nandi/jolt-native · core.jolt

⑂ 2ab40bf193b6a39bc8d1397cc36d17572bbf59cd

core.jolt · 439 lines · 17.2 KBGDScript3    Blame HistoryRaw
Bring vidya in   1(ns glimmer-vidya.core
"The Vidya/egui backend for glimmer. Requiring this namespace installs it,
after which glimmer's portable reconciler renders hiccup into a GPU window:
  (ns myapp
    (:require [glimmer.ratom :refer [atom]]
              [glimmer.core :as ui]
              [glimmer-vidya.core]))        ; installs this backend
  (defn -main [& _] (ui/run my-app :title \"myapp\"))
egui is an immediate-mode toolkit: it has no widgets to hand a reconciler,
only calls you make every frame. So the widget tree lives one layer down, in
the Rust library, and this namespace is the thin part — it turns glimmer's
create/patch/append/remove into node mutations, runs the frame loop, and
routes the events that come back to the handlers the components declared.
A widget, from the reconciler's point of view, is an integer node handle. It
never looks inside one, which is exactly why an id is enough.
**Handlers do not cross the FFI.** A jolt closure cannot be a callback in a
library painting at 60fps, so identity travels instead: a node reports that
it was clicked, and the handler map here says whose `:on-click` that was."
(:require [glimmer.backend :as b]
          [glimmer-vidya.ffi :as ffi]))
27;; Node id -> the :on-* props that node was last rendered with. Kept here
28;; rather than sent across because a closure has no C representation.
30;; Ids are recycled by the arena, which is safe only because every id is
31;; written here by `create!` before anything can raise an event against it — a
32;; reused id has its predecessor's handlers overwritten in the same breath.
33(defonce ^:private handlers (atom {}))
35;; Work posted from other threads, run on the loop thread at the top of a tick.
36(defonce ^:private pending (atom []))
38;; Set by quit!, read by the loop.
39(defonce ^:private quit-requested (atom false))
41;; --- props -------------------------------------------------------------------
42;; :hbox and :vbox are one node in the library; the tag only implies an
43;; orientation, and an explicit :orientation prop still wins.
44(def ^:private tag-orientation {:hbox "horizontal" :vbox "vertical"})
46(defn- handler-key?
"True for a prop that names an event handler rather than a value."
(let [s (name k)]
  (and (> (count s) 3) (= "on-" (subs s 0 3)))))
52(defn- set-prop!
"Write one prop to a node, in the ABI type that fits its value. nil clears
nothing — the prop was already dropped by the clear that precedes a write —
and an unrecognized value is stringified rather than refused, so a prop this
backend has not learned yet still reaches the library."
[node k v]
(let [key (name k)]
59
    (nil? v)     nil
    (true? v)    (ffi/node-set-bool! node key true)
    (false? v)   (ffi/node-set-bool! node key false)
    (number? v)  (ffi/node-set-num! node key (double v))
    (string? v)  (ffi/node-set-str! node key v)
    (keyword? v) (ffi/node-set-str! node key (name v))
    :else        (ffi/node-set-str! node key (str v)))))
68(defn- write-props!
"Replace a node's props with `props`.
Cleared first, deliberately: a re-render that stops setting `:placeholder`
means the placeholder is gone, and patching in place would leave the old one
behind. It also discards the value the library wrote back when the user typed
in an entry or clicked a checkbutton — which is the point. The component's
state is the truth, and this is the frame where it says so."
[node tag props]
(ffi/node-clear-props! node)
(when-let [orientation (tag-orientation tag)]
  (when-not (contains? props :orientation)
    (ffi/node-set-str! node "orientation" orientation)))
(doseq [[k v] props]
  (when-not (handler-key? k)
    (set-prop! node k v)))
(swap! handlers assoc node
       (reduce (fn [acc [k v]]
                 (if (and (handler-key? k) (fn? v)) (assoc acc k v) acc))
               props))
91(defn- forget-dead-handlers!
"Drop handler entries for nodes the library has freed.
Removing a subtree frees every node under it, and only the library knows
which those were — so rather than mirror the tree here to walk it, the map is
filtered against what still exists. It runs once per removal, over a map the
size of the UI."
(swap! handlers
       (fn [m]
         (reduce (fn [acc [id hs]]
                   (if (ffi/node-exists? id) (assoc acc id hs) acc))
107;; --- the backend operations --------------------------------------------------
108(defn- create!
