From 30da787ea4287e1eda3f1a68d9bdd1c4a883f02d Mon Sep 17 00:00:00 2001
From: Almar Klein <almar@almarklein.org>
Date: Sun, 29 Jun 2025 12:44:57 +0200
Subject: [PATCH] poc event task

---
 examples/drag.py        | 60 +++++++++++++++++++++++++++++++++++++++++
 rendercanvas/_events.py | 27 +++++++++++++++++++
 rendercanvas/base.py    |  8 +++++-
 3 files changed, 94 insertions(+), 1 deletion(-)
 create mode 100644 examples/drag.py

diff --git a/examples/drag.py b/examples/drag.py
new file mode 100644
index 0000000..fbe7ac3
--- /dev/null
+++ b/examples/drag.py
@@ -0,0 +1,60 @@
+"""
+Noise
+-----
+
+Simple example that uses the bitmap-context to show images of noise.
+"""
+
+# run_example = true
+
+import numpy as np
+from rendercanvas.auto import RenderCanvas, loop
+
+
+canvas = RenderCanvas(update_mode="continuous")
+context = canvas.get_context("bitmap")
+
+
+w, h = 12, 12
+currentpos = [1, 1]
+
+@canvas.request_draw
+def animate():
+    x, y = currentpos
+
+    bitmap = np.zeros((h, w, 4), np.uint8)
+    bitmap[y, x] = 255
+
+    context.set_bitmap(bitmap)
+
+
+
+@canvas.add_event_task
+async def foo(emitter):
+    while True:
+
+        # Wait for pointer down
+        event = await emitter.for_event("pointer_down")
+
+        # Does this select the current position of the active block?
+        width, height = canvas.get_logical_size()
+        x = int(w * event["x"] / width)
+        y = int(h * event["y"] / height)
+        if [x, y] != currentpos:
+            print("nope", x, y)
+            continue
+
+        # Move until pointer up
+        while True:
+            event = await emitter.for_event("pointer_move", "pointer_up")
+            if event["event_type"] == "pointer_up":
+                break
+
+            width, height = canvas.get_logical_size()
+            x = int(w * event["x"] / width)
+            y = int(h * event["y"] / height)
+            print(x, y)
+            currentpos[:] = x, y
+
+
+loop.run()
diff --git a/rendercanvas/_events.py b/rendercanvas/_events.py
index 4552e4e..cf98bac 100644
--- a/rendercanvas/_events.py
+++ b/rendercanvas/_events.py
@@ -69,6 +69,7 @@ class EventEmitter:
     def __init__(self):
         self._pending_events = deque()
         self._event_handlers = defaultdict(list)
+        self._signals = []
         self._closed = False
 
     def _release(self):
@@ -76,6 +77,22 @@ def _release(self):
         self._pending_events.clear()
         self._event_handlers.clear()
 
+    async def for_event(self, *event_types: str):
+        from .utils.asyncs import Event as AsyncSignal  # rename to avoid confusion
+
+        for type in event_types:
+            if not (type == "*" or type in valid_event_types):
+                raise ValueError(f"Calling for_event with invalid event_type: '{type}'")
+
+        # Get signal. This is an asyncio, trio, rendercanvas.utils._async_adapter, or anything else from sniffio
+        # This is a low level asyncio construct that's actually called "Event", but let's call it signal here.
+        signal = AsyncSignal()
+        signal.event_types = set(event_types)
+        self._signals.append(signal)
+
+        await signal.wait()
+        return signal.event
+
     def add_handler(self, *args, order: float = 0):
         """Register an event handler to receive events.
 
@@ -225,6 +242,16 @@ async def emit(self, event):
                     await callback(event)
                 else:
                     callback(event)
+        # Handle signals that ``await for_event(..)``.
+        # TODO: Use more performent data structure so we can avoid iterating over all waiting signals.
+        # TODO: maybe it makes more sense to think of the signals as tasks; each signal represents a waiting task.
+        # TODO: is there also a common construct that we can pass a value to?
+        signals_to_remove = []
+        for signal in self._signals:
+            if event_type in signal.event_types:
+                signals_to_remove.append(signal)
+                signal.event = event
+                signal.set()
         # Close?
         if event_type == "close":
             self._release()
diff --git a/rendercanvas/base.py b/rendercanvas/base.py
index 32ca623..43d581c 100644
--- a/rendercanvas/base.py
+++ b/rendercanvas/base.py
@@ -15,7 +15,7 @@
 from ._coreutils import logger, log_exception, BaseEnum
 
 if TYPE_CHECKING:
-    from typing import Callable, List, Optional, Tuple
+    from typing import Callable, Coroutine, List, Optional, Tuple
 
     EventHandlerFunction = Callable[[dict], None]
     DrawFunction = Callable[[], None]
@@ -309,6 +309,12 @@ def add_event_handler(
     def remove_event_handler(self, callback: EventHandlerFunction, *types: str) -> None:
         return self._events.remove_handler(callback, *types)
 
+    def add_event_task(
+        self, async_func: Callable[[], Coroutine], name: str = "unnamed"
+    ):
+        loop = self._rc_canvas_group.get_loop()
+        loop.add_task(async_func, self._events)
+
     def submit_event(self, event: dict) -> None:
         # Not strictly necessary for normal use-cases, but this allows
         # the ._event to be an implementation detail to subclasses, and it