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====================================
Transforms and Transitions in Python
====================================
Python can be used to create new transforms and transitions for use by
Ren'Py scripts.
.. _transforms-python:
Transforms
----------
*Main articles:* :doc:`transforms` *and* :doc:`atl`
A transform is a Python callable that, when called with a displayable,
returns another displayable.
For example::
init python:
# This is a transform that uses the right and
# left transforms.
def right_or_left(d):
if switch:
return right(d)
else:
return left(d)
The Python equivalent of an ATL transform is a Transform object.
.. class:: Transform(child=None, function=None, **properties)
A transform applies operations such as cropping, rotation, scaling, and
alpha-blending to its child. A transform object has fields corresponding
to the :ref:`transform properties <transform-properties>`, which it applies
to its child.
`child`
The child the transform applies to.
`function`
If not none, this is a function that is called when the transform
is rendered. The function is called with three arguments:
* The transform object.
* The shown timebase, in seconds.
* The animation timebase, in seconds.
The function should return a delay, in seconds, after which it will
be called again, or None to be called again at the start of the next
interaction.
This function should not have side effects other
than changing the Transform object in the first argument, and may be
called at any time with any value to enable prediction.
Additional keyword arguments are values that transform properties are set
to. These particular transform properties will be set each time the
transform is drawn, and so may not be changed after the Transform object
is created. Fields corresponding to other transform properties, however,
can be set and changed afterwards, either within the function passed as
the ``function`` parameter, or immediately before calling the
:meth:`update` method.
.. attribute:: hide_request
This is set to true when the function is called, to indicate that the
transform is being hidden.
.. attribute:: hide_response
If hide request is true, this can be set to false to prevent the
transform from being hidden.
.. method:: set_child(child)
Call this method with a new `child` to change the child of
this transform.
.. method:: update()
This should be called when a transform property field is updated
outside of the function passed as the `function` argument, to ensure
that the change takes effect.
.. _transitions-python:
Transitions
-----------
*Main article:* :doc:`transitions`
*See also:* :ref:`atl-transitions`
A transition is a Python callable that, when called with two keyword
arguments, returns a displayable that performs the transition effect.
The two keyword arguments are:
`old_widget`
A displayable representing the old screen.
`new_widget`
A displayable representing the new screen.
The returned displayable should have a ``delay`` field, which gives
the number of seconds the transition should run for.
For example::
init python:
def dissolve_or_pixellate(old_widget=None, new_widget=None):
if persistent.want_pixellate:
return pixellate(old_widget=old_widget, new_widget=new_widget)
else:
return dissolve(old_widget=old_widget, new_widget=new_widget)
|