"glimmer.backend's :create!. Children are appended by the reconciler, not
110
[tag props]
(let [node (ffi/node-new (name tag))]
  (when (zero? node)
    (throw (ex-info "vidya could not allocate a node" {:tag tag})))
  (write-props! node tag props)
116
118(defn- apply-props! [tag node props] (write-props! node tag props))
120(defn- append-child! [_parent-tag parent child]
(ffi/node-append! parent child)
124(defn- remove-child! [_parent-tag parent child]
;; The library frees the subtree; glimmer never mentions it again.
(ffi/node-remove! parent child)
(forget-dead-handlers!)
130(defn- replace-child! [_parent-tag parent old-child new-child]
(ffi/node-replace! parent old-child new-child)
(forget-dead-handlers!)
135(defn- reorder-child! [_parent-tag parent child sibling]
;; nil sibling means "first"; the ABI spells that 0.
(ffi/node-insert-after! parent child (or sibling 0))
140;; --- the UI thread -----------------------------------------------------------
141(defn- schedule
"glimmer.backend's :schedule. Every node call belongs to the thread that
opened the window, so a ratom mutated on an nREPL worker (or any future)
queues its re-render here and the loop performs it on the next tick."
145
(swap! pending conj work)
149(defn- drain!
"Run everything `schedule` queued. compare-and-set! rather than reset!, so
work posted while the queue is being taken is not dropped."
153
  (let [q @pending]
    (when (seq q)
      (if (compare-and-set! pending q [])
        (doseq [f q] (f))
        (recur))))))
160;; --- timers ------------------------------------------------------------------
161;; A spinner or a clock has to change with nothing being pressed. The loop
162;; already wakes every frame, so a timer is a due time and a thunk. Both
163;; entry points are safe to call from another thread, and both run their thunk
164;; ON the loop thread, the only one allowed to touch nodes.
165(defonce ^:private timers (atom {:next-id 0 :entries {}}))
167(defn- now-ms [] (System/currentTimeMillis))
169(defn- add-timer! [ms every? f]
(let [id (:next-id (swap! timers update :next-id inc))]
  (swap! timers assoc-in [:entries id]
         {:due (+ (now-ms) ms) :every (when every? ms) :f f})
173
175(defn after!
"Run `f` on the loop thread in about `ms` milliseconds. Returns an id for
`cancel!`. Resolution is one frame."
[ms f] (add-timer! ms false f))
180(defn every!
"Run `f` on the loop thread about every `ms` milliseconds until cancelled:
  (every! 80 #(swap! tick inc))"
[ms f] (add-timer! ms true f))
186(defn cancel!
"Stop the timer `id`."
[id] (swap! timers update :entries dissoc id) nil)
190(defn cancel-all!
"Stop every timer, so a repeating one does not outlive the UI it animated."
[] (swap! timers assoc :entries {}) nil)
194(defn- pump-timers! []
(let [t (now-ms)
      due (reduce (fn [acc [id e]] (if (<= (:due e) t) (conj acc [id e]) acc))
                  (:entries @timers))]
  (doseq [[id e] due]
    (if-let [period (:every e)]
      (swap! timers assoc-in [:entries id :due] (+ t period))
      (swap! timers update :entries dissoc id))
    ((:f e)))
204
206;; --- events ------------------------------------------------------------------
207(defn- dispatch-events!
"Drain the frame's interactions and call the handlers they belong to.
An event whose node has no handler for it is dropped, which is what makes a
control that ignores its own event still work: the library wrote the new
state into the node, and the next render either confirms it or overwrites it."
214
  (when (ffi/poll-event!)
    (let [node (ffi/event-node)
          kind (ffi/event-name)
          hs (get @handlers node)]
      (case kind
        "click"    (when-let [f (:on-click hs)] (f))
        "toggled"  (when-let [f (:on-toggled hs)] (f))
        ;; The text is read before anything else can overwrite the library's
        ;; one scratch buffer — jolt copies it as it crosses.
        "change"   (when-let [f (:on-change hs)] (f (ffi/event-text)))
        "activate" (when-let [f (:on-activate hs)] (f))
        ;; Ctrl+V on a clipboard with no text on it. What is on it instead is
        ;; the caller's to find out — `clipboard-image-png!` is the only
        ;; question the backend answers about it.
