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# PiTiVi , Non-linear video editor
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# ui/projectsettings.py
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# Copyright (c) 2010, Brandon Lewis <brandon.lewis@collabora.co.uk>
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# This program is free software; you can redistribute it and/or
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# modify it under the terms of the GNU Lesser General Public
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# License as published by the Free Software Foundation; either
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# version 2.1 of the License, or (at your option) any later version.
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# Lesser General Public License for more details.
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# You should have received a copy of the GNU Lesser General Public
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# License along with this program; if not, write to the
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# Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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# Boston, MA 02111-1307, USA.
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class RippleUpdateGroup(object):
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"""Allows for event-driven spreadsheet-like ripple updates without
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This class allows you to express an event-driven sequence of operations in
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terms of a directed graph. It is not a constraint solver: The goal is to
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allow the programmer to reduce complex logic to a set of simple functions
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and predicates combined declaratively.
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Events propagate through the graph in breadth first order. During an
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update cycle, each vertex is visited only once, so cycles can exist in the
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graph without creating infinite loops.
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Each vertex represents a unique object. The following may also be
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associated with a vertex:
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- the name of a signal on the object. when this signal fires, it
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triggers an update cycle beginning at this object. during an update
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cycle, further signal emissions from this or any other vertex will
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be ignored to prevent infinite loops.
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- an update function, which will be called when the vertex is visited
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as part of an update cycle. It will not be called when the object
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- zero or more user-specified arguments, passed to the
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An edge between two verticies represents a sequence of operations. If an
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edge exists from object A to object B, then whenever A is perfomred, B
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should be performed too -- unless it has already been visited as part of
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In addition to a a pair of objects, each edge also has the following
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- a predicate function. called during an update cycle when this edge
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is reached, and before any other processing is done. If this
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function returns false, it will be as if this edge otherwise did not
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- a function to be called whenver the edge is visited during an update
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cycle. this function will not be called if the condition function
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def __init__(self, *widgets):
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self.update_funcs = {}
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self.ignore_new_signals = False
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for widget in widgets:
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self.add_vertex(*widget)
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def add_vertex(self, widget, update_func=None, signal=None, *args):
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widget.connect(signal, self._widget_value_changed)
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self.update_funcs[widget] = (update_func, args)
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self.arcs[widget] = []
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def add_edge(self, a, b, predicate = None,
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self.arcs[a].append((b, predicate, edge_func))
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def add_bi_edge(self, a, b, predicate = None,
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self.add_edge(a, b, predicate, edge_func)
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self.add_edge(b, a, predicate, edge_func)
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def _widget_value_changed(self, widget, *unused):
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if self.ignore_new_signals:
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self.ignore_new_signals = True
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self._updateValues(widget)
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self.ignore_new_signals = False
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def _updateValues(self, widget):
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queue = [(widget, v) for v in self.arcs[widget]]
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visited = set([widget])
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parent, (cur, predicate, edge_func) = queue.pop(0)
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# ignore nodes we've seen
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# check whether conditions permit this edge to be followed
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if predicate and (not predicate()):
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# if so call the edge function
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update_func, args = self.update_funcs[cur]
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update_func(parent, cur, *args)
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queue.extend(((cur, v) for v in self.arcs[cur]))
added
removed
pitivi/ui/ripple_update_group.py
