The general process:
user requested format-\
______\______
___________ | |
| |/---> Asset 1 --->| Transcoder |--> Asset 1 in user requested format
File -->| Analyzer |----> Asset 2 |____________|
|__________|\---> Asset 3
\ /
\--Metadata-/
Example: A blend file is given to the analyzer, the analyzer looks up the plugin for .blend files by mimetype. The plugin then begins to scan the file, and it will output a list of all blender objects(which from now on will be called assets), the assets are given an internal mimetype of ‘x-blender/object’ and additional information like face/vertex count, number of materials, etc is scanned and added to the asset as metadata. All this information is stored in the database. Note: at this point we haven’t done anything with the file except for having scanned it. An asset is just an unique ID combined with a file reference, a name(unique for that file), an internal mimetype and some metadata!
Now say a user wants asset 1 in CS format, he’d request it with the mimetype ‘application/x-crystalspace.library+xml’, asset 1 is then looked up in the database, this tells us it has the internal mimetype of ‘x-blender/object’ , so now we can lookup a transcoder for ‘application/x-crystalspace.library+xml’ –>’x-blender/object’. The asset is passed to the transcoder plugin, it reads the file, finds the object by name and extracts its data and converts it to the CS format.
Any .py file in the transcoders/ directory will be automatically scanned on startup and registered as a plugin if it has the following requirements: It has a function ‘transcode(self, anAsset, aFormat, kwargs)’ It has a member dictionary convert_map and it has a member dictionary options_map
This specifies the source and destination mimetypes this transcoder supports. Each entry describes a ‘source –> destination’-mapping and is of the format:
"source-mimetype": "destination-mimetype"
or:
"source-mimetype": ["destination-mimetype1", "destination-mimetype2", ...]
Example:
convert_map = {"image/png" : "image/jpeg", "image/tga" : ["image/jpeg", "image/png"]}
It can convert png to jpeg or convert tga to either jpeg or png.
This specifies what options/arguments can be given when transcoding an asset. Each entry specifies a source mimetype(corresponding to one in the convert_map) and a dictionary of options; each tuple consists of the option’s name and a function used to convert the input to the correct type(all inputs are string).
Example:
convert_map = {"x-blender/object" : "image/jpeg"}
options_map = {"x-blender/object" : {'sizex': int, 'sizey': int, 'angley': float, 'cameraType': str, 'cameraAngley': float, 'anglesy': floatArray}}
This one renders a blender object to a jpeg, it’s options are size(x/y): specifying the width and height of the rendered image. angley: the rotation around the Y axis of the object. cameraType: blender options for camera type, ORTHO or PERSP. cameraAngley: the angle of the camera.
(This transcoder is used for the 2D previews of blender objects in the DAMN interface, it can also be used for sprites for a 2D game(use ortho and a camera angle to get top-down views of the asset))