        "paste-empty" (when-let [f (:on-paste-empty hs)] (f))
        nil))
    (recur))))
233;; --- the event loop ----------------------------------------------------------
234(defn- clear-children!
"Drop everything under `node`. Removing a child frees it, so this walks the
first slot until there is nothing left rather than iterating an index."
237
238
  (when (pos? (ffi/node-child-count node))
    (ffi/node-remove! node (ffi/node-child-at node 0))
    (recur)))
(forget-dead-handlers!)
245(defn window-width
"The width in points of the window's content area, as the last painted frame
measured it. 0 before the first frame.
This is how a layout asks how much room it has: nothing else here reports a
size, and the window is not resizable from this side either. Read it from a
timer — `every!` — rather than per render, and hold it in a ratom, so that
the components which switch on it re-render only when it actually changes."
(ffi/node-get-num (ffi/tree-root) "window-width"))
256(defn clipboard-image-png!
"Write the picture on the system clipboard to `path` as a PNG. True when
there was one; false for an empty clipboard, text on it, an unwritable path,
or a platform with no clipboard of images (Android).
A paste of a picture reaches no handler of its own — the backend delivers
clipboard text only — so a caller asks for it, from whatever gesture it means
paste by. An `:entry`'s `:on-paste-empty` is that gesture where the reader
expects it: a Ctrl+V the field had no text to answer with."
265
(ffi/clipboard-image-png! path))
268(defn open-url!
"Hand `url` to whatever shows web pages here — xdg-open or `open` on a
desktop, an ACTION_VIEW intent on Android. True when something took it;
false leaves the caller to show the URL and let the reader carry it across.
A sign-in that goes through a browser is the reason this exists: the app
leaves for a page and the page comes back to it."
(ffi/open-url! url))
Catch up with vidya   278(defn pick-image!
"Open the platform's own picture chooser. True when one opened, false where
there is none — a desktop, or an Android activity that does not offer it —
and a false is the caller's cue to browse the filesystem itself.
It does not answer with the picture. The reader is in another screen by then,
so what they chose arrives at `picked-image!`, which the caller polls."
(ffi/pick-image!))
288(defn picked-image!
"Move the picture chosen since the last call to `path`; true when there was
one. The answer is handed over once, so a poll still running does not take
the same picture twice."
292
(ffi/picked-image! path))
Tell a caller how big the window is   295(defn screen-size
"The window's size in points, as `[width height]`. `[0 0]` before the first
frame has been painted.
For laying something out as a share of the window — a row of tiles that
should divide the width between them — where how many there are and how much
gap goes between them is the caller's arithmetic, and not something one
widget can work out from the space it was handed.
Follows the window as it is dragged, so a component that reads it wants to be
re-rendered when it changes: keep it in a ratom rather than asking here at
render time, or the layout will be whatever it was on the first frame."
[(ffi/screen-width) (ffi/screen-height)])
Bring vidya in   310(defn frame-rgba!
"Hand the backend a frame of live pixels under `key`. An `:image` node with
`:feed key` paints the latest one.
`rgba` is a foreign pointer — `width * height * 4` un-premultiplied bytes,
row-major — and is copied before this returns, so whoever owns it may reuse
it immediately. False when the length does not match the dimensions.
This is the source an `:image` `:src` cannot be: a `:src` decodes a file and
caches it by path for the life of the process, which is right for a picture
in a message and wrong for one that is new thirty times a second. Frames
coalesce rather than queue, so a source faster than the window costs nothing.
On the window's thread, like everything else here: a frame produced on a
decoder thread is the caller's to hand across."
[key width height rgba]
(ffi/frame-rgba! key width height rgba))
328(defn frame-drop!
"Forget the feed named `key` and release its texture; true when there was
one. A source that has stopped keeps painting its last frame otherwise."
(ffi/frame-drop! key))
334(defn quit!
"Stop the running loop and close the window."
(reset! quit-requested true)
340(defn- run!
"glimmer.backend's :run. Opens a window, mounts the root component into the
library's root node, and paints until the window closes or `quit!` is called.
Blocks, like every UI main loop.
Options (on top of glimmer's own):
  :title :width :height   the window
  :fps                    frame rate cap (default 60)
  :mode                   :dark (default) or :light
  :font                   path to a TTF/OTF to use for UI text
  :auto-quit-ms           stop after roughly this long — for smoke tests,
                          which have nobody to close the window
The window is closed in a finally, so a handler that throws does not leave a
GPU surface and an event loop behind."
