[Kdenlive-devel] 1. Refactoring Update

[Simon A. Eugster]

On 13.05.2012 15:02, Till Theato wrote:
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> Hey guys,
>
> so finally here it is.
> I've been working on a new effect system and I think it is now in a
> state were I can write about it a bit, at least to the fellow
> developers, since there isn't much to see yet. Only the basic
> structures are done, but they should allow to add the old
> functionality quickly.
>
> The new initEffects, has turned into a much lighter EffectRepository.
> Here we look for available filters and Kdenlive XML effect
> descriptions. MLT metadata is now only used when no XML effect
> description is present so there is no need anymore to blacklist those
> effects. The metadata or the XML is then handled by object of the
> EffectDescription class. Here information like name, kdenlive id,
> tag/mlt name, author, description are extracted and stored. The
> parameter elements or MLT properties also have their own objects. All
> information about them is processed and stored in classes inheriting
> from AbstractEffectDescription. Each parameter type has its own class
> so there is for example DoubleParameterDescription, but more about
> parameters later on.
> So after the initial loading process we don't need any XML DOM
> anymore, which means that there is no need for functions spreading
> across the whole code to take care of it.
>
> Now, the actual use of effects. Since there are multiple items that
> can have effects, currently tracks and clips, there is a class called
> EffectDevice which takes care of handling anything effects related. It
> has direct access to the MLT service the effects should work on, so it
> is responsible for inserting and deleting the effects' filters there.
> When an effect should be added its description object is told to
> create it. This way no information about it has to be passed around.
> The effect object creates an MLT filter and will then handle all
> changes which should happen to it. By keeping a pointer to the effect
> description object in the repository it is not necessary to duplicate
> any information like name, description, ... . The parameters are also
> created by their description objects so no knowledge is required about
> their type.
> All these different levels (from device down to parameter) have
> currently 3 different views: the traditional effectstack, now called
> properties view (not fix though yet), the timeline view, to draw for
> example effect names or keyframes and the monitor view for on monitor
> editing.
> So when this is all finished we should have a completely
> self-contained effect system with very short connections and one that
> is also easy to enhance and enlarge.
>
> That was the trigger for some words on the parameter implementation ;).
> Parameters are where most specialization is required. They are
> therefore now kept as plugins. A .desktop file tells the repository
> which types the plugin handles but everything else is plugin internal,
> from parameter description to the actual implementation to the
> different views.
>
> This however required the introduction of a Kdenlive library since the
> parameters are not based on mere interfaces but on abstract base
> classes and since they also need to have access to some widgets for
> example.
> The plan is to expand this library during the refactoring so that in
> the end (given that I'm fast enough ;)) almost everything is either in
> a plugin or in the library to be accessible by plugins.
>
> As a next stept I want to port some more functionality to the new
> effect system and then start working on the timeline, which should be
> quite similar though much more complex.
>
>
> Let me know what you think of all this, whether I missed something
> completely, or whatever ;)

Inmidst of the bazillion of homework and projects and soon exam 
preparations I finally found time to read this. (The code not yet.)

Sounds all very well-structured and clean, looking forward to working 
with it if I ever have to. Since I cannot give any helpful comments, I 
just say: Thank you :)

Simon