multitouch/src/trackers/transform.py

from __future__ import division

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


class TransformationTracker(GestureTracker):
    """
    Tracker for linear transformations. This implementation detects rotation,
    scaling and translation using the centroid of all touch points.
    """
    __gesture_types__ = ['rotate', 'pinch', 'move']

    def __init__(self, window=None):
        super(TransformationTracker, self).__init__(window)

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

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

    def update_centroid(self):
        self.prev_centroid = self.centroid

        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, point):
        self.points.append(point)
        self.update_centroid()

    def on_point_move(self, point):
        l = len(self.points)

        if l > 1:
            # Rotation (around the previous centroid)
            if self.is_type_bound('rotate'):
                rotation = point.rotation_around(self.centroid) / l
                self.trigger(RotationGesture(self.centroid, rotation))

            # Scale
            if self.is_type_bound('pinch'):
                prev = point.get_previous_position().distance_to(self.centroid)
                dist = point.distance_to(self.centroid)
                dist = prev + (dist - prev) / l
                scale = dist / prev
                self.trigger(PinchGesture(self.centroid, scale))

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

        # Movement
        self.trigger(MovementGesture(self.centroid,
                                     self.centroid.translation()))

    def on_point_up(self, point):
        self.points.remove(point)
        self.update_centroid()


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

    def __init__(self, centroid, angle):
        Positionable.__init__(self, *centroid.get_position())
        self.angle = angle

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

    def __init__(self, centroid, scale):
        Positionable.__init__(self, *centroid.get_position())
        self.scale = scale

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

    def get_scale(self):
        return self.scale


class MovementGesture(Positionable, Gesture):
    """
    A momevent gesture has an initial position, and a translation from that
    position.
    """
    __type__ = 'move'

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

    def __str__(self):
        return '<MovementGesture at (%s, %s) translation=(%s, %s)>' \
               % (self.get_position() + self.translation.get_position())