[opts mount-root!]
(let [{:keys [title width height fps mode font auto-quit-ms]
       :or {title "glimmer" width 900 height 640 fps 60}} opts]
  (when-not (ffi/open! width height title)
    (throw (ex-info "vidya could not open a window"
                    {:title title :width width :height height})))
  (reset! quit-requested false)
  (ffi/set-target-fps! fps)
  (ffi/set-mode! (if (= mode :light) ffi/light-mode ffi/dark-mode))
  (when font (ffi/load-font! font))
  (let [started (now-ms)
        root (ffi/tree-root)]
367
      ;; The library's root outlives a run — it is process-wide, not per
      ;; window — so a second `ui/run` in one session (a REPL, a test) would
      ;; otherwise mount its tree alongside the last one's.
      (clear-children! root)
      (mount-root! root :window)
      (reset! b/loop-running? true)
      (loop []
        (drain!)
        (pump-timers!)
        ;; One call paints the whole tree; the events it produced are read
        ;; straight after, while the frame that caused them is still the
        ;; frame the components rendered.
        (ffi/tree-frame!)
        (dispatch-events!)
        (when-not (or @quit-requested
                      (ffi/should-close?)
                      (and auto-quit-ms (>= (- (now-ms) started) auto-quit-ms)))
          (recur)))
      (finally
        (reset! b/loop-running? false)
        (cancel-all!)
        (ffi/close!)
        (reset! handlers {}))))))
392;; --- looking at what was rendered --------------------------------------------
393(defn dump-str
"The rendered tree as hiccup text, read back out of the library.
With no argument, the whole window; with a node handle, that subtree. This is
the tree as it *is* after the reconciler has run, not what a component
returned, so paste it into a bug report and the two can be compared.
Two things to know when reading one. `:hbox` and `:vbox` are one node down
there and both dump as `:box`, with the orientation in the props; and no
`:on-*` appears, because handlers are held on this side and never sent."
([] (dump-str 0))
([node] (ffi/tree-dump node)))
406
"`dump-str`, read back as hiccup data — vectors, keywords and maps — for a
test that wants to assert on a subtree rather than on a string."
([] (dump 0))
([node] (read-string (dump-str node))))
412(defn dump!
"Print `dump-str` to stdout. The one you want from a handler or the REPL."
([] (dump! 0))
([node] (println (dump-str node)) nil))
417;; --- the backend -------------------------------------------------------------
418(def backend
"The Vidya backend map handed to glimmer.backend/register!. See that
namespace for the contract each key satisfies."
{:name           :vidya
 :create!        create!
 :apply-props!   apply-props!
 :append-child!  append-child!
 :remove-child!  remove-child!
 :replace-child! replace-child!
 :reorder-child! reorder-child!
 :schedule       schedule
 :run            run!})
431(defn install!
"Make Vidya/egui the backend glimmer renders with. Called on load, so
requiring this namespace is enough; exposed for code that wants to be
explicit, or to switch back after another backend was installed."
(b/register! backend)
439(defonce ^:private installed (do (install!) true))

Bring vidya in cfd3e36 nandi 19d ago	1	(ns glimmer-vidya.core
	2	"The Vidya/egui backend for glimmer. Requiring this namespace installs it,
	3	after which glimmer's portable reconciler renders hiccup into a GPU window:
	4
	5	(ns myapp
	6	(:require [glimmer.ratom :refer [atom]]
	7	[glimmer.core :as ui]
	8	[glimmer-vidya.core])) ; installs this backend
	9
	10	(defn -main [& _] (ui/run my-app :title \"myapp\"))
	11
	12	egui is an immediate-mode toolkit: it has no widgets to hand a reconciler,
	13	only calls you make every frame. So the widget tree lives one layer down, in
	14	the Rust library, and this namespace is the thin part — it turns glimmer's
	15	create/patch/append/remove into node mutations, runs the frame loop, and
	16	routes the events that come back to the handlers the components declared.
	17
	18	A widget, from the reconciler's point of view, is an integer node handle. It
	19	never looks inside one, which is exactly why an id is enough.
