[Ohrrpgce] .dmg format for Distribute Game on Mac

[Ralph Versteegen]

I had actually forgotten about the compression, so I've been looking into
it.

I was surprised to see on the man page for mkisofs that it can create HFS
(not HFS+) file system images, because those are used by Apple for CDs.
The .dmg file format is called UDIF, which is a wrapper around a file
system image which may be HFS/HFS+, FAT, and so on. The HFS+ file system
itself seems to be fairly well supported in Linux. Unfortunately the
compression of an .dmg is added by UDIF, not HFS (though HFS also supports
compression). And UDIF is undocumented and there are almost no 3rd party
tools for dealing with it (I only saw ones for reading, not writing); the
best I could find was http://newosxbook.com/DMG.html

I don't think .dmg.zip would make much sense (Why not just use .zip?) even
if it were true that OSX magically accepts .isos.

On 8 July 2015 at 03:17, <ziggythehamster at outlook.com> wrote:

>  MacOS X doesn't primarily rely on file extensions. Renaming an ISO to
> DMG doesn't do anything. You could rename it .jpg and it'll still be an ISO
> disk image.
>
> You pretty much have to use hdiutil on a Mac to make DMGs. You would have
> better luck making a .pkg (really, the gzipped variant) that installs to
> /Applications. I believe all you need to make a .pkg is gzip, cpio, and an
> XML plist creator. All of which work on every platform.
>
>
>
> On Tue, Jul 7, 2015 at 7:26 AM -0700, "James Paige" <
> Bob at HamsterRepublic.com> wrote:
>
>    Annd. I remembered why that wouldn't work. No compression. I feel like
> TMC discovered all of this years ago, and I am just now remember what he
> said and thinking that I am figuring it out myself ;P
>
>  Would a zipped dmg be more or less confusing than a tar.gz?
>
>  Also, is anybody even getting these mailing list posts? I never get
> copies of my own, so I don't even know if the list server is working right
> now.
>
> ---
>  James
>
>
>
> On Mon, Jul 6, 2015 at 3:01 PM, James Paige <Bob at hamsterrepublic.com>
> wrote:
>
>     I just discovered/remembered something really nifty.
>
>  So the reason we went with .tar.gz on Mac was because we couldn't figure
> out how to create .dmg files.
>
>  .dmg files are normally Disk images formatted as HSF+ and although tools
> for formatting as HSF+ exist on Windows and Linux, we could not find any
> good simple ones that we could redistribute.
>
>  Turns out that the important thing about a .dmg file is that it is a disk
> image. HFS+ happens to be the preffered format, but any format supported by
> Macs should work.
>
>  In particular, .iso works.
>
>  I tried building a .iso image, renamed it to .dmg, and my Mac was able to
> open it smoothly with no problems at all.
>
>  Tools to generate .iso images are far more ubiquitous, so maybe we can
> find one that we can redistribute and we can use it to build .dmg files
> directly from the Export Games menu :)
>
> ---
>  James
>
>
>
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