115 lines
3.4 KiB
Python
115 lines
3.4 KiB
Python
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'''
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Damped scroll effect
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====================
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.. versionadded:: 1.7.0
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This damped scroll effect will use the
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:attr:`~kivy.effects.scroll.ScrollEffect.overscroll` to calculate the scroll
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value, and slows going back to the upper or lower limit.
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'''
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__all__ = ('DampedScrollEffect',)
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from kivy.effects.scroll import ScrollEffect
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from kivy.properties import NumericProperty, BooleanProperty
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from kivy.metrics import sp
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class DampedScrollEffect(ScrollEffect):
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'''DampedScrollEffect class. See the module documentation for more
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information.
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'''
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edge_damping = NumericProperty(0.25)
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'''Edge damping.
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:attr:`edge_damping` is a :class:`~kivy.properties.NumericProperty` and
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defaults to 0.25
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'''
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spring_constant = NumericProperty(2.0)
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'''Spring constant.
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:attr:`spring_constant` is a :class:`~kivy.properties.NumericProperty` and
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defaults to 2.0
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'''
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min_overscroll = NumericProperty(.5)
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'''An overscroll less than this amount will be normalized to 0.
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.. versionadded:: 1.8.0
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:attr:`min_overscroll` is a :class:`~kivy.properties.NumericProperty` and
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defaults to .5.
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'''
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round_value = BooleanProperty(True)
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'''If True, when the motion stops, :attr:`value` is rounded to the nearest
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integer.
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.. versionadded:: 1.8.0
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:attr:`round_value` is a :class:`~kivy.properties.BooleanProperty` and
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defaults to True.
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'''
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def update_velocity(self, dt):
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if abs(self.velocity) <= self.min_velocity and self.overscroll == 0:
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self.velocity = 0
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# why does this need to be rounded? For now refactored it.
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if self.round_value:
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self.value = round(self.value)
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return
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total_force = self.velocity * self.friction * dt / self.std_dt
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if abs(self.overscroll) > self.min_overscroll:
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total_force += self.velocity * self.edge_damping
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total_force += self.overscroll * self.spring_constant
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else:
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self.overscroll = 0
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stop_overscroll = ''
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if not self.is_manual:
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if self.overscroll > 0 and self.velocity < 0:
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stop_overscroll = 'max'
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elif self.overscroll < 0 and self.velocity > 0:
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stop_overscroll = 'min'
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self.velocity = self.velocity - total_force
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if not self.is_manual:
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self.apply_distance(self.velocity * dt)
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if stop_overscroll == 'min' and self.value > self.min:
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self.value = self.min
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self.velocity = 0
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return
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if stop_overscroll == 'max' and self.value < self.max:
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self.value = self.max
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self.velocity = 0
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return
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self.trigger_velocity_update()
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def on_value(self, *args):
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scroll_min = self.min
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scroll_max = self.max
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if scroll_min > scroll_max:
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scroll_min, scroll_max = scroll_max, scroll_min
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if self.value < scroll_min:
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self.overscroll = self.value - scroll_min
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elif self.value > scroll_max:
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self.overscroll = self.value - scroll_max
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else:
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self.overscroll = 0
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self.scroll = self.value
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def on_overscroll(self, *args):
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self.trigger_velocity_update()
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def apply_distance(self, distance):
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os = abs(self.overscroll)
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if os:
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distance /= 1. + os / sp(200.)
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super(DampedScrollEffect, self).apply_distance(distance)
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