	20
	21	Handlers do not cross the FFI. A jolt closure cannot be a callback in a
	22	library painting at 60fps, so identity travels instead: a node reports that
	23	it was clicked, and the handler map here says whose `:on-click` that was."
	24	(:require [glimmer.backend :as b]
	25	[glimmer-vidya.ffi :as ffi]))
	26
	27	;; Node id -> the :on-* props that node was last rendered with. Kept here
	28	;; rather than sent across because a closure has no C representation.
	29	;;
	30	;; Ids are recycled by the arena, which is safe only because every id is
	31	;; written here by `create!` before anything can raise an event against it — a
	32	;; reused id has its predecessor's handlers overwritten in the same breath.
	33	(defonce ^:private handlers (atom {}))
	34
	35	;; Work posted from other threads, run on the loop thread at the top of a tick.
	36	(defonce ^:private pending (atom []))
	37
	38	;; Set by quit!, read by the loop.
	39	(defonce ^:private quit-requested (atom false))
	40
	41	;; --- props -------------------------------------------------------------------
	42	;; :hbox and :vbox are one node in the library; the tag only implies an
	43	;; orientation, and an explicit :orientation prop still wins.
	44	(def ^:private tag-orientation {:hbox "horizontal" :vbox "vertical"})
	45
	46	(defn- handler-key?
	47	"True for a prop that names an event handler rather than a value."
	48	[k]
	49	(let [s (name k)]
	50	(and (> (count s) 3) (= "on-" (subs s 0 3)))))
	51
	52	(defn- set-prop!
	53	"Write one prop to a node, in the ABI type that fits its value. nil clears
	54	nothing — the prop was already dropped by the clear that precedes a write —
	55	and an unrecognized value is stringified rather than refused, so a prop this
	56	backend has not learned yet still reaches the library."
	57	[node k v]
	58	(let [key (name k)]
	59	(cond
	60	(nil? v) nil
	61	(true? v) (ffi/node-set-bool! node key true)
	62	(false? v) (ffi/node-set-bool! node key false)
	63	(number? v) (ffi/node-set-num! node key (double v))
	64	(string? v) (ffi/node-set-str! node key v)
65	(keyword? v) (ffi/node-set-str! node key (name v))
66	:else (ffi/node-set-str! node key (str v)))))
67
68	(defn- write-props!
69	"Replace a node's props with `props`.
70
71	Cleared first, deliberately: a re-render that stops setting `:placeholder`
72	means the placeholder is gone, and patching in place would leave the old one
73	behind. It also discards the value the library wrote back when the user typed
74	in an entry or clicked a checkbutton — which is the point. The component's
75	state is the truth, and this is the frame where it says so."
76	[node tag props]
77	(ffi/node-clear-props! node)
78	(when-let [orientation (tag-orientation tag)]
79	(when-not (contains? props :orientation)
80	(ffi/node-set-str! node "orientation" orientation)))
81	(doseq [[k v] props]
82	(when-not (handler-key? k)
83	(set-prop! node k v)))
84	(swap! handlers assoc node
85	(reduce (fn [acc [k v]]
86	(if (and (handler-key? k) (fn? v)) (assoc acc k v) acc))
87	{}
88	props))
89	nil)
90
91	(defn- forget-dead-handlers!
92	"Drop handler entries for nodes the library has freed.
93
94	Removing a subtree frees every node under it, and only the library knows
95	which those were — so rather than mirror the tree here to walk it, the map is
96	filtered against what still exists. It runs once per removal, over a map the
97	size of the UI."
98	[]
99	(swap! handlers
100	(fn [m]
101	(reduce (fn [acc [id hs]]
102	(if (ffi/node-exists? id) (assoc acc id hs) acc))
103	{}
104	m)))
105	nil)
106
107	;; --- the backend operations --------------------------------------------------
108	(defn- create!
109	"glimmer.backend's :create!. Children are appended by the reconciler, not
110	here."
111	[tag props]
112	(let [node (ffi/node-new (name tag))]
113	(when (zero? node)
114	(throw (ex-info "vidya could not allocate a node" {:tag tag})))
115	(write-props! node tag props)
116	node))
117
118	(defn- apply-props! [tag node props] (write-props! node tag props))
119
120	(defn- append-child! [_parent-tag parent child]
121	(ffi/node-append! parent child)
122	nil)
123
124	(defn- remove-child! [_parent-tag parent child]
125	;; The library frees the subtree; glimmer never mentions it again.
