Are the Save methods implemented, which would allow rudimentary file format conversion?
The picture.datatype supports DTM_WRITE, and so do the sound and the animation.datatype.
Thanks but what I mean is do the sub types support it, for example Multiview has a Save menu, which by and large does nothing. It would be nice if you could load a file in ILBM format into Multiview and then save it out as PNG for example or vice versa, assuming save method was properly supported. Multiview would need some way of picking the target format from the list of compatible types too. This for me always seems like one of the features Commodore weren't able to finish what they intended, and while DefIcons picked up the slack of integrating datatypes with Workbench, I'd love to see this feature "finished".
As for progressive loading, datatypes should in theory allow creation from both a file handle, and a memory buffer, but the buffer needed to be fully populated already, datatypes couldn't provide partial renders based on progressive population of the buffer from say, and http stream, making it impossible for web browsers to progressively display jpegs, for example, decoding them line by line. Admittedly, that's less of an issue now in 2018 that everyone has megabit connectivity and images generally download instantly. I'm not familiar with OS4, but did they ever implement that capability?
By the way I used to work at Symbian, and we had a technology that allowed instantaneous blitting of compressed JPG and PNG files to the display, so you didn't need to store the uncompressed bitmap in ram before transferring it to the screen buffer. It would be decompressed at copy time.
