-lifetime      (: Avalonia.Controls.ApplicationLifetimes.ClassicDesktopStyleApplicationLifetime.Start
                           (-> Lifetime (Array ClrString) int)))
   (window-title!       (: Avalonia.Controls.Window.Title (-> Window string void) #:set))
+  (shutdown!           (: Avalonia.Controls.ApplicationLifetimes.ClassicDesktopStyleApplicationLifetime.Shutdown
+                          (-> Lifetime int void)))
+
+  ;; A picture of the window, for `#:screenshot`.
+  (seconds->span   (: System.TimeSpan.FromSeconds (-> double TimeSpan)))
+  (interval!       (: Avalonia.Threading.DispatcherTimer.Interval (-> Timer TimeSpan void) #:set))
+  (timer-start!    (: Avalonia.Threading.DispatcherTimer.Start (-> Timer void)))
+  (timer-stop!     (: Avalonia.Threading.DispatcherTimer.Stop (-> Timer void)))
+  (render-into!    (: Avalonia.Media.Imaging.RenderTargetBitmap.Render (-> RenderBitmap Visual void)))
+  (save-png!       (: Avalonia.Media.Imaging.Bitmap.Save (-> Bitmap string (Nullable int) void)))
   (window-content!     (: Avalonia.Controls.ContentControl.Content (-> ContentControl Object void) #:set)))
 
 ;; ---------------------------------------------------------------------------
@@ -931,14 +948,40 @@
   (step! app '())
   app)
 
+;; Saves a picture of the window to `path` once it has been shown and laid
+;; out, and closes it. Twice the pixels of the window, so that it is sharp on
+;; a screen with a scale of 2.
+(: (-> Lifetime Window double double string void))
+(defun (screenshot-later! lifetime w width height path)
+  (def timer (Timer.))
+  (interval! timer (seconds->span 1.0))
+  (ignore (add-event-handler! timer "Tick"
+            (: (fun (sender e)
+                 (timer-stop! timer)
+                 (def bitmap (RenderBitmap. (PixelSize. (cast System.Int32 (* 2.0 width))
+                                                        (cast System.Int32 (* 2.0 height)))
+                                            (Vector. 192.0 192.0)))
+                 (render-into! bitmap (cast Visual w))
+                 (save-png! (cast Bitmap bitmap) path (clr-default))
+                 (shutdown! lifetime 0))
+               (-> Object EventArgs void))))
+  (timer-start! timer))
+
 ;; Runs the program in a window, until the window is closed. Then the
 ;; subscriptions and the commands still running are cancelled.
+;;
+;; With `#:screenshot`, a path, the window saves a PNG of itself there once it
+;; is shown, and closes. It is the environment variable BJOGUI_SCREENSHOT
+;; unless told otherwise, so any program can be pictured with no change:
+;;
+;;     BJOGUI_SCREENSHOT=shot.png bjo run examples/todo.bjo
 (: (-> %model (-> %m %model (Tuple %model (List (Event %m)))) (-> %model (View %m))
        (#:subscriptions (-> %model (List (Sub %m))))
-       (#:title string) (#:width double) (#:height double)
+       (#:title string) (#:width double) (#:height double) (#:screenshot string)
        void))
 (defun (run-app init gui-update view #:subscriptions (fun (m) '())
-                #:title "bjogui" #:width 400.0 #:height 300.0)
+                #:title "bjogui" #:width 400.0 #:height 300.0
+                #:screenshot (option-ref-or (get-environment-variable "BJOGUI_SCREENSHOT") ""))
   ;; The Application is made inside the setup, because making one uses the
   ;; dispatcher, and the dispatcher is the platform's only after the setup.
   (def lifetime (Lifetime.))
@@ -956,6 +999,8 @@
                         (fun (c) (window-content! (cast ContentControl w) (cast Object c)))
                         #:subscriptions subscriptions))
     (main-window! lifetime w)
+    (unless (string-empty? screenshot)
+      (screenshot-later! lifetime w width height screenshot))
     (ignore (start-lifetime lifetime (: (make-array 0) (Array ClrString))))
     (app-stop! app)
     (cancel (Requested "the window is closed"))))