.. currentModule:: Autograph

Edit a Composition
==================

Accessing a Composition
------------------------

A :class:`Composition` can be retrieved from a :class:`ProjectItem` with :meth:`ProjectItem.getMainEffectInstance()`

Change Composition parameters
------------------------------

Since the :class:`Composition<Autograph.Composition>` class inherits :class:`Effect<Autograph.Effect>` , all its :class:`Param<Autograph.Param>` can be accessed with :meth:`Autograph.Effect.param(uniqueName)` or :meth:`Autograph.Effect.getParams()` . 
However, some commonly used Params have a dedicated API to make it easier:

.. code-block::

	comp.setFormat(width, height, pixelAspectRatio)
	comp.framerate = 60.0
	# 300 frames at 60fps is 5 seconds
	comp.duration = 300



Manage layers
--------------

:class:`Composition<Autograph.Composition>` contains is a list-like API for managing layers:

.. code-block::

	comp.addLayer(Autograph.Layer2D())
	allLayers = comp.getLayers()
	for i in range(len(allLayers)):
		print("Layer %i is %r" % (i, allLayers[i]))


To create a layer with a project item as source, use the dedicated constructor:


.. code-block::

	project=Autograph.app.getActiveProject()
	myFootage=project.importFootage('/media/myfiles/video.mov')

	...

	comp.addLayer(Autograph.Layer2D(myFootage))


Under the hood, this constructor assigns an :class:`Effect<Autograph.Effect>` returned from :meth:`Autograph.ProjectItem.createEffectSharedInstance()` to the generator slot of the source param of the layer. Here is the equivalent:

.. code-block::

	project=Autograph.app.getActiveProject()
	myFootage=project.importFootage('/media/myfiles/video.mov')

	layer=Autograph.Layer2D()

	# Note that we create a shared copy of the effect so that the user can unshare parameters if needed
	layer.source.setGeneratorEffect(myFootage.createEffectSharedInstance())

	comp.addLayer(layer)



Setting the layer transform
----------------------------

The layer transform parameters can be accessed with the :attr:`Layer2D.transform` attribute or with the generic :meth:`Effect.param` accessor.

.. code-block::
	
	layer.transform.position.setValues([300.,0.])