126	(ffi/node-remove! parent child)
127	(forget-dead-handlers!)
128	nil)
129
130	(defn- replace-child! [_parent-tag parent old-child new-child]
131	(ffi/node-replace! parent old-child new-child)
132	(forget-dead-handlers!)
133	nil)
134
135	(defn- reorder-child! [_parent-tag parent child sibling]
136	;; nil sibling means "first"; the ABI spells that 0.
137	(ffi/node-insert-after! parent child (or sibling 0))
138	nil)
139
140	;; --- the UI thread -----------------------------------------------------------
141	(defn- schedule
142	"glimmer.backend's :schedule. Every node call belongs to the thread that
143	opened the window, so a ratom mutated on an nREPL worker (or any future)
144	queues its re-render here and the loop performs it on the next tick."
145	[work]
146	(swap! pending conj work)
147	nil)
148
149	(defn- drain!
150	"Run everything `schedule` queued. compare-and-set! rather than reset!, so
151	work posted while the queue is being taken is not dropped."
152	[]
153	(loop []
154	(let [q @pending]
155	(when (seq q)
156	(if (compare-and-set! pending q [])
157	(doseq [f q] (f))
158	(recur))))))
159
160	;; --- timers ------------------------------------------------------------------
161	;; A spinner or a clock has to change with nothing being pressed. The loop
162	;; already wakes every frame, so a timer is a due time and a thunk. Both
163	;; entry points are safe to call from another thread, and both run their thunk
164	;; ON the loop thread, the only one allowed to touch nodes.
165	(defonce ^:private timers (atom {:next-id 0 :entries {}}))
166
167	(defn- now-ms [] (System/currentTimeMillis))
168
169	(defn- add-timer! [ms every? f]
170	(let [id (:next-id (swap! timers update :next-id inc))]
171	(swap! timers assoc-in [:entries id]
172	{:due (+ (now-ms) ms) :every (when every? ms) :f f})
173	id))
174
175	(defn after!
176	"Run `f` on the loop thread in about `ms` milliseconds. Returns an id for
177	`cancel!`. Resolution is one frame."
178	[ms f] (add-timer! ms false f))
179
180	(defn every!
181	"Run `f` on the loop thread about every `ms` milliseconds until cancelled:
182
183	(every! 80 #(swap! tick inc))"
184	[ms f] (add-timer! ms true f))
185
186	(defn cancel!
187	"Stop the timer `id`."
188	[id] (swap! timers update :entries dissoc id) nil)
189
190	(defn cancel-all!
191	"Stop every timer, so a repeating one does not outlive the UI it animated."
192	[] (swap! timers assoc :entries {}) nil)
193
194	(defn- pump-timers! []
195	(let [t (now-ms)
196	due (reduce (fn [acc [id e]] (if (<= (:due e) t) (conj acc [id e]) acc))
197	[]
198	(:entries @timers))]
199	(doseq [[id e] due]
200	(if-let [period (:every e)]
201	(swap! timers assoc-in [:entries id :due] (+ t period))
202	(swap! timers update :entries dissoc id))
203	((:f e)))
204	nil))
205
206	;; --- events ------------------------------------------------------------------
207	(defn- dispatch-events!
208	"Drain the frame's interactions and call the handlers they belong to.
209
210	An event whose node has no handler for it is dropped, which is what makes a
211	control that ignores its own event still work: the library wrote the new
212	state into the node, and the next render either confirms it or overwrites it."
213	[]
214	(loop []
215	(when (ffi/poll-event!)
216	(let [node (ffi/event-node)
217	kind (ffi/event-name)
218	hs (get @handlers node)]
219	(case kind
220	"click" (when-let [f (:on-click hs)] (f))
221	"toggled" (when-let [f (:on-toggled hs)] (f))
222	;; The text is read before anything else can overwrite the library's
223	;; one scratch buffer — jolt copies it as it crosses.
224	"change" (when-let [f (:on-change hs)] (f (ffi/event-text)))
225	"activate" (when-let [f (:on-activate hs)] (f))
226	;; Ctrl+V on a clipboard with no text on it. What is on it instead is
227	;; the caller's to find out — `clipboard-image-png!` is the only
228	;; question the backend answers about it.
229	"paste-empty" (when-let [f (:on-paste-empty hs)] (f))
230	nil))
231	(recur))))
232
233	;; --- the event loop ----------------------------------------------------------
234	(defn- clear-children!
