multitouch/src/trackers/transform.py

from __future__ import division

from ..tracker import GestureTracker, Gesture
from ..geometry import Positionable, MovingPositionable


class RotationGesture(Gesture, Positionable):
    """
    A rotation gesture has a angle in radians and a rotational centroid.
    """
    _type = 'rotate'

    def __init__(self, event, centroid, angle, n=1):
        Gesture.__init__(self, event)
        Positionable.__init__(self, *centroid.get_position())
        self.angle = angle
        self.n = n

    def __str__(self):
        return '<RotationGesture at (%s, %s) angle=%s>' \
               % (self.x, self.y, self.angle)

    def get_angle(self):
        return -self.angle


class PinchGesture(Gesture, Positionable):
    """
    A pinch gesture has a scale (1.0 means no scaling) and a centroid from
    which the scaling originates.
    """
    _type = 'pinch'

    def __init__(self, event, centroid, scale, n=1):
        Gesture.__init__(self, event)
        Positionable.__init__(self, *centroid.get_position())
        self.scale = scale
        self.n = n

    def __str__(self):
        return '<PinchGesture at (%s, %s) scale=%s>' \
               % (self.x, self.y, self.scale)

    def get_scale(self):
        return self.scale


class DragGesture(Gesture, Positionable):
    """
    A momevent gesture has an initial position, and a translation from that
    position.
    """
    _type = 'drag'

    def __init__(self, event, initial_position, translation, n=1):
        Gesture.__init__(self, event)
        Positionable.__init__(self, *initial_position.get_position())
        self.translation = translation
        self.n = n

    def __str__(self):
        x, y = self
        tx, ty = self.translation
        return '<DragGesture at (%s, %s) translation=(%s, %s) n=%d>' \
               % (x, y, tx, ty, self.n)

    def get_translation(self):
        return self.translation


class FlickGesture(Gesture, Positionable):
    _type = 'flick'

    def __init__(self, event, initial_position, translation):
        Gesture.__init__(self, event)
        Positionable.__init__(self, *initial_position.get_position())
        self.translation = translation

    def __str__(self):
        x, y = self.get_position()
        tx, ty = self.translation
        return '<FlickGesture at (%s, %s) translation=(%s, %s)>' \
               % (x, y, tx, ty)

    def get_translation(self):
        return self.translation


class TransformationTracker(GestureTracker):
    """
    Tracker for linear transformations. This implementation detects rotation,
    scaling and translation using the centroid of all touch points.
    """
    supported_gestures = [RotationGesture, PinchGesture, DragGesture,
                          FlickGesture]

    def __init__(self, area):
        super(TransformationTracker, self).__init__(area)

        # All touch points performing the transformation
        self.points = []

        # Current and previous centroid of all touch points
        self.centroid = None

        self.deleted = []

    def update_centroid(self):
        if not self.points:
            self.centroid = None
            return

        # Calculate average touch point coordinates
        l = len(self.points)
        coords = [p.get_position() for p in self.points]
        all_x, all_y = zip(*coords)
        x = sum(all_x) / l
        y = sum(all_y) / l

        # Update centroid positionable
        if self.centroid:
            self.centroid.set_position(x, y)
        else:
            self.centroid = MovingPositionable(x, y)

    def on_point_down(self, event):
        self.points.append(event.point)
        self.update_centroid()
        event.stop_propagation()

    def on_point_move(self, event):
        point = event.point

        if point not in self.points:
            pid = point.get_id()

            if pid not in self.deleted:
                return

            self.debug('recovered %s' % point)
            self.deleted.remove(pid)
            self.points.append(point)
            self.update_centroid()

        event.stop_propagation()
        self.invalidate_points()
        l = len(self.points)

        if l > 1:
            offset_centroid = self.centroid - self.area.get_screen_offset()

            # Rotation (around the previous centroid)
            rotation = point.rotation_around(self.centroid) / l
            self.trigger(RotationGesture(event, offset_centroid, rotation, l))

            # Scale
            prev = self.centroid.distance_to(point.get_previous_position())
            dist = self.centroid.distance_to(point)
            dist = prev + (dist - prev) / l
            scale = dist / prev
            self.trigger(PinchGesture(event, offset_centroid, scale, l))

        # Update centroid before movement can be detected
        self.update_centroid()

        # Movement using multiple touch points
        self.trigger(DragGesture(event, self.centroid,
                                 self.centroid.translation(), l))

    def on_point_up(self, event):
        if event.point in self.points:
            self.points.remove(event.point)

            if not self.points:
                self.trigger(FlickGesture(event, self.centroid,
                                          self.centroid.translation()))
            self.update_centroid()
            event.stop_propagation()


    def invalidate_points(self):
        """
        Check if all points are still in the corresponding area, and remove
        those which are not.
        """
        delete = []

        if self.area.parent:
            ox, oy = self.area.parent.get_screen_offset()
        else:
            ox = oy = 0

        for i, p in enumerate(self.points):
            x, y = p.get_position()

            if not self.area.contains(x - ox, y - oy):
                self.debug('deleted %s' % p)
                delete.append(i)
                self.deleted.append(p.get_id())

        if delete:
            self.points = [p for i, p in enumerate(self.points)
                           if i not in delete]
            self.update_centroid()