Unify widget callback mechanism with closure

[jserv]

Previous design had widget-specific callback mechanisms (button signals, scroll signals) with duplicated closure management code.

This commit introduces two complementary callback patterns:

1. Widget-level dispatch (for custom widgets and complex event handling)
   • Added twin_widget_proc_t with (widget, event, closure) signature
   • Unified closure storage in twin_widget_t
   • Used by custom widgets and applications needing full event access
2. Button-specific API (for simple click handling)
   • Added twin_button_on_clicked(button, callback, data)
   • Simplified signature: void (*)(twin_button_t*, void*)
   • Direct callback invocation on button click
   • Used by calc, image, spline demos

Button signals promoted to standard events (TwinEventButtonSignal*). Removed obsolete scroll signal typedefs and button-specific fields.

---

Summary by cubic

Unifies widget event handling with a closure-based API and adds a simple button click callback to replace widget-specific signal plumbing. This standardizes callbacks across widgets and simplifies demo apps.

• New Features

  • Added twin_widget_proc_t(widget, event, closure) and closure storage on twin_widget_t.
  • Added twin_widget_set_callback(widget, callback, data) for app-level event callbacks.
  • Added twin_button_on_clicked(button, callback, data) for straightforward click handling.
  • Standardized button signals as events: TwinEventButtonSignalDown/Up.

• Migration

  • Replace dispatch with handler everywhere; use twin_widget_create_with_handler(...) and update function signatures to include void *closure.
  • For custom widgets, pass a handler to twin_custom_widget_create(...).
  • Stop using button signal callbacks; use twin_button_on_clicked(...).
  • Removed scroll signal typedefs and button-specific signal fields.

[cubic-dev-ai]

3 issues found across 14 files

Prompt for AI agents (all 3 issues)

Understand the root cause of the following 3 issues and fix them.


<file name="src/widget.c">

<violation number="1" location="src/widget.c:91">
Forward the closure you received when calling the copy widget’s handler; otherwise its user data is lost and the new closure-based API breaks for geometry-copy scenarios.</violation>

<violation number="2" location="src/widget.c:354">
Pass the closure argument to the user’s custom widget handler; dropping it to NULL means their registered user data never reaches the handler in the destroy path.</violation>

<violation number="3" location="src/widget.c:378">
Return the user dispatch with the closure you were passed; otherwise custom widget handlers cannot access their user data during normal event handling.</violation>
</file>

_{React with 👍 or 👎 to teach cubic. Mention @cubic-dev-ai to give feedback, ask questions, or re-run the review.}

[cubic-dev-ai]

4 issues found across 14 files

Prompt for AI agents (all 4 issues)

Understand the root cause of the following 4 issues and fix them.


<file name="src/box.c">

<violation number="1" location="src/box.c:44">
Passing NULL as the closure when dispatching to a child widget discards its callback_data, so widgets relying on per-instance state stop receiving their context. Please forward the child’s stored closure instead.</violation>

<violation number="2" location="src/box.c:191">
Pointer events forwarded to the pressed child must pass its callback_data; returning with a NULL closure prevents handlers from seeing their per-instance context.</violation>

<violation number="3" location="src/box.c:198">
Keyboard events sent to the focused child need to include its callback_data; passing NULL strips away the closure context and breaks stateful handlers.</violation>

<violation number="4" location="src/box.c:217">
Paint callbacks must receive the widget’s callback_data closure; forwarding NULL causes stateful renderers to lose their context.</violation>
</file>

_{React with 👍 or 👎 to teach cubic. Mention @cubic-dev-ai to give feedback, ask questions, or re-run the review.}

[cubic-dev-ai]

6 issues found across 14 files

Prompt for AI agents (all 6 issues)

Understand the root cause of the following 6 issues and fix them.


<file name="src/button.c">

<violation number="1" location="src/button.c:69">
The new click dispatch emits TwinEventButtonSignalDown from the TwinEventButtonUp handler, so button release events are misreported and the matching TwinEventButtonSignalUp is never sent. This breaks release handlers and mislabels clicks.</violation>
</file>

<file name="src/widget.c">

<violation number="1" location="src/widget.c:91">
Forward the incoming closure when delegating QueryGeometry to the copy widget; replacing it with callback_data loses the caller-provided context and breaks custom handlers.</violation>
</file>

<file name="src/box.c">

<violation number="1" location="src/box.c:44">
Forward the widget’s closure when dispatching to children; passing NULL drops application state for QueryGeometry handlers.</violation>

<violation number="2" location="src/box.c:191">
Propagate the child widget’s closure when sending pointer events; NULL strips the handler’s state.</violation>

<violation number="3" location="src/box.c:198">
Return the focused child with its closure so key handlers can access state; passing NULL breaks them.</violation>

<violation number="4" location="src/box.c:217">
Forward the child’s closure when invoking its paint handler; NULL removes the required state.</violation>
</file>

_{React with 👍 or 👎 to teach cubic. Mention @cubic-dev-ai to give feedback, ask questions, or re-run the review.}

[cubic-dev-ai]

Forward the incoming closure when delegating QueryGeometry to the copy widget; replacing it with callback_data loses the caller-provided context and breaks custom handlers.

Prompt for AI agents

Address the following comment on src/widget.c at line 91:

<comment>Forward the incoming closure when delegating QueryGeometry to the copy widget; replacing it with callback_data loses the caller-provided context and breaks custom handlers.</comment>

<file context>
@@ -75,16 +75,20 @@ static void _twin_widget_paint(twin_widget_t *widget)
             twin_widget_t *copy = widget-&gt;copy_geom;
             if (copy-&gt;layout)
-                (*copy-&gt;dispatch)(copy, event);
+                copy-&gt;handler(copy, event, copy-&gt;callback_data);
             widget-&gt;preferred = copy-&gt;preferred;
             return TwinDispatchDone;
</file context>

Suggested change

	copy->handler(copy, event, copy->callback_data);
	copy->handler(copy, event, closure);

[cubic-dev-ai]

1 issue found across 14 files

Prompt for AI agents (all 1 issues)

Understand the root cause of the following 1 issues and fix them.


<file name="src/box.c">

<violation number="1" location="src/box.c:132">
Passing NULL here discards the widget&#39;s callback_data, so configure handlers that rely on their closure will now be called with NULL and malfunction. Forward the stored closure instead.</violation>
</file>

_{React with 👍 or 👎 to teach cubic. Mention @cubic-dev-ai to give feedback, ask questions, or re-run the review.}