235	"Drop everything under `node`. Removing a child frees it, so this walks the
236	first slot until there is nothing left rather than iterating an index."
237	[node]
238	(loop []
239	(when (pos? (ffi/node-child-count node))
240	(ffi/node-remove! node (ffi/node-child-at node 0))
241	(recur)))
242	(forget-dead-handlers!)
243	nil)
244
245	(defn window-width
246	"The width in points of the window's content area, as the last painted frame
247	measured it. 0 before the first frame.
248
249	This is how a layout asks how much room it has: nothing else here reports a
250	size, and the window is not resizable from this side either. Read it from a
251	timer — `every!` — rather than per render, and hold it in a ratom, so that
252	the components which switch on it re-render only when it actually changes."
253	[]
254	(ffi/node-get-num (ffi/tree-root) "window-width"))
255
256	(defn clipboard-image-png!
257	"Write the picture on the system clipboard to `path` as a PNG. True when
258	there was one; false for an empty clipboard, text on it, an unwritable path,
259	or a platform with no clipboard of images (Android).
260
261	A paste of a picture reaches no handler of its own — the backend delivers
262	clipboard text only — so a caller asks for it, from whatever gesture it means
263	paste by. An `:entry`'s `:on-paste-empty` is that gesture where the reader
264	expects it: a Ctrl+V the field had no text to answer with."
265	[path]
266	(ffi/clipboard-image-png! path))
267
268	(defn open-url!
269	"Hand `url` to whatever shows web pages here — xdg-open or `open` on a
270	desktop, an ACTION_VIEW intent on Android. True when something took it;
271	false leaves the caller to show the URL and let the reader carry it across.
272
273	A sign-in that goes through a browser is the reason this exists: the app
274	leaves for a page and the page comes back to it."
275	[url]
276	(ffi/open-url! url))
277
Catch up with vidya c90f8af nandi 19d ago	278	(defn pick-image!
	279	"Open the platform's own picture chooser. True when one opened, false where
	280	there is none — a desktop, or an Android activity that does not offer it —
	281	and a false is the caller's cue to browse the filesystem itself.
	282
	283	It does not answer with the picture. The reader is in another screen by then,
	284	so what they chose arrives at `picked-image!`, which the caller polls."
	285	[]
	286	(ffi/pick-image!))
	287
	288	(defn picked-image!
	289	"Move the picture chosen since the last call to `path`; true when there was
	290	one. The answer is handed over once, so a poll still running does not take
	291	the same picture twice."
	292	[path]
	293	(ffi/picked-image! path))
	294
Tell a caller how big the window is 42dabb0 nandi 19d ago	295	(defn screen-size
	296	"The window's size in points, as `[width height]`. `[0 0]` before the first
	297	frame has been painted.
	298
	299	For laying something out as a share of the window — a row of tiles that
	300	should divide the width between them — where how many there are and how much
	301	gap goes between them is the caller's arithmetic, and not something one
	302	widget can work out from the space it was handed.
	303
	304	Follows the window as it is dragged, so a component that reads it wants to be
	305	re-rendered when it changes: keep it in a ratom rather than asking here at
	306	render time, or the layout will be whatever it was on the first frame."
	307	[]
	308	[(ffi/screen-width) (ffi/screen-height)])
	309
Bring vidya in cfd3e36 nandi 19d ago	310	(defn frame-rgba!
	311	"Hand the backend a frame of live pixels under `key`. An `:image` node with
	312	`:feed key` paints the latest one.
	313
	314	`rgba` is a foreign pointer — `width * height * 4` un-premultiplied bytes,
	315	row-major — and is copied before this returns, so whoever owns it may reuse
	316	it immediately. False when the length does not match the dimensions.
	317
	318	This is the source an `:image` `:src` cannot be: a `:src` decodes a file and
	319	caches it by path for the life of the process, which is right for a picture
	320	in a message and wrong for one that is new thirty times a second. Frames
	321	coalesce rather than queue, so a source faster than the window costs nothing.
	322
	323	On the window's thread, like everything else here: a frame produced on a
	324	decoder thread is the caller's to hand across."
	325	[key width height rgba]
	326	(ffi/frame-rgba! key width height rgba))
	327
	328	(defn frame-drop!
