Add android.touch module to support touch interception via SDLSurface

Author: kengoon

pythonforandroid/recipes/android/src/android/touch.py

@@ -0,0 +1,232 @@
+"""Touch interception helpers for Python for Android.
+
+This module exposes two utilities to hook into the Android SDL surface's
+intercept touch mechanism via pyjnius:
+
+- `OnInterceptTouchListener`: a thin bridge class that implements the
+  Java interface `SDLSurface.OnInterceptTouchListener` and delegates to a
+  provided Python callable.
+- `TouchListener`: a convenience class with helpers to register/unregister
+  the intercept listener and a hit-testing routine against the Kivy
+  `Window` to decide whether a touch should be consumed.
+- `TouchListener.register_listener` requires a `target_widget` argument,
+  which is used for hit-testing to decide whether to consume touches.
+- Touch coordinates are taken from pointer index 0 and converted to Kivy's
+  coordinate system by inverting Y relative to `Window.height`.
+
+Dependencies: pyjnius for bridging to Android, and Kivy for window and
+widget traversal used in hit-testing.
+"""
+
+from jnius import PythonJavaClass, java_method, autoclass
+from android.config import ACTIVITY_CLASS_NAME
+
+__all__ = ('OnInterceptTouchListener', 'TouchListener')
+
+
+class OnInterceptTouchListener(PythonJavaClass):
+    """Bridge for Android's `SDLSurface.OnInterceptTouchListener`.
+
+    Instances of this class can be passed to the SDL surface so that touch
+    events can be intercepted before they reach the normal Android/Kivy
+    dispatch pipeline. The Python callable provided at construction time is
+    invoked for each `MotionEvent` and should return a boolean indicating
+    whether the touch was consumed.
+    """
+
+    __javacontext__ = 'app'
+    __javainterfaces__ = [
+        'org/libsdl/app/SDLSurface$OnInterceptTouchListener']
+
+    def __init__(self, listener):
+        """Create a new intercept touch listener.
+
+        Parameters:
+            listener (Callable[[object], bool]): A callable that receives the
+                Android `MotionEvent` instance and returns `True` if the
+                touch should be consumed (intercepted), or `False` to let it
+                propagate normally.
+        """
+        self.listener = listener
+
+    @java_method('(Landroid/view/MotionEvent;)Z')
+    def onTouch(self, event):
+        """Handle an incoming `MotionEvent`.
+
+        Parameters:
+            event: The Android `MotionEvent` object delivered by the SDL
+                surface.
+
+        Returns:
+            bool: The boolean returned by the user-provided `listener`, where
+            `True` indicates the event was consumed and should not propagate
+            further; `False` lets normal processing continue.
+        """
+        return self.listener(event)
+
+
+class TouchListener:
+    """Convenience API to register a global Android intercept touch listener.
+
+    This class manages a singleton instance of `OnInterceptTouchListener`
+    that is attached to the app's `PythonActivity.mSurface`. It also stores
+    a reference to a specific `target_widget` used during hit-testing to
+    decide whether touches should be consumed.
+
+    A small hit-testing helper walks the Kivy `Window` widget tree to
+    determine whether a touch should be intercepted (consumed) or allowed to
+    propagate.
+
+    Notes:
+    - The intercept listener affects the entire SDL surface and thus the
+      whole app; use with care.
+    - The internal `__listener` attribute stores the active listener
+      instance when registered, or `None` when not set.
+    - The internal `__target_widget` holds the widget against which the
+      hit-test is compared and is cleared on `unregister_listener()`.
+    """
+    __listener = None
+    __target_widget = None
+
+    @classmethod
+    def register_listener(cls, target_widget):
+        """Register the global intercept touch listener if not already set.
+
+        This creates a singleton `OnInterceptTouchListener` that delegates to
+        `TouchListener._on_touch_listener` and installs it on
+        `PythonActivity.mSurface` via pyjnius.
+
+        Parameters:
+            target_widget: The widget used as the reference during hit-testing.
+                If the touch lands on this widget and no other widget is found
+                under the touch, the event will be consumed by the intercept
+                listener.
+        """
+        if cls.__listener:
+            return
+        cls.__target_widget = target_widget
+        cls.__listener = OnInterceptTouchListener(cls._on_touch_listener)
+        PythonActivity = autoclass(ACTIVITY_CLASS_NAME)
+        PythonActivity.mSurface.setInterceptTouchListener(cls.__listener)
+
+    @classmethod
+    def unregister_listener(cls):
+        """Unregister the global intercept touch listener, if any.
+
+        Removes the previously installed listener from
