Expand file format support for graphics software integration

@711GM Hi. Yes, eventually Pencil2D would strive to become a complement to more robust programs like OpenToonz, Synfig, Tupi, Krita etc. and to function as part of an animation pipeline while still retaining capability to allow finishing an entire animation inside the Pencil2D editor.

We believe Pencil2D has it's own place in the FOSS animation community and considering that the Pencil2D project files are very similar in structure to Synfig or OT (all of them are made up of XML or Text files, a converter would be able to happen rather easily.

The problem however lies with time and human resources. Pencil2D has barely enough people to keep it going and there's a lot of critical issues that have to be fixed before dabbling into these kind of requests for pipeline integration. If you know someone who'd like to contribute such functionalities they would be more than welcome to do it provided they also discuss it with the team in order to have a smooth integration of said features.

Let's keep this issue open to focus the discussion for a conversion / file format integration feature from Pencil2D to other scene compressed text-based formats such as:

-- Compressed Text-based (XML) Files

These file formats could support Bidirectional Data Exchange (BDE) from and to Pencil2D

[ ] SIFZ (Synfig)
[ ] TNZ (OpenToonz)
[ ] TUP [TPP / TPL / TPS] (Tupi)
[ ] KRA (Krita)

-- Import / Export For Specific Functionality

[ ] ODS / CVS Note: Either Based in XML or Plain Text, this format would only be worked on to Import / export timeline frame position data from and to an X-Sheet template.
[ ] Inkscape SVG Note: Inkscape has a specific arrangement of the SVG specification which is slightly different to Plain SVG for the web as an export file. This would be used to bring proper SVG files into and to export SVG images to other software.
[ ] KDENLIVE Note: This format is based in XML, which would make it perfect for quickly integrating with the KDEnlive video editor for post-production and Video Editing purposes in animation production. Ideally this would be to go back and forth between software in order to handle editing and refining video work for animatics, rough demos for supervisors and anything else that is related.

-- Indirect or Limited Integration

Due to functionality or Format specifications these software formats would either lack all the required information (e.g. frames) or can't be directly converted to / from Pencil2D Project files, however there could be a direct integration with the base program through other file formats

[ ] GIMP Note: The XCF native file format is not recommended for data exchange, GIMP devs recommend KRA, ORA or other filetypes since XCF is a binary image file that describes what happens in the GIMP Document AFAIK. For more info read the XCF specification here https://gitlab.gnome.org/GNOME/gimp/blob/master/devel-docs/xcf.txt

-- Integration through (Python) API Scripting

[ ] BLEND (Blender) Note: a .blend file is not a data exchange format but a binary created from the inner structures of the program. I've read you can create a parser for this filetype, but it might be really difficult to get a 1:1 conversion due to obvious differences in functionality and scope between software packages inner structures. Also said converters should be geared towards a particular task, From a Pencil2D to Blender functionality, if you want to either use the VSE you have to only touch the editor API, or if you want import the layers as planes in 3D Space you use another part of the API, etc.

From a Blender to Pencil2D functionality, for example, It would be possible to have 3D layers in Pencil2D for quick reference and drawing, but this goes beyond the scope of Pencil2D as an animation software and would be treated as plug-in functionality, that is to say, it won't be maintained by the core Pencil2D team.

The other problem is that Pencil2D does not currently have it's API exposed, and although it's been proposed in the past it will take time for any kind of scripting or API handling to come to the project.

-- Beyond Scope Integration

Due to limited function compatibility or simply because it's not needed for animation pipelines

SLA (Scribus) Note: Based in XML

pencil2d / pencil