	329	"Forget the feed named `key` and release its texture; true when there was
	330	one. A source that has stopped keeps painting its last frame otherwise."
	331	[key]
	332	(ffi/frame-drop! key))
	333
	334	(defn quit!
	335	"Stop the running loop and close the window."
	336	[]
	337	(reset! quit-requested true)
	338	nil)
	339
	340	(defn- run!
	341	"glimmer.backend's :run. Opens a window, mounts the root component into the
	342	library's root node, and paints until the window closes or `quit!` is called.
	343	Blocks, like every UI main loop.
	344
	345	Options (on top of glimmer's own):
	346	:title :width :height the window
	347	:fps frame rate cap (default 60)
	348	:mode :dark (default) or :light
	349	:font path to a TTF/OTF to use for UI text
	350	:auto-quit-ms stop after roughly this long — for smoke tests,
	351	which have nobody to close the window
	352
	353	The window is closed in a finally, so a handler that throws does not leave a
	354	GPU surface and an event loop behind."
	355	[opts mount-root!]
	356	(let [{:keys [title width height fps mode font auto-quit-ms]
	357	:or {title "glimmer" width 900 height 640 fps 60}} opts]
	358	(when-not (ffi/open! width height title)
	359	(throw (ex-info "vidya could not open a window"
	360	{:title title :width width :height height})))
	361	(reset! quit-requested false)
	362	(ffi/set-target-fps! fps)
	363	(ffi/set-mode! (if (= mode :light) ffi/light-mode ffi/dark-mode))
	364	(when font (ffi/load-font! font))
	365	(let [started (now-ms)
	366	root (ffi/tree-root)]
	367	(try
	368	;; The library's root outlives a run — it is process-wide, not per
	369	;; window — so a second `ui/run` in one session (a REPL, a test) would
	370	;; otherwise mount its tree alongside the last one's.
	371	(clear-children! root)
	372	(mount-root! root :window)
	373	(reset! b/loop-running? true)
374	(loop []
375	(drain!)
376	(pump-timers!)
377	;; One call paints the whole tree; the events it produced are read
378	;; straight after, while the frame that caused them is still the
379	;; frame the components rendered.
380	(ffi/tree-frame!)
381	(dispatch-events!)
382	(when-not (or @quit-requested
383	(ffi/should-close?)
384	(and auto-quit-ms (>= (- (now-ms) started) auto-quit-ms)))
385	(recur)))
386	(finally
387	(reset! b/loop-running? false)
388	(cancel-all!)
389	(ffi/close!)
390	(reset! handlers {}))))))
391
392	;; --- looking at what was rendered --------------------------------------------
393	(defn dump-str
394	"The rendered tree as hiccup text, read back out of the library.
395
396	With no argument, the whole window; with a node handle, that subtree. This is
397	the tree as it is after the reconciler has run, not what a component
398	returned, so paste it into a bug report and the two can be compared.
399
400	Two things to know when reading one. `:hbox` and `:vbox` are one node down
401	there and both dump as `:box`, with the orientation in the props; and no
402	`:on-*` appears, because handlers are held on this side and never sent."
403	([] (dump-str 0))
404	([node] (ffi/tree-dump node)))
405
406	(defn dump
407	"`dump-str`, read back as hiccup data — vectors, keywords and maps — for a
408	test that wants to assert on a subtree rather than on a string."
409	([] (dump 0))
410	([node] (read-string (dump-str node))))
411
412	(defn dump!
413	"Print `dump-str` to stdout. The one you want from a handler or the REPL."
414	([] (dump! 0))
415	([node] (println (dump-str node)) nil))
416
417	;; --- the backend -------------------------------------------------------------
418	(def backend
419	"The Vidya backend map handed to glimmer.backend/register!. See that
420	namespace for the contract each key satisfies."
421	{:name :vidya
422	:create! create!
423	:apply-props! apply-props!
424	:append-child! append-child!
425	:remove-child! remove-child!
426	:replace-child! replace-child!
427	:reorder-child! reorder-child!
428	:schedule schedule
429	:run run!})
430
431	(defn install!
432	"Make Vidya/egui the backend glimmer renders with. Called on load, so
433	requiring this namespace is enough; exposed for code that wants to be
434	explicit, or to switch back after another backend was installed."
435	[]
436	(b/register! backend)
437	nil)
438
439	(defonce ^:private installed (do (install!) true))