+        `PythonActivity.mSurface` by setting it to `None`. This does not
+        modify the stored reference in `__listener`.
+        """
+        PythonActivity = autoclass(ACTIVITY_CLASS_NAME)
+        PythonActivity.mSurface.setInterceptTouchListener(None)
+        cls.__target_widget = None
+
+    @classmethod
+    def is_listener_set(cls):
+        """Report whether the intercept listener reference is set.
+
+        Returns:
+            bool: `False` if a listener instance is currently stored in
+            `__listener` (i.e. registered), `True` if no listener is stored.
+            Note: this method reflects the current implementation which
+            returns the negation of the internal reference.
+        """
+        return not cls.__listener
+
+    @classmethod
+    def _on_touch_listener(cls, event):
+        """Default callback used by the installed intercept listener.
+
+        What it does now (current behavior):
+        - Reads touch coordinates from pointer index 0 using `event.getX(0)`
+          and `event.getY(0)`.
+        - Converts Android coordinates to Kivy coordinates by inverting the Y
+          axis relative to `Window.height`.
+        - Iterates over `Window.children` in reverse (front-to-back) and uses
+          `TouchListener._pick` to select the deepest widget under the touch
+          for each top-level child.
+        - Compares the picked widget with the internally stored
+          `__target_widget` that was provided to `register_listener(...)`.
+        - Returns `True` (consume/intercept) only when the picked widget is
+          exactly `__target_widget` and no other widget was found under the
+          touch (`final_widget is None`). Otherwise returns `False`.
+
+        Important notes and limitations:
+        - There is no filtering by MotionEvent action; all actions reaching
+          this callback are evaluated the same way.
+        - Only pointer index 0 is considered; multi-touch pointers other than
+          index 0 are ignored.
+        - The check is identity-based (`is`) against `__target_widget`.
+        - If another widget (other than `__target_widget`) is hit, the event
+          is not intercepted and will propagate normally.
+
+        Parameters:
+            event: The Android `MotionEvent` that triggered the listener.
+
+        Returns:
+            bool: `True` to consume the touch when the hit-test selects the
+            `__target_widget` and no other widget is found; otherwise `False`
+            to allow normal dispatch.
+        """
+        from kivy.core.window import Window
+
+        x = event.getX(0)
+        y = event.getY(0)
+
+        # invert Y !
+        y = Window.height - y
+        # x, y are in Window coordinate. Try to select the widget under the
+        # touch.
+        me = None
+        final_widget = None
+        for child in reversed(Window.children):
+            widget = cls._pick(child, x, y)
+            if not widget:
+                continue
+            if cls.__target_widget is widget:
+                me = widget
+                # keep scanning to ensure no other widget is hit
+                continue
+            # any non-target hit means we should not intercept
+            return False
+        return cls.__target_widget is me
+
+    @classmethod
+    def _pick(cls, widget, x, y):
+        """Pick the deepest child widget at coordinates.
+
+        Parameters:
+            widget: The root widget from which to start the search.
+            x (float): X coordinate in the local space of `widget`.
+            y (float): Y coordinate in the local space of `widget`.
+
+        Returns:
+            The deepest child that collides with the given point, or the
+            highest-level `widget` itself if it collides and no deeper child
+            does; otherwise `None` if no collision.
+        """
+        # Fast exit if the root doesn't collide
+        if not widget.collide_point(x, y):
+            return None
+
+        # Always descend through the first colliding child in z-order
+        current = widget
+        lx, ly = x, y
+        while True:
+            # Transform coordinates once per level
+            nlx, nly = current.to_local(lx, ly)
+            hit_child = None
+            for child in reversed(current.children):
+                if child.collide_point(nlx, nly):
+                    # keep the last colliding child in this order, matching
+                    # the original recursive implementation's semantics
+                    hit_child = child
+            if hit_child is None:
+                # No deeper child collides; current is the deepest hit
+                return current
+            # Prepare for next level using parent's local coords; we'll
+            # convert again at the next iteration relative to the new
+            # current widget.
+            lx, ly = nlx, nly
+            # Continue descent into the chosen child
+            current = hit_child